Up on the roof

Green roofs have become increasingly popular in urban sustainability initiatives, as they provide a number of ecosystem services that mitigate the effects of urbanization such as decreased storm water runoff, enhanced building energy-use efficiency, and reduced urban heat island effects. However, little research has been done on the biodiversity of those communities especially the non-plant biota associated with green roofs, which likely affect their functionality. 

In a new study, a group of US researchers evaluated whether or not green roofs planted with two native plant communities in New York City functioned as habitats for soil fungal communities, and compared fungal communities in green roof growing media to soil microbial composition in five city parks

Sampling schemes for soil cores

The reserarchers utiilzed massive parallel sequencing of the fungal DNA Barcode region (ITS) and found that green roofs supported a diverse fungal community, with numerous taxa belonging to fungal groups capable of surviving in disturbed and polluted habitats. Across roofs, there was significant biogeographical clustering of fungal communities, indicating that community assembly of roof microbes across the greater New York City area is locally variable. Green roof fungal communities were distinct from city parks and only about half of the green roof taxa were also found in the park soils.

While fungal communities were compositionally distinct across green roofs, they did not differentiate by plant community. Together, these results suggest that fungi living in the growing medium of green roofs may be an underestimated component of these biotic systems functioning to support some of the valued ecological services of green roofs.

Understanding how biodiversity is assembled and maintained will be useful for managing green roof systems to maximize their provision of ecosystem services while simultaneously minimizing external inputs and roof maintenance. In addition to their practical aspects, green roofs that represent vegetated islands can also function as ideal experimental systems for asking ecological questions about community assembly and habitat fragmentation .