Abstract: The characteristics of inorganic phosphorus in the rhizosphere and nonrhizosphere soils under 3,5,11 year I69 clone stands were studied by means of investigating experimental sites and ecological sequential comparison in Dongtai forestry farm,Dongtai county,Jiangsu province.The results showed that in the soil developed on new coastal sediment,most forms of inorganic phosphorus were CaP of which insoluble Ca10P was the main form,approximately accounting for 90%.AvailableP(DAP) was accumulated clearly in the rhizosphere of 3,5,11 year I69 clone stands respectively,and the accumulating rates(RS)/S were increased with the stand ages of I69 clone.Poplar roots have the obvious induced influences on the distribution characteristics of soil inorganic phosphorus fractions.Ca2P was accumulated in the rhizospheres of 3 experimental stands,Ca8P was also accumulated evidently in the rhizospheres of 5,11 year I69 stands,whereas Ca10P was depleted clearly,but not in the rhizosphere of 3 year stand.There were no obvious differences in amounts of AlP,FeP,OP between rhizosphere and nonrhizosphere soils under 3 stands.Tree roots could induce transformation of various CaP fractions,indicating the accumulation of Ca2P and Ca8P corresponding with the depletion of Ca10P in the rhizosphere.Regression analysis indicated that Ca2P had the most contribution to DAP and its accumulation was the essential reason that the amount of DAP was much higher in the rhizosphere.Ca10P was also related to DAP and was the potential P source for plant growth.