Special Issue: Plant Responses to Climate Change   

November 2008, Volume 50 Issue 11, Pages 1337-1496.

Cover Caption:
Human activity-caused changes in Earths environment,including climate, will alter plant functions, affecting the productivity of natural vegetation and crops, and species distributions and community diversity. The cover photo was taken near Chinas Arctic Huanghe Station. Ecosystems in the north pole region are likely to be strongly affected by these changes. In recognition of the critical situation, this special issue is devoted to furthering our understanding of the impact of global environmental change on plants (photography provided by Prof. Cheng-Sen Li, cover design: Ying Wang).


Plants and Global Environmental Change: A Special Issue Highlighting Younger Scientists  
Author: Scott A. Heckathorn and Jiquan Chen
Journal of Integrative Plant Biology 2008 50(11): 1337-1338
DOI: 10.1111/j.1744-7909.2008.00744.x
    Humans are changing the global environment to such an extent that they are changing global climate (IPCC 2007; http://www.ipcc.ch/). The pace, if not the eventual extent, of this climate change may be rare in Earth's history, and these rapid changes in climate will have profound negative impacts on biodiversity of the planet and on the quality of human life (Millennium Ecosystem Assessment; http://www.maweb.org//en/Index.aspx). It is already widely believed that the Earth has entered a new geological period termed the Anthropocene, in recognition of the impact that humans are having on the Earth, and it is predicted that human-caused changes to Earth's environment and climate will likely be the foremost problems facing humans in the coming decades. Plants are directly or indirectly the primary source of food for most terrestrial organisms, and humans are often dependent on plants for fuel, fibers, medicine, clean water, etc., as well as for food. Hence, our ability to understand and predict the effects of global environmental change on terrestrial ecosystems and humankind requires an understanding of the effects of global environmental change on plants. Not surprisingly then, much scientific research effort has been devoted to plants and global environmental change, and this research effort is not likely to diminish in the coming decades. To date, much of the global-change research on plants has focused on single-factor effects, particularly effects of elevated CO2 and increased mean growth temperature, with less effort, understandably, on simultaneous multi-factor effects. However, since the major global-change factors can have opposite (e.g., elevated CO2 and temperature) or additive/synergistic effects (e.g., elevated CO2 and N) on plant performance, additional multi-factor studies will be necessary to understand plant responses to global environmental change. For practical reasons, much of the past research in this area has been carried out in laboratory studies, especially for certain global-change factors for which field experiments are logistically difficult (e.g., drought or warming effects on large plants or plant communities). In many instances, alternative approaches, such as modeling and long-term monitoring, will be necessary to elucidate effects of global environmental change on plants, communities, and ecosystems. Also, relatively less previous work in this arena has been devoted to investigating global-change effects on interactions of plants with non-plant organisms, and such work will be necessary to understand global-change effects on the biosphere. In recognition of the tremendous ecological and societal importance of human-caused changes in the Earth's environment and climate, this issue of the Journal of Integrative Plant Biology features a diverse collection of papers concerning plants (or algae) and global environmental change. An initial goal of this special issue was to high-light younger scientists, and in this regard, we have succeeded. Of the 13 papers in this issue concerning global environmental change, 12 have lead authors in early stages of their scientific careers (three are graduate students, three are post-doctoral researchers, and six are in early stages of academic careers). These papers span the range from describing results of laboratory experiments to field studies to modeling to reviews or analyses of pre-existing literature results. Included here are papers examining the effects of several abiotic global-environmental-change factors (CO2, temperature, ozone, water, nitrogen), as well as biotic factors (invasive species, herbivory, species composition). These papers make important contributions to our understanding of plants and global environmental change, and several of them put forth intriguing novel hypotheses that should generate additional research. Among the exciting findings in these global-change papers are those derived from review or analysis of literature results or from modeling approaches to understanding global-change effects on plants or algae. For example, in a review and analysis of pre-existing results, Taub and Wang examine existing hypotheses as to why growth of plants under elevated CO2 typically decreases tissue N concentration. They conclude