Browsing by Subject "warming"

Now showing 1 - 5 of 5
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    Convergent acclimation of leaf photosynthesis and respiration to prevailing ambient temperatures under current and warmer climates in Eucalyptus tereticornis
    (2016) Aspinwall, Michael J; Drake, John E; Campany, Courtney; Vårhammar, Angelica; Ghannoum, Oula; Tissue, David T; Reich, Peter B; Tjoelker, Mark G
    Understanding physiological acclimation of photosynthesis and respiration is important in elucidating the metabolic performance of trees in a changing climate. Does physiological acclimation to climate warming mirror acclimation to seasonal temperature changes? We grew Eucalyptus tereticornis trees in the field for 14 months inside 9-m tall whole-tree chambers tracking ambient air temperature (Tair) or ambient Tair + 3°C (i.e. ‘warmed’). We measured light- and CO2-saturated net photosynthesis (Amax) and night-time dark respiration (R) each month at 25°C to quantify acclimation. Tree growth was measured, and leaf nitrogen (N) and total nonstructural carbohydrate (TNC) concentrations were determined to investigate mechanisms of acclimation. Warming reduced Amax and R measured at 25°C compared to ambient-grown trees. Both traits also declined as mean daily Tair increased, and did so in a similar way across temperature treatments. Amax and R (at 25°C) both increased as TNC concentrations increased seasonally; these relationships appeared to arise from source–sink imbalances, suggesting potential substrate regulation of thermal acclimation. We found that photosynthesis and respiration each acclimated equivalently to experimental warming and seasonal temperature change of a similar magnitude, reflecting a common, nearly homeostatic constraint on leaf carbon exchange that will be important in governing tree responses to climate warming.
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    Data Supporting Reich et al 2022: Even modest climate change may lead to major transitions in boreal forests
    (2022-06-27) Reich, Peter, B.; Bermudez, Raimundo; Montgomery, Rebecca, A.; Rich, Roy, L.; Rice, Karen, E.; Hobbie, Sarah, E.; Stefanski, Artur; preich@umn.edu; Reich, Peter, B.
    To test the uncertainty of the sensitivity of forests to near–term warming and associated precipitation we used a five–year open–air experiment in southern boreal forest located at two research sites in northern Minnesota. The experiment used juveniles of nine temperate and boreal tree species that grew under ambient and seasonally warmed (+1.6C and +3.1C above- and belowground) and rainfall reduced (~30% less rainfall) conditions. Each year we surveyed all trees for their survival and growth and measured in situ light-saturated net photosynthesis (Anet) and leaf diffusive conductance (gs).
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    Does physiological acclimation to climate warming stabilize the ratio of canopy respiration to photosynthesis?
    (Wiley, 2016) Drake, John E; Tjoelker, Mark G; Aspinwall, Michael J; Reich, Peter B; Barton, Craig V. M.; Medlyn, Belinda E; Duursma, Remko A
    Given the contrasting short-term temperature dependences of gross primary production (GPP) and autotrophic respiration, the fraction of GPP respired by trees is predicted to increase with warming, providing a positive feedback to climate change. However, physiological acclimation may dampen or eliminate this response. We measured the fluxes of aboveground respiration (Ra), GPP and their ratio (Ra/GPP) in large, field-grown Eucalyptus tereticornis trees exposed to ambient or warmed air temperatures (+3°C). We report continuous measurements of whole-canopy CO2 exchange, direct temperature response curves of leaf and canopy respiration, leaf and branch wood respiration, and diurnal photosynthetic measurements. Warming reduced photosynthesis, whereas physiological acclimation prevented a coincident increase in Ra. Ambient and warmed trees had a common nonlinear relationship between the fraction of GPP that was respired above ground (Ra/GPP) and the mean daily temperature. Thus, warming significantly increased Ra/GPP by moving plants to higher positions on the shared Ra/GPP vs daily temperature relationship, but this effect was modest and only notable during hot conditions. Despite the physiological acclimation of autotrophic respiration to warming, increases in temperature and the frequency of heat waves may modestly increase tree Ra/GPP, contributing to a positive feedback between climate warming and atmospheric CO2 accumulation.
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    Plant diversity effects on soil microbial functions and enzymes are stronger than warming in a grassland experiment
    (Ecological Society of America, 2015) Steinauer, Katja; Tilman, G David; Wragg, Peter Douglas; Cesarz, Simone; Cowles, Jane M; Pritsch, Karin; Reich, Peter B; Weisser, Wolfgang W; Eisenhauer, Nico;
    Anthropogenic changes in biodiversity and atmospheric temperature significantly influence ecosystem processes. However, little is known about potential interactive effects of plant diversity and warming on essential ecosystem properties, such as soil microbial functions and element cycling. We studied the effects of orthogonal manipulations of plant diversity (one, four, and 16 species) and warming (ambient, +1.5°C, and +3°C) on soil microbial biomass, respiration, growth after nutrient additions, and activities of extracellular enzymes in 2011 and 2012 in the BAC (biodiversity and climate) perennial grassland experiment site at Cedar Creek, Minnesota, USA. Focal enzymes are involved in essential biogeochemical processes of the carbon, nitrogen, and phosphorus cycles. Soil microbial biomass and some enzyme activities involved in the C and N cycle increased significantly with increasing plant diversity in both years. In addition, 16-species mixtures buffered warming induced reductions in topsoil water content. We found no interactive effects of plant diversity and warming on soil microbial biomass and growth rates. However, the activity of several enzymes (1,4-β-glucosidase, 1,4-β-N-acetylglucosaminidase, phosphatase, peroxidase) depended on interactions between plant diversity and warming with elevated activities of enzymes involved in the C, N, and P cycles at both high plant diversity and high warming levels. Increasing plant diversity consistently decreased microbial biomass-specific enzyme activities and altered soil microbial growth responses to nutrient additions, indicating that plant diversity changed nutrient limitations and/or microbial community composition. In contrast to our expectations, higher plant diversity only buffered temperature effects on soil water content, but not on microbial functions. Temperature effects on some soil enzymes were greatest at high plant diversity. In total, our results suggest that the fundamental temperature ranges of soil microbial communities may be sufficiently broad to buffer their functioning against changes in temperature and that plant diversity may be a dominant control of soil microbial processes in a changing world.
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    Response of boreal peatland ecosystems to global change: A remote sensing approach
    (2017-08) McPartland, Mara
    Global climate change is expected to result in anywhere from two to four degrees of warming, with consequences for terrestrial ecosystems. The rate of climate change is disproportionally greater at high latitudes, resulting in landscape-scale effects on the composition, structure, and function of arctic and boreal ecology. Remote sensing offers scientists the ability to track large-scale changes through the detection of biophysical processes occurring in terrestrial ecosystems. In this research, I measured the response of boreal peatland ecosystems to a suite of different climate-related drivers including increased temperature, elevated carbon dioxide levels, and hydrologic change. Working within large-scale ecosystem manipulation experiments, I used passive remote sensing to measure the response of two different types of boreal peatlands, a rich fen and an ombrotrophic bog, to simulated climate change. Chapter 1 describes my research on the use of hyperspectral remote sensing to examine changes in the composition and biodiversity of peatlands in response to long-term experimental manipulation. Chapter 2 details my findings on using simple remote sensing techniques to detect changes in peatland ecosystem productivity in response to warming, elevated carbon dioxide, and hydrologic change. Through this work, I demonstrate that remote sensing can be used to characterize the response of a range of different ecosystem properties to global change.