Browsing by Author "Drake, John E"
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Item 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 GUnderstanding 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.Item 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 AGiven 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.