Spacial Heterogeneities Of Soil Nutrients And Biological Activities In Caragana Microphylla Plantation

The objective of this study was to determine the effects of the spatial position on soil nutrients and biological activites, with26-year-old Caragana microphylla plantation in western Horqin Sand Land selected as the study object. The characteristics for change of the soil nutrient contents and biological activites among different slope positions (windward slope, leeward slope and top slope), between two sites (under shrubs and between shrubs), and among the soil layers (0～10cm,10～20cm and20～30cm) were studied, the involved index including the contents of soil organic matter, total nitrogen, available nitrogen, total phosphorus, avaliable phosphorus, total potassium, available potassium, total calcium, total magnesium, and the activities of polyphenoloxidase, phosphomonoesterase, dehydrogenase, urease, protease, nitrate reductase, and the contents of soil total DNA, microbial biomass C、 Nand P, and the quantities of bacteria, fungi and actinomyces.The results showed that there is the obvious spacial heterogeneities in the distributions of soil nutrients and biological activities under the C. microphylla plantation. The majority index in surface layer and in’under shrub’are higher than those in the other soil depths and in ’between shrub’respectivley. The soil available N, P and K contents in windward slope are higher than those in other slopes. There is significant relevance among soil nutrients in the aeolian sandy soil, i.e. organic matter has positive correlations with total nitrogen, total phosphorus, available nitrogen, phosphorus and potassium respectivley, the same corrlations also lie among the available nutrients. There is significant correlations among the soil enzymes activities (urease, phosphomonoesterase, proteinase, dehydrogenase, nitratereductase), and between soil enzymes activities and microbial biomass C, N, total DNA, organic matter, totoal N, P, and K contents respectively. There are less microorganisms in the aeolian sandy soil than in other soil, the quantities of bacteria>>actinomyces>fungi in each treatment; slope position and position of brush have less influence on the quantities of bacteria and actinomyces, but have greater influence on the quantity of fungi; the soil layer give greater influence on the content of soil total DNA, the microbial biomass C and N, position of brush give greater influence on microbial biomass P.According to gray relative analysis method and system cluster analysis, obtain the soil quality is higher in windward slope under shrubs surface layer, slope crest under shrubs surface layer and leeward slope under shrubs surface layer than it in other position. Order of influence on soil quality from various spatial positions is:soil layer> brush position> slope position. We obtain limiting factors of26-year-old C. microphylla plantation by using factorial analysis, i.e. organic matter, total nitrogen, available N, total phosphorus, available potassium, dehydrogenase, urease, nitratereductase, soil DNA, microorganism biomass C, N and conductivity.