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/A) 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/A are not well understood. We compiled an A/A 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/A to be 0.63 m cm, with its variation largely driven by growing-season precipitation (P), which accounted for 18% of the variation in A/A. Species in tropical rainforests exhibited the highest A/A (0.82 m cm), whereas desert species showed the lowest A/A (0.16 m cm). Soil factors such as soil nitrogen and soil organic carbon exhibited positive effects on A/A, whereas soil pH was negatively correlated with A/A. Tree density accounted for 7% of the variation in A/A. All biotic and abiotic predictors collectively explained up to 45% of the variation in A/A. Additionally, A/A was positively correlated to the net primary productivity (NPP) of the ecosystem. Our study provides insights into the driving factors of A/A at the global scale and highlights the importance of A/A in ecosystem productivity. Given that P is the most critical driver of A/A, alterations in global precipitation belts, particularly seasonal precipitation, may induce changes in plant leaf area on the branches.