Long-term leaf nitrogen and phosphorus dynamics and drivers in China's forests under global change

The leaf nitrogen (N) to phosphorus (P) ratio (N:P) is a critical indicator of nutrient dynamics and ecosystem function. Investigating temporal variations in leaf N:P can provide valuable insights into how plants adapt to environmental changes and nutrient availability. However, limited research has been conducted on long-term temporal leaf N:P variation over a range of temperature zones. Using long-term monitoring data from the Chinese Ecosystem Research Network (CERN), we investigated temporal changes in leaf N and P stoichiometry for 50 dominant tree species from 10 typical forest sites across temperate and subtropical regions, and identified the underlying mechanisms driving these changes. For both regions combined, leaf P concentration of the 50 dominant tree species decreased (20.6%), whereas leaf N:P increased (52.0%) from 2005 to 2020. Leaf P decreased and leaf N:P increased in 67% and 69% of the tree species, respectively. The leaf N:P increase was primarily driven by the tree species in eastern subtropical forests, where global change factors and soil nutrients explained 68% of leaf N:P variation. The P limitation exhibited by tree species in eastern subtropical forest ecosystems intensified over time, and elevated temperature and CO2 levels, coupled with decreased soil available P concentrations, appear to be the main factors driving long-term leaf N:P increases in these forests. Investigating long-term variations in soil nutrients together with global change factors will improve our understanding of the nutrient status of forest ecosystems in the context of global change and will support effective forest ecosystem management.