Effects of heat waves on photosynthetic performance in Douglas-fir

Andre, D.*; Nadine, R.*; Katata, Genki

The frequency and intensity of climate extremes, such as heat waves, are predicted to increase in the future. Temperature could rise beyond the threshold that allows trees to function optimally, and have severe implications on plant growth and productivity. In this context, the present study aims to assess how photosynthetic traits in Douglas-fir, a tree of worldwide economic and environmental importance, is affected by exposure to three heat waves with temperatures about 10 degree above ambient. A combined set of parameters was assessed, including maximum photosynthetic capacity (A), maximal rate of carboxylation () and electron transport (), minimum stomatal conductance (g), needle carbon and nitrogen content. The temporary increase in growth temperature caused A, , and g to decrease, indicating high-temperature limitations on photochemistry. The observed decline in electron transport rates, carboxylation activity, and stomatal conductance reflected the increase in photorespiration and concomitant decrease in photosynthetic rates. Moreover, even one month after the last heat wave, the photosynthetic apparatus was still impaired. These results can offer new insights into the physiological response of Douglas-fir to consecutive episodes of increased temperatures, and help further our understanding of the limitations that heat waves could impose on the development and functioning of Douglas-fir in future climatic scenarios.