Evidence for widespread thermal acclimation of canopy photosynthesis

Abstract 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 (Amax,2000) and growth temperature (\({-}{{T}ₐᵢᵣ}\)) 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 Amax,2000 under higher \({-}{{T}ₐᵢᵣ}\), 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.