that such decreases in N concentration occur due to growth dilution, as is often assumed, but also because of decreases in specific uptake rates of N by roots, and they discuss the likely reasons for this decrease in uptake rate. Bidart-Bouzat and Imeh-Nathaniel conduct an in-depth review of existing literature on how global-change factors (CO2, O3, UV, and temperature) impact plant chemical defenses against herbivores, and they find that despite much variability in past results, there are unique patterns that emerge for each global-change factor. Burton and colleagues combine analysis of literature results and their own experimental data to re-examine the influence of temperature on root respiration, and they provide compelling evidence that long-term adaptive responses to higher temperature are lower than those often observed in short-term responses, and this will have important relevance to the wide-spread use of Q10= 2 in most modeling studies. Phillips and co-authors also combine analysis of pre-existing results with their own data to provide evidence that, contrary to conventional wisdom, mature trees are capable of strong growth responses to global environmental change (elevated CO2 in this case). Using a modeling approach, Chiang and colleagues investigate the relative importance of changes in forest tree composition compared with changes in climate (here temperature, precipitation, and light) on forest net primary production, and they conclude that although climate effects will be larger, the effects of changes in forest composition will be significant. Also using a modeling approach in combination with experimental results, Cecala and co-authors estimate the impact that the highly-invasive mussel species, Dreissena polymorpha, zebra mussels, has on benthic primary production in temperate lakes in the northeast USA, showing that these ecosystem engineers increase benthic production and decrease its year-to-year variability. Three of the papers in this special feature use an experimental approach on field-grown plants to investigate plant responses to global-change factors, which is often logistically more difficult than conducting laboratory experiments. Chen and co-authors used mesocosms installed in the field to examine the effects of warming and water-table manipulation on soil temperatures of peatland communities, finding that both factors alter the length of the non-frozen season, though in sometimes unexpected ways. Mishra and colleagues conduct the first field study of effects of elevated CO2 and O3 on heat-stress tolerance in plants, and find that elevated CO2 increases thermotolerance in soybean, thereby confirming previous laboratory studies. And Wang and co-authors examine the effects of N on heat-wave tolerance in prairie plants, finding that heat stress and N have differential effects on the C and N relations of the two co-dominant plants, and these effects have implications for community composition, herbivory, and decomposition. The remaining four papers in this feature describe results from laboratory studies of global-change effects on plants. Ward and co-authors examine the influence of reduced growth temperatures at low CO2 on the growth and physiology of a C3 and C4 plant, providing evidence that during low CO2 periods in the geological past, C4 species likely had a competitive advantage over C3 species, even at lower growth temperatures. Hamilton and colleagues examine the interactive effects of growth temperature and CO2 on photosynthetic tolerance to heat stress, finding that elevated CO2 often decreases heat tolerance in C4 species, especially at supra-optimal growth temperatures, and in C3 species, high CO2 generally benefits heat tolerance, except at supra-optimal growth temperatures. Barua and co-authors examine differences in heat-shock protein (HSP) production and leaf thermotolerance among ecotypes of a species and how this is influenced by growth temperature, and their results indicate that increased heat tolerance, either among ecotypes or with acclimation to higher growth temperatures, is associated with decreased HSP levels and increased basal (vs. inducible) thermotolerance C a finding that has implications for population ecology of individual species in a warmer world. Finally, Kassem and colleagues investigate the effects of elevated CO2 and drought on soil microbial communities associated with roots, finding that CO2 and drought have unique and interactive effects on microbial activity and that elevated CO2 ameliorates drought effects, but that neither factor affects the composition of the microbial community. In addition to increasing our knowledge of the effects of global environmental change on plants, and in stimulating new research in this area, we are hopeful that this special feature will serve to stimulate consideration of JIPB as an outlet for global-change research, in part by introducing JIPB to researchers unfamiliar with this journal. Finally, we express our appreciation to JIPB for supporting this special issue and its focus on younger scientists, and we thank our colleagues who contributed to this feature for their patience and cooperation, as well as their high-quality papers.
