Acclimation of leaf photosynthesis and respiration to warming in field‐grown wheat

Climate change and future warming will significantly affect crop yield. The capacity of crops to dynamically adjust physiological processes (i.e., acclimate) to warming might improve overall performance. Understanding and quantifying the degree of acclimation in field crops could ensure better parameterization of crop and Earth System models and predictions of crop performance. We hypothesized that for field‐grown wheat, when measured at a common temperature (25°C), crops grown under warmer conditions would exhibit acclimation, leading to enhanced crop performance and yield. Acclimation was defined as (a) decreased rates of net photosynthesis at 25°C (A25) coupled with lower maximum carboxylation capacity (Vcmax25), (b) reduced leaf dark respiration at 25°C (both in terms of O2 consumption Rdark_O225 and CO2 efflux Rdark_CO225) and (c) lower Rdark_CO225 to Vcmax25 ratio. Field experiments were conducted over two seasons with 20 wheat genotypes, sown at three different planting dates, to test these hypotheses. Leaf‐level CO2‐based traits (A25, Rdark_CO225 and Vcmax25) did not show the classic acclimation responses that we hypothesized; by contrast, the hypothesized changes in Rdark_O2 were observed. These findings have implications for predictive crop models that assume similar temperature response among these physiological processes and for predictions of crop performance in a future warmer world. In field‐grown wheat, leaf‐level CO2‐based traits (photosynthesis, carboxylation capacity and respiration measured at 25°C) did not exhibit classic acclimation responses to warming generated by varying time of sowing; by contrast, O2‐based respiration did.