Abdel-Raheem, A. and C. A. Shearer (2002). "Extracellular enzyme production by freshwater ascomycetes." Fungal Diversity 11: 1-19.

Thirty species of freshwater ascomycetes isolated from woody and/or herbaceous substrates were screened for their ability to produce extracellular degradative enzymes on solid media. Enzymes tested included: amylase, endoglucanase, endoxylanase, beta-glucosidase, laccase, lipase, pectinase, peroxidase, polygalacturonase, polyphenoloxidase, protease, tyrosinase and B-xylosidase. All species were positive for cellulase and endoxylanase/beta-xylosidase. Two species, Chaetomastia typhicola (herbicolous) and Massarina sp. A25 (lignicolous) tested positive for all enzyme assays. Submersisphaeria aquatica (lignicolous) was positive for all enzymes except tyrosinase and Jahnula sp. A322 (lignicolous) was positive for all enzymes except polyphenoloxidase. Generally, the species which were isolated from herbaceous substrates and woody/herbaceous substrates had good growth rates on different types of enzyme media used (such as, peptone, yeast extract, glucose agar, etc.). Fifty percent of the lignicolous species produced pectin degrading enzymes, compared to about 80% for herbicolous and woody/herbicolous species, suggesting that there may be some specialization in the types of enzymes produced within substrate groups. The greatest differences among species occurred in the production of enzymes associated with detection of lignin degradation. Laccase and peroxidase detection depended on the assay technique used. Freshwater ascomycetes, as a group, produce many of the extracellular enzymes important in the decomposition of plant structural materials thereby supporting the idea that they play an important role in recycling in aquatic habitats. [References: 70]

Ainsworth, E. A., P. A. Davey, et al. (2002). "A meta-analysis of elevated." Global Change Biology 8(8): 695-709.

The effects of elevated [CO2] on 25 variables describing soybean physiology, growth and yield are reviewed using meta-analytic techniques. This is the first meta-analysis to our knowledge performed on a single crop species and summarizes the effects of 111 studies. These primary studies include numerous soybean growth forms, various stress and experimental treatments, and a range of elevated [CO2] levels (from 450 to 1250 p.p.m.), with a mean of 689 p.p.m. across all studies. Stimulation of soybean leaf CO2 assimilation rate with growth at elevated [CO2] was 39%, despite a 40% decrease in stomatal conductance and a 11% decrease in Rubisco activity. Increased leaf CO2 uptake combined with an 18% stimulation in leaf area to provide a 59% increase in canopy photosynthetic rate. The increase in total dry weight was lower at 37%, and seed yield still lower at 24%. This shows that even in an agronomic species selected for maximum investment in seed, several plant level feedbacks prevent additional investment in reproduction, such that yield fails to reflect fully the increase in whole plant carbon uptake. Large soil containers (> 9 L) have been considered adequate for assessing plant responses to elevated [CO2]. However, in open-top chamber experiments, soybeans grown in large pots showed a significant threefold smaller stimulation in yield than soybeans grown in the ground. This suggests that conclusions about plant yield based on pot studies, even when using very large containers, are a poor reflection of performance in the absence of any physical restriction on root growth. This review supports a number of current paradigms of plant responses to elevated [CO2]. Namely, stimulation of photosynthesis is greater in plants that fix N and have additional carbohydrate sinks in nodules. This supports the notion that photosynthetic capacity decreases when plants are N-limited, but not when plants have adequate N and sink strength. The root:shoot ratio did not change with growth at elevated [CO2], sustaining the charge that biomass allocation is unaffected by growth at elevated [CO2] when plant size and ontogeny are considered. [References: 144]

Ainsworth, E. A., P. A. Davey, et al. (2002). "Long-term response of photosynthesis to elevated carbon dioxide in a Florida scrub-oak ecosystem." Ecological Applications 12(5): 1267-1275.

The response of photosynthesis was analyzed during canopy closure in a Florida scrub-oak ecosystem exposed to elevated [CO2] (704 mumol CO2/mol air; concentration Of CO2). The species were measured on six occasions, covering different seasons, during the third. and fourth year of exposure to elevated [CO2]. The entire regrowth cycle of this community has been under elevated [CO2], providing a rare opportunity to assess the differential responses of species during the critical phase of canopy closure. Measurements were taken in order to determine both season-specific and species-specific differences' in the response of photosynthesis to elevated [CO2]. Photosynthesis was measured with an open-gas exchange system, and in vivo rates of Rubisco carboxylation (V-c,V-max) and electron transport (J(max)) were derived to assess changes in the photosynthetic capacity in the co-dominant, evergreen oak species. Quercus myrtifolia did not show any change in photosynthetic capacity with prolonged exposure to elevated [CO2] during any season, and as a result the increase in photosynthesis due to the increased Supply Of CO2 was sustained at 72%. The codominant, Q. geminata, showed a loss of photosynthetic capacity with growth at elevated [CO2], such that during most measurement periods light-saturated photosynthesis in leaves grown and measured at elevated [CO2] was no higher than in leaves grown and measured at ambient CO2. A third oak, Q. chapmanii, showed a response similar to that of Q. myrtifolia. This suggests that at the critical phase of canopy closure in a woody community,, elevation Of [CO2] causes a species-dependent and time-dependent change in the capacity of the codominants to acquire carbon and energy. [References: 34]

Ainsworth, E. A., A. Rogers, et al. (2003). "Variation in acclimation of photosynthesis in Trifolium repens after eight years of exposure to Free Air CO2 Enrichment (FACE)." Journal of Experimental Botany 54(393): 2769-2774.

The initial stimulation of photosynthesis observed on elevation of [CO2] in grasslands has been predicted to be a transient phenomenon constrained by the loss of photosynthetic capacity due to other limitations, notably nutrients and sinks for carbohydrates. Legumes might be expected partially to escape these feedbacks through symbiotic N-2 fixation. The Free-Air Carbon dioxide Enrichment (FACE) experiment at Eschikon, Switzerland, has been the longest running investigation of the effects of open-air elevation of [CO2] on vegetation. The prediction of a long-term loss of photosynthetic capacity was tested by analysing photosynthesis in Trifolium repens L. (cv. Milkanova) in the spring and autumn of the eighth, ninth and tenth years of treatment. A high and low N treatment also allowed a test of the significance of exogenous N-supply in maintaining a stimulation of photosynthetic capacity in the long-term. Prior work in this Free Air CO2 Enrichment (FACE) experiment has revealed that elevated [CO2] increased both vegetative and reproductive growth of T. repens independent of N treatment. It is shown here that the photosynthetic response of T. repens was also independent of N fertilization under both current ambient and elevated (600 mumol mol(-1)) [CO2]. There was a strong effect of season on photosynthesis, with light-saturated rates (A(sat)) 37% higher in spring than in autumn. Higher A(sat) in the spring was supported by higher maximum Rubisco carboxylation rates (V,,m,x) and maximum rates of electron transport (J(max)) contributing to RuBP regeneration. Elevated [CO2] increased A(sat) by 37% when averaged across all measurement periods and both N fertilization levels, and decreased stomatal conductance by 25%. In spring, there was no effect of elevated [CO2] on photosynthetic capacity of leaves, but in autumn both V-c,V-max and J(max) were reduced by approximately 20% in elevated [CO2]. The results show that acclimation of photosynthetic capacity can occur in a nitrogen-fixing species, in the field where there are no artificial restrictions on sink capacity. However, even with acclimation there was a highly significant increase in photosynthesis at elevated [CO2]. [References: 28]

Ainsworth, E. A., P. J. Tranel, et al. (2003). "The clonal structure of Quercus geminata revealed by conserved microsatellite loci." Molecular Ecology 12(2): 527-532.

The scrub oak communities of the southeastern USA may have existed at their present locations for thousands of years. These oaks form suckers, and excavations of root systems suggest that clones may occupy very large areas. Resolution of the clonal nature of scrub oaks is important both to manage the tracts of this ecosystem that remain, and in conducting long-term ecological studies, where the study area must substantially exceed the area occupied by any single clone. Microsatellites were used to determine the genetic diversity of a dominant oak species within a 2-ha long-term experimental site on Merritt Island at the Kennedy Space Center. This area contains a long-term study of the effects of elevated CO2 on the ecosystem. Conservation of seven microsatellite loci, previously identified in the sessile oak, Quercus petraea , was tested in two Florida scrub oak species, Q. geminata and Q. myrtifolia . Sequence analysis revealed that all seven microsatellite loci were conserved in Q. geminata and five loci were conserved in Q. myrtifolia . Six microsatellite loci were polymorphic in Q. geminata and these were subsequently used to investigate the clonal structure of the Q. geminata population. Twenty-one unique combinations of microsatellites, or haplotypes, occurred only once, whereas the remaining 26 individuals belonged to a total of seven different haplotypes. Trees with identical haplotypes were in close proximity, supporting the interpretation that they were clones. The results showed that there is significant genetic diversity within the 2-ha experimental site. Microsatellites provided a powerful and noninvasive tool for distinguishing individual genotypes and determining an adequate area for long-term ecosystem studies. [References: 22]

Anderson, J. L. and C. A. Shearer (2002). "Halosarpheia heteroguttulata: Anamorph and report from the northern hemisphere." Mycotaxon 82: 115-120.

Halosarpheia heteroguttulata is reported for the first time from North America. This freshwater ascomycete was cultured from woody debris collected from the Fakahatchee Strand Preserve State Park, Florida USA. A Trichocladium anamorph is reported for H. heteroguttulata. The teleomorph and anamorph are illustrated and morphological similarities of the anamorph to T constrictum are discussed. [References: 9]

Augspurger, C. K. and E. A. Bartlett (2003). "Differences in leaf phenology between juvenile and adult trees in a temperate deciduous forest." Tree Physiology 23(8): 517-525.

In a deciduous forest, differences in leaf phenology between juvenile and adult trees could result in juvenile trees avoiding canopy shade for part of the growing season. By expanding leaves earlier or initiating senescence later than canopy trees, juvenile trees would have some period in high light and therefore greater potential carbon gain. We observed leaf phenology of 376 individuals of 13 canopy tree species weekly over 3 years in a deciduous forest in east central Illinois, USA. Our objectives were: (1) to quantify for each species the extent of differences in leaf phenology between juvenile and conspecific adult trees; and (2) to determine the extent of phenological differences between juvenile Aesculus glabra Willd. and Acer saccharum Marsh. trees in understory and gap micro-habitats. All species displayed phenological. differences between life stages. For 10 species, bud break was significantly earlier, by an average of 8 days, for subcanopy individuals than for canopy individuals. In 11 species, completion of leaf expansion was earlier, by an average of 6 days, for subcanopy individuals than for canopy individuals. In contrast, there were no significant differences between life stages for start of senescence in 10 species and completion of leaf drop in nine species, For eight species, leaf longevity was significantly greater for subcanopy individuals than for canopy individuals by an average of 7 days (range = 4-10 days). Leaf phenology of subcanopy individuals of both Aesculus glabra and Acer saccharum responded to gap conditions. Leaf longevity was 11 days less in the understory than in gaps for Aesculus glabra, but 14 days more in the understory than in gaps for Acer saccharum. Therefore, leaf phenology differed broadly both between life stages and within the juvenile life stage in this community. A vertical gradient in temperature sums is the proposed mechanism explaining the patterns. Temperature sums accumulated more rapidly in the sheltered understory than in an open elevated area, similar to the canopy. Early leaf expansion by juvenile trees may result in a period of disproportionately higher carbon gain, similar to gains made during summer months from use of sun flecks. [References: 54]

Bernacchi, C. J., C. Calfapietra, et al. (2003). "Photosynthesis and stomatal conductance responses of poplars to free-air CO2 enrichment (PopFACE) during the first growth cycle and immediately following coppice." New Phytologist 159(3): 609-621.

Using the Poplar Free Air CO2 Enrichement (PopFACE) facility we investigated the effects of elevated [CO2] on the diurnal and growth cycle responses of photosynthesis and conductance in three poplar species. In situ diurnal measurements of photosynthesis were made on Populus alba, P. nigra and P. xeuramericana and, in parallel, in vivo maximum capacity for carboxylation (V-c,V-max) and maximum rates of electron transport (J(max)) were determined by gas exchange measurement. Light saturated (A(sat)) and daily integrated (A ') photosynthesis increased at elevated [CO2] in all species. Elevated [CO2] decreased V-c,V-max and J(max) for P. nigra and J(max) for P. $euramericana but had no effect on stomatal conductance in any of the species throughout the first growth cycle. During post-coppice re-growth, elevated [CO2] did not increase A(sat) in P. nigra and P. xeuramericana due to large decreases in V-c,V-max and J(max). A 50% increase in [CO2] under these open-air field conditions resulted in a large and sustained increase in A(sat). Although there were some differences between the species, these had little effect on photosynthetic rates at the growth [CO2]. Nevertheless the results show that even fast growing trees grown without rooting volume restriction in the open may still show some down-regulation of photosynthetic potential at elevated [CO2]. [References: 61]

Bernacchi, C. J., C. Pimentel, et al. (2003). "In vivo temperature response functions of parameters required to model RuBP-limited photosynthesis." Plant, Cell & Environment 26(9): 1419-1430.