Abstract (Browse 3509)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
          Invited Expert Reviews
Global Change Effects on Plant Chemical Defenses against Insect Herbivores  
Author: M. Gabriela Bidart-Bouzat and Adebobola Imeh-Nathaniel
Journal of Integrative Plant Biology 2008 50(11): 1339-1354
DOI: 10.1111/j.1744-7909.2008.00751.x
    This review focuses on individual effects of major global change factors, such as elevated CO2, O3, UV light and temperature, on plant secondary chemistry. These secondary metabolites are well-known for their role in plant defense against insect herbivory. Global change effects on secondary chemicals appear to be plant species-specific and dependent on the chemical type. Even though plant chemical responses induced by these factors are highly variable, there seems to be some specificity in the response to different environmental stressors. For example, even though the production of phenolic compounds is enhanced by both elevated CO2 and UV light levels, the latter appears to primarily increase the concentrations of flavonoids. Likewise, specific phenolic metabolites seem to be induced by O3 but not by other factors, and an increase in volatile organic compounds has been particularly detected under elevated temperature. More information is needed regarding how global change factors influence inducibility of plant chemical defenses as well as how their indirect and direct effects impact insect performance and behavior, herbivory rates and pathogen attack. This knowledge is crucial to better understand how plants and their associated natural enemies will be affected in future changing environments.
Abstract (Browse 2807)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Capacity of Old Trees to Respond to Environmental Change  
Author: Nathan G. Phillips, Thomas N. Buckley and David T. Tissue
Journal of Integrative Plant Biology 2008 50(11): 1355-1364
DOI: 10.1111/j.1744-7909.2008.00746.x
    Atmospheric carbon dioxide ([CO2]) has increased dramatically within the current life spans of long-lived trees and old forests. Consider that a 500-year-old tree in the early 21st century has spent 70% of its life growing under pre-industrial levels of [CO2], which were 30% lower than current levels. Here we address the question of whether old trees have already responded to the rapid rise in [CO2] occurring over the past 150 years. In spite of limited data, aging trees have been shown to possess a substantial capacity for increased net growth after a period of post-maturity growth decline. Observations of renewed growth and physiological function in old trees have, in some instances, coincided with Industrial Age increases in key environmental resources, including [CO2], suggesting the potential for continued growth in old trees as a function of continued global climate change.
Abstract (Browse 2314)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Why are Nitrogen Concentrations in Plant Tissues Lower under Elevated CO2? A Critical Examination of the Hypotheses  
Author: Daniel R. Taub and Xianzhong Wang
Journal of Integrative Plant Biology 2008 50(11): 1365-1374
DOI: 10.1111/j.1744-7909.2008.00754.x
    Plants grown under elevated atmospheric [CO2] typically have decreased tissue concentrations of N compared with plants grown under current ambient [CO2]. The physiological mechanisms responsible for this phenomenon have not been definitely established, although a considerable number of hypotheses have been advanced to account for it. In this review we discuss and critically evaluate these hypotheses. One contributing factor to the decreases in tissue N concentrations clearly is dilution of N by increased photosynthetic assimilation of C. In addition, studies on intact plants show strong evidence for a general decrease in the specific uptake rates (uptake per unit mass or length of root) of N by roots under elevated CO2, This decreased root uptake appears likely to be the result both of decreased N demand by shoots and of decreased ability of the soil-root system to supply N. The best-supported mechanism for decreased N supply is a decrease in transpiration-driven mass flow of N in soils due to decreased stomatal conductance at elevated CO2, although some evidence suggests that altered root system architecture may also play a role. There is also limited evidence suggesting that under elevated CO2, plants may exhibit increased rates of N loss through volatilization and/or root exudation, further contributing to lowering tissue N concentrations.
Abstract (Browse 2482)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
          Research Articles
Interactive Effects of Elevated CO2 and Growth Temperature on the Tolerance of Photosynthesis to Acute Heat Stress in C3 and C4 Species  
Author: E. William Hamilton III, Scott A. Heckathorn, Puneet Joshi, Dan Wang and Deepak Barua
Journal of Integrative Plant Biology 2008 50(11): 1375-1387
DOI: 10.1111/j.1744-7909.2008.00747.x
    Determining effects of elevated CO2 on the tolerance of photosynthesis to acute heat-stress (heat wave) is necessary for predicting plant responses to global warming, as photosynthesis is thermolabile and acute heat-stress and atmospheric CO2 will increase in the future. Few studies have examined this, and past results are variable, which may be due to methodological variation. To address this, we grew two C3 and two C4 species at current or elevated CO2 and three different growth temperatures (GT). We assessed photosynthetic thermotolerance in both unacclimated (basal tolerance) and pre-heat-stressed (preHS=acclimated) plants. In C3 species, basal thermotolerance of net photosynthesis (Pn) was increased in high CO2, but in C4 species, Pn thermotlerance was decreased by high CO2 (except Z. mays at low GT); CO2 effects in preHS plants were mostly small or absent, though high CO2 was detrimental in one C3 and one C4 species at warmer GT. Though high CO2 generally decreased stomatal conductance, decreases in Pn during heat stress were mostly due to non-stomatal effects. Photosystem II (PSII) efficiency was often decreased by high CO2 during heat stress, especially at high GT; CO2 effects on post-PSII electron transport were variable. Thus, high CO2 often affected photosynthetic theromotolerance, and the effects varied with photosynthetic pathway, growth temperature, and acclimation state. Most importantly, pre-heat stressed plants at normal or warmer growth temperatures, high CO2 may often decrease, or not benefit as expected, tolerance of photosynthesis to acute heat stress. Therefore, interactive effects of elevated CO2 and warmer growth temperatures on acute heat tolerance may contribute to future changes in plant productivity, distribution, and diversity.
