Global patterns and drivers of leaf photosynthetic capacity: The relative importance of environmental factors and evolutionary history

Aim: Understanding the considerable variability and drivers of global leaf photosynthetic capacity [indicated by the maximum carboxylation rate standardized to 25°C (V_c,max25)] is an essential step for accurate modelling of terrestrial plant photosynthesis and carbon uptake under climate change. Although current environmental conditions have often been connected with empirical and theoretical models to explain global V_c,max25 variability through acclimatization and adaptation, long-term evolutionary history has largely been neglected, but might also explicitly play a role in shaping the V_c,max25 variability. Location: Global. Time period: Contemporary. Major taxa studied: Terrestrial plants. Methods: We compiled a geographically comprehensive global dataset of V_c,max25 for C₃ plants (n = 6917 observations from 2157 species and 425 sites covering all major biomes world-wide), explored the biogeographical and phylogenetic patterns of V_c,max25, and quantified the relative importance of current environmental factors and evolutionary history in driving global V_c,max25 variability. Results: We found that V_c,max25 differed across different biomes, with higher mean values in relatively drier regions, and across different life-forms, with higher mean values in non-woody relative to woody plants and in legumes relative to non-leguminous plants. The values of V_c,max25 displayed a significant phylogenetic signal and diverged in a contrasting manner across phylogenetic groups, with a significant trend along the evolutionary axis towards a higher V_c,max25 in more modern clades. A Bayesian phylogenetic linear mixed model revealed that evolutionary history (indicated by phylogeny and species) explained nearly 3-fold more of the variation in global V_c,max25 than present-day environment (53 vs. 18%). Main conclusions: These findings contribute to a comprehensive assessment of the patterns and drivers of global V_c,max25 variability, highlighting the importance of evolutionary history in driving global V_c,max25 variability, hence terrestrial plant photosynthesis.