Study On Phosphorus Fraction And Loss Risk Of Castanopsis Hystrix,Pinus Massoniana And Their Mixture Forest Soil In South Subtropical China

It is of great significance to study on the phosphorus fraction and loss risk of the South subtropical pure Castanopsis hystrix,pure Pinus massoniana and its mixed forests soil for improving the utilization ratio of forest resources and the function of forest ecological service.In this study,three forest plantations of the same age,pure Castanopsis hystrix(CHP),pure Pinus massoniana(PMP)and mixed C.hystrix and P.massoniana(MCP),were selected as the research objects at the Experimental Centre of Tropical Forestry,Chinese Academy of Forestry.The morphological distribution characteristics of phosphorus in soil of 3 kinds of plantation(0?20cm),middle layer(20?40cm)and bottom(40?60cm)were compared and analyzed.The main factors affecting the phosphorus were discussed,and the risk of soil phosphorus loss was evaluated.The results show that:(1)The total amount of inorganic phosphorus of 3 kinds of forest soil is 61.69?175.94mg·kg-1,and Fe-P content has high value among different soil layers.The Fe-P content in the middle and bottom layer of MCP was significantly lower than the surface layer(P<0.05),and was also lower than that of 2 kinds of artificial forests of same soil layer.At the same time,the O-P content of each layer of MCP was significantly lower than that of the artificial pure forest(P<0.05).It indicated that the soil in the mixed plantation was stable to the pure coniferous forest and the broad-leaved pure forest.The phosphorus content in closed storage decreased obviously.(2)The total soil inorganic phosphorus(Pi)is mainly affected by water content(X1),porosity(X3),total P(X7)and soil phosphatase(X12),and the absolute value of direct path coefficient:X12>X1>X3>X7,and the regression equation is:Y1=0.043-0.636X,+0.004X3+0.219 X7+0.087X12(R2=0.508).(3)The total amount of organic phosphorus in soil of 3 kinds of plantation is 46.09?107.39mg·Kg-1,MCP is increased by 26.98%and 28.16%compared with CHP and PMP,and the organic phosphorus components are mainly medium active organophosphorus and medium stable organophosphorus.The two content all present the law of layer(0?20cm)>middle layer(20?40cm)>bottom(40?60cm).(4)The total amount of soil organic phosphorus(Po)was mainly influenced by the factors such as bulk density(X2),pH(X4),all C(X5),total P(X7)and actinomycetes(X10),and the absolute value of direct path coefficient was:X7>X4>X2>X10>X5,the regression equation is:Y2=0.049+0.071X2-0.027X4+0.001X5+0.211X7+0.054Xi,(R2=0.843).(5)The analysis method of Olsen-P grade of soil solid phosphorus index all show that the phosphorus loss potential of each stand is the trend of soil layer>middle layer>bottom layer,and more than 75%of the soil samples are in medium or high level,which can pose potential threat to the water environment.