Growing‐Season Precipitation Is a Key Driver of Plant Leaf Area to Sapwood Area Ratio at the Global Scale

Leaf area to sapwood area ratio (A_L/A_S) influences carbon sequestration, community composition, and ecosystem functioning in terrestrial vegetation and is closely related to leaf economics and hydraulics. However, critical predictors of A_L/A_S are not well understood. We compiled an A_L/A_S data set with 1612 species-site combinations (1137 species from 285 sites worldwide) from our field experiments and published literature. We found the global mean A_L/A_S to be 0.63 m² cm^-2, with its variation largely driven by growing-season precipitation (P_gs), which accounted for 18% of the variation in A_L/A_S. Species in tropical rainforests exhibited the highest A_L/A_S (0.82 m² cm^-2), whereas desert species showed the lowest A_L/A_S (0.16 m² cm^-2). Soil factors such as soil nitrogen and soil organic carbon exhibited positive effects on A_L/A_S, whereas soil pH was negatively correlated with A_L/A_S. Tree density accounted for 7% of the variation in A_L/A_S. All biotic and abiotic predictors collectively explained up to 45% of the variation in A_L/A_S. Additionally, A_L/A_S was positively correlated to the net primary productivity (NPP) of the ecosystem. Our study provides insights into the driving factors of A_L/A_S at the global scale and highlights the importance of A_L/A_S in ecosystem productivity. Given that P_gs is the most critical driver of A_L/A_S, alterations in global precipitation belts, particularly seasonal precipitation, may induce changes in plant leaf area on the branches.