Abstract: We conducted a systematic census of leaf N for 102 plant species at 112 research sites along the North-South Transect of Eastern China (NSTEC) following the same protocol, to explore how plant functional types (PFTs) and environmental factors affect the spatial pattern of leaf N. The results showed that mean leaf N was 17.7 mg g^-1 for all plant species. The highest and lowest leaf N were found in deciduous-broadleaf and evergreen-conifer species, respectively, and the ranking of leaf N from high to low was: deciduous > evergreen species, broadleaf > coniferous species, shrubs ≈ trees > grasses. For all data pooled, leaf N showed a convex quadratic response to mean annual temperature (MAT), and a negative linear relationship with mean annual precipitation (MAP), but a positive linear relationship with soil nitrogen concentration (N_soil). These patterns were similar when PFTs were examined individually. Importantly, PFTs, climate and N_soil jointly explained 46.1% of the spatial variation in leaf N, of which the independent explanatory powers of PFTs, climate and N_soil were 15.6%, 2.3% and 4.7%, respectively. Our findings suggest that leaf N is regulated by climate and N_soil mainly via plant species composition. The wide scale empirical relationships developed here are useful for understanding and modeling of the effects of PFTs and environmental factors on leaf N.

Key words: forest ecosystem, plant functional type, temperature, precipitation, soil nitrogen