Rubisco deactivation and chloroplast electron transport rates co-limit photosynthesis above optimal leaf temperature in terrestrial plants.

Net photosynthetic CO assimilation rate (A) decreases at leaf temperatures above a relatively mild optimum (T) in most higher plants. This decline is often attributed to reduced CO conductance, increased CO loss from photorespiration and respiration, reduced chloroplast electron transport rate (J), or deactivation of Ribulose-1,5-bisphosphate Carboxylase Oxygenase (Rubisco). However, it is unclear which of these factors can best predict species independent declines in A at high temperature. We show that independent of species, and on a global scale, the observed decline in A with rising temperatures can be effectively accounted for by Rubisco deactivation and declines in J. Our finding that A declines with Rubisco deactivation and J supports a coordinated down-regulation of Rubisco and chloroplast electron transport rates to heat stress. We provide a model that, in the absence of CO supply limitations, can predict the response of photosynthesis to short-term increases in leaf temperature.