Stoichiometric characteristics of nitrogen and phosphorus in leaf-litter-soil system of Pinus sylvestris var. mongolica plantations.

To reveal the allocation pattern and stoichiometric characteristics of N and P in Pinus sylvestris var. mongolica plantation, we selected three P. sylvestris plantation with different stand ages (middle-aged, near-mature, mature) in the Hulunbuir, Horqin, and Mu Us sandy land as objects, and analyzed the contents of nitrogen, phosphorus and the N:P stoichiometry ratios in the leaf, litter, and soil. The results showed that the contents of N, P and N/P ratios in leaf, litter and soil varied in the range of 0.17-49.02, 0.11-3.01 g·kg-1 and 0.51-19.74, respectively, with the order of leaf>litter>soil. The content of N and N:P ratio were significantly different between leaf, litter and soil; the P content in leaf was significantly higher than that in litter and soil. The different areas and stand ages affected N, P content and N/P stoichiometry ratio, but the interaction of area and stand age had no significant effect on N/P stoichiometry ratio. The N, P contents in leaf, litter and soil increased with stand age, and were highest in the mature forest. The contents of N, P and N/P ratios were significantly positively correlated among the leaf, litter and soil. In the Hulunbuir and Horqin sandy land, the N/P ratros of leaf were between 14.53 to 15.57, which indicated that the P. sylvestris var. mongolica plantations was restricted by both N and P availability. In Mu Us sand land, the N:P ratios of leaf were between 18.56 to 19.71, which indicated P limitation. The stand age had no significant influence on soil N and P limitation. To improve the productivity of P. sylvestris var. mongolica plantations, we could appropriately add N or P fertilization in the plantation tending management based on local conditions. Our findings could contribute to a further understanding of the mechanism of interactions and constraints between N and P in the leaf-litter-soil system of P. sylvestris var. mongolica plantations, and provide a scientific guidance for the management.