Unique species of tree,selective nutrients absorption and special environmental effects of pure plantation may lead to soil degradation.So study on the biochemical characteristics of soil and its reaction to external C and N disturbances of pure plantation can theoretically direct the nutrients management of forestland and control of soil degradation.According to fix-positional soil sampling,determining and field disturbance experiments in 4 typical pure plantation of larix kaempferi,Pinus tabulaeformis,Catalpa fargesii and Quercus aliena var.acuteserrata in Qinling Mountain,we can get following conclusions:Contents of organic-C,total N,enzyme activities of urease,amounts of microbes and contents of micro-biomass C and N in soil of broad-leaved forests are all more than its of needle-leaved forests except for enzyme activities of sucrase and catalase.External fertilization of C(cane sugar)can popularly raise the enzyme activities of urease,sucrase and catalase,amounts of microbes and contents of micro-biomass C and N,and rates of litter decomposition of planted forests(both needle-leaved forests and broad-leaved forests).External fertilization of N(urea)can raise the enzyme activities of urease,amounts of microbes and contents of micro-biomass C and N,and rates of litter decomposition of needle-leaved forests,but lower the involved biochemical indices of broad-leaved forests.In summary,as a whole,broad-leaved forests are conductive to soil improvement,whereas,needle-leaved forests are harmful.Both C and N are limited nutrients for biochemical characteristics of needle-leaved forests,whereas,only C is limited for broad-leaved forests,and N is not lack,more N has no good but is harmful.