The leaf model of C-3 photosynthesis of Farquhar, von Caemmerer & Berry ( Planta 149, 78 - 90, 1980) provides the basis for scaling carbon exchange from leaf to canopy and Earth-System models, and is widely used to project biosphere responses to global change. This scaling requires using the leaf model over a wider temperature range than that for which the model was originally parameterized. The leaf model assumes that photosynthetic CO2 uptake within a leaf is either limited by the rate of ribulose-1,5-bisphosphate (RuBP) regeneration or the activity of RuBP carboxylase-oxygenase ( Rubisco). Previously we reported a re-parameterization of the temperature responses of Rubisco activity that proved robust when applied to a range of species. Herein this is extended to re-parameterizing the response of RuBP-limited photosynthesis to temperature. RuBP-limited photosynthesis is assumed to depend on the whole chain electron transport rate, which is described as a three-parameter non-rectangular hyperbolic function of photon flux. Herein these three parameters are determined from simultaneous measurement of chlorophyll fluorescence and CO2 exchange of tobacco leaves, at temperatures from 10 to 40 degreesC. All varied significantly with temperature and were modified further with variation in growth temperature from 15 to 35 degreesC. These parameters closely predicted the response of RuBP-limited photosynthesis to temperature measured in both lemon and poplar and showed a significant improvement over predictions based on earlier parameterizations. We provide the necessary equations for use of the model of Farquhar et al. (1980) with our newly derived temperature functions for predicting both Rubiscoand RuBP-limited photosynthesis. [References: 53]

Bernacchi, C. J., A. R. Portis, et al. (2002). "Temperature response of mesophyll conductance. Implications for the determination of Rubisco enzyme kinetics and for limitations to photosynthesis in vivo." Plant Physiology 130(4): 1992-1998.

CO2 transfer conductance from the intercellular airspaces of the leaf into the chloroplast, defined as mesophyll conductance (g(m)) is finite. Therefore, it will limit photosynthesis when CO2 is not saturating, as in C3 leaves in the present atmosphere. Little is known about the processes that determine the magnitude of g(m). The process dominating g(m) is uncertain, though carbonic anhydrase, aquaporins, and the diffusivity of CO2 in water have all been suggested. The response of g(m) to temperature (10degreesC-40degreesC) in mature leaves of tobacco (Nicotiana tabacum L. cv W38) was determined using measurements of leaf carbon dioxide and water vapor exchange, coupled with modulated chlorophyll fluorescence. These measurements revealed a temperature coefficient (Q(10)) of approximately 2.2 for g(m), suggesting control by a protein-facilitated process because the Q(10) for diffusion of CO2 in water is about 1.25. Further, g(m), values are maximal at 35degreesC to 37.5degreesC, again suggesting a protein-facilitated process, but with a lower energy of deactivation than Rubisco. Using the temperature response of g(m) to calculate CO2 at Rubisco, the kinetic parameters of Rubisco were calculated in vivo from 10degreesC to 40degreesC. Using these parameters, we determined the limitation imposed on photosynthesis by g(m). Despite an exponential rise with temperature, g(m) does not keep pace with increased capacity for CO2 uptake at the site of Rubisco. The fraction of the total limitations to CO2 uptake within the leaf attributable to g(m) rose from 0.10 at 10degreesC to 0.22 at 40degreesC. This shows that transfer of CO2 from the intercellular air space to Rubisco is a very substantial limitation on photosynthesis, especially at high temperature. [References: 41]

Bohnert, H. J. and J. C. Cushman (2002). "Plants and environmental stress adaptation strategies." Plant Biotechnology And Transgenic Plants. Pg.: 635-664.

Campbell, J., J. L. Anderson, et al. (2003). "Systematics of Halosarpheia based on morphological and molecular data." Mycologia 95(3): 530-552.

The genus Halosarpheia (Halosphaeriales) was established for marine ascomycetes with obpyriform to sub-globose, coriaceous, brown to black ostiolate ascomata with long necks; hamathecia of catenophyses; thin-walled, unitunicate, persistent asci with thick-walled apices; and ellipsoid, one septate, hyaline ascospores equipped with coiled, threadlike apical appendages that unfurl in water. Emphasis on ascospore appendage morphology has led to the inclusion in the genus of morphologically disparate fungi from a variety of marine and freshwater habitats. To better understand the evolutionary relationships of Halosarpheia species, phylogenetic analyses were conducted on 16 Halosarpheia species, 13 other species of Halosphaeriales and representatives of the Microascales, Hypocreales, Sordariales and Xylariales using 18S and 28S rDNA sequence data. All of the Halosarpheia species occurred on the Halosphaeriales clade. The type species of the genus, H. fibrosa, occurred on a well-supported clade with two morphologically similar species, H. trullifera and H. unicellulafis. This clade, which phylogenetically was distant from the clades of other Halosarpheia species, represents the genus Halosarpheia sensu stricto. The other Halosarpheia species were distributed among eight other well-supported clades clearly separated from one another based on molecular data. New generic names are established for six of these clades, one new species is described, and one species is transferred to Aniptodera. A table (TABLE I) comparing the morphology, habitat, substrate and distribution of the genera of aquatic ascomycetes with coiled, threadlike apical appendages treated in this study is provided, along with a key for their identification. [References: 69]

Campbell, J. and C. A. Shearer (2003). "A reassessment of two freshwater ascomycetes, Ceriospora caudae-suis and Submersisphaeria aquatica." Mycologia 95(1): 41-53.

Ceriospora caudae-suis and Submersisphaeria aquatica, two freshwater pyrenomycetes reported infrequently since their original description, occur commonly on submerged woody debris in the USA. Based on analyses of 28S rDNA sequence data and morphology, both species belong in the annulatascaceae. Ceriospora caudae-suis is transferred to Pseudoproboscispora, a genus in the Annulatascaceae with similar overall morphology and ecology. Submersisphaeria aquatica is redescribed and illustrated based on additional collections. [References: 42]

Campbell, J., C. A. Shearer, et al. (2002). "Corollospora revisited: a molecular approach." Fungi In Marine Environemnts 7: 15-33.

Chen, J. S., M. R. Berenbaum, et al. (2002). "Amino acids in SRS1 and SRS6 are critical for furanocoumarin metabolism by CYP6B1v1, a cytochrome P450 monooxygenase." Insect Molecular Biology 11(2): 175-186.

CYP6B1v1 is the principal cytochrome P450 monooxygenase (P450) that detoxifies dietary furanocoumarins in the guts of Papilio polyxenes , the black swallowtail caterpillar. Sequence alignments and structure comparisons of CYP6B1v1 with the mouse CYP2A5 and bacterial CYP102 proteins, which are also capable of metabolizing the linear furanocoumarin xanthotoxin (8-methoxypsoralen), suggested that Phe116, His117, Val368 and Phe484 might be active site residues. In a homology model developed for CYP6B1v1, the side chains of Phe116 and His117 located in the B'-C loop of SRS1 are predicted to be positioned above the haem plane, while the side chain of Phe484 located in SRS6 is predicted near the entrance of the catalytic pocket. Site-directed mutagenesis of residues Phe116, His117 and Phe484 indicated that these residues represent several of those that determine this protein's stability and substrate specificity. Whereas all aromatic mutants of Phe116 and Phe484 generated CO-difference spectra with maxima at 450 nm indicative of correctly configured monooxygenases, aromatic mutants of Phe116 exhibited reduced reactivities toward some furanocoumarins and aromatic mutants of Phe484 eliminated all reactivities toward furanocoumarins. All single and double aliphatic mutants of Phe116, His117 and Phe484 and aromatic mutants of His117 generated carbon monoxide (CO) difference spectra with maxima at 420 nm (P420) indicative of incorrectly configured monooxygenases. These studies define residues Phe116, His117 and Phe484 as determinants of this insect P450's catalytic site integrity and residues Phe116 and Phe484 as determinants of its substrate specificity. Conservation of Phe116 and His117 in an array of lepidopteran CYP6B proteins implies that these amino acids serve a similar function in other monooxygenases of the insect CYP6B subfamily. [References: 56]

Cornic, G. and C. Fresneau (2002). "Photosynthetic carbon reduction and carbon oxidation cycles are the main electron sinks for photosystem II activity during a mild drought." Annals of Botany 89(Special Issue SI): 887-894.

Stomatal closure can explain the inhibition of net CO2 uptake by a leaf subjected to a mild drought: the photosynthetic apparatus appears resistant to lack of water. Changes in both the water content of leaves maintained in a constant environment and the ambient CO2 molar fraction during measurements on well-hydrated leaves lead to similar effects on net CO2 uptake and whole chain electron transport as estimated by leaf chlorophyll fluorescence measurements. In particular, it is shown that photosystem 11 (PSII) functioning and its regulation are not qualitatively changed during desiccation and that the variations in PSII photochemistry can simply be understood by changes in substrate availability in this condition. Moreover, an analysis of the literature shows that when inhibition of net CO2 uptake by C-3 leaves under drought (Phaseolus vulgaris L., Helianthus annus L. and Solanum tuberosum L.) was lower than 80 %, elevated CO2 completely restored the photosynthetic capacity. The CO2 molar fraction in the chloroplasts declines as stomata close in drying leaves. As a consequence, in C-3 plants, ribulose-1,5-bisphosphate oxygenation increases and becomes the main sink for photosynthetic electrons. Depending on the prevailing photon flux density, the O-2 uptake through photorespiratory activity can entirely replace carbon dioxide as an electron acceptor, or not. The rate of the Mehler reaction remains low and unchanged during desiccation. However, drought could also involve CO2-sensitive modification of the photosynthetic metabolism depending on plant growth conditions and possibly also on plant species. (C) 2002 Annals of Botany Company. [References: 33]

Dalling, J. W. and S. P. Hubbell (2002). "Seed size, growth rate and gap microsite conditions as determinants of recruitment success for pioneer species." Journal of Ecology 90(3): 557-568.

1 We examined how seed size and seedling growth rate influence recruitment success of neotropical pioneer species. We investigated the soil seed bank, and followed seedlings from emergence and establishment to the sapling stage in artificially created gaps in secondary forest on the Barro Colorado Nature Monument, Panama. 2 To simulate microsite variation within gaps, litter addition/removal and soil disturbance treatments were applied to seedling plots in a factorial design. 3 Seedling emergence was almost three-fold higher in litter-free plots than in control plots. 4 We found a negative relationship between seed mass and seed abundance in the soil, seed mass was positively correlated with seedling emergence success from the seed bank and with seedling survival through to the end of the first dry season. 5 In the 18 months following the first dry season we observed an uncoupling of seed mass from seedling performance. Seedling mortality was now a function of maximum relative growth rate, with higher mortality of fast-growing species attributable to herbivory, notably by shoot-borers. 6 We propose that a seed size-dependent trade-off between dispersal success (selecting for large seed number), and emergence-establishment success (selecting for large seed size) can explain the maintenance of wide variation in seed size among pioneer species. Secondarily, a trade-off between growth rate and susceptibility to herbivores acting at the post-establishment phase may contribute to observed differences in light requirements among pioneer species. [References: 74]

Dalling, J. W., H. C. Muller-Landau, et al. (2002). "Role of dispersal in the recruitment limitation of neotropical pioneer species." Journal of Ecology 90(4): 714-727.

1 We examined the importance of seed dispersal in predicting the pioneer seedling composition in recent gaps in a forest plot on Barro Colorado Island (BCI), Panama. We characterize seed dispersal for 13 taxa from seed rain data collected over 13 years in 200 mesh traps, and for an additional species from germination from soil samples collected in one year. We describe seedling distribution patterns from a complete census of all seedlings of these 14 taxa present in 36 treefall gaps. 2 A maximum likelihood model, incorporating both distance to adult trees and tree size, fitted observed seed rain to traps quite well for all taxa. 3 The ability to predict seedling recruit number per gap varied greatly among taxa. For 8 of 14 taxa, regression models incorporating predicted seed rain were significantly better predictors of seedling recruitment than models in which recruitment probability was assumed constant in all sites. 4 To see if variation in local dispersal patterns determined the community composition of gaps, we examined the relative abundances of these 14 pioneer taxa in the 36 gaps. We found that taxon abundances were significantly positively correlated with abundances predicted from seed dispersal models and seed-seedling regressions for 27 out of 36 gaps. 5 Overall, we find evidence that limited seed dispersal is an important factor contributing, together with factors affecting post-dispersal recruitment success, to seedling distribution patterns in gaps. [References: 53]

Daws, M. I., D. Burslem, et al. (2002). "Differences in seed germination responses may promote coexistence of four sympatric Piper species." Functional Ecology 16(2): 258-267.

1. Species-specific responses to the range of microsites resulting from canopy gap formation may contribute to coexistence in tropical forests. We investigated the effects of four factors affected by canopy gap formation (red : far-red light, soil nitrate concentrations, soil temperature fluctuations and soil water potential) on the germination response of four pioneer Piper species (P. dilatatum, P. hispidum, P. marginatum and P peltatum) that are typically found in canopy gaps and clearings. 2. All four Piper species required light for maximum germination. However, the ratio of red : far-red light (R : FR) resulting in maximum germination varied between species. Piper peltatum will germinate in simulated understorey light conditions; P. dilatatum and P. hispidum require conditions typically found in small to medium gaps; while P. marginatum requires the conditions appropriate to large gaps. 3. Only P. marginatum was affected by nitrate concentration: elevated concentrations increased the germination rate. This suggests that this species could detect canopy gaps using a combination of high R : FR and elevated soil nitrate concentrations. 4. The germination rate of P. marginatum was least sensitive to low water potentials and high daytime temperatures characteristic of large gaps. Piper peltatum was most sensitive to these treatments, while P. dilatatum and P. hispidum were intermediate in response. 5. A principal components analysis of the ratios of germination in understorey to large gap conditions, for four variables, generated a significant axis that explained 88.5% of the variance in germination response between species. Differential species distribution along this axis, based on species-specific responses, may allow germination to occur in the most suitable microsite for onward growth of the seedling and contribute to species coexistence by reducing interspecific competition. [References: 42]

Daws, M. I., C. E. Mullins, et al. (2002). "Topographic position affects the water regime in a semideciduous tropical forest in Panama." Plant & Soil 238(1): 79-90.

