Effects Of External Sources C,N Disturbances On Artificial Forest Ecosystem

The declination of land fertility which is the main reason that causes the slowing down of forest growth is becoming one of the focuses of current ecological research of forest. The traditional research which regarding physical and chemical characteristics as the forest soil quality index has already made a great achievements, but research on the biological characteristic of soil is very few. In this paper,four kinds of artificial forest (C.japonicum, P. massoniana , B.utilis and P.asperata ) in the upper reach of Mingjiang River in Sichuan were studied. Through field plots experiments of external sources C (cane sugar) and N (NH4NO3) disturbances with different intensities to forest, the dynamic characteristics of soil microorganisms, the decomposition of withered leaves and forest growth were studied, the relationship between the soil microorganisms'activity and main chemical property, the relationship between soil characteristics and tree growth were analyzed and the soil quality was comprehensively appraised. The main conclusions are as follows: (1) C ,N disturbance made the content of microorganism biomass C(MB-C) in lower soil layer ( 20-40cm) of P. massoniana, B. utilis and P. asperata soil increase, but the content of MB-C in C. japonicum soil maintain nearly the same compared with the control. C,N disturbances made the content of MB-C in B.utilis and P. massoniana soil increase, but made it decrease in C.japonicum soil. Low N disturbance made the content of MB-C in P.asperata soil increase, but it is not significant to P. massoniana, B.utilis and C.japonicum. C ,N disturbances reduced the upper layer ( 0-20cm ) content of microorganism biomass N(MB-N) in P. massoniana, B.utilis , P.asperata soil significantly, but the content of MB-N in C.japonicum soil maintain nearly the same compared with the control, however the total content of MB-N showed a decreased tendency. N disturbance can increase the microorganism biomass C/N (MB-C/N) rate in B.utilises, P. massoniana and P.asperata soil, C disturbance could increase the rate of MB-C/N in C.japonicum soil,but N disturbance decreased it. (2) C,N disturbance reduced urea enzyme activity in upper soil layer but increased in the lower soil layer significantly and the total activity of urea enzyme is lower than the control (except B.utilis). C,N disturbance didn't influence the protease activity of the P. massoniana soil obviously. Low N can increase protease activity of C.japonicum , B.utilis and P.asperata soil. C,N disturbance had great influence on the catalase enzyme activity in P. massoniana soil, high N and low C had greater effect on it, it is not significant to the other three forest type. Low N and high C disturbances increased the invertase enzyme activity of C.japonicum and B.utilis　soil, high N and low C had bigger effect in P.asperata soil, different C,N disturbances were not significant to P. massoniana soil. (3) The decomposition experiment of withered leaves indicates: only high N disturbance could increase the decomposition of withered leaves of C.japonicum, the other disturbances were not significant. (4) C,N disturbances could increase the C content in C.japonicum and P.asperata leaves, and the C content increased with the increasing of the C,N disturbances. C disturbance didn't influence the C content in P. massoniana and B.utilis leaves, however it's increased under N disturbance. C,N disturbances can increase N content in B.utilises and P.asperata leaves, C disturbouldance can increase the N content in C.japonicum and P. massoniana leaves. C,N disturbances can intensify the growth of diameter in breast-height (DBH),the annual growth of C.japonicum, P. massoniana and P.asperata was about 1.25-2.6 times of the control, but the C,N disturbances were not significant to B.utilis. (5) The canonical correlation analysis indicated: soil organic carbon (SOC) was in close relationship with catalase enzyme, the soil total N was in close relation with urea enzyme, therefore the urea enzyme and catalase enzyme could be seen as indexes of soil fertility. The DBH with soil urea enzyme,MB-C,SOC and PH all had significant correlation. Soil PH with protease enzyme,catalase enzyme,invertase enzyme had very significant or significant correlation. Correlation analysis indicated that SOC of soil was a main decision variable, soil PH was a secondary decision variable, the MB-N of soil was a main restricted variable. Known by the comprehensive appraisal of soil quality, C,N disturbances could increased the soil quality of P. massoniana and P.asperata significantly, but not so significant to C.japonicum and B.utilis.