title: Nitrogen to phosphorus ratios of tree species in response to elevated carbon dioxide and nitrogen addition in subtropical forests.
abstract: Increased atmospheric carbon dioxide (CO2 ) concentrations and nitrogen (N) deposition induced by human activities have greatly influenced the stoichiometry of N and phosphorus (P). We used model forest ecosystems in open-top chambers to study the effects of elevated CO2 (ca. 700 μmol mol(-1) ) alone and together with N addition (100 kg N ha(-1)  yr(-1) ) on N to P (N : P) ratios in leaves, stems and roots of five tree species, including four non-N2 fixers and one N2 fixer, in subtropical China from 2006 to 2009. Elevated CO2 decreased or had no effects on N : P ratios in plant tissues of tree species. N addition, especially under elevated CO2 , lowered N : P ratios in the N2 fixer, and this effect was significant in the stems and the roots. However, only one species of the non-N2 fixers showed significantly lower N : P ratios under N addition in 2009, and the others were not affected by N addition. The reductions of N : P ratios in response to elevated CO2 and N addition were mainly associated with the increases in P concentrations. Our results imply that elevated CO2 and N addition could facilitate tree species to mitigate P limitation by more strongly influencing P dynamics than N in the subtropical forests.
authors.affiliation: South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China.
authors.forename: Juxiu
authors.initials: J
authors.lastname: Liu
authors.forename: Wenjuan
authors.initials: W
authors.lastname: Huang
authors.forename: Guoyi
authors.initials: G
authors.lastname: Zhou
authors.forename: Deqiang
authors.initials: D
authors.lastname: Zhang
authors.forename: Shizhong
authors.initials: S
authors.lastname: Liu
authors.forename: Yiyong
authors.initials: Y
authors.lastname: Li
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D009584:Nitrogen / Q000008:administration & dosage / Q000378:metabolism*; D010758:Phosphorus / Q000378:metabolism*; D014197:Trees / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide; D010758:Phosphorus; D009584:Nitrogen