The effects of grazing and nitrogen addition on the spatial variability of soil microbial community structure and enzymatic activities at fine spatial scales are poorly understood, which can lead to substantial uncertainty in soil nutrient cycling. To examine how changes in grassland structure and ecosystem properties in response to grazing and nitrogen addition affect the microbial community and enzymatic activities spatial structure and to explore the underlying ecological mechanisms, we conducted a manipulative experiment with control (CK), grazing (G), nitrogen addition (N) and grazing plus nitrogen addition (NG) treatments in a Leymus chinensis meadow steppe, in northeastern China. Simultaneous measurements of microbial community structure (total PLFAs, F:B ratio and G+:G- ratio) and soil hydrolytic enzymatic activities (C, N and P acquiring enzymes activity) , along with a suite of plant (aboveground biomass, root biomass and litter biomass ), soil environment ( soil temperature, soil water content, bulk density and pH) and soil nutrient (SOC/TN ratio, dissolved organic C and soluble inorganic N) response variables, were conducted for 75 sampling points in each of the four 15 × 15 m plots.
Results/Conclusions
Compared to the CK, all treatments reduced the degree of spatial dependence of soil microbial community structure and enzymatic activities, except N acquiring enzymes activity. The autocorrelation range for microbial community structure in the CK treatment was lower under (<2 m) than enzymatic activities (>4 m). The autocorrelation range for microbial community structure under the G, N and NG treatments were higher or equal to those of enzymatic activities. The suite of plant, soil environment and soil nutrient variables explained 14%-28% of the spatial variability of total PLFAs, F:B ratio and G+:G- ratio, and explained 37%-65% of the spatial variability of soil enzymatic activities. The factors driving the spatial variability in soil microbial community structure and enzymatic activities and their contributions to the models varied among the different treatments. Our results demonstrated that under G and N treatments, soil environment and nutrient variables are important controlling factors of soil microbial community structure; but for enzymatic activities, plant biomass and soil nutrient are most important controlling factors. Under NG treatment, soil microbial community structure and enzymatic activities are controlled by plant biomass. The results are essential for understanding the relationship between aboveground and belowground processes of grassland ecosystems and predicting how microbial community structure and function of L. chinensis meadow steppe response to global change and land-use.