Colonization processes of soil fauna and mycorrhizal fungi

Abstract: Colonization consists of two parts, a dispersal phase followed by establishment and reproduction at a new site. Dispersal behaviour influences survival and the access to resources and mates of individuals and is thus closely linked to an organism's fitness. The dispersal ability of two collembolan species, Protaphorura armata and Folsomia fimentaria, was determined in a laboratory experiment. The dispersal ability of the two species did not differ in sieved soil and was low, 2 cm2 day-1, as calculated by a diffusion model. However, dispersal was four times lower in compact soil cores. Competition might play an important role during colonization, as a simulation shows that the proportion of an invading species compared to a resident species will not increase in the habitat even if its dispersal is high, unless its competitive ability increases. Many organisms with low abilitiy of active movement are dependent on biotic and abiotic agents to be dispersed. This is true for arbuscular mycorrhizal fungi, which do not produce above-ground fruit bodies, that enable wind dispersal of their spores. In a laboratory experiment, the effect of collembolans and earthworms on the extension of the external mycorrhizal mycelium was studied. Even though fungal biomass increased in the presence of earthworms, this had no impact on the colonization of plant roots by AM fungi over a distance of 20 cm. When setting aside arable land, it will undergo a change from a high-nutrient input agricultural ecosystem to a later successional pasture or forest ecosystem. In a European project CLUE five field sites were established on abandoned arable land. Plant seeds were sown in a high and a low diversity mixture, and soil from a late successtional stage was inoculated to find out how these management practices affect the density and diversity of the soil faunal and mycorrhizal community. The management alterations had either a negative effect on the soil microbial and faunal community or no effect at all, over a time scale of three years.