Effects of mesofauna in a spruce forest on soil microbial communities and N cycling in field mesocosms

Using field mesocosms maintained for 6 months in an acid spruce forest, we investigated the influence of microarthropods on biomass, structure and function of the soil microbial community. In the litter layer (L/F layer), the re-immigration of mesofauna into mesocosms did not significantly affect substrate-induced respiration (SIR), biomass C, biomass N, biomass P, N-mineralisation or enzymes involved in N cycling. There was no effect of the mesofauna on the biomarkers for fungal biomass (ergosterol and phospholipid fatty acid 18:2ω6) in the litter layer. Mesofauna activities increased microbial biomass (biomass C, N and P) in the H layer, and significantly increased soil protease activity and phosphate content in the H layer. Since biomass P did not change significantly when mesofauna recolonised mesocosms, they presumably affected P-mineralisation by producing P-rich faeces. Discriminant analysis showed that mesofauna affected microbial N-mobilisation in the H layer. Higher protease and arginine deaminase activities in mesocosms with mesofauna may have been caused by faunal grazing on soil microorganisms.