Spatial variability of soil nutrients and microbiological properties after the establishment of leguminous shrub Caragana microphylla Lam. plantation on sand dune in the Horqin Sandy Land of Northeast China

The objective of this study is to determine the spatial variability of nutrients, microbial biomass, and enzyme activities of soil due to the establishment of shrub plantation on moving sandy dunes, as part of an effort to understand the microenvironmental factors that control the soil microbiological properties. Caragana microphylla Lam., an indigenous leguminous shrub, is the dominant plant species used to control desertification in the semi-arid Horqin Sandy Land of Northeast China. In a 26-year-old C. microphylla plantation, soil samples were collected from three soil depths (0-5 cm, 5-10 cm, and 10-20 cm), three slope positions (windward slope, top slope, and leeward slope), and two microsites (under shrubs and between shrubs). The results showed significant differences in soil EC, nutrient content (except for total K), microbial biomass C and N, and the activities of dehydrogenase, urease, and protease at different slopes, soil depths, and microsites. Significant differences in pH at different microsites and slopes, soil moisture and polyphenol oxidase activity at different soil depths and slopes, and activities of phosphomonoesterase and nitrate reductase at different soil depths were also observed. The soil nutrient contents and microbiological activities were greater in the surface soil layer and decreased with the increase of soil depth. Soil organic C, total N, total P, available P and K, microbial biomass C and N, and the activities of enzymes tested (except for protease) under shrubs were higher than those in between shrubs. Furthermore, significant correlations among soil organic C, microbial biomass C and N, the activities of phosphomonoesterase, dehydrogenase, urease, protease, and nitrate reductase were observed, and correlations were also found among EC, total N, total P, available P and K, enzyme (except for polyphenol oxidase) activities, and microbial biomass C and N contents. These results suggest that microenvironmental factors (slope, soil depth and microsite) have significant influences on the spatial distribution of soil nutrients and microbiological properties when the C. microphylla sand-fixing plantation is established in the moving sand dunes in the Horqin Sandy Land.