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

Yuzhen Fan, Daniel W.A. Noble, Belinda E. Medlyn, Russell K. Monson, Rowan F. Sage, Nicholas G. Smith, Elizabeth A. Ainsworth, Florian A. Busch, Florence R. Danila, Maria Ermakova, Patrick Friesen, Robert T. Furbank, Shu Han Gan, Oula Ghannoum, Daniel M. Griffith, Lianhong Gu, Vinod Jacob, Jürgen Knauer, Andrew D.B. Leakey, Shuai Li, Danica L. Lombardozzi, Martha Ludwig, Varsha S. Pathare, Murilo M. Peixoto, Karine Prado, Balasaheb V. Sonawane, Christopher J. Still, Susanne von Caemmerer, Russell Woodford, Danielle Way 

• Our understanding of how photosynthesis varies among C4 species and across different growth and measurement conditions remains limited.
• We collated 1,696 CO2 response curves of net CO2 assimilation rate (A/Ci curves) from C4 species grown and measured at various environmental conditions and used these data to estimate the apparent maximum carboxylation activity of phosphoenolpyruvate carboxylase (VpmaxA) and CO2-saturated net photosynthetic rate (Amax), two key parameters describing C4 photosynthetic capacity. We examined how VpmaxA and Amax vary with species-specific traits, growth and measurement conditions.
• We show that VpmaxA and Amax do not differ between C4 biochemical subtypes or growth forms, and highlight that growth temperature and measurement conditions are major factors determining photosynthetic capacity. We found no evidence that common C4 model species (e.g., maize, sorghum and Setaria viridis) differ in photosynthetic capacity from other C4 species when grown in controlled environments. However, C4 model species showed up to twice the photosynthetic capacity of other C4 species when grown in the field.
• Our multivariate model accounts for 47-51% of the variation reported in VpmaxA and Amax, and we argue that environmental conditions have a greater influence on C4 photosynthetic capacity than inherent biochemical subtypes or growth forms.