Characterisation of the Carpinus betulus L. Phyllomicrobiome in Urban and Forest Areas

Unraveling two decades of phyllosphere endophytes: tracing research trends and insights through visualized knowledge maps, with emphasis on microbial interactions as emerging frontiers

Phyllosphere endophytes play a critical role in a myriad of biological functions, such as maintaining plant health and overall fitness. They play a determinative role in crop yield and quality by regulating vital processes, such as leaf functionality and longevity, seed mass, apical growth, flowering, and fruit development. This study conducted a comprehensive bibliometric analysis aiming to review the prevailing research trajectories in phyllosphere endophytes and harness both primary areas of interest and emerging challenges. A total of 156 research articles on phyllosphere endophytes, published between 2002 and 2022, were retrieved from the Web of Science Core Collection (WoSCC). A systematic analysis was conducted using CiteSpace to visualize the evolution of publication frequency, the collaboration network, the co-citation network, and keywords co-occurrence. The findings indicated that initially, there were few publications on the topic of phyllosphere endophytes. However, from 2011 onwards, there was a notable increase in the number of publications on phyllosphere endophytes, gaining worldwide attention. Among authors, Arnold, A Elizabeth is widely recognized as a leading author in this research area. In terms of countries, the USA and China hold the highest rankings. As for institutional ranking, the University of Arizona is the most prevalent and leading institute in this particular subject. Collaborative efforts among the authors and institutions tend to be confined to small groups, and a large-scale collaborative network needs to be established. This study identified the influential journals, literature, and hot research topics. These findings also highlight the interconnected nature of key themes, e.g., phyllosphere endophyte research revolves around the four pillars: diversity, fungal endophytes, growth, and endophytic fungi. This study provides an in-depth perspective on phyllosphere endophytes studies, revealing the identification of biodiversity and microbial interaction of phyllosphere endophytes as the principal research frontiers. These analytical findings not only elucidate the recent trajectory of phyllosphere endophyte research but also provide invaluable insights for similar studies and their potential applications on a global scale.

The Good, the Bad, and the Useable Microbes within the Common Alder (Alnus glutinosa) Microbiome-Potential Bio-Agents to Combat Alder Dieback

Common Alder (Alnus glutinosa (L.) Gaertn.) is a tree species native to Ireland and Europe with high economic and ecological importance. The presence of Alder has many benefits including the ability to adapt to multiple climate types, as well as aiding in ecosystem restoration due to its colonization capabilities within disturbed soils. However, Alder is susceptible to infection of the root rot pathogen Phytophthora alni, amongst other pathogens associated with this tree species. P. alni has become an issue within the forestry sector as it continues to spread across Europe, infecting Alder plantations, thus affecting their growth and survival and altering ecosystem dynamics. Beneficial microbiota and biocontrol agents play a crucial role in maintaining the health and resilience of plants. Studies have shown that beneficial microbes promote plant growth as well as aid in the protection against pathogens and abiotic stress. Understanding the interactions between A. glutinosa and its microbiota, both beneficial and pathogenic, is essential for developing integrated management strategies to mitigate the impact of P. alni and maintain the health of Alder trees. This review is focused on collating the relevant literature associated with Alder, current threats to the species, what is known about its microbial composition, and Common Alder-microbe interactions that have been observed worldwide to date. It also summarizes the beneficial fungi, bacteria, and biocontrol agents, underpinning genetic mechanisms and secondary metabolites identified within the forestry sector in relation to the Alder tree species. In addition, biocontrol mechanisms and microbiome-assisted breeding as well as gaps within research that require further attention are discussed.

Ozone pollution, water deficit stress and time drive poplar phyllospheric bacterial community structure

Ground-level ozone (O₃) pollution often rise in the summer and coincide with drought stress, which alters the relationships between trees and associated microbial communities in a manner that can have pronounced effects on associated biological activity and ecosystem integrity. Discerning the responses of phyllosphere microbial communities to O₃ and water deficit could highlight the ability of plant-microbe interactions to either exacerbate or mitigate the effects of these stressors. Accordingly, this study was designed as the first report to specifically interrogate the impacts of elevated O₃ and water deficit stress on phyllospheric bacterial community composition and diversity in hybrid poplar saplings. Significant reductions in phyllospheric bacterial alpha diversity indices were observed, with clear evidence of significant time × water deficit stress interactions. The combination of elevated O₃ and water deficit stress shifted in the bacterial community composition over sampling time, resulted in significant increases in the relative abundance of the dominant Gammaproteobacteria phyla together with reductions in Betaproteobacteria. An increased prevalence of Gammaproteobacteria may represent a potential diagnostic dysbiosis-related biosignature associated with poplar disease risk. Significant positive correlations were observed between both Betaproteobacteria abundance and diversity indices and key foliar photosynthetic traits and isoprene emissions, whereas these parameters were negatively correlated with Gammaproteobacteria abundance. These findings suggest that the photosynthesis-related properties in plant leaves are closely related to the makeup of the phyllosphere bacterial community. These data provide novel insight into how plant-associated microbes can help maintain plant health and the stability of the local ecosystem in O₃-polluted and dried environments.

