Abstract: We examined the carbon (C), nitrogen (N) and phosphorus (P) stoichiometry in different organs (current-year needle, one-year-old needle, current-year branch, one-year-old branch, and fine root) along with the N and P resorption efficiencies in needles of Pinus sylvestris var. mongolica in pure forest with six densities (490, 750, 1110, 1550, 1930 and 2560 trees·hm^-2). The results showed that C concentrations in the current-year and one-year-old needles and P concentrations in the current-year and one-year-old branches exhibited downward trends with increasing stand density, except for the 1550 trees·hm^-2 stand. With the increases of stand density, C concentrations in current-year branch, one-year-old branch and fine root, the N concentrations in all organs, and P concentrations in current-year needle, one-year-old needle and fine root tended to increase and then decrease, with the highest values in the 1550 trees·hm^-2 stand. The C∶N in current-year needle, one-year-old needle and fine root, C∶P in current-year needle and branch, and N∶P in current-year needle, current-year and one-year-old branches displayed decreasing and then increasing trends with increasing stand density, whereas C∶P in one-year-old needle and branch showed an upward trend. With increasing stand density, C concentrations in leaf litter increased and then decreased, N concentrations exhibited an increasing trend, and P concentrations decreased and then increased. With increasing stand density, N resorption efficiency and the ratio of N resorption efficiency to P resorption efficiency decreased, and P resorption efficiency increased and then decreased. These findings indicated that N limitation weakened but P limitation enhanced with increasing stand density. The optimal management density for P. sylvestris var. mongolica stand should be 1550 trees·hm^-2, in which more nutrients are allocated to needles and fine roots and thus contribute to high growth rate.

Key words: Pinus sylvestris var.mongolica plantation, organ difference, density control, nutrient distribution pattern, Horqin sandy land.