Plant stoichiometry characteristics and relationships with soil nutrients in Robinia pseudoacacia communities of different planting ages

Ecological stoichiometry is the study of mass balance of multiple chemical elements in ecosystems; it analyzes the constraints and consequences of these mass balances during ecological processes, based on universal laws of physics, chemistry, and biology. To understand the variation in stoichiometry characteristics of Robinia pseudoacacia of different planting ages, and determine the main soil factors influencing stoichiometry characteristics of R. pseudoacacia, relationships between leaf and branch stoichiometry and soil nutrient characteristics in R. pseudoacacia communities of different planting ages were analyzed in this study. Results showed that: (1) with increasing planting age, the C, N, P contents in leaves and branches, as well as the N/P ratio in leaves increased initially and then decreased, with the highest value in 40a (40 years old). The C/N and C/P ratios in leaves and in branches decreased initially and then increased with the increase of planting age. The N, P contents, and C/N and C/P ratios in leaves had nonlinear relationships with R. pseudoacacia age. The average N, P contents, and C/N, C/P ratios in leaves were affected significantly by planting age (P > 0.05). (2) With increasing planting age, soil C, N, P contents, and C/P, N/P ratios in R. pseudoacacia communities increased initially and then decreased. (3) Soil total N content was the main factor influencing C and N contents in leaves and C, N, P contents and C/P ratio in branches. The C, P contents and C/N, C/P ratios in leaves and C/N ratio in branches were influenced by the soil N/P ratio. The C content and N/P ratio in leaves were affected by the soil organic C content. In conclusion, with increasing planting age, 12 stoichiometry characteristic indices in R. pseudoacacia communities and soil increased initially and then decreased. Stoichiometry characteristic indices in R. pseudoacacia communities showed the highest value in 40a. Stoichiometry characteristic indices in R. pseudoacacia were mainly affected by soil total N content, the N/P ratio, and organic C content.