Abstract: In this study, we analyzed the concentrations of C, N and P in plant organs (leaf, branch and fine root), leaf litter and soils (0-10, 10-20, and 20-40 cm soil layer) in Pinus tabuliformis and Ulmus pumila plantations. Foliar N and P resorption efficiencies were calculated, and the nutrient cycling characteristics of the twoplantations were discussed. The results showed that concentrations of C, N and P in different organs of P.tabuliformis were 493-577, 6.34-17.22 and 0.66-1.91 g·kg^-1. The C and P concentrations of leaves and branches were higher than those of fine roots, while N concentrations followed the rank of leaf > branch > fine root. With the increased leaf and branch age of P. tabuliformis, N and P concentrations gradually decreased, while C∶N and C∶P gradually increased. The C, N and P concentrations in different organs of U. pumila were 404-472, 3.22-17.45 and 1.73-3.48 g·kg^-1. C concentrations were higher in leaves and branches than in fine roots, while N and P concentrations followed the rank of leaf > branch > fine root. C concentrations, C∶P and N∶P in leaves, branches and fine roots, and N concentrations in fine roots, and C∶N in leaves and branches of P.tabuliformis were higher than those of U. pumila, while P concentrations in leaves, branches and fine roots, N concentrations in leaves and C∶N in fine roots of P.tabuliformis were lower than those of U. pumila. Leaf litter C concentration, C∶N, C∶P, and N∶P were higher but N and P concentrations were lower in P. tabuliformis than in U. pumila.  P resorptionefficiency was higher in P. tabuliformisthan in U. pumila. Soil C, N and P concentrations were lower in P. tabuliformis plantation (2.47-5.52, 0.21-0.53 and 0.015-0.063 g·kg^-1) than in U. pumila plantation (4.82-12.22, 0.41-1.10 and 0.075-0.081 g·kg^-1). These results indicated that relatively more nutrients were allocated to leaves and branches and higher P resorption efficiency in P. tabuliformis plantation, resulting in less dependence on soil P. U. pumila allocated more nutrients to leaves and that returned to the soil through leaf litter, which were beneficial for nutrient cycling in plant-litter soil systems.

Key words: nutrient cycle, organ, nutrient resorption, interspecific difference, Horqin Sandy Land.