Patterns and controlling factors of plant nitrogen and phosphorus stoichiometry across China's forests

Plant stoichiometry is critical for the structure and functions of ecosystems. Previous studies on large-scale patterns of plant stoichiometry have focused on single tissues; and the controlling factors have focused on climatic factors or plant functional groups. Here we present results based on an intensive field investigation across China's forest ecosystems, to comprehensively assess the effect of climatic factors, plant functional groups, soil N and P stoichiometry on N and P stoichiometry of different tree tissues. The P concentrations in all tissues were significantly lower when mean annual temperature (MAT) and mean annual precipitation (MAP) were higher, and the N:P ratios in all tissues were significantly higher when MAT and MAP were higher. The N concentrations of branches and trunks were negatively related to MAT and MAP, however, the leaf N concentrations did not change with MAT and MAP. The root N also did not change with MAT, but decreased significantly with MAP. Soil total N had little influence on tree N, however, tree tissue P concentrations significantly increased when soil P increased. The N contents of all tissues were mainly affected by plant functional groups, however, climate factors and soil P content were the main predictors of P and N:P ratios of all tissues. Our results suggest that tree tissue N:P ratios were largely related to climatic factors, and were shaped by soil P rather than soil N in China's forest ecosystems