Relationships between below-ground biomass and foliar N:P stoichiometry along climatic and altitudinal gradients of the Chinese grassland transect

N and P concentrations and their ratios were determined for 132 foliar and 120 below-ground biomass (BGB) samples obtained at 132 sites along the 4500 km Chinese Grassland Transect (CGT) across the Inner Mongolian and Qinghai–Tibet Plateaus. Patterns of foliar and BGB N, P and their ratio (N/P) at the community level were related to altitude, temperature, and precipitation gradients. Also, patterns of relative N and P foliar and BGB concentrations were determined (N_F/B, foliar N/BGB N; P_F/B, foliar P/BGB P). The relationship between foliar N concentrations and mean annual temperature (MAT) was negative, agreeing with the Temperature-Plant Physiological hypothesis, whereas BGB N decreased with decreasing MAT, supporting the Biogeochemical hypothesis. Patterns of BGB N varying with altitude, MAP and MAT differed from the patterns for leaf N, which may indicate differences in nutrient allocation and utilization by leaves and BGB. N_F/B and P_F/B may reflect trade-offs by plants for N and P in leaves and BGB. For the entire CGT, N_F/B and P_F/B increased as altitude increased. N_F/B was positively related with MAP but negatively related with MAT, while P_F/B showed no correlations with MAP and MAT. Results suggest that ecological stoichiometry at the community level is similar to that at the species level. Strategies of nutrient utilization by leaves and BGB are indicated to be different, and abiotic environmental conditions could influence the stoichiometric characteristics and nutrient allocation to leaves and BGB.