Eects of mesofauna in a spruce forest on soil microbial communities and N cycling in ®eld mesocosms

Using ®eld mesocosms maintained for 6 months in an acid spruce forest, we investigated the in ̄uence 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 signi®cantly a€ect substrate-induced respiration (SIR), biomass C, biomass N, biomass P, Nmineralisation or enzymes involved in N cycling. There was no e€ect of the mesofauna on the biomarkers for fungal biomass (ergosterol and phospholipid fatty acid 18:2o6) in the litter layer. Mesofauna activities increased microbial biomass (biomass C, N and P) in the H layer, and signi®cantly increased soil protease activity and phosphate content in the H layer. Since biomass P did not change signi®cantly when mesofauna recolonised mesocosms, they presumably a€ected P-mineralisation by producing Prich faeces. Discriminant analysis showed that mesofauna a€ected 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. # 1999 Elsevier Science Ltd. All rights reserved.