Nematode–collembolan-interaction promotes the degradation of Fusarium biomass and deoxynivalenol according to soil texture

Despite well-known positive aspects of conservation tillage combined with mulching on arable fields, one drawback may be the survival of phytopathogenic fungi on plant residues. Therefore, plant pathogen repression is an important ecosystem service to prevent cultivated plants from fungal diseases and mycotoxin contamination. A microcosm-study was conducted under constant laboratory conditions to assess the impact of soil microfauna (Aphelenchoides saprophilus, Nematoda) and soil mesofauna (Folsomia candida, Collembola) on soil-borne phytopathogenic fungi (Fusarium culmorum) and its mycotoxin deoxynivalenol (DON). Our hypotheses were: (1) nematodes and collembolans reduce the biomass of F. culmorum and the content of DON in infected wheat straw; (2) the species interaction of A. saprophilus and F. candida enhances the degradation of Fusarium biomass and DON concentration in wheat straw; (3) the degradation efficiency of nematodes and collembolans is affected by soil texture. Therefore, microcosms were filled with soil of different texture and finely chopped wheat straw (Fusarium-infected vs. non-infected). The microcosms were inoculated with the two species in different combinations (single and mixed species, non-faunal control). After 2 and 4 weeks of incubation, the individual densities in all soil faunal treatments increased with highest individual numbers in the non-infected treatments in case of collembolans and in the infected treatments in case of nematodes. The Fusarium biomass (Fusarium protein equivalents = FPE) of all infected treatments decreased by at least one order of magnitude after 2 weeks. At the end of 4 weeks Fusarium-biomass was reduced by 93% in sandy and silt loam and 89% in clay loam mostly in mixed species treatments. Also DON concentrations were reduced significantly compared to the initial concentration in all treatments after 4 weeks. The highest reduction was found in mixed species treatments, where DON was degraded by 92%, 95% and 39% for sandy loam, silt loam and clay loam, respectively. We concluded that particularly interacting collembolans and nematodes play an important role in plant pathogen repression and mycotoxin degradation. In any case, soil texture matters in the provision of these ecosystem services by collembolans and nematodes.