Bacterial succession and community dynamics of the emerging leaf phyllosphere in spring

Every year, deciduous trees shed their leaves, and when new leaves emerge next spring, they establish a characteristic bacterial leaf community. In this exploratory study, we assessed the bacterial phyllosphere (aboveground plant surfaces) of eight London plane trees (Platanus × acerifolia) in Antwerp and Milan by sampling weekly during leaf emergence and expansion. We sampled the surfaces of different tree compartments: leaves, leaf buds, branches, and trunk, for up to 6 weeks. Phyllosphere community composition was most strongly determined by tree compartment. Only the communities on the emerging leaves showed changing dynamics over time. The rate of change in the leaf phyllosphere composition, expressed as the beta dissimilarity between consecutive time points, was very high following leaf emergence, with decreasing speed over time, indicating that these communities stabilize over time. We also identified cooccurring groups of bacteria associated with potential stages of ecological succession on the leaves and accordingly named them general cluster, early cluster, middle cluster, and late cluster. Taxa of the general cluster were not only more abundant than the others on leaves, but they were also widespread on other tree compartments. The late cluster was most pronounced in trees surrounded by trafficked urban land use. This study mainly generates hypotheses on the ecological succession on the emerging leaves of deciduous trees in urban environments and contributes to understanding the development of the tree leaf phyllosphere in spring. IMPORTANCE Improving our understanding of phyllosphere ecology is key in successfully applying bacterial biological agents or modulating the leaf microbiome in order to achieve valuable ecosystem services, such as plant protection, plant growth, air purification, and developing a healthy human immune system. Modulation of the phyllosphere microbiome in the field works only with variable success. To improve the impact of our applications in the field, a better understanding of the ecological principles governing phyllosphere dynamics is required. This exploratory study demonstrates how the combination of different analyses of a chronosequence of bacterial communities can provide new ecological insights. With a limited number of sampled trees, we demonstrated different indications of ecological succession of bacterial communities in the leaves and observed a potential impact of intensely trafficked land use becoming apparent in the leaf bacterial communities approximately 3 weeks after leaf emergence, consisting of a separate stage in community development

The magnetic signal from trunk bark of urban trees catches the variation in particulate matter exposure within and across six European cities

Biomagnetic monitoring increasingly is applied to assess particulate matter (PM) concentrations, mainly using plant leaves sampled in small geographical area and from a limited number of species. Here, the potential of magnetic analysis of urban tree trunk bark to discriminate between PM exposure levels was evaluated and bark magnetic variation was investigated at different spatial scales. Trunk bark was sampled from 684 urban trees of 39 genera in 173 urban green areas across six European cities. Samples were analysed magnetically for the Saturation isothermal remanent magnetisation (SIRM). The bark SIRM reflected well the PM exposure level at city and local scale, as the bark SIRM (i) differed between the cities in accordance with the mean atmospheric PM concentrations and (ii) increased with the cover of roads and industrial area around the trees. Furthermore, with increasing tree circumferences, the SIRM values increased, as a reflection of a tree age effect related to PM accumulation over time. Moreover, bark SIRM was higher at the side of the trunk facing the prevailing wind direction. Significant relationships between SIRM of different genera validate the possibility to combine bark SIRM from different genera to improve sampling resolution and coverage in biomagnetic studies. Thus, the SIRM signal of trunk bark from urban trees is a reliable proxy for atmospheric coarse to fine PM exposure in areas dominated by one PM source, as long as variation caused by genus, circumference and trunk side is taken into account.info:eu-repo/semantics/acceptedVersio

How do urban green space designs shape avian communities? Testing the area-heterogeneity trade-off

Abstract: In cities, green areas are essential for biodiversity conservation, with land cover heterogeneity being a decisive factor. Yet, as heterogeneity increases for a given green area, the patch size of land covers automatically decreases, as the area available for individual species, especially habitat specialist species. This relationship, known as the area-heterogeneity trade-off, is expected to lead to a unimodal relationship between species richness and land cover heterogeneity, and contrasted effects between species according to their level of urban avoidance. We investigated the potential consequences of this trade-off on birds in green areas selected along an urban intensity gradient in six European cities. Using a European database on bird occurrences in nesting habitats, we defined a continuous gradient of urban avian avoidance. We confirmed the marked area-heterogeneity trade-off in urban green areas but found no effect of land cover heterogeneity on total avian richness at green area level. However, both land cover heterogeneity and patch size were positively associated with richness of urban avoider species, indicating that urban avoiders fared better in green areas with large and heterogeneous patches. Total richness was also higher in green areas surrounded by an urban matrix composed of a variety of land covers. To protect urban bird avoiders, which are most at risk in cities, green area managers and urban planners should thus be aware that land cover heterogeneity is not a panacea if patch sizes are too small. To conserve avian richness, we stress the importance of maintaining large vegetated areas as well as heterogeneity in land covers within the urban matrix

Phyllosphere bacterial communities in urban green areas throughout Europe relate to urban intensity

