Functional redundancy and community homogenization: Effects of urbanization and vegetation on soil microbiota across climatic zones

Urbanization fundamentally reshapes terrestrial environments, leading to significant alterations in soil microbial communities which play crucial roles in ecosystem functioning. This comprehensive study utilizes amplicon sequencing and GeoChip arrays to assess how urbanization and tree functional types impact the composition and functional capacity of soil microbiota across various climatic zones, including boreal (Lahti, Finland), moderate (Baltimore, USA) and tropical regions (Singapore). By comparing urban parks with varying ages and vegetation types to reference forests, the research provides a nuanced understanding of how urban settings influence microbial dynamics.

Our analysis revealed that urban parks host unique microbial communities, distinct from those found in semi-natural forests. Notably, these communities display a surprising functional redundancy with their forest counterparts, suggesting that urban microbiota maintain essential ecosystem processes despite altered environmental conditions. However, the degree of microbial community homogenization differs by microbial type; bacterial communities showed greater homogenization effects than fungal ones. This differential response highlights inherent differences in ecological strategies between bacteria and fungi, with bacteria more readily adapting to the environmental constraints imposed by urban landscapes.

Furthermore, the type of vegetation significantly influences these patterns. Soils under trees producing recalcitrant litter harbored richer fungal communities compared to those with labile litter types. In contrast, lawns—despite their simplicity—supported unexpectedly high diversities of both bacterial and fungal species. These findings emphasize that both the quality of plant-derived organic matter and the structure of plant communities are critical in shaping soil microbial diversity and function in urban environments.

This study underscores the complex interplay between urbanization, vegetation diversity, and microbial community dynamics, highlighting the resilience of soil microbiota to urban stresses. The implications of these findings are significant for urban ecology and biogeochemistry, providing insights into maintaining biodiversity and ecosystem services in rapidly urbanizing regions.