The effects of topographic position on water regime in a semideciduous tropical forest on Barro Colorado Island in Panama were assessed by measuring soil matric potential using the filter paper technique and by using measured soil water release characteristics to convert a long-term (20 years) gravimetric water content data-set to matric potential. These were also compared against predictions from a simple water balance model. Soil matric potentials on slope sites were significantly higher than on plateau sites throughout the measurement interval and slopes experienced a shorter duration of drought during the annual dry-season. Measured values of matric potential agreed with those predicted from converting the gravimetric measurements using water release characteristics. Annual duration of drought predicted by the simple water balance model agreed with values determined from the converted long term water content data-set and was able to predict the annual duration of drought on plateau sites. On slope sites, the water balance systematically and significantly overestimated the duration of drought obtained from the water content data-set, suggesting that slope sites were supplied with water from upslope. Predictions of annual drought duration from sites with higher annual rainfall than Barro Colorado Island (BCI), suggest that while plateau sites on BCI experience a water regime consistent with annual rainfall, slopes experience a water regime more similar to that of forests with much higher rainfall. We conclude that such large variations in water regime over small spatial scales may play a role in maintaining high species richness through providing opportunities for niche specialisation and by buffering slopes against possible climate change. [References: 46]

De Lucia, E. H., D. Whitehead, et al. (2003). "The relative limitation of photosynthesis by mesophyll conductance in co-occurring species in a temperate rainforest dominated by the conifer Dacrydium cupressinum." Functional Plant Biology 30(12): 1197-1204.

The capacity to conduct CO2 from the intercellar spaces in leaves to the site of fixation (mesophyll conductance, g(m)) may pose a significant limitation to photosynthesis. Dacrydium cupressinum Sol. ex Lamb. (rimu), a native conifer of New Zealand, and other members of the Podocarpaceae evolved during the Jurassic when the partial pressure of CO2 exceeded 200 Pa. This species has low rates of photosynthesis and high levels of leaf nitrogen, which have led to the hypothesis that low g(m) restricts photosynthesis. Mesophyll conductance was estimated from gas-exchange and fluorescence measurements for this and other co-occurring tree species [Prumnopitys ferruginea D. Don (miro), Weinmannia racemosa L. f. (kamahi), Meterosideros umbellata Cav. (rata)]. Pinus radiata D. Don (radiata pine) and Phaseolus vulgaris L. (bean) were included to provide comparisons with a rapidly growing tree and herbaceous plant with relatively high photosynthetic rates. Mesophyll conductance was not statistically different among indigenous tree species but was lowest for D. cupressinum. This species also had the lowest ratio of mesophyll to stomatal conductance, g(m)/g(st) and was the only species where the decline in partial pressure of CO2 was greater from the intercellular air space to the site of fixation (16.3 Pa) than between the bulk air and the intercellular spaces (8.8 Pa), providing support for the hypotheses that low g(m) limits photosynthesis in this species. As a group, conifers had marginally lower g(m) and g(m)/g(st) ratio than angiosperms, but this difference was strongly influenced by the high values for Phaseolus vulgaris. That co-occurring members of the Podocarpaceae operated differently suggests that low g(m) may reflect a response to evolutionary pressures other than high atmospheric CO2 partial pressure. [References: 44]

DeLucia, E. H., K. George, et al. (2002). "Radiation-use efficiency of a forest exposed to elevated concentrations of atmospheric carbon dioxide." Tree Physiology 22(14): 1003-1010.

We compared radiation-use efficiency of growth (F), defined as rate of biomass accumulation per unit of absorbed photosynthetically active radiation, of forest plots exposed to ambient (similar to360 mul l(-1)) or elevated (similar to560 mul l(-1)) atmospheric CO2 concentration ([CO2]). Large plots (30-m diameter) in a loblolly pine (Pinus taeda L.) plantation, which contained several hardwood species in the understory, were fumigated with a free-air CO2 enrichment system. Biomass accumulation of the dominant loblolly pines was calculated from monthly measurements of tree growth and site-specific allometric equations. Depending on the species, leaf area index (L*) was estimated by three methods: optical, allometric and litterfall. Based on the relationship between tree height and diameter during the first 3 years of exposure, we conclude that elevated [CO2] did not alter the pattern of aboveground biomass allocation in loblolly pine. There was considerable variation in L* estimates by the different methods; total L* was 18-42% lower when estimated by the optical method compared with estimates from allometric calculations, and this discrepancy was reduced when optical measurements were corrected for the non-random distribution of loblolly pine foliage. The allometric + litterfall approach revealed a seasonal maximum total L* of 6.2-7.1 with about 1/3 of the total from hardwood foliage. Elevated [CO2] had only a slight effect on L* in the first 3 years of this study. Mean F, ( SD), calculated for loblolly pine only, was 0.49 +/- 0.05 and 0.62 +/- 0.04 g MJ(-1) for trees in the ambient and elevated [CO2] plots, respectively. The 27% increase in F, in response to CO2 enrichment was caused primarily by the stimulation of biomass increment, as there was only a small effect of elevated [CO2] on L* during the initial years of fumigation. Long-terrn increases in atmospheric [CO2] can increase epsilon in closed-canopy forests but the absolute magnitude and duration of this increase remain uncertain. [References: 57]

DeLucia, E. H., M. H. Turnbull, et al. (2003). "The contribution of bryophytes to the carbon exchange for a temperate rainforest." Global Change Biology 9(8): 1158-1170.

Bryophytes blanket the floor of temperate rainforests in New Zealand and may influence a number of important ecosystem processes, including carbon cycling. Their contribution to forest floor carbon exchange was determined in a mature, undisturbed podocarp-broadleaved forest in New Zealand, dominated by 100-400-year-old rimu (Dacrydium cupressimum ) trees. Eight species of mosses and 13 species of liverworts contributed to the 62% cover of the diverse forest floor community. The bryophyte community developed a relatively thin (depth <30 mm), but dense, canopy that experienced elevated CO2 partial pressures (median 46.6 Pa immediately below the bryophyte canopy) relative to the surrounding air (median 37.6 Pa at 100 mm above the canopy). Light-saturated rates of net CO2 exchange from 14 microcosms collected from the forest floor were highly variable; the maximum rate of net uptake (bryophyte photosynthesis - whole-plant respiration) per unit ground area at saturating irradiance was 1.9 mumol m(-2) s(-1) and in one microcosm, the net rate of CO2 exchange was negative (respiration). CO2 exchange for all microcosms was strongly dependent on water content. The average water content in the microcosms ranged from 1375% when fully saturated to 250% when air-dried. Reduction in water content across this range resulted in an average decrease of 85% in net CO2 uptake per unit ground area. The results from the microcosms were used in a model to estimate annual carbon exchange for the forest floor. This model incorporated hourly variability in average irradiance reaching the forest floor, water content of the bryophyte layer, and air and soil temperature. The annual net carbon uptake by forest floor bryophytes was 103 g m(-2) , compared to annual carbon efflux from the forest floor (bryophyte and soil respiration) of -1010 g m(-2) . To put this in perspective of the magnitude of the components of CO2 exchange for the forest floor, the bryophyte layer reclaimed an amount of CO2 equivalent to only about 10% of forest floor respiration (bryophyte plus soil) or similar to11% of soil respiration. The contribution of forest floor bryophytes to productivity in this temperate rainforest was much smaller than in boreal forests, possibly because of differences in species composition and environmental limitations to photosynthesis. Because of their close dependence on water table depth, the contribution of the bryophyte community to ecosystem CO2 exchange may be highly responsive to rapid changes in climate. [References: 48]

DiMichele, W. A. and T. L. Phillips (2002). "The ecology of Paleozoic ferns." Review of Palaeobotany & Palynology 119(1-2): 143-159.

Ferns or fern-like plants have been important elements of terrestrial vegetation since the Late Devonian. Rhacophyton, a fern-like plant of the Late Devonian, appears to have been a colonizer of wet substrates, often forming large, nearly monotypic stands in peat-accumulating swamps. The earliest true ferns have been found in environments with high levels of disturbance, often tire, which suggest opportunistic, colonizing life histories, consistent with small, scrambling body plans. During the Early Carboniferous all major body plans and life histories of ferns appear, including scrambling ground cover, tree habit, and lianas. These ecological roles are distributed across several major lineages, including the Zygopteridales, Filicales, and Marattiales, plus some fern-like groups of uncertain affinity, and disappear and reappear independently within these groups. Until the Stephanian, the later part of the Late Carboniferous, ferns largely were confined to secondary ecological roles: colonists, understory vegetation, small vines. Beginning in the latter part of the Westphalian and expanding dramatically in the Stephanian, marattialean tree ferns became the dominant trees of tropical lowland, wetland forests. This dominance continued locally into the Permian in wetter parts of the landscape. The Paleozoic ferns suffered major extinctions at several times, beginning in the Late Carboniferous. By the Permian, new lineages were appearing, some of which would persist into and become dominant vegetational components during the Mesozoic. Among these lineages virtually all of the life histories and body plans that characterized Paleozoic ferns would reappear independently, plus some new kinds of organization and ecology, emphasizing the great evolutionary flexibility and responsiveness of fern-like construction and reproductive biology. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 102]

DiMichele, W. A., T. L. Phillips, et al. (2002). "Place vs. time and vegetational persistence: a comparison of four tropical mires from the Illinois Basin during the height of the Pennsylvanian ice age." International Journal of Coal Geology 50(1-4): 43-72.

Coal balls were collected from four coal beds in the southeastern part of the Illinois Basin. Collections were made from the Springfield, Herrin, and Baker coals in western Kentucky, and from the Danville Coal in southwestern Indiana. These four coal beds are among the principal mineable coals of the Illinois Basin and belong to the Carbondale and Shelburn Formations of late Middle Pennsylvanian age. Vegetational composition was analyzed quantitatively. Coal-ball samples from the Springfield, Herrin, and Baker are dominated by the lycopsid tree Lepidophloios, with lesser numbers of Psaronius tree ferns, medullosan pteridosperms, and the lycopsid trees Synchysidendron and Diaphorodendron. This vegetation is similar to that found in the Springfield and Herrin coals elsewhere in the Illinois Basin, as reported in previous studies. The Danville coal sample, which is considerably smaller than the others, is dominated by Psaronius with the lycopsids Sigillaria and Synchysidendron as subdominants. Coal balls from the Springfield coal were collected in zones directly from the coal bed and their zone-by-zone composition indicates three to four distinct plant assemblages. The other coals were analyzed as whole-seam random samples, averaging the landscape composition of the parent mire environments. This analysis indicates that these coals, separated from each other by marine and terrestrial-clastic deposits, have essentially the same floristic composition and, thus, appear to represent a common species pool that persisted throughout the late Middle Pennsylvanian, despite changes in baselevel and climate attendant the glacial-interglacial cyclicity of the Pennsylvanian ice age. Patterns of species abundance and diversity are much the same for the Springfield, Herrin, and Baker, although each coal, both in the local area sampled, and regionally, has its own paleobotanical peculiarities. Despite minor differences, these coals indicate a high degree of recurrence of assemblage and landscape organization. The Danville departs dramatically from the dominance-diversity composition of the older coals, presaging patterns of tree-fern and Sigillaria dominance of Late Pennsylvanian coals of the eastern United States, but, nonetheless, built on a species pool shared with the older coals. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 54]

Downie, S. R., R. L. Hartman, et al. (2002). "Polyphyly of the spring-parsleys (Cymopterus): molecular and morphological evidence suggests complex relationships among the perennial endemic genera of western North American Apiaceae." Canadian Journal of Botany-Revue Canadienne de Botanique 80(12): 1295-1324.

Cladistic analyses of DNA sequences from the nuclear rDNA internal transcribed spacer region and cpDNA rps16 intron and, for a subset of taxa, the cpDNA trnF-trnL-trnT locus were carried out to evaluate the monophyly of Cymopterus and to ascertain its phylogenetic placement among the other perennial genera of Apiaceae (Umbelliferae) subfamily Apioideae endemic to western North America. To elucidate patterns in the evolution of specific fruit characters and to evaluate their utility in circumscribing genera unambiguously, additional evidence was procured from cross-sections of mature fruits and the results of cladistic analysis of 25 morphological characters. Analyses of the partitioned data sets resulted in weakly supported and largely unresolved phylogenetic hypotheses, possibly due to the rapid radiation of the group, whereas the combined analysis of all molecular evidence resulted in a well-resolved phylogeny with higher bootstrap support. The traditionally used fruit characters of wing shape and composition and orientation of mericarp compression are highly variable. The results of these analyses reveal that Cymopterus and Lomatium, the two largest genera of western North American Apiaceae, are polyphyletic, and that their species are inextricably linked with those of other endemic perennial genera of the region (such as, Aletes, Musineon, Oreoxis, Pseudocymopterus, Pteryxia, and Tauschia), many of which are also not monophyletic. Prior emphasis on characters of the fruit in all systems of classification of the group has led to highly artificial assemblages of species. A complete reassessment of generic limits of all western endemic Apiaceae is required, as is further systematic study of this intractable group. [References: 95]

Ebinger, J. E., D. S. Seigler, et al. (2002). "Notes on the segregates of Acacia farnesiana (L.) Willd. (Fabaceae : Mimosoideae) and related species in North America." Southwestern Naturalist 47(1): 86-91.

