Biochemical acclimation, stomatal limitation and precipitation patterns underlie decreases in photosynthetic stimulation of soybean (Glycine max) at elevated [CO₂] and temperatures under fully open air field conditions

The net effect of elevated [CO₂] and temperature on photosynthetic acclimation and plant productivity is poorly resolved. We assessed the effects of canopy warming and fully open air [CO₂] enrichment on (1) the acclimation of two biochemical parameters that frequently limit photosynthesis (A), the maximum carboxylation capacity of Rubisco (V_c,max) and the maximum potential linear electron flux through photosystem II (J_max), (2) the associated responses of leaf structural and chemical properties related to A, as well as (3) the stomatal limitation (l) imposed on A, for soybean over two growing seasons in a conventionally managed agricultural field in Illinois, USA. Acclimation to elevated [CO₂] was consistent over two growing seasons with respect to V_c,max and J_max. However, elevated temperature significantly decreased J_max contributing to lower photosynthetic stimulation by elevated CO₂. Large seasonal differences in precipitation altered soil moisture availability modulating the complex effects of elevated temperature and CO₂ on biochemical and structural properties related to A. Elevated temperature also reduced the benefit of elevated [CO₂] by eliminating decreases in stomatal limitation at elevated [CO₂]. These results highlight the critical importance of considering multiple environmental factors (i.e. temperature, moisture, [CO₂]) when trying to predict plant productivity in the context of climate change.