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

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