Section outline
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Microbial communities in urban greenspaces differ significantly from those in natural ecosystems due to unique urban pressures. While habitats like the phyllosphere and air play significant roles, soil remains the cornerstone of microbial diversity in urban forests ecosystems (7). It often favors higher proportions of fast-growing and fast-adapting taxa such are Gammaproteobacteria, Deltaproteobacteria, Bacteroidetes, Gemmatimonadetes, Ascomycota, Chlorophyta, and Amoebozoa. For example, Gammaproteobacteria and Bacteroidetes in soil benefit from high nitrogen and phosphorus availability while Amoebozoa prefer frequent irrigation. Photosynthetic organisms like Chlorophyta are also common in urban soils, colonizing exposed, nutrient-rich surfaces (2,11).
Urban soils, tend to have reduced diversity of mycorrhizal fungi, crucial for nutrient exchange with plant roots, likely caused by soil disturbance, habitat fragmentation, chemical pollutants and lack of suitable host plants, which can negatively affect urban forest health (12). Additionally, urban forests harbor a higher concentration of fungal pathogens and plant parasites, including Fusarium, Pythium, and Verticillium, which can outcompete beneficial microbes in polluted and degraded areas (13). Once established, these pathogens can reduce plant growth, decrease biodiversity, and increase tree mortality. Urban trade hubs are particularly vulnerable to invasive pathogens like Phytophthora ramorum and Xylella fastidiosa, often introduced through ornamental plant movements. Without natural antagonists, these invasive species disrupt microbial communities and pose significant biosecurity risks (5,13).
Interestingly, while urban greenspaces often exhibit high local (alpha) diversity of microbial taxa such as bacteria and protists, they display reduced geographic variation (beta diversity) compared to natural ecosystems. This pattern found on 56 cities across the world underscores the global homogenizing effects of urbanization. Urban soils in cities around the world increasingly share similar microbial characteristics due to common urban pressures, reducing the capacity of microbial communities to provide location-specific ecosystem services. This homogenization makes urban forests more vulnerable to uniform stressors, such as climate change and invasive pathogens (11)