LAUSR

The nutrient concentrations and carbon:nitrogen:phosphorus stoichiometries of plants have been greatly altered by elevated CO2 concentrations and nitrogen (N) deposition. Studies of these changes, however, are mostly limited to tropical and subtropical forests. In this study, a C4 herbaceous grass (Bothriochloa ischaemum) was grown in a pot experiment at two CO2 concentrations (400 and 800 μmol mol−1) and three levels of N fertilization (0, 2.5 and 5 g N m−2 y−1) in a full factorial design. Plant biomass and the concentrations of non-structural carbohydrates (NSCs), N and phosphorus (P) in the shoots and roots were determined. The elevated CO2 concentration and N addition significantly increased total biomass, starch and NSC concentrations and root:shoot, starch:N, NSC:N, starch:P and NSC:P ratios in whole plants and roots. N addition alone decreased the soluble sugar (SS) concentration in whole plants and increased N concentration and decreased P concentration in whole plants and roots and thus decreased the SS:N ratio and increased the SS:P and N:P ratios. Our results suggested that SS, N and P concentrations and their stoichiometries responded more strongly to N addition than elevated CO2 concentration. Plant growth in this region suffers more from P than N limitation, and N addition would exacerbate the P limitation on plant growth.