Plant identity shapes phyllosphere microbiome structure and abundance of genes involved in nutrient cycling

The phyllosphere is a fluctuant micro-environment habitat that harbors diverse microbial communities that have the potential to influence plant growth through their effect on host fitness. However, we know little about the driving factors of phyllosphere microbial functional traits, e.g., genes related to nutrient cycling and microbial community structure under anthropic disturbance. Here, we characterized phyllosphere microbial communities and the abundance of genes related to nutrient cycling from diverse plant species between urban and natural habitats. We measured leaf functional traits to investigate the potential drivers of the phyllosphere microbial profile. Results indicated that phyllosphere microbial communities differed significantly between urban and natural habitats, and that this variation was dependent upon plant species. Host plant species had a greater influence on the abundance of genes involved in nutrient cycling in the phyllosphere than habitat. In addition, phyllosphere microbial diversity and functional gene abundance were significantly correlated. Furthermore, host leaf functional traits (e.g., specific leaf area and nutrient content) were potential driving factors of both phyllosphere microbial community structure and the abundance of genes involved in nutrient cycling. These findings contribute to a better understanding of the phyllosphere microbiome and its biotic and abiotic controlling factors, which improves our understanding of plant-microbe interactions and their ecosystem functions under anthropic disturbance.

Urbanization Reduces Phyllosphere Microbial Network Complexity and Species Richness of Camphor Trees

Studies on microbial communities associated with foliage in natural ecosystems have grown in number in recent years yet have rarely focused on urban ecosystems. With urbanization, phyllosphere microorganisms in the urban environment have come under pressures from increasing human activities. To explore the effects of urbanization on the phyllosphere microbial communities of urban ecosystems, we investigated the phyllosphere microbial structure and the diversity of camphor trees in eight parks along a suburban-to-urban gradient. The results showed that the number of ASVs (amplicon sequence variants), unique on the phyllosphere microbial communities of three different urbanization gradients, was 4.54 to 17.99 times higher than that of the shared ASVs. Specific microbial biomarkers were also found for leaf samples from each urbanization gradient. Moreover, significant differences (R² = 0.133, p = 0.005) were observed in the phyllosphere microbial structure among the three urbanization gradients. Alpha diversity and co-occurrence patterns of bacterial communities showed that urbanization can strongly reduce the complexity and species richness of the phyllosphere microbial network of camphor trees. Correlation analysis with environmental factors showed that leaf total carbon (C), nitrogen (N), and sulfur (S), as well as leaf C/N, soil pH, and artificial light intensity at night (ALIAN) were the important drivers in determining the divergence of phyllosphere microbial communities across the urbanization gradient. Together, we found that urbanization can affect the composition of the phyllosphere bacterial community of camphor trees, and that the interplay between human activities and plant microbial communities may contribute to shaping the urban microbiome.

Above- and below-ground microbiome in the annual developmental cycle of two olive tree varieties

The olive tree is a hallmark crop in the Mediterranean region. Its cultivation is characterized by an enormous variability in existing genotypes and geographical areas. As regards the associated microbial communities of the olive tree, despite progress, we still lack comprehensive knowledge in the description of these key determinants of plant health and productivity. Here, we determined the prokaryotic, fungal and arbuscular mycorrhizal fungal (AMF) microbiome in below- (rhizospheric soil, roots) and above-ground (phyllosphere and carposphere) plant compartments of two olive varieties 'Koroneiki' and 'Chondrolia Chalkidikis' grown in Southern and Northern Greece respectively, in five developmental stages along a full fruit-bearing season. Distinct microbial communities were supported in above- and below-ground plant parts; while the former tended to be similar between the two varieties/locations, the latter were location specific. In both varieties/locations, a seasonally stable root microbiome was observed over time; in contrast the plant microbiome in the other compartments were prone to changes over time, which may be related to seasonal environmental change and/or to plant developmental stage. We noted that olive roots exhibited an AMF-specific filtering effect (not observed for bacteria and general fungi) onto the rhizosphere AMF communities of the two olive varieties/locations/, leading to the assemblage of homogenous intraradical AMF communities. Finally, shared microbiome members between the two olive varieties/locations include bacterial and fungal taxa with putative functional attributes that may contribute to olive tree tolerance to abiotic and biotic stress.

