Microbial characteristics during the initial stages of litter decomposition in forest and adjacent cropland soil

To evaluate the functional microbial changes during initial decomposition stages of one model litter type in two ecosystems with lower and higher human impact, straw was buried in nylon bags for 52 days in soil under beech forest and cropland. In the two adjacent soils, microbial biomass in the litter estimated by fumigation-extraction (FE) decreased continuously after day 10 and the substrate-induced respiration (SIR) peaked at day 17. As a result, the SIR-to-FE-ratio referring to the metabolic responsive biomass increased until day 17 and decreased afterwards. This ratio indicated that metabolic responsive biomass became rapidly active and later dormant or inactive, which was most apparent in the forest soil. The basal respiration increased continuously until day 32 and then it decreased. In the first 2 weeks, bacteria estimated with the inhibition technique dominated the microbial biomass on the decomposing litter in the forest soil and fungi dominated the microbial biomass in the cropland soil. Correspondingly, high abundance of nematodes repressed the bacterial biomass in the forest soil and the fungal biomass in the two soils. We conclude that shifts in microbial physiology were similar during oat straw decomposition in the two ecosystems but microbial biomass components changed in a functionally significant manner at the initial decomposition stages of litter. (C) 2007 Elsevier B.V. All rights reserved.