Fig. 1. Deactivation of Rubisco and its implications for V_cmax and A_n.

a A collection of published fractions of total functional Rubisco sites in a leaf (Rubisco activation state—points) at a given temperature (refer to Supplementary Table 2 for metadata). A Sharpe-Schoolfield equation (solid lines) accounting for enzyme deactivation at high temperature (Eq. 1) with the numerator set to unity was fit through non-linear least squares regression for both the cool (grown at <25 °C; blue circles) and warm (grown at >25 °C; red squares) growth datasets. b The temperature responses of V_cmax that we derived from Rubisco deactivation (solid lines) and the apparent V_cmax derived from gas-exchange estimates and an Arrhenius peaked model (dashed lines) with an acclimation parameter set at 24 and 36 °C based on Kattge and Knorr²³. Cool (blue) or warm (red) grown species dependent on their day growth temperature being below or above 25 °C, respectively. c The net photosynthesis CO₂ assimilation rate (A_n) predicted from carboxylation limited photosynthesis (A_c) modelled with no O₂ (i.e. no photorespiration) and assuming Rubisco is totally active (dotted lines); or at 21% O₂ but assuming Rubisco is totally active (dashed lines), accounting for Rubisco deactivation (bold solid lines), or assuming RuBP regeneration limited photosynthesis (A_r) based on chloroplast electron transport (J) and its response to temperature (solid lines).