Finzi, A. C., E. H. DeLucia, et al. (2002). "The nitrogen budget of a pine forest under free air CO2 enrichment." Oecologia 132(4): 567-578.

Elevated concentrations of atmospheric CO2 increase plant biomass, net primary production (NPP) and plant demand for nitrogen (N). The demand for N set by rapid plant growth under elevated CO2 could be met by increasing soil N availability or by greater efficiency of N uptake. Alternatively, plants could increase their nitrogen-use efficiency (NUE), thereby maintaining high rates of growth and NPP in the face of nutrient limitation. We quantified dry matter and N budgets for a young pine forest exposed to 4 years of elevated CO2 USing free-air CO2 enrichment technology. We addressed three questions: Does elevated CO2 increase forest NPP and the demand for N by vegetation? Is demand for N met by greater uptake from soils, a shift in the distribution of N between plants, microbes, and soils, or increases in NUE under elevated CO2? Will soil N availability constrain the NPP response of this forest as CO2 fumigation continues? A step-function increase in atmospheric CO2 significantly increased NPP during the first 4 years of this study. Significant increases in NUE under elevated CO2 modulated the average annual requirement for N by vegetation in the first and third growing seasons under elevated CO2; the average stimulation of NPP in these years was 21% whereas the average annual stimulation of the N requirement was only 6%. In the second and fourth growing seasons, increases in NPP increased the annual requirement for N by 27-33%. Increases in the annual requirement for N were largely met by increases in N uptake from soils. Retranslocation of nutrients prior to senescence played only a minor role in supplying the additional N required by trees growing under elevated CO2. NPP was highly correlated with between-plot variation in the annual rate of net N mineralization and CO2 treatment. This demonstrates that NPP is colimited by C availability, as CO2 from the atmosphere, and N availability from soils. There is no evidence that soil N mineralization rates have increased under elevated CO2. The correlation between NPP and N mineralization rates and the increase in the annual requirement for N in certain years imply that soil N availability may control the long-term productivity response of this ecosystem to elevated CO2. Although we have no evidence suggesting that NPP is declining in response to >4 years of CO2 fumigation, if the annual requirement of N continues to be stimulated by elevated CO2, we predict that the productivity response of this forest ecosystem will decline over time. [References: 70]

Fitzhugh, R. D., L. M. Christenson, et al. (2003). "The fate of (NO2-)-N-15 tracer in soils under different tree species of the Catskill Mountains, New York." Soil Science Society of America Journal 67(4): 1257-1265.

The incorporation of nitrite (NO2-) into soil organic matter (SOM) has received little attention as a mechanism contributing to the retention of atmospherically deposited N in forest ecosystems, despite previous studies in agricultural systems showing that NO2- fixation by SOM is enhanced in soils with high acidity and organic matter content, characteristics commonly found in forest soils. Given previous studies showing that nitrification and nitrate (NO3-) leaching may vary significantly in soils under different tree species, the primary objectives of this study were to determine if the incorporation of NO2- into SOM was quantitatively significant and if the incorporation varied among soils under different tree species from the Catskill Mountains in New York State. A pulse-chase laboratory experiment was performed, where (NO2-)-N-15 was added to organic soils from three tree species (American beech [Fagus grandifolia], northern red oak [Quercus rubra], sugar maple [A cer saccharum]), and N-15 recoveries were determined in total soil, extractable inorganic, readily mineralizable, microbial biomass, dinitrogen (N-2), and nitrous oxide (N2O) pools. Results from our experiment demonstrate that the incorporation of NO2- into SOM can occur rapidly, at time scales of 1 d or shorter, and that NO2- incorporation into SOM is the dominant fate of the (NO2-)-N-15 tracer, suggesting that the incorporation of NO2- into SOM is a potentially important N sink in forest soils. The incorporation of NO2- into SOM did not vary significantly among tree species. Our results suggest that models of the N cycle in forest ecosystems should include considerations of NO2- incorporation into SOM. [References: 69]

Fitzhugh, R. D., C. T. Driscoll, et al. (2003). "Soil freezing and the acid-base chemistry of soil solutions in a northern hardwood forest." Soil Science Society of America Journal 67(6): 1897-1908.

Reductions in the depth and duration of snow cover under a warmer climate may cause soil freezing events to become more frequent, severe, and spatially extensive in northern temperate forest ecosystems. In this experiment, snow cover was manipulated to simulate the late development of snowpack and to induce soil freezing at sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis) stands at the Hubbard Brook Experimental Forest (HBEF) in the White Mountains of New Hampshire. The objective of this manipulation was to elucidate the effects of soil freezing on the concentrations and fluxes of soil solution H+, Ca2+, Mg2+, K+, and Na+, as well as values of acid neutralizing capacity (ANC). Mild soil freezing events (soil temperatures never decreased below -5degreesC) resulted in pronounced acidification of soil solutions, driven primarily by nitrification, in the forest floor of sugar maple stands during the growing season. This mobilization of NO3- from the forest floor of maple stands was accompanied by the leaching of Ca2+ and Mg2+ in Oa horizon solutions. Responses of soil solution acid-base chemistry to soil freezing were not evident in yellow birch stands or in the Bs horizon of either vegetation type, emphasizing the importance of vegetation type and the mineral soil in determining the effects of climatic disturbance on drainage water chemistry and nutrient loss. These results suggest that models of soil biogeochemistry in temperate forest ecosystems should consider soil-freezing events when simulating the acid-base chemistry of soil solutions and the translocation of nutrient base cations between soil horizons. [References: 61]

Fitzhugh, R. D., G. E. Likens, et al. (2003). "Role of soil freezing events in interannual patterns of stream chemistry at the Hubbard Brook experimental forest, New Hampshire." Environmental Science & Technology 37(8): 1575-1580.

Soil freezing is a disturbance of the below ground environment, potentially resulting in increased losses of NO3- and surface water acidification. Here, we report the effects of soil freezing on interannual variation in stream chemistry at the Hubbard Brook Experimental Forest, New Hampshire. Data from 1970 to 1997 of soil frost depth, snow cover, precipitation, air temperature, and stream discharge and chemistry were used in a stepwise linear regression model to select the variables that best predicted deviations of annual stream concentrations from 4-year running averages. Variables quantifying soil freezing severity were selected as significant predictors of short-term fluctuations in stream K+, NO3-, Ca2+, and Mg2+ concentrations from 1970 to 1989, explaining 59 and 47% of the short-term variability in K+ and NO3, respectively. Fine-root mortality and disturbance of root-soil-mic robe interactions, with subsequent effects on decomposition and nutrient uptake, likely contributed to the mobilization of K+ and NO3- to streamwater following severe soil freezing events. The relationship between soil freezing and stream chemistry, however, weakened during the period 1990-1997. Because soil freezing has had inconsistent effects on stream chemistry during the period 1970-1997, it is unclear whether future changes in the frequency, duration, and depth of soil freezing events as the result of changes in the snow cover regime under a warmer climate will have significant impacts on the losses of NO3 and nutrient-base cations from temperate northern ecosystems. [References: 21]

Fitzhugh, R. D., G. M. Lovett, et al. (2003). "Biotic and abiotic immobilization of ammonium, nitrite, and nitrate in soils developed under different tree species in the Catskill Mountains, New York, USA." Global Change Biology 9(11): 1591-1601.

Nitrogen retention in soil organic matter (SOM) is a key process influencing the accumulation and loss of N in forest ecosystems, but the rates and mechanisms of inorganic N retention in soils are not well understood. The primary objectives of this study were to compare ammonium (NH4+), nitrite (NO2-), and nitrate (NO3-) immobilization among soils developed under different tree species in the Catskill Mountains of New York State, and to determine the relative roles of biotic or abiotic processes in soil N retention. A laboratory experiment was performed, where N-15 was added as NH4+, NO2-, or NO3- to live and mercury-treated O horizon soils from three tree species (American beech, northern red oak, sugar maple), and N-15 recoveries were determined in the SOM pool. Mercuric chloride was used to treat soils as this chemical inhibits microbial metabolism without significantly altering the chemistry of SOM. The recovery of N-15 in SOM was almost always greater for NH4+ (mean 20%) and NO2- (47%) than for NO3- (10%). Ammonium immobilization occurred primarily by biotic processes, with mean recoveries in live soils increasing from 9% at 15 min to 53% after 28 days of incubation. The incorporation of NO2- into SOM occurred rapidly (<15 min) via abiotic processes. Abiotic immobilization of NO2- (mean recovery 58%) was significantly greater than abiotic immobilization of NH4+ (7%) or NO3- (7%). The incorporation of NO2- into SOM did not vary significantly among tree species, so this mechanism likely does not contribute to differences in soil NO3- dynamics among species. As over 30% of the (NO2-)-N-15 label was recovered in SOM within 15 min in live soils, and the products of NO2- incorporation into SOM remained relatively stable throughout the 28-day incubation, our results suggest that NO2- incorporation into SOM may be an important mechanism of N retention in forest soils. The importance of NO2- immobilization for N retention in field soils, however, will depend on the competition between incorporation into SOM and nitrification for transiently available NO2-. Further research is required to determine the importance of this process in field environments. [References: 41]

Gavin, D. G. (2003). "Forest soil disturbance intervals inferred from soil charcoal radiocarbon dates." Canadian Journal of Forest Research-Journal Canadien de la Recherche Forestiere 33(12): 2514-2518.

Forest soil disturbance intervals are usually too long to measure using plot-based studies, and thus they are poorly understood. The mean soil disturbance interval (MSDI) in an old-growth forest on the west coast of Vancouver Island was estimated from radiocarbon dates of charcoal from organic and mineral soil horizons. Two assumptions are required to estimate the MSDI: (1) charcoal from forest fires is deposited within the organic horizon and eventually mixed into deeper mineral horizons by soil disturbances, and (2) the probability of soil disturbance is spatially homogeneous and affected only by the time since the last fire or the last soil disturbance. The MSDI is then estimated by the rate at which the proportion of undisturbed sample sites (determined by the proportion of sites with charcoal from the most recent fire in the organic horizon) decreases with increasing time since the last fire. Soil charcoal evidence of time since fire was determined at 83 sites using 141 radiocarbon dates. The estimated MSDI was greater on slopes (ca. 2010 years) than on terraces (ca. 920 years). The long periods between soil disturbances, especially on slopes, are consistent with other evidence from the study area that suggests infrequent tree uprooting is the predominant mode of soil disturbance. [References: 28]

Gavin, D. G., L. B. Brubaker, et al. (2003). "An 1800-year record of the spatial and temporal distribution of fire from the west coast of Vancouver Island, Canada (vol 33, pg 573, 2003)." Canadian Journal of Forest Research-Journal Canadien de la Recherche Forestiere 33(6): 1167.

Gavin, D. G., L. B. Brubaker, et al. (2003). "An 1800-year record of the spatial and temporal distribution of fire from the west coast of Vancouver Island, Canada." Canadian Journal of Forest Research-Journal Canadien de la Recherche Forestiere 33(4): 573-586.

Charcoal records from lake sediments may show changes in fire frequency over thousands of years, but such records are ambiguous with regard to the actual locations of fires. Using a comparison of fire dates from an 1800-year lake sediment record from the west coast of Vancouver Island (British Columbia, Canada) and dates of last fire from 38 sites in the same watershed using tree-ring and soil-charcoal C-14 dates, we estimated the source area that contributes to charcoal peaks and determined the degree to which fires were biased to certain locations. Twenty-three charcoal peaks, likely corresponding with individual fire events, were objectively identified from the sediment record. Comparison of fire dates from charcoal peaks in the sediment record with fire dates from points near the lake suggests that the charcoal source area is within 500 m of the lake edge. Fire occurrence within this charcoal source area increased sharply at AD 1100 from ca. 50 to ca. 300 years between charcoal peaks, coeval with the first "Little Ice Age" cooling. Soil-charcoal radiocarbon dates revealed that 37% of the charcoal source area had not burned over the last 1800 years and that the 23 fires identified in the sediment record were restricted to south-facing slopes near the lake. This spatial pattern may result only if fire is >25 times more likely to occur on susceptible sites (south-facing slopes) than on less susceptible sites. This strong bias in fire location ensured the millennial-scale persistence of large areas of late-successional forest through past climatic periods. [References: 69]

Gavin, D. G., L. B. Brubaker, et al. (2003). "Holocene fire history of a coastal temperate rain forest based on soil charcoal radiocarbon dates." Ecology 84(1): 186-201.

