Microbial communities on New York City green roofs across space and time
The microbial ecology of urban soils is a salient area research as more than half of the world’s population currently resides in cities. Recent interest in sustainability efforts includes expanding urban green infrastructure, and microbial communities in the soils and growing media of green infrastructure facilitate many of the benefits that green infrastructure is valued for. However, few studies have assessed the composition and function of soil microbes in the urban environment. For the current study we addressed the following questions: 1) How do green roof fungal and bacterial communities compare to urban parks, non-urban soil ecosystems, and other types of green infrastructure?, 2) How are green roof microbes affected by seasonality?, and 3) How does community assembly of green roof microbes occur over time? To address these questions we characterized fungi and bacteria using Illumina sequencing and phospholipid fatty acid analysis in the growing media of ten experimental green roofs in New York City that were established with identical plant communities and growing media. These microbial communities were compared to soils from parks in urban, suburban, and rural environments and to other types of urban green infrastructure soils including tree pits, medians, and bioswales.
We found diverse fungal and bacterial communities in green roof growing media that were distinct from communities in ground-level parks and other types of green infrastructure, suggesting the importance of infrastructure-specific abiotic soil conditions in structuring urban soil microbes. Across green roofs and parks, there was significant biogeographical clustering of microbial communities, indicating that community assembly of microbes across the greater New York City area is locally variable possibly due to microclimatic differences. We also found evidence for seasonality in green roof microbes, although location and green infrastructure type were more significant drivers of microbial composition than season. Across the urban to rural gradient we also found that urban soils had lower microbial biomass than both suburban and rural soils implicating the role of anthropogenic stressors in modifying urban microbial communities. Together, these results have implications for the design and management of urban green infrastructure and provide insight into the biotic and abiotic factors involved in urban microbial community assembly.