Global spectrum of leaf nitrogen allocation driven by evolution and environment.

Terrestrial carbon uptake under climate change is significantly constrained by nitrogen (N) availability. While plants can alleviate this limitation through flexible leaf N allocation, the global patterns of such partitioning remain poorly understood. Here, by analyzing a global dataset of 520 seed plant species spanning 98 families, we find that plants averagely allocate 38.7% of leaf N to photosynthetic components (including Rubisco, bioenergetics, and light‑capture machinery) and 13.1% to cell walls. The leaf N allocation pattern exhibits a distinct evolutionary shift: early-diverging plants preferentially invest N in cell walls, while recently evolved species allocate more N to photosynthesis. This pattern is fundamentally constrained by evolutionary history and further shaped by recent environmental factors, ultimately leading to a trade-off in leaf N partitioning between photosynthetic components and cell walls. Such a trade-off refines the leaf economics spectrum, demonstrating that conservative-strategy species favor structural investment (cell walls), whereas acquisitive-strategy species prioritize metabolic gain (photosynthesis). These findings suggest that incorporating lineage-specific N allocation strategies can improve projections of global vegetation responses to nutrient limitation and climate change.