Recipe
Soil microbes perform a multitude of functions, including nutrient cycling. Recently, there has been a growing interest in the potential relationship between soil microbes and human health. The biodiversity hypothesis suggests that urban residents require contact with diverse natural environments to ensure the development of a protective microbiome on the human skin, which correlates with a reduction in inflammatory diseases. The soil of urban green spaces, which exhibit 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, despite this being an unexpected result. 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. Concerning the nitrogen cycle all studied green spaces were potentially denitrifying environments, and metagenomic analyses revealed that all three urban spaces potentially converted nitrite into gaseous forms of nitrogen, rather than ammonium, with more nitrous oxide (N2O) being formed in urban forest soils.    From the perspective of urban planning, our findings indicate that also the soils of built green spaces are microbiologically diverse, offering the potential for the design of different types of plantations to attract residents to an urban park of their choosing. Furthermore, it is recommended that efforts be made to preserve the existing urban forests to provide the local population with the opportunity to interact with an alternative environmental microbiome.