Indirect effects of carbon and nutrient amendments on the soil meso- and microfauna of a beechwood

To investigate the importance of the availability of food resources for soi l micro- and mesofauna, carbon (as glucose) and nutrients (nitrogen as NH4N O3;, phosphorus as NaH2PO4) were added separately and in combination to exp erimental plots in a beechwood on limestone (Gottinger Wald) for 15 months. The aim of the study was to increase the amount of resources (microorganis ms) for the soil micro- and mesofauna and to observe changes in their densi ty, i.e. to evaluate the strength of bottom-up forces. Furthermore, we want ed to investigate changes in the density of animals which feed on micro- an d mesofauna. i.e. predacious animals including Gamasina, Uropodina and pred atory Nematoda. In the litter layer the density of all animal groups studie d was not significantly affected by experimental manipulations. In the soil animal groups responded differently but not parallel to the amount of resp ective food resources. The density of oribatid and uropodid mites declined in the C only treatment and the decline in oribatid mites was more pronounc ed when C and P were added in combination. Collembolan density also decline d in the CP treatment. In contrast, Nematoda and Protozoa increased in dens ity after the addition of C, N or P. The number of amoebae increased when P was added and this increase was most pronounced in the CP treatment. Flage llate density increased slightly in C treatment but the increase was strong er in CN, CP and CNP treatments. Gamasina did not respond significantly to experimental manipulations. The results point to a differential response of soil animal groups to an increased supply of food resources. We assume tha t the responses were strongly influenced by indirect effects caused by the increased number and biomass of earthworms in C treatments. Presumably, hig h density and biomass of earthworms stimulated populations of Nematoda. Amo ebae and Flagellata while it detrimentally affected collembolans and partic ularly oribatid mites. It is concluded that in the forest studied litter co nsumption, bioturbation and mucus excretion by earthworms negatively affect s the habitable space of collembolans and oribatid mites but improves habit at conditions for microfauna by increasing the water content. Therefore, ea rthworm effects may superimpose bottom-up forces confirming that earthworms are important ecosystem engineers in mull forest soils.