Sustainable rewilding of urban spaces increases microbial diversity

Soil sealing and biodiversity loss are major drivers of altered microbial communities in urban environments. Little is known about how rewilding reshapes these communities and enriches surrounding sealed surfaces with microbiota. To fill this gap, we first tested whether existing urban green spaces are associated with increased microbial diversity and abundance beyond their boundaries on adjacent impermeable surfaces. We then rewilded a barren, sealed city square using vegetation, compost-based growing medium, and decaying wood. We hypothesized that proximity to green spaces predicts microbial communities more than geographic location, and that rewilding enriches bacterial diversity on nearby sealed surfaces, with diminishing effects across distance. Microbial samples were collected from five green spaces at 0-100 m distances, and from the rewilded and a neighboring non-rewilded square before and after rewilding. In the green space experiment, bacterial richness and relative abundance of Rhizobacter declined steadily with distance from green spaces. In the rewilding experiment, bacterial alpha diversity increased compared to baseline conditions and co-occurrence networks contained more nodes and connections post-rewilding. These findings demonstrate that existing green spaces are associated with elevated microbial diversity on surrounding sealed surfaces, and that rewilding urban areas provides a low-cost, nature-based strategy to increase urban microbial diversity.