title: Leaf nitrogen:phosphorus stoichiometry across Chinese grassland biomes.
abstract: Leaf N and P stoichiometry covaries with many aspects of plant biology, yet the drivers of this trait at biogeographic scales remain uncertain. Recently we reported the patterns of leaf C and N based on systematic census of 213 species over 199 research sites in the grassland biomes of China. With the expanded analysis of leaf P, here we report patterns of leaf P and N:P ratios, and analyze the relative contribution of climatic variables and phylogeny in structuring patterns of leaf N:P stoichiometry. Average values of leaf P and N:P ratio were 1.9 mg g(-1) and 15.3 (mass ratio), respectively, consistent with the previous observation of a higher N:P ratio in China's flora than the global averages (ca. 13.8), resulting from a lower leaf P. Climatic variables had very little direct correlation with leaf P and N:P ratios, with growing season precipitation and temperature together explaining less than 2% of the variation, while inter-site differences and within-site phylogenetic variation explained 55 and 26% of the total variation in leaf P and N:P ratios. Across all sites and species, leaf N and P were highly positively correlated at all levels. However, the within-site, within-species covariations of leaf N and P were weaker than those across sites and across species. Leaf N and P relationships are driven by both variation between sites at the landscape scale (explaining 58% of the variance) and within sites at the local scale (explaining 24%), while the climatic factors exerted limited influence (explaining less than 3%). In addition, leaf N:P ratios in two dominant genera Kobresia and Stipa had different responses to precipitation. This study suggests that geographic variation and between-species variation, rather than climatic variation, are the major determinants of grassland foliar stoichiometry at the biome level.
authors.affiliation: Department of Ecology, Peking University, 5 Yiheyuan Road, 100871 Beijing, China. jshe@pku.edu.cn
authors.forename: Jin-Sheng
authors.initials: JS
authors.lastname: He
authors.forename: Liang
authors.initials: L
authors.lastname: Wang
authors.forename: Dan F B
authors.initials: DF
authors.lastname: Flynn
authors.forename: Xiangping
authors.initials: X
authors.lastname: Wang
authors.forename: Wenhong
authors.initials: W
authors.lastname: Ma
authors.forename: Jingyun
authors.initials: J
authors.lastname: Fang
mesh_terms: D002681:China; D002980:Climate; D017753:Ecosystem; D009584:Nitrogen / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism*; D010802:Phylogeny; D018515:Plant Leaves / Q000378:metabolism*; D006109:Poaceae / Q000378:metabolism*
chemical_list: D010758:Phosphorus; D009584:Nitrogen