Temperature response of mesophyll conductance in three C4 species calculated with two methods: 18O discrimination and in vitro Vpmax

center dot Mesophyll conductance (g(m)) is an important factor limiting rates of C-3 photosynthesis. However, its role in C-4 photosynthesis is poorly understood because it has been historically difficult to estimate. center dot We use two methods to derive the temperature responses of g(m) in C-4 species. The first (Delta O-18 combines measurements of gas exchange with models and measurements of O-18 discrimination. The second method (in vitro V-pmax) derives g(m) by retrofitting models of C-4 photosynthesis and C-13 discrimination with gas exchange, kinetic constants and in vitro V-pmax measurements. center dot The two methods produced similar g(m) for Setaria viridis and Zea mays. Additionally, we present the first temperature response (10-40 degrees C) of C-4 g(m) in S. viridis, Z. mays and Miscanthus x giganteus. Values for g(m) at 25 degrees C ranged from 2.90 to 7.85 mu molm(-2) s(-1) Pa-1. center dot Our study demonstrated that: the two described methods are suitable to calculate g(m) in C-4 species; g(m) values in C-4 are similar to high-end values reported for C-3 species; and g(m) increases with temperature analogous to reports for C-3 species and the response is species specific. These results improve our mechanistic understanding of C-4 photosynthesis.