Evidence for widespread thermal acclimation of canopy photosynthesis

Plants acclimate to temperature by adjusting their photosynthetic capacity over weeks to months. However, most evidence for photosynthetic acclimation derives from leaf-scale experiments. Here, we address the scarcity of evidence for canopy-scale photosynthetic acclimation by examining the correlation between maximum photosynthetic rates (A_max,2000) and growth temperature (\(\stackrel{-}{{T}_{air}}\)) across a range of concurrent temperatures and canopy foliage quantity, using data from over 200 eddy covariance sites. We detect widespread thermal acclimation of canopy-scale photosynthesis, demonstrated by enhanced A_max,2000 under higher \(\stackrel{-}{{T}_{air}}\), across flux sites with adequate water availability. A 14-day period is identified as the most relevant time scale for acclimation across all sites, with a range of 12–25 days for different plant functional types. The mean apparent thermal acclimation rate across all ecosystems is 0.41 (-0.47–1.05 for 5th–95th percentile range) µmol m^{− 2} s^{− 1} °C^{− 1}, with croplands showing the largest and grasslands the lowest acclimation rates. Incorporating optimality-based leaf photosynthetic capacity acclimation into a biochemical photosynthesis model is shown to improve the representation of thermal acclimation rates. Our results underscore the critical need for enhanced understanding and modelling of canopy-scale photosynthetic capacity to accurately predict plant responses to warmer growing seasons.