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Variation in Heat-shock Proteins and Photosynthetic Thermotolerance among Natural Populations of Chenopodium album *** Contrasting Thermal Environments:Implications for Plant Responses to Global Warming

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Journal of Integrative Plant Biology 2008年第11期50卷 1440-1451页

作者： Deepak Barua scott a.heckathorn James S.Coleman Department of Biology Syracuse University Department of Organismic and Evolutionary Biology Harvard University Department of Environmental Sciences University of Toledo

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 versus inducible thermotolerance.

关键词： acclimation photosynthesis stress proteins temperature.

Effects of N on Plant Response to Heat-wave:A Field Study with Prairie Vegetation

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Journal of Integrative Plant Biology 2008年第11期50卷 1416-1425页

作者： Dan Wang scott A. heckathorn Kumar Mainali E. William Hamilton Department of Environmental Sciences University of Toledo Toledo Ohio 43606 USA Department of Biology Washington and Lee University Lexington Virginia 24450 USA

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 d at ambient or 40.5 ℃） and N treatments （±N） were applied to 16 1 m^2 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 （ФpsⅡ）, stomatal conductance （gs）, and leaf water potential （ψw） of the dominant species and soil respiration （Rsoll） 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, ψw, 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, whereas 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.

关键词： global climate change heat stress N resorption rate photosynthesis photosynthetic N-use efficiency.

Effect of Elevated CO_2 and Drought on Soil Microbial Communities Associated with Andropogon gerardii

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Journal of Integrative Plant Biology 2008年第11期50卷 1406-1415页

作者： Issmat I. Kassem Puneet Joshi Yon Sigler scott heckathorn Qi Wang Department of Environmental Sciences University of Toledo Ohio 43606 USA Department of Civil Engineering University of Toledo Ohio 43606 USA

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 Vitman. 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, whereas drought alone decreased both. Drought significantly decreased soil microbial biomass. In contrast, elevated CO2 increased biomass while ameliorating biomass decreases that were 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.

关键词： denaturing gradient gel electrophoresis drought elevated CO2 soil microbial communities.

Interactive Effects of Elevated CO_2 and Growth Temperature on the Tolerance of Photosynthesis to Acute Heat Stress in C_3 and C_4 Species

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Journal of Integrative Plant Biology 2008年第11期50卷 1375-1387页

作者： E. William Hamilton III scott A. heckathorn Puneet Joshi Dan Wang Deepak Barua Department of Biology Washington and Lee University Lexington Virginia USA Department of Environmental Sciences University of Toledo Toledo Ohio USA

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 preheat-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 Zea 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 P, 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, in 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.

关键词： carbon dioxide global climate change photosynthesis thermotolerance.

Interactive Effects of Elevated CO_2 and Ozone on Leaf Thermotolerance in Field-grown Glycine max

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Journal of Integrative Plant Biology 2008年第11期50卷 1396-1405页

作者： Sasmita Mishra scott A. heckathorn Deepak Barua Dan Wang Puneet Joshi E. William Hamilton III Jonathan Frantz Department of Environmental Sciences University of Toledo Toledo Ohio USA Department of Biology Washington and Lee University Lexington Virginia USA United States Department of Agricuffure-Agricultural Research Service University of Toledo Toledo Ohio 43606 USA

Humans are increasing atmospheric CO2, ground-level ozone （O3）, and mean and acute high temperatures. Laboratory studies show that elevated CO2 can increase thermotolerance of photosynthesis in C3 plants. O3-related oxidative stress may offset benefits of elevated CO2 during heat-waves. We determined effects of elevated CO2 and O3 on leaf thermotolerance of field-grown Glycine max （soybean, C3）. Photosynthetic electron transport （Фet） was measured in attached leaves heated in situ and detached leaves heated under ambient CO2 and O3. Heating decreased Фet, which O3 exacerbated. Elevated CO2 prevented O3-related decreases during heating, but only increased Фet under ambient O3 in the field. Heating decreased chlorophyll and carotenoids, especially under elevated CO2. Neither CO2 nor O3 affected heat-shock proteins. Heating increased catalase （except in high O3） and Cu/Zn-superoxide dismutase （SOD）, but not Mn- SOD; CO2 and O3 decreased catalase but neither SOD. Soluble carbohydrates were unaffected by heating, but increased in elevated CO2. Thus, protection of photosynthesis during heat stress by elevated CO2 occurs in field-grown soybean under ambient O3, as in the lab, and high CO2 limits heat damage under elevated O3, but this protection is likely from decreased photorespiration and stomatal conductance rather than production of heat-stress adaptations.

