Abstract: To understand the phosphorus (P) mobilization mechanism of Mongolian pine (Pinus sylvestrisvar. mongolica) on a Pdeficient semiarid sandy soil of northern China, this paper compared the P fractions and acid phosphomonoesterase (AP) activity in the bulk and rhizosphere soils under different age Mongolian pine plantations. The results showed that when compared with the bulk soil, the organic C, labile organic P, and organic C/P ratio increased significantly, microbial and AP activities improved, and organic P mineralization accelerated in the rhizosphere soil. Root activity of the Mongolian pine significantly increased the bioavailability of soil P, and accelerated the shift of organic P and Ca-P to Fe-P and Al-P. The rhizosphere effects on soil P in different forms enhanced with stand age, whereas in adverse on AP activity. The bulk and rhizosphere soil had the similar trend in the dynamics of its P fractions with stand age. Soil total P pool reduced gradually while labile P pool increased with stand age. It should be essential to protect forest floor to replenish soil P pool and guarantee a longterm soil P supply.

Key words: Zoophthora anhuiensis, Myzus persicae, Virul ence, Latent period, Fecundity, Intrinsic increase rate