Abstract: Moss crust, one of the main types of biological soil crust in deserts, influences sand surface stability, soil water and nutrition distribution, and the growth of vascular plants. In natural conditions, moss crusts mainly occur in patches with different sizes. However, the horizontal distribution pattern and edge effect of the patches remain unclear. In this study, three circles with different distances (r=3.5, 7, and 10 cm, respectively) from the center to the edge of the moss crust patch (about r=10 cm) were settled, and soil physicochemical properties, enzyme activities, and microbial biomass were analyzed. The results showed that: (1) Soil organic matter, total nitrogen and total potassium concentrations were significantly influenced by the edge effect, being higher in the inner and middle circles and lower in the outer circle. There was no significant difference of other soil indicators in the three circles. (2) The activities of urease and catalase in the outer circle were significantly lower than that in the middle and inner circles, while the activities of sucrase and alkaline phosphatase had no significant difference among the three circles. Soil microbial biomass carbon (SMBC) and nitrogen (SMBN) significantly decreased from inner to outer circle, while there was no significant difference between the inner and middle circles. (3) Results from the path analysis showed that soil organic matter concentration was the direct and main factor influencing urease activity. Catalase activity and SMBC were more sensitive to the edge effect, with the direct path coefficient of distance to these two variables being higher than other direct path coefficients (-1.108 and -1.224, respectively). The soil organic matter concentration, pH, and available and total K concentrations had high direct path coefficients for SMBN, with high indirect path coefficients for SMBN via organic matter concentration. Therefore, SMBN was affected by multiple physical and chemical factors and distance. In addition, the residual path coefficients of catalase activity and SMBC were relatively high, implying that other factors being not considered had strong influence on the two variables.

Key words: karst hill, Loropetalum chinense, spatial association, Ripley K(r) function, spatial distribution