Biochemical acclimation, stomatal limitation and precipitationpatterns underlie decreases in photosynthetic stimulation of soybean(\u3ci\u3eGlycine max\u3c/i\u3e) at elevated [CO\u3csub\u3e2\u3c/sub\u3e] and temperatures under fully open airfield conditions

The net effect of elevated [CO2] and temperature on photosynthetic acclimation and plant productivityis 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 maximumcarboxylation capacity of Rubisco (Vc,max) and the maximum potential linear electron flux through photo-system II (Jmax), (2) the associated responses of leaf structural and chemical properties related to A, as wellas (3) the stomatal limitation (l) imposed on A, for soybean over two growing seasons in a conventionallymanaged agricultural field in Illinois, USA. Acclimation to elevated [CO2] was consistent over two grow-ing seasons with respect to Vc,maxand Jmax. However, elevated temperature significantly decreased Jmaxcontributing to lower photosynthetic stimulation by elevated CO2. Large seasonal differences in precipi-tation 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 ofelevated [CO2] by eliminating decreases in stomatal limitation at elevated [CO2]. These results highlightthe critical importance of considering multiple environmental factors (i.e. temperature, moisture, [CO2])when trying to predict plant productivity in the context of climate change