Biological cycling of nutrients in Pinus forest and Pinus-Hardwood mixed forest in karst area——A case study in Longli,Guizhou

The standing biomass,the accumulation,distribution and biological cycling of nutrients in pure Pinus forest and in Pinus -Hardwood mixed forest are studied in Longli karst area. The results show that the total biomass is 40.62 t/hm2 in pure forest,48.32 t/hm2 in mixed forest respectively. The biomass in arbor layer of the mixed forest is 18.97% higher than that in the pure forest,and the biomass in root of the mixed forest is 65.12% higher than that in the pure forest. The contents of nutrient elements in most organs in arbor layer of the mixed forest are higher than that in Pinus forest,and the contents of N,P,K,S of various organs in the two forests show the following orders:leavesrootsstockswoods. The accumulative amounts of the six elements in arbor layer of the mixed forest are 47.97%~197.67% higher than those in arbor layer of Pinus forest. The accumulative amounts of the six elements in litter layer of the mixed forest are 85.40%~318.301% higher than those in pure forest. The amounts of annual assimilation,annual returning,annual retention,and cycling coefficients of nutrient elements in the mixed forest are all higher than those in pure forest. Planting hardwoods in pure Pinus forest can effectively enhance the biomass and nutrient cycling ability in the community.