LAUSR

This study chose dominant tree species including Picea crassifolia, Pinus armandii and Pinus tabuliformis which are distributed in Qilian Mountains, Xiaolongshan Mountains, and Bailongjiang River. According to the different tree species, ages and components, we sampled leaves, branches, stems, and roots, and measured the contents of Nitrogen, Phosphorus, Potassium, along with soil fertility. The changes of N, P, and K contents in the different tree species were studied, and the relationship between nutrient content and environmental factors was analyzed. The results indicated that the content of P in all three species was the lowest (0.039–0.28 g kg−1), while N content was the highest (0.095–1.72 g kg−1). As the terminal organ of nutrient transport, the nutrient content of leaves was the highest. P. armandii (0.45 g kg−1) had a higher nutrient concentration than P. tabulaeformis (0.19 g kg−1) and P. crassifolia (0.29 g kg−1). The nutrient content of each species was highest in a young forest, but lowest in a mature forest. The nutrient content of all three tree species was significantly affected by soil nutrient content, and negatively correlated with available soil nutrients.