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 (V_cmax²⁵ ), (b) reduced leaf dark respiration at 25°C (both in terms of O₂ consumption R_dark _O₂²⁵ and CO₂ efflux R_dark _CO₂²⁵ ) and (c) lower R_dark _CO₂²⁵ to V_cmax²⁵ 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 , R_dark _CO₂²⁵ and V_cmax²⁵ ) did not show the classic acclimation responses that we hypothesized; by contrast, the hypothesized changes in R_{dark_} 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.