Changes of soil chemical properties, microbial biomass and enzymatic activities along a gradient of forest degradation in logged over tropical rain forests, Borneo

Purpose The purpose of our study was to investigate soil chemical properties, soil microbial biomass and soil enzyme activities in a gradient of forest degradation in logged over tropical rain forests, Borneo. We hypothesized that the changes of above-ground vegetation could affect soil organic matter, which further influenced soil microbial biomass and enzyme activities. Methods A total of 35 forest plots with varying magnitude of logging influences were investigated for vegetation composition and soil parameters. The 35 plots were sorted based on tree genus compositions by a Principal Co-ordinates analysis (PCoA) and PCoA axis-1 values represented a gradient of forest degradation. Soil physicochemical properties, microbial biomass carbon and nitrogen, and four extracellular enzymes were measured. Results Linear regression analyses showed that soil organic carbon and total nitrogen concentrations decreased with decreasing PCoA axis-1 values (i.e., increasing magnitude of degradation), while soil pH values increased. Soil microbial biomass carbon and nitrogen, and the activities of four extracellular enzymes all decreased with decreasing PCoA axis-1 values. The activities of four enzymes were correlated with soil microbial biomass. Structural equation modeling showed that soil organic carbon explained the greatest variation of soil microbial biomass. Conclusion Above-ground forest degradation directly affects soil organic matter, which then affects soil microbial biomass. The combined actions of reduced microbial biomass and reduced soil organic matter as the substrate for the enzymes decrease microbial enzyme activities during the process of forest degradation. These changes may in turn feed back to the regrowth or succession of degraded forest ecosystems.