The boreal soil microbiome of different urban green spaces – Do city residents meet different microbes?

Soil microbes perform a wide range of functions, including nutrient cycling. Soils in urban green spaces also provide a nearby source of natural microbiota for human residents, potentially promoting the development of skin microbiomes and having beneficial impact on health. The soil of urban green spaces, which have distinctive vegetation characteristics, was analysed in two boreal cities to investigate whether residents are exposed to different microbial communities. The analysis included built, open and forested green spaces. Built green spaces, characterized by flower beds and lawns, and open green spaces, such as meadows, had a similar soil microbiome, although this was an unexpected finding. The bacterial and fungal communities of urban forests differed from those of built and open green spaces. In contrast to the bacterial diversity of urban forests, which increased in the soil of built and open spaces, fungal diversity did not differ. According to metagenomic analyses all the green spaces were potentially denitrifying environments and revealed that all three urban spaces harboured genes that could possibly lead to the formation of more nitrous oxide (N 2 O) in urban forest soils. This finding highlights the importance of incorporating greenhouse gas flux measurements and functional microbial analyses in future research on the impact of urbanization on soil microbiology. From the perspective of urban planning, our results indicate that the soils of built green spaces are microbiologically diverse, offering the potential to design different types of plantations that attract residents to urban parks of their choice. Furthermore, we recommend making efforts to preserve existing urban forests to provide opportunities for local populations to interact with alternative environmental microbiomes. • Soil microbial communities of urban green spaces are highly diverse • Citizens are exposed to different microbes in urban forests than in built and open green spaces • Urban soil microbes are shaped by soil CEC, C%, pH and vegetation composition • All urban green spaces may lose soil N through denitrification