Response of soil microfauna to organic fertilisation in sandy virgin soils of coastal dunes

In young white-dune soils with a very low content of organic matter, the influence of organic fertilisation on microfauna, ciliates and nematodes, was investigated. Three fertilisers - straw, rabbit dung, and wheat bran - were added to the soil in order to mimic natural conditions in older dunes. Abundances of nematodes and ciliates were significantly increased with respect to controls, where only about 3 individuals g^-1 dry matter could be counted. The numbers of nematodes and ciliates reached 103 and 77 ind g^-1 in the bran treatment, respectively. Stimulation of microfaunal production from straw and dung fertilisation was less pronounced but also significant. The results show that nematodes and ciliates react quickly to favourable conditions with excystment and production up to the abundance values of dune soils with natural organic matter accumulation. Considering the species composition of ciliates, it becomes clear that, in spite of the fast development of ciliate species, the community does not develop into natural communities of higher organic matter soils within 3 months. The increase in abundance is mainly due to rapid development of a few bacterial feeding species so that dominance concentration is much more pronounced. Organic matter concentration is an important factor for microfaunal abundance, but the quality of organic matter and the age of its accumulation seem to determine ciliate community composition. It is concluded that, due to the fertilisation, the habitat character for ciliates has evolved from an adverse habitat to a higher favourableness but lower predictability and thus has changed from A- to r-selection, whereas in natural development of the dunes it develops from A- to K-selection.