Aridity modulates spatiotemporal changes in carbon allocation to leaves in Northern Hemisphere grasslands

Carbon (C) allocation, which refers to the partitioning of the primary products of photosynthesis into different functional pools, has important implications for plants in optimizing growth and development under variable environmental conditions. The large-scale spatiotemporal pattern of C allocation to leaves (P leaf , the ratio of leaf C to gross primary productivity) in grasslands and its relationship with local aridity remain poorly understood. Here, we developed a remote sensing-based framework to quantify C allocation to leaves across grasslands in the Northern Hemisphere (north of 23.5°N) from 2001 to 2019. By integrating two leaf area index (LAI) products (GLASS and GLOBMAP), two gross primary productivity (GPP) datasets (GLASS and FluxSat), and two global specific leaf area (SLA) maps, we derived pixel-level estimates of P leaf. We then analyzed the spatial patterns, temporal trends, and climatic drivers of P leaf , as well as their relationship with local aridity. Our results revealed that P leaf ranged from 0.008 to 0.455, with significantly lower mean values in arid regions (0.067) than in humid regions (0.089). Over 60 % of grassland pixels exhibited increasing P leaf , particularly in hyper-arid and arid regions. The impact of CO 2 concentration exceeds that of temperature, precipitation, and radiation, emerging as the dominant factor driving interannual variations in P leaf . Our results underscore the role of aridity in modulating C allocation to leaves and enhance our understanding of how climate change affects C allocation to leaves in Northern Hemisphere grasslands.