Effects Of Forest Thinning On Soil Microbes And Enzymes In Pine-oak Mixed Forest

Microbes and enzymes are the biological active substances in the soil, the microbespromote the decomposition of plants and animal residues, the enzymes involve in theformation of humus and the cycling of carbon, nitrogen, phosphorus and other organicelements. They are sensitive active substances that can respond to external changes, reflectthe status of soil fertility, and jointly promote the soil nutrient cycling and energy flow.Combing with a comprehensive survey of stand, the experiment was conducted to explore theeffects of forest thinning on soil microorganisms, soil enzymes, to analyze the traits of soilmicrobes, soil enzymes and to provide the fundamental theory for forest thinning. Thepine-oak forest is one of widely distributed forest types in the middle Qinling Mountains atHuoditang forest zone. The design of universal quadratic rotation combination was used toarrange the experiment. The method field sampling combined with laboratory analysis wasapplied to measure quantities of soil microbes, the content of microbial biomass carbon(MBC), microbial biomass nitrogen (MBN) and activities of soil enzymes. By analyzing allthe data, this paper found the best choice of forest thinning, and the main study results are asfollows:1. Both the quantities of soil microbes and the activities of soil enzymes in the forestdecrease with the increase of the depth. The bacteria dominate in soil microbial communitywith the ratio90%of total microbes, followed by actinomycetes and the fungi minimum.2. The content of soil moisture, the content of organic and total nitrogen impact thequantities of soil microbes and the activities of soil enzymes significantly; all the4enzymeshave negative correlation with the soil pH, while, the soil pH has better correlation with thesoil microbes; there are good correlations between most of the activities of soil enzymes andthe quantities of soil microbes.3. After the forest thinning, the quantity of bacteria shows the highest number in summer,the least in spring; the spring has more actinomycetes than the summer and autumn; thequantity of fungi showed a higher trend in summer than in spring and autumn; the peak value of the MBC and MBN’s content exists respectively in summer and spring; the low peak ofcatalase’s activity exists in summer; the activities of urease, sucrase and acidity phophataseeach show the trend that there is a highest activity in autumn. Overall, the soil microbes andsoil enzymes show an apparent seasonal change.4. When the soil microbes have the most quantities and the soil enzymes have the bestactivities, the forest thinning choice is: forest thinning intensity15.92～18.99%, the residueremoval intensity61.39～63.76%.