Scientists at the University of Cambridge have discovered that trees growing in cities are losing beneficial microorganisms and acquiring harmful bacteria. This makes them more vulnerable to disease and degrades the quality of the urban environment.
Life in megacities affects not only people but also trees. A new study by Cambridge researchers, published in the journal Nature Cities, shows that trees in urban environments are losing their natural microbial allies—the fungi and bacteria that help them grow and protect them from disease—while acquiring detrimental microorganisms that weaken their immunity.
The scientists compared the microbiome of the leaves and roots of trees in natural forests versus those in major city centers. They found that the number of beneficial fungi, which help with nutrient uptake, is reduced by more than half in the city. Conversely, there is an increase in bacteria that cause tissue inflammation, rot, and weakening of the root system.
The main culprits identified are air pollution, soil compaction, lack of organic matter, elevated temperatures, and limited contact with other plants and animals. All of these factors disrupt the natural exchange of microflora, making the trees vulnerable.
“A tree’s microbiome is like its invisible immune system. When it breaks down, the tree becomes vulnerable, even if it looks healthy on the outside,” notes Dr. Jason Hill, a co-author of the study.
The researchers propose concrete actions to restore the ‘health’ of urban trees: using permeable soils, abandoning chemical agents, and introducing mycorrhizal fungi alongside new saplings. These methods have already yielded initial success in several Northern European cities.
The researchers emphasize that urban trees are not just decorations; they are living ecosystems whose condition affects air quality and residents’ comfort. When caring for them, we must also remember their invisible helpers—the microorganisms.