The long-term role of fire in coastal temperate rain forest is poorly understood. To determine the historical role of fire on western Vancouver Island (British Columbia, Canada), we constructed a long-term spatially explicit fire history and examined the spatial and temporal distribution of fire during the Holocene. Two fire-history parameters (time-since-fire [TSF] and fire extent) were related to three landscape parameters landform [hill slope or terrace]. aspect, and forest composition) at 83 sites in a 730-ha low-elevation (less than similar to200 m) area of a mountainous watershed. We dated fires using tree rings ( 18 sites) and 120 soil-charcoal radiocarbon dates (65 sites). Comparisons among multiple radiocarbon dates indicated a high probability that the charcoal dated at each site represented the most recent fire, though we expect greater error in TSF estimates at sites where charcoal was very old (>6000 yr) and was restricted to mineral soil horizons. TSF estimates ranged from 64 to similar to12 220 yr; 45% of the sites have burned in the last 1000 yr, whereas 2017( of the sites have not burned for over 6000 yr. Differences in median TSF were more significant between landform types or across aspects than among forest types, Median TSF was significantly greater on terraces (4410 yr) than on hill slopes (740 yr). On hill slopes. all south-facing and southwest-facing sites have burned within the last 1000 yr compared to only 27% of north- and east-facing sites burning over the same period. Comparison of fire dates among neighboring sites indicated that fires rarely extended >250 m. During the late Holocene, landform controls have been strong. resulting in the bias of fires to south-facing hillslopes and thus allowing late-successional forest structure to persist for thousands of years in a large portion of the watershed. In contrast, the early Holocene regional climate and forest composition likely resulted in larger landscape tires that were not strongly controlled by landform factors. The millennial-scale TSF detected in this study supports the distinction of coastal temperate rain forest as being under a fundamentally different disturbance regime than other Pacific Northwest forests to the cast and south. [References: 83]

Gavin, D. G., W. W. Oswald, et al. (2003). "A statistical approach to evaluating distance metrics and analog assignments for pollen records." Quaternary Research 60(3): 356-367.

The modern analog technique typically uses a distance metric to determine the dissimilarity between fossil and modern biological assemblages. Despite this quantitative approach, interpretation of distance metrics is usually qualitative and rules for selection of analogs tend to be ad hoe. We present a statistical tool, the receiver operating characteristic (ROC) curve, which provides a framework for identifying analogs from distance metrics. If modern assemblages are placed into groups (e.g., biomes), this method can (1) evaluate the ability of different distance metrics to distinguish among groups, (2) objectively identify thresholds of the distance metric for determining analogs, and (3) compute a likelihood ratio and a Bayesian probability that a modern group is an analog for an unknown (fossil) assemblage. Applied to a set of 1689 modern pollen assemblages from eastern North America classified into eight biomes, ROC analysis confirmed that the squared-chord distance (SCD) outperforms most other distance metrics. The optimal threshold increased when more dissimilar biomes were compared. The probability of an analog vs no-analog result (a likelihood ratio) increased sharply when SCD decreased below the optimal threshold, indicating a nonlinear relationship between SCD and the probability of analog. Probabilities of analog computed for a postglacial pollen record at Tannersville Bog (Pennsylvania, USA) identified transitions between biomes and periods of no analog. (C) 2003 Elsevier Science (USA). Published by Elsevier Inc. All rights reserved. [References: 35]

George, K., R. J. Norby, et al. (2003). "Fine-root respiration in a loblolly pine and sweetgum forest growing in elevated CO2." New Phytologist 160(3): 511-522.

The loss of carbon below-ground through respiration of fine roots may be modified by global change. Here we tested the hypothesis that a reduction in N concentration of tree fine-roots grown in an elevated atmospheric CO2 concentration would reduce maintenance respiration and that more energy would be used for root growth and N uptake. We partitioned total fine-root respiration (R-T) between maintenance (R-M), growth (R-G), and N uptake respiration (R-N) for loblolly pine (Pinus taeda) and sweetgum (Liquidambar styraciflua) forests exposed to elevated CO2. A substantial increase in fine-root production contributed to a 151% increase in R-G for loblolly pine in elevated CO2. Root specific R-M for pine was 24% lower under elevated CO2 but when extrapolated to the entire forest, no treatment effect could be detected. R-G (< 10%) and R-N (< 3%) were small components of R-M in both forests. Maintenance respiration was the vast majority of R-T, and contributed 92% and 86% of these totals at the pine and sweetgum forests, respectively. The hypothesis was rejected because the majority of fine-root respiration was used for maintenance and was not reduced by changes in root N concentration in elevated CO2. Because of its large contribution to R-T and total soil CO2 efflux, changes in R-M caused by warming may greatly alter carbon losses from forests to the atmosphere. [References: 85]

Golldack, D., F. Quigley, et al. (2003). "Salinity stress-tolerant and -sensitive rice (Oryza sativa L.) regulate AKT1-type potassium channel transcripts differently." Plant Molecular Biology 51(1): 71-81.

In the indica rice (Oryza sativa L.) a cDNA was characterized that encoded OsAKT1 homologous to inward-rectifying potassium channels of the AKT/KAT subfamily. Transcript analysis located OsAKT1 predominantly in roots with low abundance in leaves. Cell-specificity of OsAKT expression was analyzed by in situ hybridizations. In roots, strongest signals were localized to the epidermis and the endodermis, whereas lower transcript levels were detected in cells of the vasculature and the cortex. In leaves, expression was detected in xylem parenchyma, phloem, and mesophyll cells. Transcriptional regulation and cell specificity of OsAKT1 during salt stress was compared in rice lines showing different salinity tolerance. In the salt-tolerant, sodium-excluding varieties Pokkali and BK, OsAKT1 transcripts disappeared from the exodermis in plants treated with 150 mM NaCl for 48 h but OsAKT1 transcription was not repressed in these cells in the salt-sensitive, sodium-accumulating variety IR29. Significantly, all lines were able to maintain potassium levels under sodium stress conditions, while sodium concentrations in the leaves of IR29 increased 5-10-fold relative to the sodium concentration in BK or Pokkali. The divergent, line-dependent and salt-dependent, regulation of this channel does not significantly affect potassium homeostasis under salinity stress. Rather, repression in Pokkali/BK and lack of repression in IR29 correlate with the overall tolerance character of these lines. [References: 48]

Golldack, D., H. Su, et al. (2002). "Characterization of a HKT-type transporter in rice as a general alkali cation transporter." Plant Journal 31(4): 529-542.

We report the characterization of rice OsHKT1 (Oryza sativa ssp. indica) homologous to the wheat K+/ Na+-symporter HKT1. Expression of OsHKT1 in the yeast strain CY162 defective in K+-uptake restored growth at mM and muM concentrations of K+ and mediated hypersensitivity to Na+. When expressed in Xenopus oocytes, rice OsHKT1 showed uptake characteristics of a Na+-transporter but mediated transport of other alkali cations as well. OsHKT1 expression was analysed in salt-tolerant rice Pokkali and salt-sensitive IR29 in response to external cation concentrations. OsHKT1 is expressed in roots and leaves. Exposure to Na+, Rb+, Li+, and Cs+ reduced OsHKT1 transcript amounts in both varieties and, in some cases, incompletely spliced transcripts were observed. By in situ hybridizations the expression of OsHKT1 was localized to the root epidermis and the vascular tissue inside the endodermis. In leaves, OsHKT1 showed strongest signals in cells surrounding the vasculature. The repression of OsHKT1 in the two rice varieties during salt stress was different in various cell types with main differences in the root vascular tissue. The data suggest control over HKT expression as a factor that may distinguish salt stress-sensitive and stress-tolerant lines. Differences in transcript expression in space and time in different lines of the same species appear to be a component of ion homeostasis correlated with salt sensitivity and tolerance. [References: 56]

Govindjee, J. T. Beatty, et al. (2003). "Celebrating the millennium-historical highlights of photosynthesis research, Part 2." Photosynthesis Research 76(1-3): 1-11.

This paper is an introduction to Part 2 of our celebrations of the historical highlights of photosynthesis research. Part 1 was published in October 2002 as Volume 73 of Photosynthesis Research. After a brief introduction, we recognize two giants in the field: Cornelis B. van Niel ( for anoxygenic photosynthesis), and Robert Hill ( for oxygenic photosynthesis). This is followed by recognition of a 1960 book by Hans Gaffron, and a multi-authored book edited by W. Ruhland and Andre Pirson, and inclusion in the appendix of a list of selected books. Our celebration is enhanced by the inclusion of beautiful paintings of cells by Antoinette Ryter. After introducing all the historical papers contained in this volume, we honor Louis N. M. Duysens, one of the greatest biophysicists of our time, and finally we dedicate this volume to a great scientist, humanist and peacemaker: Eugene I. Rabinowitch. [References: 82]

Govindjee and H. Gest (2002). "Celebrating the millennium - historical highlights of photosynthesis research." Photosynthesis Research 73(1-3): 1-6.

Govindjee and D. W. Krogmann (2002). "A list of personal perspectives with selected quotations, along with lists of tributes, historical notes, Nobel and Kettering awards related to photosynthesis." Photosynthesis Research 73(1-3): 11-20.

The history of photosynthesis research can be found in original papers and books. However, a special history is available from the prefatory chapters and the personal perspectives of various researchers who published them in several journals over the last 40 years. We have compiled a list of such perspectives published since 1964. Selection is not easy, especially of authors who were not directly engaged in photosynthesis research; some are included for their special insights related to central issues in the study of photosynthesis. Our journal, Photosynthesis Research, contains other valuable historic data in the occasional tributes, obituaries and historical notes, that have been published. Lists of these items are included. This article ends by listing the Nobel prizes related to photosynthesis and the Kettering Awards for Excellence in Photosynthesis Research. Wherever possible, a web page address is provided. The web page addresses have been taken from the article 'Photosynthesis and the Web: 2001' by Larry Orr and Govindjee, available at http://www.life.uiuc.edu/govindjee/photoweb and at http://photoscience.la.asu.edu/photosyn/photoweb/default.html. [References]

Govindjee, Z. Sestak, et al. (2002). "The early history of "Photosynthetica", "Photosynthesis Research", and their publishers." Photosynthetica 40(1): 1-11.

The history of the journals "Photosynthetica" and "Photosynthesis Research" is traced from its beginning. Their development is related to the history of several publishers (Dr W. Junk Publishers, Martinus Nijhoff, Kluwer Academic Publishers). This account is based on recollections and records of the authors, Ad C. Plaizier, and Rene Marcelle (the first Editor-in-Chief of Photosynthesis Research). [References: 5]

Govindjee and P. Spilotro (2002). "An Arabidopsis thaliana mutant, altered in the gamma-subunit of ATP synthase, has a different pattern of intensity-dependent changes in non-photochemical quenching and kinetics of the P-to-S fluorescence decay." Functional Plant Biology 29(4): 425-434.

A major photoprotective mechanism that plants employ against excess light involves interplay between the xanthophyll cycle and the accumulation of protons. Using mutants in the xanthophyll cycle, the roles of violaxanthin, antheraxanthin and zeaxanthin have already been well established. In this paper, we present data on intact leaves of a mutant [coupling factor quick recovery mutant (cfq); atpC1: E244K] of Arabidopsis thaliana that we expected, based on 515-nm absorbance changes (Gabrys et al. 1994, Plant Physiology 104, 769-776), to have differences in light-induced DeltapH. The significance of this paper is: (i) it is the first study of the photoprotective energy dissipation involving a mutant of the pH gradient; it establishes that protons play an important role in the pattern of non-photochemical quenching (NPQ) of chlorophyll (Chl) a fluorescence; and (ii) differences between the cfq and the wild type (wt) are observed only under subsaturating light intensities, and are strongest in the initial few minutes of the induction period. Our results on light-intensity dependent Chl* a fluorescence transients (the Kautsky effect), and on NPQ of Chl a fluorescence, at 50-250 mumol photons m(-2) s(-1) demonstrate: (i) the 'P-to-S' (or 'T') decay, known to be related to [H+] (Briantais et al. 1979, Biochimica et Biophysica Acta 548, 128-138), is slowed in the mutant; and (ii) the pattern of NPQ kinetics is different in the initial 100 s-in the wt leaves, there is a marked rise and decline, and in the cfq mutant, there is a slowed rise. These differences are absent at 750 mumol photons m(-2) s(-1). Pre-illumination and nigericin (an uncoupler that dissipates the proton gradient) treatment of the cfq mutant, which has lower DeltapH relative to wild type, confirm the conclusion that protons play an important role in the quenching of Chl a fluorescence. [References: 30]

Hamilton, J. G., E. H. DeLucia, et al. (2002). "Forest carbon balance under elevated CO2." Oecologia 131(2): 250-260.

Free-air CO2 enrichment (FACE) technology was used to expose a loblolly pine (Pinus taeda L.) forest to elevated atmospheric CO2 (ambient + 200 mu1 1(-1)). After 4 years, basal area of pine trees was 9.2% larger in elevated than in ambient CO2 plots. During the first 3 years the growth rate of pine was stimulated by similar to26%. In the fourth year this stimulation declined to 23%. The average net ecosystem production (NEP) in the ambient plots was 428 gC m(-2) year(-1), indicating that the forest was a net sink for atmospheric CO2. Elevated atmospheric CO, stimulated NEP by 41%. This increase was primarily an increase in plant biomass increment (57%). and secondarily increased accumulation of carbon in the forest floor (35%) and fine root increment (8%). Net primary production (NPP) was stimulated by 27%, driven primarily by increases in the growth rate of the pines. Total heterotrophic respiration (R-h) increased by 165%, but total autotrophic respiration (R-a) was unaffected. Gross primary production was increased by 18%. The largest uncertainties in the carbon budget remain in separating below ground heterotrophic (soil microbes) and autotrophic (root) respiration. If applied to temperate forests globally, the increase in NEP that we measured would fix less than 10% of the anthropogenic CO2 projected to be released into the atmosphere in the year 2050. This may represent an upper limit because rising global temperatures, land disturbance, and heterotrophic decomposition of woody tissues will ultimately cause an increased flux of carbon back to the atmosphere. [References: 71]

Harrington, G. N. and D. R. Bush (2003). "The bifunctional role of hexokinase in metabolism and glucose signaling." Plant Cell 15(11): 2493-2496.

