Abstract: To understand the relationship between tree density and soil nutrient status, we analyzed the concentrations and stoichiometry of soil carbon, nitrogen and phosphorus in Pinus sylvestris var.mongolica plantations planted in 1980 with different densities (490, 750, 1550, 1930 and 2560 trees·hm^-2) in Horqin sandy land. The results showed that with the increases of tree density, the concentrations of soil organic carbon, total nitrogen, total phosphorus and C∶N increased and then decreased, while soil available phosphorus concentration decreased and then increased at 0-10, 10-20 and 20-40 cm soil layers. Lower soil organic carbon concentration and higher available phosphorus concentration were found in the stand density of 490 trees·hm^-2 than others. Soil C∶P and N∶P at the density of 2560 trees·hm^-2 were significantly higher than that of other densities. The concentrations of soil organic carbon, total nitrogen, total phosphorus and available phosphorus were significantly higher at the depths of 0-10 cm than those at 10-20 and 20-40 cm of P. sylvestris var.mongolica plantations with different densities, suggesting that soil nutrients had surface accumulation characteristics. According to the canonical correspondence analysis, the most important soil nutrient factors affected by stand density were soil organic carbon, total nitrogen and total phosphorus. Higher soil organic carbon, total nitrogen, total phosphorus and available nitrogen concentrations and lower soil C∶P and N∶P were found at the stand density of 1550 trees·hm^-2. Therefore, 1550 trees·hm^-2 was an optimal density for P. sylvestris var.mongolica plantations with higher soil nutrient concentrations and better growth.

Key words: organic carbon, cultivation practice, soil fertility, total nitrogen., soil aggregate