Distribution of microbial biomass and activity of extracellular enzymes in a hardwood forest soil reflect soil moisture content

Forest soils show a considerable level of spatial heterogeneity. It was previously reported that soil moisture content affects microbial biomass and respiration in the soil as well as enzyme-catalyzed processes; as such it can be one of the potential drivers of heterogeneity of microbial distribution and decomposition in forest soils. The moisture mass content in samples of Quercus petraea forest soil varied substantially and ranged between 0.35-0.70 g g(-1) soil wet mass in the litter horizon and 0.10-0.60 g g(-1) in the humus horizon within a single sampling of a 144m(2) area as well as of a 0.11 m(2) area. Soil moisture content positively and significantly correlated with microbial (bacterial and fungal) biomass, explained up to 60% of the total variability in microbial biomass and a significant difference in the ratio of fungal to bacterial biomass was found among the samples with high and low moisture content. Also the activity of several extracellular enzymes involved in decomposition (i.e., laccase, Mn-peroxidase, endo-1,4-beta-glucanase, endo-1,4-beta-xylanase, cellobiohydrolase, beta-glucosidase, beta-xylosidase, chitinase and acid phosphatase) correlated with soil moisture, although the response varied among soil horizons and sampling dates. The effect of moisture on enzyme activities was probably partially mediated by the changes in biomass content. Forest soil was demonstrated to be a mosaic of small dry and moist patches where the differences in microbial biomass content or enzyme activities vary by tens of percents due to differential moisture content. (C) 2010 Elsevier B.V. All rights reserved.