Houtz, R. L. and A. R. Portis (2003). "The life of ribulose 1,5-bisphosphate carboxylase/oxygenase-posttranslational facts and mysteries." Archives of Biochemistry & Biophysics 414(2): 150-158.

The life of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), from gene to protein to irreplaceable component of photosynthetic CO2 assimilation, has successfully served as a model for a number of essential cellular processes centered on protein chemistry and amino acid modifications. Once translated, the two subunits of Rubisco undergo a myriad of co- and posttranslational modifications accompanied by constant interactions with structurally modifying enzymes. Even after final assembly, the essential role played by Rubisco in photosynthetic CO2 assimilation is dependent on continuous conformation modifications by Rubisco activase. Rubisco is also continuously assaulted by various environmental factors, resulting in its turnover and degradation by processes that appear to be enhanced during plant senescence. (C) 2003 Elsevier Science (USA). All rights reserved. [References: 161]

Hu, F. S., D. Kaufman, et al. (2003). "Cyclic variation and solar forcing of Holocene climate in the Alaskan subarctic." Science 301(5641): 1890-1893.

High-resolution analyses of lake sediment from southwestern Alaska reveal cyclic variations in climate and ecosystems during the Holocene. These variations occurred with periodicities similar to those of solar activity and appear to be coherent with time series of the cosmogenic nuclides C-14 and Be-10 as well as North Atlantic drift ice. Our results imply that small variations in solar irradiance induced pronounced cyclic changes in northern high-latitude environments. They also provide evidence that centennial-scale shifts in the Holocene climate were similar between the subpolar regions of the North Atlantic and North Pacific, possibly because of Sun-ocean-climate linkages. [References: 41]

Hu, F. S., B. Y. Lee, et al. (2002). "Response of tundra ecosystem in southwestern Alaska to Younger-Dryas climatic oscillation." Global Change Biology 8(11): 1156-1163.

Climatic warming during the last glacial-interglacial transition (LGIT) was punctuated by reversals to glacial-like conditions. Palaeorecords of ecosystem change can help document the geographical extent of these events and improve our understanding of biotic sensitivity to climatic forcing. To reconstruct ecosystem and climatic variations during the LGIT, we analyzed lake sediments from southwestern Alaska for fossil pollen assemblages, biogenic-silica content (BSiO2 %), and organic-carbon content (OC%). Betula shrub tundra replaced herb tundra as the dominant vegetation of the region around 13 600 cal BP (cal BP: (14) C calibrated calendar years before present), as inferred from an increase of Betula pollen percentages from < 5% to > 20% with associated decreases in Cyperaceae, Poaceae, and Artemisia . At c . 13 000 cal BP, a decrease of Betula pollen from 28 to < 5% suggests that shrub tundra reverted to herb tundra. Shrub tundra replaced herb tundra to resume as the dominant vegetation at 11 600 cal BP. Higher OC% and BSiO2 % values suggest more stable soils and higher aquatic productivity during shrub-tundra periods than during herb-tundra periods, although pollen changes lagged behind changes in the biogeochemical indicators before c . 13 000 cal BP. Comparison of our palaeoecological data with the ice-core ddelta(18) O record from Greenland reveals strikingly similar patterns from the onset through the termination of the Younger Dryas (YD). This similarity supports the hypothesis that, as in the North Atlantic region, pronounced YD climatic oscillations occurred in the North Pacific region. The rapidity and magnitude of ecological changes at the termination of the YD are consistent with greenhouse experiments and historic photographs demonstrating tundra sensitivity to climatic forcing. [References: 42]

Hu, F. S. and A. Shemesh (2003). "A biogenic-silica delta O-18 record of climatic change during the last glacial-interglacial transition in southwestern Alaska." Quaternary Research 59(3): 379-385.

Despite growing evidence for environmental oscillations during the last glacial-interglacial transition from high latitude, terrestrial sites of the North Pacific rim, oxygen-isotopic records of these oscillations remain sparse. The lack of data is due partially to the paucity of lakes that contain carbonate sediment suitable for oxygen-isotopic analysis. We report here the first record of oxygen-isotopic composition in diatom silica (delta(18)O(Si)) from a lake in that region. delta(18)O(Si) increases gradually from 19.0 to 23.5parts per thousand between 12,340 and 11,000 C-14 yr B.P., reflecting marked climatic warming at the end of the last glaciation. Around 11,000 C-14 yr B.P., delta(18)O(Si) decreases by 1.7parts per thousand, suggesting a temperature decrease of 3.5-8.9 degreesC at the onset of the Younger Dryas (YD) in southwestern Alaska. Climatic recovery began ca. 10,740 C-14 yr B.P., as inferred from the increase of delta(18)O(Si) to a maximum of 23.9parts per thousand near the end of the YD. Our data reveal that a YD climatic reversal in southwestern coastal areas of Alaska occurred, but the YD climate did not return to full-glacial conditions. (C) 2003 Elsevier Science (USA). All rights reserved. [References: 35]

Hua, B. G., R. W. Mercier, et al. (2003). "Functional interaction of calmodulin with a plant cyclic nucleotide gated cation channel." Plant Physiology & Biochemistry 41(11-12): 945-954.

A family of plant ligand gated nonselective cation channels (cngcs) can be activated by direct, and reversible binding of cyclic nucleotide. These proteins have a cytoplasm-localized cyclic nucleotide binding domain (CNBD) at the carboxy-terminus of the polypeptide. A portion of the cngc CNBD also acts as a calmodulin (CaM) binding domain (CaMBD). The objective of this work is to further characterize interaction of cyclic nucleotide and CaM in gating plant cngc currents. The three-dimensional structure of an Arabidopsis thaliana cngc (Atcngc2) CNBD was modeled, indicating cAMP binding to the Atcngc2 CNBD in a pocket formed by a beta barrel structure appressing a shortened (relative to animal cngc CNBDs) alphaC helix. The Atcngc2 CaMBD was expressed as a fusion peptide linking blue and green fluorescent proteins, and used to quantify CaM (A. thaliana CaM isoform 4) binding. CaM bound the fusion protein in a Ca2+-dependent manner with a K-d of 7.6 nM and a Ca2+ binding K-d of 200 nM. Functional characterization (voltage clamp analysis) of Atcngc2 was undertaken by expression in human embryonic kidney cells. CaM reversed cAMP activation of Atcngc2 currents. This functional interaction was dependent on free cytosolic Ca2+. Increasing cytosolic Ca2+ was found to inhibit cAMP activation of the channel in the absence of added CaM. We conclude that the physical interaction of Ca2+/CaM with plant cngcs blocks cyclic nucleotide activation of these channels. Thus, the cytosolic secondary messengers CaM, cAMP, and Ca2+ can act in an integrated fashion to gate currents through these plant ion channels. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved. [References: 40]

Husband, R., E. A. Herre, et al. (2002). "Molecular diversity of arbuscular mycorrhizal fungi and patterns of host association over time and space in a tropical forest." Molecular Ecology 11(12): 2669-2678.

We have used molecular techniques to investigate the diversity and distribution of the arbuscular mycorrhizal (AM) fungi colonizing tree seedling roots in the tropical forest on Barro Colorado Island (BCI), Republic of Panama. In the first year, we sampled newly emergent seedlings of the understory treelet Faramea occidentalis and the canopy emergent Tetragastris panamensis, from mixed seedling carpets at each of two sites. The following year we sampled surviving seedlings from these cohorts. The roots of 48 plants were analysed using AM fungal-specific primers to amplify and clone partial small subunit (SSU) ribosomal RNA gene sequences. Over 1300 clones were screened for random fragment length polymorphism (RFLP) variation and 7% of these were sequenced. Compared with AM fungal communities sampled from temperate habitats using the same method, the overall diversity was high, with a total of 30 AM fungal types identified. Seventeen of these types have not been recorded previously, with the remainder being similar to types reported from temperate habitats. The tropical mycorrhizal population showed significant spatial heterogeneity and nonrandom associations with the different hosts. Moreover there was a strong shift in the mycorrhizal communities over time. AM fungal types that were dominant in the newly germinated seedlings were almost entirely replaced by previously rare types in the surviving seedlings the following year. The high diversity and huge variation detected across time points, sites and hosts, implies that the AM fungal types are ecologically distinct and thus may have the potential to influence recruitment and host composition in tropical forests. [References: 49]

Kandil, F. E., M. A. L. Smith, et al. (2002). "Composition of a chemopreventive proanthocyanidin-rich fraction from cranberry fruits responsible for the inhibition of 12-O-tetradecanoyl phorbol-13-acetate (TPA)-induced ornithine, decarboxylase (ODC) activity." Journal of Agricultural & Food Chemistry 50(5): 1063-1069.

Phenolics from the American cranberry (Vaccinium macrocarpon) were fractionated into a series of proanthocyanidins and other flavonoid compounds by vacuum chromatography on a hydrophilic, porous polyvinylic gel permeation polymer. Antioxidant activity was not restricted to a particular class of components in the extract but was found in a wide range of the fractions. Significant chemopreventive activity, as indicated by an ornithine decarboxylase assay, was localized in one particular proanthocyanidin-rich fraction from the initial fractionation procedure. Further fractionation of the active anticarcinogenic fraction revealed the following components: seven flavonoids, mainly quercetin, myricetin, the corresponding 3-O-glycosides, (-)-epicatechin, (+)-catechin, and dimers of both gallocatechin and epigallocatechin types, and a series of oligomeric proanthocyanidins. [References: 38]

Kaufman, D. S., F. S. Hu, et al. (2003). "A similar to 33,000 year record of environmental change from Arolik Lake, Ahklun Mountains, Alaska, USA." Journal of Paleolimnology 30(4): 343-362.

A continuous record of lacustrine sedimentation capturing the entire full-glacial period was obtained from Arolik Lake in the Ahklun Mountains, southwestern Alaska. Fluctuations in magnetic susceptibility ( MS), grain size, organic-matter (OM) content, C/N ratios, delta(13)C, and biogenic silica (BSi) record marked environmental changes within the lake and its watershed during the last similar to 33 cal ka. Age control is provided by 31 C-14 ages on plant macrofossils in four cores between 5.2 and 8.6 m long. Major stratigraphic units are traceable throughout the lake subbottom in acoustical profiles, and provisional ages are derived for six prominent tephra beds, which are correlated among the cores. During the interstadial interval between similar to 33 and 30 cal ka, OM and BSi contents are relatively high with values similar to those of the Pleistocene-Holocene transition, suggesting a similar level of aquatic productivity. During the glacial interval that followed ( similar to 30 - 15 cal ka), OM and BSi decrease in parallel with declining summer insolation. OM and BSi values remain relatively uniform compared with the higher variability before and after this interval, and they show no major shifts that might correlate with climate fluctuations evidenced by the local moraine record, nor with other global climate changes. The glacial interval includes a clay-rich unit with a depauperate diatom assemblage that records the meltwater spillover of an ice-dammed lake. The meltwater pulse, and therefore the maximum extent of ice attained by a major outlet glacier of the Ahklun Mountain ice cap, lasted from similar to 24 to 22 cal ka. The Pleistocene - Holocene transition ( similar to 15 - 11 cal ka) exhibits the most prominent shifts in OM and BSi, but rapid and dramatic fluctuations in OM and BSi continue throughout the Holocene, indicating pronounced paleoenvrionmental changes. [References: 43]

Labandeira, C. C. and T. L. Phillips (2002). "Stem borings and petiole galls from Pennsylvanian tree ferns of Illinois, USA: Implications for the origin of the borer and galler functional-feeding-groups and holometabolous insects." Palaeontographica Abteilung a Palaeozoologie-Stratigraphie 264(1-4): 1-+.

