The Tree Phyllosphere in Urban Environments

Last week the last paper of my phyllosphere project got published at mSystems. It is fair to say that my publishing journey at this journal was, by far, the best yet. Both reviewers gave us great comments and suggestions, which improved the quality of our final work. Trees in urban environments expose their leaves to both chemical contamination and biotic deposition that can come from many unusual sources (i.e. humans, exotic species). This project was aimed to enable comparisons with the more “natural” forest microbiome.

Here is the importance statement we wrote for this project: “In natural forests, tree leaf surfaces host diverse bacterial communities whose structure and composition are primarily driven by host species identity. Tree leaf bacterial diversity has also been shown to influence tree community productivity, a key function of terrestrial ecosystems. However, most urban microbiome studies have focused on the built environment, improving our understanding of indoor microbial communities but leaving much to be understood, especially in the nonbuilt microbiome. Here, we provide the first multiple-species comparison of tree phyllosphere bacterial structures and diversity along a gradient of urban intensity. We demonstrate that urban trees possess characteristic bacterial communities that differ from those seen with trees in nonurban environments, with microbial community structure on trees influenced by host species identity but also by the gradient of urban intensity and by the degree of isolation from other trees. Our results suggest that feedback between human activity and plant microbiomes could shape urban microbiomes.”

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Fig. 4. Nonmetric multidimensional scaling (NMDS) ordination of variation in bacterial community structure of tree phyllosphere along a gradient of urban intensity. Data represent ordination based on Bray-Curtis distances among 108 samples. Samples (points) are colored based on the urban gradient (blue for low intensity, orange for medium intensity, and red for high intensity). In panel a, shapes represent host species identity (squares for Acer platanoides; circles for Acer rubrum; triangles for Acer saccharum; diamonds for Celtis occidentalis; sun crosses for Fraxinus Americana; squares with cross for Fraxinus pennsylvanica; stars for Picea glauca); ellipses indicate 1 standard deviation confidence intervals around samples from urban gradient intensity. In panel b, arrows represent the significant (P < 0.001) correlations between NMDS axes versus the relative abundances of bacterial classes in communities.

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