Abstract (Browse 2662)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Physiological and Growth Responses of C3 and C4 Plants to Reduced Temperature when Grown at Low CO2 of the Last Ice Age  
Author: Joy K. Ward, David A. Myers and Richard B. Thomas
Journal of Integrative Plant Biology 2008 50(11): 1388-1395
DOI: 10.1111/j.1744-7909.2008.00753.x
    During the last ice age, atmospheric [CO2] was 180-200 ppm compared with the modern value of 380 ppm, and temperatures were ~8 ˚C cooler. Relatively little is known about the responses of C3 and C4 species to long-term exposure to glacial conditions. Here Abutilon theophrasti (C3) and Amaranthus retroflexus (C4) were grown at 200 ppm CO2 with current (30/24 ˚C) and glacial (22/16 ˚C) temperatures for 22 d. Overall, the C4 species exhibited a large growth advantage over the C3 species at low [CO2]. However, this advantage was reduced at low temperature, where the C4 species produced 5X the total mass of the C3 species versus 14X at the high temperature. This difference was due to a reduction in C4 growth at the low temperature, since the C3 species exhibited similar growth between temperatures. Physiological differences between temperatures were not detected for either species, although photorespiration/net photosynthesis was reduced in the C3 species grown at low temperature, suggesting evidence of improved carbon balance at this treatment. This system suggests that C4 species exhibited a growth advantage over C3 species during low [CO2] of the last ice age, although concurrent reductions in temperatures may have reduced this advantage.
Abstract (Browse 2992)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Interactive Effects of Elevated CO2 and Ozone on Leaf Thermotolerance in Field-grown Glycine max  
Author: Sasmita Mishra, Scott A. Heckathorn, Deepak Barua, Dan Wang, Puneet Joshi, E. William Hamilton III and Jonathan Frantz
Journal of Integrative Plant Biology 2008 50(11): 1396-1405
DOI: 10.1111/j.1744-7909.2008.00745.x
    Human activity is increasing atmospheric CO2 and both global mean and acute high temperatures (heat waves). Laboratory studies have shown that elevated CO2 can increase heat tolerance of photosynthesis in C3 plants. However, human-caused increases in ground-level ozone (O3), which causes oxidative stress, may offset benefits of elevated CO2 during heat waves. In this study, we determined the effects of elevated CO2 and O3 on the heat tolerance of leaves of field-grown Glycine max (soybean, C3). Photosynthetic electron transport (et) was measured in attached leaves heated in situ and in heated detached leaves under ambient CO2 and O3; biochemical assays were conducted on leaves of plants heated in the lab. Heat stress decreased et, and O3 exacerbated this decrease. Elevated CO2 prevented O3-related decreases during heat stress, but only increased et under ambient O3 in the field. CO2 and O3 effects on et during heat stress were light dependent. Heat stress decreased chlorophyll and carotenoid content, especially under elevated CO2. Neither CO2 nor O3 had any effect on production of heat-shock proteins. Heat stress increased catalase (except in high O3) and Cu/Zn-SOD (superoxide dismutase) content, but not Mn-SOD; CO2 and O3 decreased catalase and did not affect Mn- or Cu/Zn-SOD. Soluble carbohydrates were unaffected by heat stress, but increased in elevated CO2. Together, these results indicate that modest protection of photosynthetic metabolism during heat stress by elevated CO2 is observed in field-grown soybean under ambient O3, as in the lab, and high CO2 limits damage during heat stress under elevated O3, but this protection is likely related to decreased photorespiration and stomatal conductance rather than production of heat-stress adaptations.
