Dysbiosis in the urban tree microbiome

The tree microbiome is a critical determinant of tree and ecosystem functioning, but human disturbances can disrupt natural microbe-tree relationships. Here, we show that urban trees exhibit microbial dysbiosis along a model urbanization gradient, with declines in mutualistic root and leaf symbionts, but increases in decomposers and pathogens, including those relevant to plant, animal, and human health. These shifts correlate with urban stressors such as heat, drought, and atmospheric deposition. Urban tree microbiomes also show altered biogeochemical cycling capabilities, with high potential for nitrogen loss through greenhouse gas (N2O) production and reduced capacity for methane consumption relative to rural trees. Additionally, urbanization reduces overall tree microbiome diversity, particularly among non-pathogenic microbes, potentially diminishing the ecological and health benefits of diverse environmental microbiomes in cities. These findings underscore the need to consider the microbiome in urban forestry management practices to maximize the ecological and health benefits of city greening and forest conservation efforts.