Elevated O3 concentrations alter the compartment-specific microbial communities inhabiting rust-infected poplars

Elevated ozone (O₃ ) can affect the susceptivity of plants to rust pathogens. However, the collective role of microbiomes involved in such interaction remains largely elusive. We exposed two cultivated poplar clones exhibiting differential O₃ sensitivities, to non-filtered ambient air (NF), NF + 40 ppb or NF + 60 ppb O₃ -enriched air in field open-top chambers and then inoculated Melampsora larici-populina urediniospores to study their response to rust infection and to investigate how microbiomes inhabiting four compartments (phyllosphere, rhizosphere, root endosphere, bulk soil) are involved in this response. We found that hosts with higher O₃ sensitivity had significantly lower rust severity than hosts with lower sensitivity. Furthermore, the effect of increased O₃ on the diversity and composition of microbial communities was highly dependent on poplar compartments, with the microbial network complexity patterns being completely opposite between the two clones. Notably, microbial source analysis estimated that phyllosphere fungal communities predominately derived from root endosphere and vice versa, suggesting a potential transmission mechanism between plant above- and below-ground systems. These promising results suggest that further investigations are needed to better understand the interactions of abiotic and biotic stresses on plant performance and the role of the microbiome in driving these changes.

Quercus ilex Phyllosphere Microbiome Environmental-Driven Structure and Composition Shifts in a Mediterranean Contex

The intra- and interdomain phyllosphere microbiome features of Quercus ilex L. in a Mediterranean context is reported. We hypothesized that the main driver of the phyllosphere microbiome might be the season and that atmospheric pollutants might have a co-effect. Hence, we investigated the composition of epiphytic bacteria and fungi of leaves sampled in urban and natural areas (in Southern Italy) in summer and winter, using microscopy and metagenomic analysis. To assess possible co-effects on the composition of the phyllosphere microbiome, concentrations of particulate matter and polycyclic aromatic hydrocarbons (PAHs) were determined from sampled leaves. We found that environmental factors had a significative influence on the phyllosphere biodiversity, altering the taxa relative abundances. Ascomycota and Firmicutes were higher in summer and in urban areas, whereas a significant increase in Proteobacteria was observed in the winter season, with higher abundance in natural areas. Network analysis suggested that OTUs belonging to Acidobacteria, Cytophagia, unkn. Firmicutes(p), Actinobacteria are keystone of the Q. ilex phyllosphere microbiome. In addition, 83 genes coding for 5 enzymes involved in PAH degradation pathways were identified. Given that the phyllosphere microbiome can be considered an extension of the ecosystem services offered by trees, our results can be exploited in the framework of Next-Generation Biomonitoring.

Pathways to engineering the phyllosphere microbiome for sustainable crop production

Current disease resistance breeding, which is largely dependent on the exploitation of resistance genes in host plants, faces the serious challenges of rapidly evolving phytopathogens. The phyllosphere is the largest biological surface on Earth and an untapped reservoir of functional microbiomes. The phyllosphere microbiome has the potential to defend against plant diseases. However, the mechanisms of how the microbiota assemble and function in the phyllosphere remain largely elusive, and this restricts the exploitation of the targeted beneficial microbes in the field. Here we review the endogenous and exogenous cues impacting microbiota assembly in the phyllosphere and how the phyllosphere microbiota in turn facilitate the disease resistance of host plants. We further construct a holistic framework by integrating of holo-omics, genetic manipulation, culture-dependent characterization and emerging artificial intelligence techniques, such as deep learning, to engineer the phyllosphere microbiome for sustainable crop production.

New opportunities in plant microbiome engineering for increasing agricultural sustainability under stressful conditions

Plant microbiome (or phytomicrobiome) engineering (PME) is an anticipated untapped alternative strategy that could be exploited for plant growth, health and productivity under different environmental conditions. It has been proven that the phytomicrobiome has crucial contributions to plant health, pathogen control and tolerance under drastic environmental (a)biotic constraints. Consistent with plant health and safety, in this article we address the fundamental role of plant microbiome and its insights in plant health and productivity. We also explore the potential of plant microbiome under environmental restrictions and the proposition of improving microbial functions that can be supportive for better plant growth and production. Understanding the crucial role of plant associated microbial communities, we propose how the associated microbial actions could be enhanced to improve plant growth-promoting mechanisms, with a particular emphasis on plant beneficial fungi. Additionally, we suggest the possible plant strategies to adapt to a harsh environment by manipulating plant microbiomes. However, our current understanding of the microbiome is still in its infancy, and the major perturbations, such as anthropocentric actions, are not fully understood. Therefore, this work highlights the importance of manipulating the beneficial plant microbiome to create more sustainable agriculture, particularly under different environmental stressors.