Abstract (Browse 2696)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Effect of Elevated CO2 and Drought on Soil Microbial Communities Associated with Andropogon gerardii  
Author: Issmat I. Kassem, Puneet Joshi, Von Sigler, Scott Heckathorn and Qi Wang
Journal of Integrative Plant Biology 2008 50(11): 1406-1415
DOI: 10.1111/j.1744-7909.2008.00752.x
    Our understanding of the effects of elevated atmospheric CO2, singly and in combination with other environmental changes, on plant-soil interactions is incomplete. Elevated CO2 effects on C4 plants, though smaller than on C3 species, are mediated mostly via decreased stomatal conductance and thus water loss. Therefore, we characterized the interactive effect of elevated CO2 and drought on soil microbial communities associated with a dominant C4 prairie grass, Andropogon gerardii. Elevated CO2 and drought both affected resources available to the soil microbial community. For example, elevated CO2 increased the soil C:N ratio and water content during drought, while drought alone decreased both. Drought significantly decreased soil microbial biomass. In contrast, elevated CO2 increased biomass, while ameliorating biomass decreases induced under drought. Total and active direct bacterial counts and carbon substrate use (overall use and number of used sources) increased significantly under elevated CO2. Denaturing gradient gel electrophoresis analysis revealed that drought and elevated CO2, singly and combined, did not affect the soil bacteria community structure. We conclude that elevated CO2 alone increased bacterial abundance and microbial activity and carbon use, probably in response to increased root exudation. Elevated CO2 also limited drought-related impacts on microbial activity and biomass, which likely resulted from decreased plant water use under elevated CO2. These are among the first results showing that elevated CO2 and drought work in opposition to modulate plant-associated soil-bacteria responses, which should then influence soil resources and plant and ecosystem function.
Abstract (Browse 2611)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Effects of N on Plant Response to Heat-wave: A Field Study with Prairie Vegetation  
Author: Dan Wang, Scott A. Heckathorn, Kumar Mainali, E. William Hamilton
Journal of Integrative Plant Biology 2008 50(11): 1416-1425
DOI: 10.1111/j.1744-7909.2008.00748.x
    More intense, more frequent, and longer heat-waves are expected in the future due to global warming, which could have dramatic ecological impacts. Increasing nitrogen (N) availability and its dynamics will likely impact plant responses to heat stress and carbon (C) sequestration in terrestrial ecosystems. This field study examined the effects of N availability on plant response to heat-stress (HS) treatment in naturally-occurring vegetation. HS (5 days at ambient or 40.5 ºC) and N treatments ( N) were applied to 16 1m2 plots in restored prairie vegetation dominated by Andropogon gerardii (warm-season C4 grass) and Solidago canadensis (warm-season C3 forb). Before, during, and after HS, air, canopy, and soil temperature were monitored; net CO2 assimilation (Pn), quantum yield of photosystem II (PSII), stomatal conductance (gs), and leaf water potential (w) of the dominant species and soil respiration (Rsoil) of each plot were measured daily during HS. One week after HS, plots were harvested, and C% and N% were determined for rhizosphere and bulk soil, and above-ground tissue (green/senescent leaf, stem, and flower). Photosynthetic N-use efficiency (PNUE) and N resorption rate (NRR) were calculated. HS decreased Pn, gs, w, and PNUE for both species, and +N treatment generally increased these variables (HS), but often slowed their post-HS recovery. Aboveground biomass tended to decrease with HS in both species (and for green leaf mass in S. canadensis), but decrease with +N for A. gerardii and increase with +N for S. canadensis. For A. gerardii, HS tended to decrease N% in green tissues with +N, while in S. canadensis, HS increased N% in green leaves. Added N decreased NRR for A. gerardii and HS increased NRR for S. canadensis. These results suggest that heat waves, though transient, could have significant effects on plants, communities, and ecosystem N cycling, and N can influence the effect of heat waves.
