J MAYERHOFER¹, H RAUCH², CO PABST³, A LEUCHTMANN⁴, M HARTMANN⁵, H STRASSER³, F WIDMER¹, J ENKERLI<sup>1

1</sup>Molecular Ecology, Institute for Sustainability Sciences, Agroscope, 8046 Zurich, Switzerland, ²Research Centre for Agriculture and Forestry Laimburg, 39040 Auer, Italy, ³Institute of Microbiology, Leopold-Franzens University Innsbruck, 6020 Innsbruck, Austria, ⁴Plant Ecological Genetics, Institute of Integrative Biology, ETH Zurich, 8092 Zurich, Switzerland, ⁵Forest Soils and Biogeochemistry Rhizosphere Processes, Swiss Federal Research Institute WSL, 8903 Birmensdorf, Switzerland

A major part of the terrestrial biomass is formed by microbial communities. Soil microbial communities have a great impact on nutrient cycling, soil fertility and plant health, representing important ecosystem services for productive and sustainable agriculture. Biological and chemical plant protection treatments are well accepted measures for pest control, however, the impact particularly of biological control agents on soil microbial communities has been poorly investigated. In this study potential effects of two biological control treatments and an insecticide were assessed in a pot experiment with maize and Diabrotica virgifera virgifera as pest insect. One biological control agent was the entomopathogenic fungus Metarhizium brunneum, which was formulated as fungal colonized barley kernels or as fungal alginate capsules and the other one was a suspension of the entomopathogenic nematode Heterorhabditis bacteriophora. The pot experiment was performed in a greenhouse and consisted of eight treatments with six replicates per treatment.
Treatments including FCBKs led to a significant increase of Metarhizium spp. (3-8 x 104 CFU g-1 soil dry weight compared to about 103 CFU in untreated pots), which provided an ideal system to study effects of the applied Metarhizium brunneum strain on soil microbial communities. In order to assess microbial community composition, soil samples were collected from each pot before application, and 9 and 18 weeks after application. Soil genomic DNA was extracted and the internal transcribed spacer region 2 (fungi) and the variable regions V3-V4 of the small ribosomal subunit (prokaryota including bacteria and archaea) were amplified and sequenced using the Illumina MiSeq platform. The community structure of fungi changed over time, but no effects of the treatments were observed. Prokaryotic communities also changed over time, however, they were also affected by the application of FCBKs, nematodes as well as their combination 9 weeks after application. Eighteen weeks after application the effects had decreased suggesting resilience of the communities.