关键词： anti-oxidants global change heat-shock proteins photosynthesis.

Interactive Effects of Temperature, Nitrogen, and Zooplankton on Growth and Protein and Carbohydrate Content of Cyanobacteria from Western Lake Erie

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Journal of Water Resource and Protection 2014年第12期6卷 1139-1153页

作者： Deepesh Bista scott A. heckathorn Thomas Bridgeman Justin D. Chaffin Sasmita Mishra Department of Environmental Sciences University of Toledo Toledo USA F.T. Stone Laboratory The Ohio State University Columbus USA

Harmful algal blooms (HABs) in freshwater ecosystems, especially of cyanobacterial species, are becoming more frequent and expanding geographically, including in Lake Erie in North America. HABs are the result of complex and synergistic environmental factors, though N or P eutrophication is a leading cause. With global mean temperatures expected to increase an additional 2°C - 5°C by 2100, cyanobacterial blooms are predicted to increase even more, given their typically-high temperature optimum for growth. We investigated how increases in temperature and nitrogen, singly or in combination, affect the growth, food quality, and herbivory of Lake Erie cyanobacteria. Algal community samples collected from Lake Erie, and isolated non-N-fixing (Microcystis aeruginosa) and N-fixing (Anabaena flos-aquae) cyanobacterial species, were cultured at 20°C, 25°C, or 30°C, and at 5, 50, 150, or 250 μM N, and then analyzed for growth and (for isolates) content of total protein and non-structural carbohydrates (NSC). Temperature and N both affected algal growth, and there were temperature × N interactions, which were sometimes affected by presence/absence of zooplankton. For example, cyanobacteria (but not green algae) growth increased with both temperature and N, especially from 25°C to 30°C, but N and herbivore presence increased cyanobacterial growth primarily only at 30°C. In general, temperature and N had little consistent effect on NSC, but increasing temperature and N tended to increase protein content in Microcystis and Anabaena (temperature effects mostly at higher N levels). In Anabaena, increases in N did not increase growth or protein at 20°C or 25°C, but did increase both at 30°C, indicating that N fixation is damaged at high temperatures and that high NO3 can overcome this damage. These results indicate that future global warming and continued eutrophication will increase cyanobacterial growth, as well influence algal herbivory and competition between N-fixing and non-N-

关键词： Cyanobacteria Great Lakes Harmful Algal Blooms Nitrogen Temperature

Role of Suspended Sediments and Mixing in Reducing Photoinhibition in the Bloom-Forming Cyanobacterium Microcystis

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Journal of Water Resource and Protection 2012年第12期4卷 1029-1041页

作者： Justin D. Chaffin Thomas B. Bridgeman scott A. heckathorn Ann E. Krause Lake Erie Center and Department Environmental Sciences University of Toledo Oregon USA

Toxic cyanobacterial blooms are becoming a global problem. Previous research of cyanobacterial bloom development has examined how high nutrient concentrations promote cyanobacteria dominance, and how positive buoyancy provides an ecological advantage over sinking phytoplankton. Tributaries responsible for loading nutrients into lakes often simultaneously contribute high concentrations of suspended sediments. High concentrations of suspended sediments may also influence blooms by affecting the ambient light climate, reducing photodamage, and increasing the efficiency of photosynthesis. We examined the effects of sediments and vertical mixing in potentially reducing photodamage to Microcystis by measuring photosynthetic parameters and pigment content of Microcystis in western Lake Erie during the 2008 bloom and in laboratory experiments. Photosynthetic efficiency increased with increasing sediment concentration in the lake and laboratory experiment. Content of photo-protective carotenoid pigments per dry weight decreased with increasing sediment concentrations, while the light-harvesting pigments, chl a and phycocyanin, increased with sediments. These results indicate that suspended sediments reduce photoinhibition for Microcystis. Further, photosynthetic damage was higher when Microcystis was concentrated on the surface compared to a mixed water column. Measurements of Microcystis abundance and light were also recorded, in addition to photosynthetic measurements. Greatest Microcystis abundances in Lake Erie were recorded during light-limiting conditions, which offer Microcystis both physiological and ecological benefits by reducing photoinhibition and increasing Microcystis’ advantage in light competition via buoyancy. Efforts to reduce cyanobacterial blooms may include reducing suspended sediments loads in combination with reducing nutrient loading.

关键词： Chlorophyll Fluorescence Cyanobacteria Harmful Algae Bloom Lake Erie Microcystis Suspended Sediments