Effect of land use and management practices on microbial biomass and enzyme activities in subtropical top-and sub-soils

Land-use change, especially from forest to intensive agriculture, is negatively impacting soil quality and sustainability. Soil biological activities are sensitive indicators of such land-use impacts. We tested two hypotheses: i) land use and management practices affect microbial properties (microbial biomass and enzyme activities) in topsoil (0–20cm), but have no effects in subsoil (20–100cm); and ii) microbial properties in topsoil are highest in forest, followed by organic farming and then conventional farming. Total organic C and N contents as well as microbial biomass were significantly higher in the organic farming topsoil compared with conventional farming and forest. Except xylanase and acid phosphatase, enzyme activities (β-glucosidase, cellobiohydrolas, chitinase, sulfatase, leucine aminopeptidase and tyrosine aminopeptidase) were also higher in organic farming soil. Crop residues and rhizodeposits support higher microbial biomass, leading to enhanced enzyme activities in organic farming soil. Incorporation of rice stubble and limitation of available phosphorus explain the higher xylanase and acid phosphatase activities, respectively, in conventional farming soil. Litter removal leads to a deficiency of labile C and N, resulting in lower enzyme activities in forest soil. Total C and N contents were higher in subsoil under organic farming. Although there was no effect of land use on microbial biomass in subsoil, activities of most enzymes were higher under organic farming. Overall, our results indicate that land-use change significantly alters microbial properties in topsoil, with modest effects in subsoil. Microbial properties should be considered in environmental risk assessments and models as indicators of ecosystem disturbance caused by land-use and management practices.