Abstract: To reveal the dynamics of soil physicochemical properties and microbial biomass as well as their relationships in Mongolian pine (Pinus sylvestris var.mongolica) plantations with different stand ages, we examined soil physicochemical properties and soil microbial biomass C (MBC) and N (MBN) in Mongolian pine plantations of various ages in Mu Us, Horqin, and Hulunbuir sandy lands. The results showed that changes of soil physicochemical properties with increasing stand age differed among different sandy lands. In the Mu Us Sandy Land, soil bulk density and soil nutrients significantly decreased. In the Horqin Sandy Land, soil porosity and nutrients significantly increased. In the Hulunbuir Sandy Land, soil nutrients increased first and then decreased. With increasing stand age, soil MBN decreased in the Mu Us Sandy Land, increased in the Horqin Sandy Land, and increased first and then decreased in the Hulunbuir Sandy Land. The major factors affecting soil MBN were the concentrations of nitrate, ammonium, and organic matter in the Mu Us, Horqin, and Hulunbuir Sandy Land, respectively. Soil nitrogen was the main limiting factor of Mongolian pine plantation in the Mu Us and Horqin Sandy Land, while soil organic carbon was the main limiting factor in the Hulunbuir Sandy Land.

Key words: Cd contamination, soil-vegetable system, transfer function, species sensitivity distribution., risk threshold