Environmental factors have a greater influence on photosynthetic capacity in C₄ plants than biochemical subtypes or growth forms

Summary Our understanding of how photosynthetic capacity varies among C 4 species and across growth and measurement conditions remains limited. We collated 1696 CO 2 response curves of net CO 2 assimilation rate ( A / C i curves) from C 4 species grown and measured at various environmental conditions and used these data to estimate the apparent maximum carboxylation activity of phosphoenolpyruvate carboxylase ( V pmaxA ) and CO 2 ‐saturated net photosynthetic rate ( A max ), two key parameters describing photosynthetic capacity. We examined how V pmaxA and A max vary with species‐specific traits, growth and measurement conditions. We found little systematic variation of V pmaxA and A max across the classical C 4 biochemical subtypes or growth forms, but showed that growth temperature and measurement conditions are major factors determining C 4 photosynthetic capacity. We found no evidence that common C 4 model species (e.g. maize, sorghum and Setaria viridis ) differ in photosynthetic capacity from other C 4 species when grown in controlled environments. However, C 4 model species showed up to twice the photosynthetic capacity of other C 4 species when grown in the field. Our multivariate model accounts for 47–51% of the variation reported in V pmaxA and A max , and we argue that environmental conditions have a greater influence on C 4 photosynthetic capacity than biochemical subtypes or growth forms.