Short-term thermal photosynthetic responses of C4 grasses are independent of the biochemical subtype

C 4 photosynthesis evolved independently many times, resulting in multiple biochemical pathways; however, little is known about how these different pathways respond to temperature. We investigated the photosynthetic responses of eight C 4 grasses belonging to three biochemical subtypes (NADP-ME, PEP-CK, and NAD-ME) to four leaf temperatures (18, 25, 32, and 40 °C). We also explored whether the biochemical subtype influences the thermal responses of (i) in vitro PEPC (Vpmax) and Rubisco (Vcmax) maximal activities, (ii) initial slope (IS) and CO 2-saturated rate (CSR) derived from the A-Ci curves, and (iii) CO 2 leakage out of the bundle sheath estimated from carbon isotope discrimination. We focussed on leakiness and the two carboxylases because they determine the coordination of the CO 2-concentrating mechanism and are important for parameterizing the semi-mechanistic C 4 photosynthesis model. We found that the thermal responses of Vpmax and Vcmax, IS, CSR, and leakiness varied among the C 4 species independently of the biochemical subtype. No correlation was observed between Vpmax and IS or between Vcmax and CSR; while the ratios V pmax/Vcmax and IS/CSR did not correlate with leakiness among the C 4 grasses. Determining mesophyll and bundle sheath conductances in diverse C 4 grasses is required to further elucidate how C 4 photosynthesis responds to temperature.