Influence Of Different Forest Gap Reconstruction Mode On The Soil Biochemistry Character Of Low-efficiency Cypress Forest

Hilly area of Central Sichuan, where virgin forest coverage rate is extremely low and subsequent plantation form a large area of low efficiency forests because of too extreme early plant density and poor management which lead to seriously soil erosion and bad ecology environment, is located in the upper Yangtze river. By forming forest gap, forest belt and so on to explore an effective way for transformation of low efficient forest in this region during "Twelfth five-year" period. Forest soil microorganism is an important part of underground ecosystem and leading factor on whether soil ecological function and forest ecological benefits can be normal play. In this study, we regard Cupressus funebris plantation in central Sichuan hilly region as our study aim to research the dynamic changes of soil nutrient content, culturable microorganism quantity, microbial biomass and soil enzyme activities so as to find the change rule for each indicator because of season change. At last, we want to explore the impact of different restore ways and area of forest gap on soil microorganism and search for a more suitable way for transforming of low efficient forest in this region which provides a reasonable reference for ecological service function promoting and fertility maintaining in this region. The main results as follows:(1) Forest gap changed the microenvironment of the forest. In January and March, the greater area of forest gap. the higher soil temperature and lower soil water content, at the same time, the forests is the highest water content and lowest soil temperature; In July and October, the influence of forest gap on microenvironment is not significant.(2) Soil nutrient was strongly influenced by forest gap. The whole soil nutrients content of forests were higher then each forest gap, but only the average of soil organic matter and total phosphorus content in 50m2,100m2 and 150m2 artificial promote recovery forest gaps were higher then forest and nature recovery forest gap, on the other hand, forest was higher then forest gaps significantly in the average of soil total nitrogen and hydrolyze nitrogen content; seasonal dynamic change in artificial promoting recovery forest gap was January> March> July> October; soil nutrient content in forest was the lowest in July, however, the highest was different; natural recovery forest gap was January/October>March>July; both the highest and lowest soil nutrient content in forest gap were in forest gap of 200m2 and 150m2. The seasonal dynamic of soil total phosphorus content in forest gap wasJuly/October> January/March.(3) Formation of forest gap provides a more appropriate environment for the underground soil microbial growth. The number of soil culturable microorganisms and microbial biomass have increased significantly in artificial promote recovery forest gap compared with forest and natural recovery forest gap. The highest values of microorganism biomass in two recovery model were all in the area of 200m2 forest gap and between two different recovery models the highest values of microbial biomass was artificial promoting recovery forest gap> forest> natural recovery forest gap; the maximum value of the total soil cultivable microorganisms were also within 200 m2 and 150 m2 forest gap; seasonal dynamic change of microbial biomass was July/October> January/March and seasonal dynamic changes of culturable microorganisms were different for the different species.(4) There is no significant difference between various in the same month of soil enzyme activities, however, through average analysis we found both two recovery models, the average of all 4 kinds of soil enzyme activity in the square of 150m2 forest gap were higher then forest even significantly. The highest value of soil enzyme activities in forest gaps were also more concentrated in the area of 150 m2 of forest gap, seasonal dynamic change was July/October> January/March.(5) Based on multiple factor variance analysis, we found the change of season was the most primary factor which impacted the soil nutrient content, the number of culturable microorganisms, microbial biomass and enzyme activity in forest soil; the impact of different recovery models was not as significant as the effects of the change of seasons and soil layers, but stronger than the effects of different forest area of the forest gap.(6) We could make a conclusion that soil nutrient content, culturable microorganisms quantity, soil microbial biomass content and soil enzyme activities in artificial promoting recovery forest gap with 150m2 was better than other forest gaps and forest through study result which might indicate that the two gaps may more suitable for the growth of soil microorganism.To sum up, the formation of forest gaps changed the forest canopy closure environment to a certain extent, however, natural recovery forest gap didn’t return more soil nutrient so as to all aspects of soil nutrient and microorganism were not better than forest. The small forest gaps of artificial promoting recovery forest was still lower than forest in the returning of soil nutrient, but there were more diversity ways for nutrient returning and the microenvironment improved in a larger extent compared with other forest gaps and forest in the bigger forest gaps with 150m2 so that there were higher than or not soil nutrient content, soil culturable microorganisms quantities, microbial biomass and soil enzyme activities which suggest that forest gaps of artificial promoting recovery with 150m2 provided more suitable environment for soil microorganism. The result provide an important theoretical reference for the transform of low efficient forest in hilly region in central Sichuan and the it’s follow-up work.