Mapping of long-term impact of conventional and organic soil management on resident and active fractions of rhizosphere communities of barley (Hordeum vulgare)

Soil biota plays an essential role in ecosystem services such as carbon fixation, nitrogen and phosphorous cycling, and disease suppressiveness. Conventional soil management with large inputs of mineral fertilizers and pesticides have a significant impact on primary decomposer communities (bacteria and fungi), as well as on protists and metazoa, representatives of the next trophic level. Organic soil management is thought to contribute to a more diverse and stable soil food web. However, information to pinpoint this supposed beneficial effect is sparse and fragmented. Keeping in mind that a substantial fraction of the soil biota is dormant, we set out to map both the resident and the active the bacterial, fungal, protozoan and metazoan communities under various soil management regimes in two distinct soil types with barley as main crop. For all four organismal groups, the contrast between resident (rDNA-based) and active (rRNA-based) was the most important explanatory variable explaining 22%, 14%, 21% and 25% of the variance among bacterial, fungal, protozoan, and metazoan communities. Less prominent were the effects of soil management and soil type, however significant as well for all four organismal groups. LEfSe was used to identify indicator taxa for both the contrasts between resident and active communities, and the effects of soil management. Our results suggest that - next to DNA-based community characterisation - mapping of the active microbial community could provide essential insights in the effects of variables such as crop and soil management on the soil living community.