Abstract (Browse 2547)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Effects of Climate Change and Shifts in Forest Composition on Forest Net Primary Production  
Author: Jyh-Min Chiang, Louis R. Iverson, Anantha Prasad and Kim J. Brown
Journal of Integrative Plant Biology 2008 50(11): 1426-1439
DOI: 10.1111/j.1744-7909.2008.00749.x
    Forests are dynamic in both structure and species composition, and these dynamics are strongly influenced by climate. Models have been created to predict shifts in tree species ranges with scenarios of future climate change. Among those, the DISTRIB model is one of the few species-specific vegetation models, and provides the most extensive coverage of species (80 tree species) and area (east of the 100th meridian in the U.S.) in North America. The overarching objective of this work was to model community-level predictions of potential species range shifts and create predictions of the sign and magnitude of the impacts on NPP that will be associated with alterations in species composition. These model outputs were combined with a physiologically based, generalized forest carbon balance model (PnET-II) to estimate the net primary production (NPP) contributed by the respective tree species. We selected four 200 x 200 km areas in Wisconsin, Maine, Arkansas, and the Ohio-West Virginia area, representing focal areas of potential species range shifts. We archived an extensive documentation of leaf traits (leaf nitrogen content, specific leaf weight, and longevity) of mature trees in North America from the published literature. Based on the leaf trait database, we determined the central tendency of leaf traits and species-specific parameterization of the PnET-II model was made possible. PnET-II model simulations were performed assuming that all forests achieved steady state, of which the species compositions were predicted by DISTRIB model with no migration limitation. The potential effects of CO2 fertilization were not reflected in this model due to the uncertainty of its long-term effects. The total NPP under the current climate ranged from 552 to 908 g C m-2 y-1. The effects of potential species redistributions on NPP were moderate (-12% to +8%) compared to the influence of future climatic changes (-60% to +25%). We expect more negative effect of species redistribution on NPP if species migration in the future were obstructed by landscape fragmentation. The direction and magnitude of climate change effects on NPP were largely dependent on the degree of warming and water balance. Thus, the magnitude of future climate change can affect the feedback system between the atmosphere and biosphere.
Abstract (Browse 2564)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Variation in Heat-shock Proteins and Photosynthetic Thermotolerance among Natural Populations of Chenopodium album L. from Contrasting Thermal Environments: Implications for Plant Responses to Global Warming  
Author: Deepak Barua, Scott A. Heckathorn and James S. Coleman
Journal of Integrative Plant Biology 2008 50(11): 1440-1451
DOI: 10.1111/j.1744-7909.2008.00756.x
    Production of heat-shock proteins (Hsps) is a key adaptation to acute heat stress and will be important in determining plant responses to climate change. Further, intraspecifc variation in Hsps, which will influence species-level response to global warming, has rarely been examined in naturally occurring plants. To understand intraspecific variation in plant Hsps and its relevance to global warming, we examined Hsp content and thermotolerance in five naturally occurring populations of Chenopodium album L. from contrasting thermal environments grown at low and high temperatures. As expected, Hsp accumulation varied between populations, but this was related more to habitat variability than to mean temperature. Unexpectedly, Hsp accumulation decreased with increasing variability of habitat temperatures. Hsp accumulation also decreased with increased experimental growth temperatures. Physiological thermotolerance was partitioned into basal and induced components. As with Hsps, induced thermotolerance decreased with increasing temperature variability. Thus, populations native to the more stressful habitats, or grown at higher temperatures, had lower Hsp levels and induced thermotolerance, suggesting a greater reliance on basal mechanisms for thermotolerance. These results suggest that future global climate change will differentially impact ecotypes within species, possibly by selecting for increased basal vs. inducible thermotolerance.
Abstract (Browse 2275)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Increased Benthic Algal Primary Production in Response to the Invasive Zebra Mussel (Dreissena polymorpha) in a Productive Ecosystem, Oneida Lake, NY  
Author: Rebecca K. Cecala, Christine M. Mayer, Kimberly L. Schulz and Edward L. Mills
Journal of Integrative Plant Biology 2008 50(11): 1452-1466
DOI: 10.1111/j.1744-7909.2008.00755.x
    Increased water clarity associated with zebra mussel (Dreissena polymorpha) populations may favor benthic algal primary production in freshwater systems previously dominated by pelagic phytoplankton production. While zebra mussel-mediated water clarity effects on benthic primary production have been implicated in the literature, few production estimates are available. This study estimates benthic primary production in Oneida Lake, NY before and after zebra mussel invasion (1992), using measured photosynthetic parameters (PBmax, B and ) from sampled benthic algal communities. In the summers of 2003 and 2004, primary production was measured as O2 evolution from algal communities on hard (cobble) and soft (sediment) substrate from several depths. We also backcast estimates of benthic primary production from measurements of light penetration since 1975. Estimates of whole-lake epipelic and epilithic algal primary production showed a significant (4%) increase and exhibited significantly less interannual variability subsequent to the establishment of zebra mussels. We applied our model to two lakes of differing trophic status; the model significantly overestimated benthic primary production in a hypereutrophic lake, but there was no significant difference between the actual and predicted primary production values in the oligotrophic lake. The hypereutrophic lake had higher zebra mussel densities than Oneida (224 vs. 41 per sample respectively). Though total community respiration (measured in total darkness) was a factored into our model predictions of production, our model may need modification when heterotrophic respiration is a large portion of total community metabolism.
