Drivers of fungal diversity and community biogeography differ between green roofs and adjacent ground-level green space.

Green roof soils are usually engineered for purposes other than urban biodiversity, which may impact their fungal communities, and in turn impact the health of plants in the urban ecosystem. We examined the drivers of fungal diversity and community composition in soil of green roofs and adjacent ground-level green spaces in three Midwestern USA cities-Chicago, Cleveland, and Minneapolis. Overall, fungal communities on green roofs were more diverse than ground-level green spaces and were correlated with plant cover (positively) and roof age (negatively) rather than abiotic soil properties. Fungal community composition was distinct between roof and ground environments, among cities, and between sampling sites, but green roofs and their immediately surrounding ground-level green space showed some similarity. This suggests dispersal limitation may result in geographic structuring at large spatial scales, but dispersal between roofs and their neighbouring sites may be occurring. Different fungal taxonomic and functional groups were better explained when roofs were classified either by depth (extensive or intensive) or functional intent of the roof design (i.e. stormwater/energy, biodiversity, or aesthetics/recreation). Our results demonstrate that green roofs are an important reservoir of fungal diversity in the urban landscape, which should be considered in future green roof design.