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Journal Articles

Immediate and potential long-term effects of consecutive heat waves on the photosynthetic performance and water balance in Douglas-fir

Duarte, A. G.*; Katata, Genki; Hoshika, Yasutomo*; Hossain, M.*; Kreuzwieser, J.*; Arneth, A.*; Ruehr, N. K.*

Journal of Plant Physiology, 205, p.57 - 66, 2016/10

 Times Cited Count:33 Percentile:80.65(Plant Sciences)

The frequency and intensity of climatic extremes, such as heat waves, are predicted to increase globally, with severe implications for terrestrial carbon and water cycling. Temperatures may rise above critical thresholds that allow trees to function optimally, with unknown long-term consequences for forest ecosystems. In this context, we investigated how photosynthetic traits and the water balance in Douglasfir are affected by exposure to three heat waves. Photosynthetic carboxylation efficiency was mostly unaffected, but electron transport and photosynthetic rates under saturating light were strongly influenced by the heat waves, with lagging limitations on photosynthesis still being observed six weeks after the last heat wave. We also observed lingering heat-induced inhibitions on transpiration, minimum stomatal conductance, and nighttime stomatal conductance. Results from the stomatal models used to calculate minimum stomatal conductance were similar to gs-night and indicated changes in leaf morphology, such as stomatal occlusions and alterations in epicuticular wax. Our results show Douglas-fir's ability to restrict water loss following heat stress, but at the price of reduced photosynthetic performance. Such limitations indicate potential long-term restrictions that heat waves can impose on tree development and functioning under extreme climatic conditions.

Oral presentation

Impacts of repeated heat waves on tree carbon and water cycling; Moving beyond the stress event

Ruehr, N.*; Bamberger, I.*; Duarte, A.*; Katata, Genki; Pointner, A.*; Arneth, A.*

no journal, , 

Heat waves strongly affect the terrestrial carbon and water cycle, with responses likely continuing past the stress event. In this study we investigated the response of carbon and water relations in Douglas-fir over three subsequent years to repeated summer heat waves under high and low water availability, intermitted by recovery periods. Tree carbon and water fluxes responded strongly to the treatments, with largest water deficits occurring under coupled heat-drought stress. Day- and nighttime transpiration increased with high temperature and evaporative demand, as long as water supply was sufficient. Assimilation in both tree species declined strongly under heat and heat-drought conditions while dark respiration increased with stress intensity in Douglas-fir. We found lagged effects on gas-exchange during the recovery periods, resulting from tight stomata regulation and impaired photosynthesis.

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