Latest Middle Pennsylvanian, lowland, equatorial communities of Euramerica occurred in equable, wetland habitats with peat substrates dominated by pole-like lycopod trees amid subdominant tree ferns and seed ferns, along with sphenopsids and rare cordaites. In these taxonomically diverse and physiognomically varied communities detritivores overwhelmingly channeled plant biomass from primary production to reduced organic matter. However, by the Late Pennsylvanian, when Psaronius tree ferns replaced lycopods as dominant floral elements, there was a dramatic increase in the spectrum and intensity of herbivore functional-feeding-groups. This shift toward the importance of herbivores is supported by a significant increase of arthropod coprolites in peat litter whose origin is most parsimoniously explained by herbivory. Equally important are the earliest documented occurrences of highly stereotyped and host specific plant damage caused by herbivorous insects. We describe two of these distinctive interactions as the newly established ichnogenera Pteridiscaphichnos, a detritivore-created, tunnel-and-gallery network in Middle- and Late Pennsylvanian Psaronius stems; and Pteriditorichnos, an elongate petiole gall from the frond of the Late Pennsylvanian Psaronius chasei, caused by an herbivorous and endophytic larval holometabolan. The Psaronius stem-boring, Pteridiscaphichnos, occurs in the late Middle Pennsylvanian form "layered cells morphotype" and the Late Pennsylvanian species Psaronius magnificus and R chasei. This distinctive stem boring is characterized by evacuated ground parenchyma replaced by frass of ellipsoidal coprolites 1.0 mm. X 3.0 min in average size and macerated fragments of processed but unconsurned parenchyma. All known specimens occur among linear to arcuate vascular strands interior to the outer sclerenchyma cylinder. The lack of reaction tissue indicates postmortem consumption of relatively soft, nutrient-rich parenchyma, although construction of the tunnel-and-gallery network preceded significant decomposition of the trunk since lignified tissues, such as sclerenchyma, vascular tissue and part of the root mantle, were still structurally sound and were avoided by the detritivores. Based on the geometry of the boring, coprolite structure, and the life-habits of modern ecologic analogs inhabiting tree fern trunks, the culprit of Pteridiscaphichnos is attributed to a roach or roach-like insect. The Late Pennsylvanian gall, Pteriditorichnos, is known only on Psaronius chasei hosts, and occurs in basal frond petioles. The structure of this gall consists of a lumen formed by removal of ground parenchyma through the petiolar axis, and its partial replacement by files of hypertrophied cells organized into radiating, impinging tufts that define a differentiated zone of callus. The lumen, encapsulated by callus, contains regions with frass consisting of coprolites and macerated parenchyma fragments. Barrel-shaped coprolites average 1.5 min X 2.5 mm in size, have smooth longitudinal surfaces but ragged ends, and contain recognizable cell types found in the surrounding callus and unmodified parenchyma. All fines of evidence indicate that an endophytic insect tunneled through medullary petiolar parenchyma, which induced plant response by production of callus, and was followed by insect consumption of the callus. Based on the three-dimensional structure of this gall, the particulate nature of the coprolites, and an extensive literature documenting known gall-making arthropods, we identify the culprit as a holometabolous larva. Although this earliest known gall resembles those made by extant tenthredinoid Hymenoptera, it is unassignable to any modern lineage of Holometabola. Although possible body fossils of the Holometabola have been mentioned in Pennsylvanian strata, Pteriditorichnos provides the first high-resolution, trace-fossil documentation of the life-habits of any Paleozoic larval holometabolan. Because of its exceptional anatomical preservation and Late Pennsylvanian age, this larval-induced gall is important in assessing existing hypotheses regarding the ancestral life-habits of the earliest larval Holometabola. Evidence indicates: 1. That the larval holometabolan galler occurred in a climatically equable, tropical, and humid swamp forest with a peat substrate. 2. That endophytic petiole galling is the earliest known life-habit for the Holometabola, and that stem galling or a related endophytic guild was an ancestral/behavior for this clade. 3. The prediction of LAMEERF, later elaborated by MALYSHFV, is vindicated: the endophytic penetration of tissues in primitive vascular plants (especially pteridophytes) was integrally associated with the holometabolous condition. These data indicate not only the occurrence of a stem borer and a herbivore galler during the Paleozoic, but also document the presence of an intimate interaction between a herbivore and its responding plant host as early as the Late Pennsylvanian. [References: 728]

Lasso, E. and M. E. Naranjo (2003). "Effect of pollinators and nectar robbers on nectar production and pollen deposition in Hamelia patens (Rubiaceae)." Biotropica 35(1): 57-66.

We conducted experimental manipulations and field observations to determine the role of members of a nectarivorous guild (pollinators and robbers) on nectar production and pollen deposition in Hamelia patens at the La Selva Biological Station (Costa Rica). Seven pollinators (hummingbirds) and four robbers (I hummingbird and 3 perching birds) comprised the avian nectarivorous guild visiting H. patens during March 1997. In addition, two florivorous birds were observed visiting H. patens during the study. Pollinators accounted for 85.6 percent of the visits, robbers for 12.4 percent, and florivores for 2 percent of the visits. Visitation by pollinators and robbers was greatest when floral nectar was highest. No aggressive interactions between pollinators and robbers were observed during the study. Pollinators differed in their ability to carry and deposit pollen on the stigma. Territorial hummingbirds were the least effective pollinators but the most frequent visitors. Flowers were frequently robbed (71%) during the study. Flowers experimentally robbed did not increase nectar production compared to control flowers; therefore, robbery may not involve an extra energy investment in terms of nectar production. The number of pollen grains deposited on artificially robbed flowers was significantly less than the number found in flowers with extra nectar (nectar added) but did not differ from the number found in non-manipulated flowers, indicating that nectar robbers may not affect the foraging behavior of hummingbirds, and therefore pollen deposition. [References: 44]

Leakey, A. D. B., M. C. Press, et al. (2003). "Patterns of dynamic irradiance affect the photosynthetic capacity and growth of dipterocarp tree seedlings." Oecologia 135(2): 184-193.

In the deeply shaded understorey of S.E. Asian rain forests the growth and survival of dipterocarp seedlings is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain in understorey plants. To test the sensitivity of photosynthesis and growth to variation in the pattern of dynamic irradiance, dipterocarp tree seedlings (Shorea leprosula and Hopea nervosa) were grown for 370 days under shaded forest light treatments of equal total daily photosynthetic photon flux density (similar to3.3 mol m(-2) day(-1)), but characterised by either long flecks (LF) or short flecks (SF). Seedling growth was more than 4-fold greater under LF, compared with SF, in both species. Variation in the relative growth rates (RGR) and light saturated rates of photosynthesis (A(max)) were strongly positively correlated with the mean duration of sunflecks. Variation in RGR was strongly correlated with greater unit leaf rate growth, indicating that photosynthetic carbon gain per unit leaf area was greater under LF. The accumulation of starch in leaves over the diurnal period was 117% greater in both species under LF, compared with SF. Greater carbon gain in seedlings under LF is likely to have resulted from the combination of (1) greater A(max) (S. leprosula 35%, H. nervosa 40%), (2) more efficient dynamic photosynthesis, and (3) greater incident photosynthetic quantum yield, compared with seedlings receiving the SF irradiance treatment. The pattern of dynamic irradiance received by seedlings may significantly impact their growth and survival to a previously unrecognised extent, with important consequences for regeneration processes and hence forest structure and composition. [References: 49]

Lertzman, K., D. Gavin, et al. (2002). "Long-term fire regime estimated from soil charcoal in coastal temperate rainforests - art. no. 5." Conservation Ecology 6(2): 5.

Coastal temperate rainforests from southeast Alaska through to southern Oregon are ecologically distinct from forests of neighboring regions, which have a drier, or more continental, climate and disturbance regimes dominated by fires. The long-term role of fire remains one of the key outstanding sources of uncertainty in the historical dynamics of the wetter and less seasonal forests that dominate the northerly two thirds of the rainforest region in British Columbia and Alaska. Here, we describe the long-term fire regime in two forests on the south coast of British Columbia by means of 244 AMS radiocarbon dates of charcoal buried in forest soils. In both forests, some sites have experienced no fire over the last 6000 years and many other sites have experienced only one or two fires during that time. Intervals between fires vary from a few centuries to several thousand years. In contrast to other conifer forests, this supports a model of forest dynamics where fires are of minor ecological importance. Instead, forest history is dominated by fine-scale processes of disturbance and recovery that maintain an ubiquitous late-successional character over the forest landscape. This has significant implications for ecosystem-based forest management and our understanding of carbon storage in forest soils. [References: 52]

Li, C., M. V. Nitka, et al. (2003). "Annularins A-H: New polyketide metabolites from the freshwater aquatic fungus Annulatascus triseptatus." Journal of Natural Products 66(10): 1302-1306.

Eight new polyketide metabolites, annularins A-H (1-8), along with the known compound (-)-(S)-p-hydroxyphenyllactic acid, were isolated from the organic extracts of the freshwater fungus Annulatascus triseptatus. Compounds 1-6 are 3,4,5-trisubstituted alpha-pyrones, and the fused bicyclic pyrone-furanone system in annularin F (6) has not been reported previously among natural products. Compounds 7 and 8 are 3,4-disubstituted alpha,beta-unsaturated gamma-lactones. Annularins A (1), B (2), C (3), and F (6) exhibited antibacterial activity. [References: 23]

Liu, X. N. and W. V. Baird (2003). "The ribosomal small-subunit protein S28 gene from Helianthus annuus (Asteraceae) is down-regulated in response to drought, high salinity, and abscisic acid." American Journal of Botany 90(4): 526-531.

A partial cDNA for the ribosomal S28 gene from sunflower was initially cloned and identified to be down-regulated by high salinity, using differential display reverse transcriptase-polymerase chain reaction (PCR). Using this sequence, a 502-base pair (bp) full-length cDNA was cloned by rapid amplification of cDNA ends. This cDNA (designated Ha-RPS28) encodes a protein component of the,,mail subunit of cytoplasmic ribosomes. The predicted 65 amino acid residue sequence of Ha-PPS28, with an estimated molecular mass of 7.5 kD. has 92. 89, and 86% identity with the S28 ribosomal proteins from peach, maize, and Arabidopsis, respectively. Ha-RPS28 was expressed in all organs examined, and the highest level was detected in fully expanded leaves. Furthermore, expression of Ha-RPS28 was down-regulated in both seedling roots and shoots in response to drought, high salinity, or abscisic acid. [References: 28]

Liu, X. N. and W. V. Baird (2003). "Differential expression of genes regulated in response to drought or salinity stress in sunflower." Crop Science 43(2): 678-687.

Structural and functional characterization of environmental stress-induced genes has contributed to a better understanding of how plants respond and adapt to different abiotic stresses. Differential display was used to compare overall differences in gene expression between drought- or salinity-stressed and unstressed (control) plants of sunflower, Helianthus annuus L. Five drought-regulated cDNAs and 12 salinity-regulated cDNAs were cloned and sequenced. Thirteen of these cDNAs were confirmed to be expressed differentially in response to drought or salinity stress by quantitative reverse transcriptase polymerase chain reaction (RT-PCR). Regulation of the expression of these 13 genes was analyzed in leaves of drought-stressed plants, and in roots and shoots of drought- and salinity-stressed seedlings. Results showed that certain genes respond to both stresses, while others are uniquely regulated either in terms of the stress stimulus or the plant tissue. Sequence analysis of these clones identified five with homology to known genes [guanylate kinase (signal transduction), lytB (antibiotic/drug resistance), selenium-binding protein (heavy metal stress), polyprotein (reverse transcriptase), and AC-like transposable element]. The possible functions of these genes in plant stress-response are discussed. [References: 47]

Long, S. P. and C. J. Bernacchi (2003). "Gas exchange measurements, what can they tell us about the underlying limitations to photosynthesis? Procedures and sources of error." Journal of Experimental Botany 54(392): 2393-2401.

The principles, equipment and procedures for measuring leaf and canopy gas exchange have been described previously as has chlorophyll fluorescence. Simultaneous measurement of the responses of leaf gas exchange and modulated chlorophyll fluorescence to light and CO2 concentration now provide a means to determine a wide range of key biochemical and biophysical limitations on photo synthesis in vivo. Here the mathematical frameworks and practical procedures for determining these parameters in vivo are consolidated. Leaf CO2 uptake (A) versus intercellular CO2 concentration (C-i) curves may now be routinely obtained from commercial gas exchange systems. The potential pitfalls, and means to avoid these, are examined. Calculation of in vivo maximum rates of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Rubisco) carboxylation (V-c,V-max), electron transport driving regeneration of RuBP (J(max)), and triose-phosphate utilization (V-TPU) are explained; these three parameters are now widely assumed to represent the major limitations to light-saturated photosynthesis. Precision in determining these in intact leaves is improved by the simultaneous measurement of electron transport via modulated chlorophyll fluorescence. The A/C-i response also provides a simple practical method for quantifying the limitation that stomata impose on CO2 assimilation. Determining the rate of photorespiratory release of oxygen (R-l) has previously only been possible by isotopic methods, now, by combining gas exchange and fluorescence measurements, R-l may be determined simply and routinely in the field. The physical diffusion of CO2 from the intercellular air space to the site of Rubisco in C-3 leaves has long been suspected of being a limitation on photosynthesis, but it has commonly been ignored because of the lack of a practical method for its determination. Again combining gas exchange and fluorescence provides a means to determine mesophyll conductance. This method is described and provides insights into the magnitude and basis of this limitation. [References: 36]

Luo, Y. Q., L. W. White, et al. (2003). "Sustainability of terrestrial carbon sequestration: A case study in Duke Forest with inversion approach - art. no. 1021." Global Biogeochemical Cycles 17(1): 1021.

