Aims Incorporation of flower strips is an agricultural measure to increase aboveground biodiversity and ecosystem services. Although soil communities are key components of terrestrial biodiversity and drive important ecosystem services, their abundance, diversity, and composition in flower strips remain largely unexplored. Here, we shed light on earthworms and soil microorganisms in flower strips. Methods We sowed a grassy field margin vegetation as well as two annual and two perennial flower strip mixtures in fully randomized plots of 9 × 28 m in three different types of soil in Germany. Two years following sowing, we determined earthworm communities using chemical extraction and investigated the soil microbiome using real-time PCR (archaea, bacteria, fungi, and soil-N-cycling genes) and amplicon sequencing (bacteria and fungi). Results Different plant mixtures (i.e. field margin, annual and perennial flower strips) harbored distinct earthworm and soil microbial communities. Earthworm density and biomass declined or remained unaffected in annual flower strips but increased in perennial flower strips as compared to the field margins. Arbuscular mycorrhizal fungi showed greater diversity and relative abundance in non-tilled (i.e. field margin and perennial flower strips) than in tilled plant mixtures (i.e. annual flower strips). Conclusions We attribute changes in earthworm and microbial communities mainly to the effect of tillage and plant diversity. Overall, we suggest that perennial flower strips serve as refugia. Future studies should compare soil biota in perennial flower strips to those in adjacent fields and investigate whether the promotion of soil communities extends into adjacent fields (‘spillover’).

Flower strips are a common agricultural practice to increase aboveground biodiversity and beneficial ecosystem services. Although soil communities are a key component of terrestrial biodiversity and drive important ecosystem services, their abundance, diversity, and composition in flower strips remain largely unexplored. Here, we shed light on earthworms and soil microorganisms in flower strips and aim to provide a starting point for research on belowground communities in flower strips. In 2020, we established a field margin vegetation as well as two annual and two perennial flower strip mixtures at three study sites in Germany that were previously conventional croplands or fallow. Two years following this conversion, we determined earthworm communities and investigated the soil microbiome using real-time PCR (archaea, bacteria, fungi, and soil-N-cycling genes) and amplicon sequencing (bacteria and fungi). Different plant mixtures (i.e. field margin, annual, and perennial flower strips) harbored distinct earthworm and soil microbial communities. Earthworm density and biomass declined or remained unaffected in annual flower strips but increased in perennial flower strips as compared to field margins. Arbuscular mycorrhizal fungi showed greater diversity and community share in non-tilled (i.e. field margin and perennial flower strips) as compared to tilled plant mixtures (i.e. annual flower strips). We attribute changes in earthworms and microorganisms mainly to the effect of tillage and plant diversity. Overall, we suggest that perennial flower strips serve as refugia for soil biota in agricultural landscapes. Future studies should compare soil biota in perennial flower strips to those in adjacent fields and investigate whether beneficial belowground effects are restricted to the flower strips or spatially extend into adjacent fields ('spillover').