Abstract (Browse 2321)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Adjustment of Forest Ecosystem Root Respiration as Temperature Warms  
Author: Andrew J Burton, Jerry M Melillo and Serita D Frey
Journal of Integrative Plant Biology 2008 50(11): 1467-1483
DOI: 10.1111/j.1744-7909.2008.00750.x
    Adjustment of ecosystem root respiration to warmer climatic conditions can alter the autotrophic portion of soil respiration and influence the amount of carbon available for biomass production. We examined 44 published values of annual forest root respiration and found an increase in ecosystem root respiration with increasing mean annual temperature (MAT), but the rate of this cross-ecosystem increase (Q10 = 1.6) is less than published values for short-term responses of root respiration to temperature within ecosystems (Q10 = 2 to 3). When specific root respiration rates and root biomass values were examined, there was a clear trend for decreasing root metabolic capacity (respiration rate at a standard temperature) with increasing MAT. There also were tradeoffs between root metabolic capacity and root system biomass, such that there were no instances of high growing season respiration rates and high root biomass occurring together. We also examined specific root respiration rates at three soil warming experiments at Harvard Forest, USA, and found decreases in metabolic capacity for roots from the heated plots. This decline could be due to either physiological acclimation or to the effects of co-occurring drier soils on the measurement date. Regardless of the cause, these findings clearly suggest that modeling efforts that allow root respiration to increase exponentially with temperature, with Q10 values of 2 or more, may over-predict root contributions to ecosystem CO2 efflux for future climates and underestimate the amount of C available for other uses, including NPP.
Abstract (Browse 2353)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
Temperature Responses to Infrared-loading and Water Table Manipulations in Peatland Mesocosms  
Author: Jiquan Chen, Scott Bridgham, Jason Keller, John Pastor, Asko Noormets and Jake F. Weltzin
Journal of Integrative Plant Biology 2008 50(11): 1484-1496
DOI: 10.1111/j.1744-7909.2008.00757.x
    Soil temperature affects virtually all other ecosystem processes and will be the variable most directly altered with global warming. We initiated a multi-factor global change experiment to explore the effects of infrared heat loading (HT) and water table level (WL) treatment on soil temperature in bog and fen peatland mesocosms. We found that the temperature of the experimental mesocosms varied highly by year, month, peatland type, soil depth, heat loading and water table manipulation. The highest effect of heat loading on the temperature at 25 cm depth was found in June for the bog mesocosms (3.34 C 4.27 C) but in May for the fen mesocosms (2.32 C 4.33 C) over the two-year study period. The effects of water table levels in the bog mesocosms were only found between August and January, with the wet mesocosms warmer than the dry mesocosms by 0.48-2.03 C over the two-year study period. In contrast, wetter fen mesocosms were generally cooler by 0.16-3.87 C. Seasonal changes of temperatures elevated by the heat loading also varied by depth and ecosystem type, with temperature differences at 5 and 10 cm depth showing smaller seasonal fluctuations than those at 25 and 40 cm in the bog mesocosms. However, increased heat loading did not always lead to warmer soil temperatures, especially in the fen mesocosms, where high latent heat loss during the growing season and sensible heat loss during the freezing season when snow cover was significantly reduced likely resulted in temporary soil cooling. Both heat loading and water table manipulations have also changed the length of the non-frozen season, including the starting and ending dates.
Abstract (Browse 2297)  |  References  |  Full Text HTML  |  Full Text PDF  |  Cited By       
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