The phyllosphere harbours a diverse and specific bacterial community, which influences plant health and ecosystem functioning. In this study, we investigated the impact of urban green areas connectivity and size on the composition and diversity of phyllosphere bacterial communities. Hereto, we evaluated the diversity and composition of phyllosphere bacterial communities of 233 Platanus x acerifolia and Acer pseudoplatanus trees in 77 urban green areas throughout 6 European cities. The community composition and diversity significantly differed between cities but only to a limited extent between tree species. We could show that urban intensity correlated significantly with the community composition of phyllosphere bacteria. In particular, a significant correlation was found between the relative abundances for 29 out of the 50 most abundant families and the urban intensity: the abundances of classic phyllosphere families, such as Acetobacteraceae, Planctomycetes, and Beijerinkiaceae, decreased with urban intensity (i.e. more abundant in areas with more green, lower air pollution, and lower temperature), while those related to human activities, such as Enterobacteriaceae and Bacillaceae, increased with urban intensity. The results of this study suggest that phyllosphere bacterial communities in European cities are associated with urban intensity and that effect is mediated by several combined stress factors.info:eu-repo/semantics/acceptedVersio

Phyllosphere bacterial communities in urban green areas throughout Europe relate to urban intensity

The phyllosphere harbours a diverse and specific bacterial community, which influences plant health and ecosystem functioning. In this study, we investigated the impact of urban green areas connectivity and size on the composition and diversity of phyllosphere bacterial communities. Hereto, we evaluated the diversity and composition of phyllosphere bacterial communities of 233 Platanus x acerifolia and Acer pseudoplatanus trees in 77 urban green areas throughout 6 European cities. The community composition and diversity significantly differed between cities but only to a limited extent between tree species. We could show that urban intensity correlated significantly with the community composition of phyllosphere bacteria. In particular, a significant correlation was found between the relative abundances for 29 out of the 50 most abundant families and the urban intensity: the abundances of classic phyllosphere families, such as Acetobacteraceae, Planctomycetes, and Beijerinkiaceae, decreased with urban intensity (i.e. more abundant in areas with more green, lower air pollution, and lower temperature), while those related to human activities, such as Enterobacteriaceae and Bacillaceae, increased with urban intensity. The results of this study suggest that phyllosphere bacterial communities in European cities are associated with urban intensity and that effect is mediated by several combined stress factors.info:eu-repo/semantics/acceptedVersio

Negative relationship between woody species density and size of urban green spaces in seven European cities

Urban green spaces (UGSs) are important elements of urban landscapes. Woody vegetation is a key component of UGSs, providing many socio-ecological benefits such as habitat provision and human well-being. Knowing plant diversity and vegetation configuration that underpin urban ecosystem processes and functions is critical to maximize nature contributions to city dwellers. Here, we present a well-replicated multi-city study showing a detailed description of taxonomic and structural diversity of woody vegetation in 225 UGSs distributed across seven European cities along a NE-SW gradient. Our aim was to understand how UGSs attributes, including size and fragmentation, influence woody vegetation features. A total of 418 woody species belonging to 76 families were identified. UGS size displayed weak positive correlations with woody species richness, but a strong negative correlation with woody species density. Alien woody species were abundant in all cities (from 40% of all species recorded in Antwerp to 64% in Lisbon and Zurich). Among the native tree species we found a predominance of Pinus spp. in southern cities and Acer spp. in cooler climates. On average, tree canopies extent was 56% of UGSs. This paper provides insights on the plant diversity and woody vegetation composition in UGSs of different size, climate and urban planning history. Our results encourage and contribute to future urban ecology studies involving different taxa and ecosystem services as well as support effective urban planning and management practices.info:eu-repo/semantics/acceptedVersio

How do urban green space designs shape avian communities? Testing the area–heterogeneity trade-off

In cities, green areas are essential for biodiversity conservation, with land cover heterogeneity being a decisive factor. Yet, as heterogeneity increases for a given green area, the patch size of land covers automatically decreases, as the area available for individual species, especially habitat specialist species. This relationship, known as the area-heterogeneity trade-off, is expected to lead to a unimodal relationship between species richness and land cover heterogeneity, and contrasted effects between species according to their level of urban avoidance. We investigated the potential consequences of this trade-off on birds in green areas selected along an urban intensity gradient in six European cities. Using a European database on bird occurrences in nesting habitats, we defined a continuous gradient of urban avian avoidance. We confirmed the marked area-heterogeneity trade-off in urban green areas but found no effect of land cover heterogeneity on total avian richness at green area level. However, both land cover heterogeneity and patch size were positively associated with richness of urban avoider species, indicating that urban avoiders fared better in green areas with large and heterogeneous patches. Total richness was also higher in green areas surrounded by an urban matrix composed of a variety of land covers. To protect urban bird avoiders, which are most at risk in cities, green area managers and urban planners should thus be aware that land cover heterogeneity is not a panacea if patch sizes are too small. To conserve avian richness, we stress the importance of maintaining large vegetated areas as well as heterogeneity in land covers within the urban matrix.info:eu-repo/semantics/acceptedVersio