[1] A sound understanding of the sustainability of terrestrial carbon ( C) sequestration is critical for the success of any policies geared toward stabilizing atmospheric greenhouse concentrations. This includes the Kyoto Protocol and/or other greenhouse strategies implemented by individual countries. However, the sustainability of C sinks and pools has not been carefully studied with either empirical or theoretical approaches. This study was intended to develop a conceptual framework to define the sustainability based on C influx and residence time (tau). The latter tau quantifies the capacity for C storage in various plant and soil pools. We estimated t via inverse analysis of multiple data sets from a Free-Air CO2 Enrichment (FACE) experiment in Duke Forest, North Carolina, United States. This study suggested that estimated residence times at elevated CO2 decreased for plant C pools and increased for litter and soil pools in comparison to those at ambient CO2. The ensemble of the residence times from all the pools at elevated CO2, however, was well correlated with that at ambient CO2. We then used the estimated residence times, combined with C influx, to simulate C sequestration rates in response to a gradual increase in atmospheric CO2 concentration (C-a). The simulated C sequestration rate gradually increased from 69 g m(-2) yr(-1) in 2000 when Ca was 378 ppm to 201 g m(-2) yr(-1) in 2100 when C-a was at 710 ppm. Thus, the current evidence from both experimental observations and inverse analysis suggested that C sequestration in the forest ecosystem was likely to increase gradually as Ca gradually increases. The model projection of the C sequestration will improve as more data on long-term processes become available in coming years. In addition, such a modeled increase in terrestrial C sequestration is too small to balance the anthropogenic C emission. [References: 52]

Lynch, J. A., J. S. Clark, et al. (2002). "Geographic and temporal variations in fire history in boreal ecosystems of Alaska - art. no. 8152." Journal of Geophysical Research-Atmospheres 108(D1): 8152.

Charcoal and pollen analyses were used to determine geographic and temporal patterns of fire importance in boreal forests of the Kenai Peninsula and interior Alaska. Sieved, large charcoal particles were measured in continuously sampled cores of Rock, Portage, and Arrow Lakes (Kenai Peninsula) and Dune and Deuce Lakes (interior Alaska) to estimate regional fire importance and fire occurrence. Charcoal accumulation rates have been low for the past 1000 years in both regions with slightly higher values in interior Alaska than on the Kenai Peninsula. An exception to this general pattern was the period of post-European settlement on the Kenai Peninsula, where charcoal accumulation rates increased by 10-fold. This increase most likely reflected increased fire occurrence due to human ignition. The Holocene charcoal and pollen records from Dune Lake indicate low fire occurrence during the early (9000 to 5500 calibrated year before present (yr BP)) birch-white spruce-alder (Betula-Picea glauca-Alnus) communities and high fire occurrence as black spruce (Picea mariana) became established after 5500 yr BP. Increased fires probably resulted from a change to fire-prone black spruce forests. For the past 5500 yr BP, two distinct fire regimes occurred. Frequent fires, with an average fire return interval of 98 years, characterized the period from 5500-2400 yr BP. Fewer fires, with an average fire interval of 198 years, characterized the period after 2400 yr BP. Fuel accumulation, stand structure, and vegetation species contributed to the natural variability in fire regimes during past changes in climate. [References: 71]

Maherali, H., B. L. Williams, et al. (2002). "Hydraulic differentiation of Ponderosa pine populations along a climate gradient is not associated with ecotypic divergence." Functional Ecology 16(4): 510-521.

1. Pinus ponderosa occurs in a range of contrasting environments in the western USA. Xeric populations typically have lower leaf : sapwood area ratio (A (L) /A (S) ) and higher whole-tree leaf specific hydraulic conductance (K (L) ) than mesic populations. These climate-driven shifts in hydraulic architecture are considered adaptive because they maintain minimum leaf water potential above levels that cause xylem cavitation. 2. Using a common garden study, we examined whether differences in biomass allocation and hydraulic architecture between P. ponderosa populations originating from isolated outcrops in the Great Basin desert and Sierran montane environments were caused by ecotypic differentiation or phenotypic plasticity. To determine if populations were genetically differentiated and if phenotypic and genetic differentiation coincided, we also characterized the genetic structure of these populations using DNA microsatellites. 3. Phenotypic differentiation in growth, biomass allocation and hydraulic architecture was variable among populations in the common garden. There were no systematic differences between desert and montane climate groups that were consistent with adaptive expectations. Drought had no effect on the root : shoot and needle : stem ratio, but reduced seedling biomass accumulation, leaf area ratio, A (L) /A (S) and K (L) . Stem hydraulic conductance (K (H) ) was strongly size-dependent, and was lower in droughted plants, primarily because of lower growth. 4. Although microsatellites were able to detect significant non-zero (P < 0.001) levels of differentiation between populations, these differences were small and were not correlated with geographic separation or climate group. Estimates of genetic differentiation among populations were low (<5%), and almost all the genetic variation (>95%) resided within populations, suggesting that gene flow was the dominant factor shaping genetic structure. 5. These results indicate that biomass allocation and hydraulic differences between desert and montane populations are not the result of ecotypic differentiation. Significant drought effects on leaf : sapwood allocation and K (L) suggest that phenotypic differentiation between desert and montane climates could be the result of phenotypic plasticity. [References: 69]

Maslin, B. R., J. T. Miler, et al. (2003). "Overview of the generic status of Acacia (Leguminosae : Mimosoideae)." Australian Systematic Botany 16(1): 1-18.

The systematic treatment and circumscription of the group of plants presently recognised as the genus Acacia has a complex history. The genus was first described by Philip Miller in 1754 and until 1842, when George Bentham clearly defined it's generic limits (by restricting the name Acacia to mimosoid plants having numerous free stamens), a number of species which are now referable to genera within tribes Ingeae and Mimoseae had been referred to it. As presently defined, Acacia is a cosmopolitan genus containing in excess of 1350 species and together with the monotypic genus Faidherbia Chev. (which occurs in Africa and the Middle East), comprises tribe Acacieae within subfamily Mimosoideae. The current classification of Acacia views the genus as comprising three large subgenera, namely subg. Acacia (c. 161 species, pantropical), subg. Aculeiferum Vassal (235 species; pantropical) and subg. Phyllodineae (DC.) Seringe (syn. subg. Heterophyllum Vassal) (960 species, largely confined to Australia). In 1986, Pedley proposed that these three subgenera be attributed generic rank, namely Acacia, Senegalia Rafinesque and Racosperma C. Martius, respectively, but this proposal was not widely adopted. Subsequently, the results of monographic and floristic works have greatly expanded knowledge, not only of Acacia, but also of its presumed relatives in tribes Ingeae and Mimoseae. Cladistic analyses of chloroplast genes have been especially informative in developing a better understanding of phylogenetic relationships of the group. The new data clearly show that the genus as presently defined (i.e. Acacia sens. lat.) is not monophyletic. Furthermore, five separate monophyletic groups can be recognised within Acacia sens. lat. and it is recommended that these each be recognised as a distinct genus. The five genera correspond to those recognised by Pedley, except that Senegalia sens. lat. is now regarded as comprising three genera, namely Senegalia sens. str., Acaciella Britton & Rose [based on Acacia subg. Aculeiferum sect. Filicinae (Benth.) Pedley] and an undescribed genus based on a group of species related to Acacia coulteri Benth. Acacia subg. Acacia appears to be located in tribe Mimoseae. The relationships of subg. Phyllodineae, subg. Aculeiferum sens. str., sect. Filicinae, the 'Acacia coulteri' group and Faidherbia are not fully resolved, although in all studies these groups are shown to be monophyletic. Although it is appropriate that each be recognised as a distinct genus, the application of the names Acacia and Racosperma is currently under consideration and it is therefore not appropriate to use these names until this matter is resolved. [References: 90]

Miyazaki, S., E. Nevo, et al. (2003). "Oxidative stress responses in yeast strains, Saccharomyces cerevisiae, from "Evolution Canyon", Israel." Monatshefte fur Chemie 134(11): 1465-1480.

The genome of baker's yeast, Saccharomyces cerevisiae, has been sequenced, many genes have been deleted for phenotypic analysis, and the tools to study gene and protein interaction and the functions of the large number of functionally unknown genes have made yeast the most advanced model for the analysis of eukaryotic organisms. The yeast research community has provided a paradigm for work in the genomics era of biology of which Professor Ruis has been an early protagonist. The genomics view is now contributing to initiate research in molecular evolution. We have taken strains from "Evolution Canyon", Israel, for an analysis by microarray hybridizations of the response of wild yeast accessions to environmental stress, in particular oxidative stress. Strains were selected from the "African" south-facing slope (SFS) of the canyon, characterized by xeric conditions and high irradiation, from the "European" north-facing slope (NFS), characterized by mesic conditions and low irradiation, and from the valley bottom. H2O2-sensitive strains included a laboratory strain (S150-2B) and most strains from the NFS. Statistically supported is a correlation between peroxide tolerance, the SFS, and micro-niche within a slope. Hierarchical clustering of regulated transcripts indicated maximum linkage of expression profiles between strains that showed the same phenotypic stress response. The analyses indicate strain-specific adaptive micro-niche evolution along the microclimatic gradient of "Evolution Canyon" that determine the response to oxidative stress. [References: 42]

Morgan, P. B., E. A. Ainsworth, et al. (2003). "How does elevated ozone impact soybean? A meta-analysis of photosynthesis, growth and yield." Plant, Cell & Environment 26(8): 1317-1328.

Surface ozone concentrations ([O-3]) during the growing season in much of the northern temperate zone reach mean peak daily concentrations of 60 p.p.b. Concentrations are predicted to continue to rise over much of the globe during the next 50 years. Although these low levels of ozone may not induce visible symptoms on most vegetation, they can result in substantial losses of production and reproductive output. Establishing the vulnerability of vegetation to rising background ozone is complicated by marked differences in findings between individual studies. Ozone effects are influenced by exposure dynamics, nutrient and moisture conditions, and the species and cultivars that are investigated. Meta-analytic techniques provide an objective means to quantitatively summarize treatment responses. Soybean has been the subject of many studies of ozone effects. It is both the most widely planted dicotyledonous crop and a model for other C-3 annual plants. Meta-analytic techniques were used to quantitatively summarize the response of soybean to an average, chronic ozone exposure of 70 p.p.b., from 53 peer-reviewed studies. At maturity, the average shoot biomass was decreased 34% and seed yield was 24% lower. Even in studies where [O-3] was <60 p.p.b., there was a significant decrease in biomass and seed production. At low [O-3], decreased production corresponded to a decrease in leaf photosynthesis, but in higher [O-3] the larger loss in production was associated with decreases in both leaf photosynthesis and leaf area. The impact of ozone increased with developmental stage, with little effect on vegetative growth and the greatest effect evident at completion of seed filling. Other stress treatments, including UV-B and drought, did not alter the ozone response. Elevated carbon dioxide significantly decreased ozone-induced losses, which may be explained by a significant decrease in stomatal conductance. [References: 97]

Naik, V., D. J. Wuebbles, et al. (2003). "Influence of geoengineered climate on the terrestrial biosphere." Environmental Management 32(3): 373-381.

Various geoengineering schemes have been proposed to counteract anthropogenically induced climate change. In a previous study, it was suggested that a 1.8% reduction in solar radiation incident on the Earth's surface could noticeably reduce regional and seasonal climate change from increased atmospheric carbon dioxide (CO2). However, the response of the terrestrial biosphere to reduced solar radiation in a CO2-rich climate was not investigated. In this study, we hypothesized that a reduction in incident solar radiation in a Doubled CO2 atmosphere will diminish the net primary productivity (NPP) of terrestrial ecosystems, potentially accelerating the accumulation of CO2 in the atmosphere. We used a dynamic global ecosystem model, the Integrated Biosphere Simulator (IBIS), to investigate this hypothesis in an unperturbed climatology. While this simplified modeling framework effectively separated the influence of CO2 and sunlight on the terrestrial biosphere, it did not consider the complex feed-backs within the Earth's climate system. Our analysis indicated that compared to a Doubled CO2 scenario, reduction in incident solar radiation by 1.8% in a double CO2 world will have negligible impact on the NPP of terrestrial ecosystems. There were, however, spatial variations in the response of NPP-engineered solar radiation. While productivity decreased by less than 2% in the tropical and boreal forests as hypothesized, it increased by a similar percentage in the temperate deciduous forests and grasslands. This increase in productivity was attributed to a similar to1% reduction in evapotranspiration in the Geoengineered scenario relative to the Doubled CO2 scenario. Our initial hypothesis was rejected because of unanticipated effects of engineered solar radiation on the hydrologic cycle. However, any geoengineering approaches that reduce incident solar radiation need to be thoroughly analyzed in view of the implications on ecosystem productivity and the hydrologic cycle. [References: 35]

Nedbal, L., V. Brezina, et al. (2003). "Negative feedback regulation is responsible for the non-linear modulation of photosynthetic activity in plants dynamic light and cyanobacteria exposed to a environment." Biochimica et Biophysica Acta - Bioenergetics 1607(1): 5-17.

Photosynthetic organisms exposed to a dynamic light environment exhibit complex transients of photosynthetic activities that are strongly dependent on the temporal pattern of the incident irradiance. In a harmonically modulated light of intensity I approximate to const. + sin(omegat), chlorophyll fluorescence response consists of a steady-state component, a component modulated with the angular frequency of the irradiance omega and several upper harmonic components (2omega, 3omega and higher). Our earlier reverse engineering analysis suggests that the non-linear response can be caused by a negative feedback regulation of photosynthesis. Here, we present experimental evidence that the negative feedback regulation of the energetic coupling between phycobilisome and Photosystem II (PSII) in the cyanobacterium, Synechocystis sp. PCC6803 indeed results in the appearance of upper harmonic modes in the chlorophyll fluorescence emission. Dynamic changes in the coupling of the phycobilisome to PSII are not accompanied by corresponding antiparallel changes in the Photosystem I (PSI) excitation,