Abstract:

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.

Key words: pure plantation, biochemistry of soil, litter decomposition, C, N disturbances