Abstract
In urban environments, green roofs provide a number of benefits, including decreased urban heat island effects and reduced energy costs for buildings. However, little research has been done on the non-plant biota associated with green roofs, which likely affect their functionality. For the current study, we 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, including Central Park and the High Line. Ten replicate roofs were sampled one year after planting; three of these roofs were more intensively sampled and compared to nearby city parks. Using Illumina sequencing of the fungal ITS region we 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 compositionally distinct from city parks and only 54% of the green roof taxa were also found in the park soils. Phospholipid fatty acid analysis revealed that park soils had greater microbial biomass and higher bacterial to fungal ratios than green roof substrates. City park soils were also more enriched with heavy metals, had lower pH, and lower quantities of total bases (Ca, K, and Mg) compared to green roof substrates. 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.
Highlights
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 [1,2,3]
This study aimed to address the following questions related to fungal communities in green roof substrates and nearby city park soils: 1) Do green roofs in New York City function as biodiversity reservoirs for fungi?; 2) Is there evidence for spatial structuring of green roof fungal communities across New York City? 3) Does vegetation type influence community composition of green roof fungi?; 4) How much overlap is there in fungal community composition of the green roof substrates and city park soils?
The most abundant operational taxonomic units (OTUs) in green roof substrates was classified as Pseudallescheria fimeti (Ascomycota), which represented 13.5% of all sequences in the roof samples
Summary
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 [1,2,3]. An additional benefit of green roofs that has not been fully explored is the potential reservoir of habitats for biota residing in or migrating across the city [4]. 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 can function as ideal experimental systems for asking ecological questions about community assembly and habitat fragmentation
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