1. Project: Effects of micro- and macrobioturbation produced by soil fauna on the stabilisation of organic matter in agricultural soils DFG SPP 1090 Justus Liebig University Giessen Klemens Ekschmitt, Oliver Fox, Silke Vetter and Volkmar Wolters Justus Liebig University, IFZ - Department of Animal Ecology Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany E-mail: Klemens.Ekschmitt @allzool.bio.uni-giessen.de IFZ – Deptartment of Animal Ecology Fig. 2: Dynamics of animal impact during the experiment, maize soil. Results Higher animal densities generally lead to accelerated decomposition of soil organic matter, as measured by soil CO 2 evolution. However, decomposition rate was limited by overgrazing effects in the mesofauna and by mutual inhibition of soil faunal groups. Animal effects were stronger and more dominant in soil without litter (R²=0,63) than in soil with litter cover (R²=0,21). Fig. 4: Contrasting effect of collembola - in soil without litter (a), - compared to soil with litter cover (b) abab Conclusions 1.Effects of improved animal densities take months to develop in initially poorly faunated agricultural soils. 2.In general, higher densities of soil animals lead to augmented soil respiration. This effect is, however, limited by overgrazing and by mutual inhibition of soil faunal groups. Animal effects vary widely depending on the age class of soil organic matter. 3.From further differentiation of soil fractions we expect to learn more about the critical hot spots of soil animal function, enabling us to extrapolate and to better predict soil animal effects in other soils. Fig. 3: Inhibition of nematode-effects by enchytraeids, maize soil Introduction Management of soil organic matter has turned into a central topic of soil ecology. The project aims at analysing the impact of soil engineers (Lumbricidae, Enchytraeidae, Collembola) and of nematodes on the stabilisation of organic matter in agricultural soils, and at clarifying 1. whether different soil animals foster or impede carbon sequestration, 2. whether there exist synergies or antagonisms among soil faunal groups, and 3. which fractions of soil organic matter are mainly affected by soil faunal groups. Experimental approach We apply three experimental approaches, gradually leading from artificial to natural experimental conditions: (a) laboratory microcosm experiments, (b) free air mesocosm experiments and (c) field trials. Here, we present results from the first project phase, i.e., from the microcosm experiments. Methods In an extensive laboratory experiment, 96 microcosms were inoculated with nematodes, lumbricids, enchytraeids and micro-arthropods, each in three different densities, as well as in combinations of these densities, according to a D-optimised design. As substrate we used two soils from the experimental facility „Eternal Rye“ (Ewiger Roggen) in Halle: maize soil unfertilised and rye soil unfertilised, covered with maize litter. In addition to analysing the single effects of soil faunal groups, the experimental design also enables to quantify interactive effects of soil faunal groups. Soil fractioning, as well as microbial analyses were performed. Surface Analysis was used to test for statistical significance of animal effects. 2. Combined effects of several faunal groups Interaktive effects of animal groups accounted for 1/8 of total animal effects (Tab. 1). Enchy- traeids had no impact on CO 2 evolution by themselves, however they interacted with other groups, e.g. they inhibited the effects of nematodes (Surface, p=0.00001) (Fig. 3). 3. Soil fractions Soil animal effects differed drastically between age classes of soil organic matter. In soil without litter, collembola accelerated CO 2 evolution rates up to three times the control rates (Surface, p<0.0001) (Fig. 4a). In soil with fresh litter, in strong contrast, collembola reduced CO 2 evolution by up to 20% (Surface, p=0.0003) (Fig. 4b). Soil probes were fractionated according to particle size classes and solubility classes of soil organic matter. Analysis is in progress. We expect to find similar differences of animal effects between some of these soil organic matter fractions. 1. Impact of single animal groups on CO 2 evolution All of the animal groups tested exhibited a pronounced dynamics of their impact on CO 2 evolution, with an initial overshoot and with differing time constants (Fig. 2). Earthworm effects developed slowly. At the end of the experiment, i.e. after eight weeks, soil animal effects on CO 2 were still augmenting. Tab. 1: Surface Analysis, maize soil Fig. 1: Three-stepped transition from artificial to natural experimental conditions Field experiments Free air Mesocosms Laboratory microcosms Research Centre of Environmental Protection