Strategic roadmap to assess forest vulnerability under air pollution and climate change

Although it is an integral part of global change, most of the research addressing the effects of climate change on forests have overlooked the role of environmental pollution. Similarly, most studies investigating the effects of air pollutants on forests have generally neglected the impacts of climate change. We review the current knowledge on combined air pollution and climate change effects on global forest ecosystems and identify several key research priorities as a roadmap for the future. Specifically, we recommend (1) the establishment of much denser array of monitoring sites, particularly in the South Hemisphere; (2) further integration of ground and satellite monitoring; (3) generation of flux-based standards and critical levels taking into account the sensitivity of dominant forest tree species; (4) long-term monitoring of N, S, P cycles and base cations deposition together at global scale; (5) intensification of experimental studies, addressing the combined effects of different abiotic factors on forests by assuring a better representation of taxonomic and functional diversity across the ~73,000 tree species on Earth; (6) more experimental focus on phenomics and genomics; (7) improved knowledge on key processes regulating the dynamics of radionuclides in forest systems; and (8) development of models integrating air pollution and climate change data from long-term monitoring programs.

Effects of elevated ozone on bacterial communities inhabiting the phyllo- and endo-spheres of rice plants

To explore the effects of elevated ozone (O₃) on microbial communities inhabiting phyllo- and endo-spheres of Japonica rice leaves, cultivars Nangeng 5055 (NG5055) and Wuyujing 27 (WYJ27) were grown in either charcoal-filtered air (CF) or elevated O₃ (ambient O₃ + 40 ppb, E-O₃) in field open-top chambers (OTCs) during a growing season. E-O₃ increased the values of the Shannon (43-80%) and Simpson (34-51%) indexes of the phyllo-and endo-spheric bacterial communities in NG5055. E-O₃ also increased the values of the phyllosphere Simpson index by 58% and the endosphere Shannon index by 54% in WYJ27. Both diversity indexes positively correlated with the contents of nitrogen, phosphorus, magnesium, and soluble sugar, and negatively correlated with the contents of starch and condensed tannins. The leaf-associated bacterial community composition significantly changed in both rice cultivars under E-O₃. Moreover, the leaf-associated bacterial communities in NG5055 were more sensitive to E-O₃ than those in WYJ27. The chemical properties explained 70% and 98% of variations in the phyllosphere and endosphere bacterial communities, respectively, suggesting a predominant role of chemical status for the endospheric bacterial community. Most variation (57.3%) in the endosphere bacterial community assembly was explained by phosphorus. Gammaproteobacteria and Pantoea were found to be the most abundant class (63-76%) and genus (38-48%) in the phyllosphere and endosphere, respectively. E-O₃ significantly increased the relative abundance of Bacteroidetes in the phyllosphere bacterial community and decreased the relative abundance of Gammaproteobacteria in the endophytic community. In conclusion, elevated O₃ increased the diversity of bacterial communities of leaf phyllosphere and endosphere, and leaf chemical properties had a more pronounced effect on the endosphere bacterial community.

Plant-microbe interactions in the phyllosphere: facing challenges of the anthropocene

Global change is a defining feature of the Anthropocene, the current human-dominated epoch, and poses imminent threats to ecosystem dynamics and services such as plant productivity, biodiversity, and environmental regulation. In this era, terrestrial ecosystems are experiencing perturbations linked to direct habitat modifications as well as indirect effects of global change on species distribution and extreme abiotic conditions. Microorganisms represent an important reservoir of biodiversity that can influence macro-organisms as they face habitat loss, rising atmospheric CO₂ concentration, pollution, global warming, and increased frequency of drought. Plant-microbe interactions in the phyllosphere have been shown to support plant growth and increase host resistance to biotic and abiotic stresses. Here, we review how plant-microbe interactions in the phyllosphere can influence host survival and fitness in the context of global change. We highlight evidence that plant-microbe interactions (1) improve urban pollution remediation through the degradation of pollutants such as ultrafine particulate matter, black carbon, and atmospheric hydrocarbons, (2) have contrasting impacts on plant species range shifts through the loss of symbionts or pathogens, and (3) drive plant host adaptation to drought and warming. Finally, we discuss how key community ecology processes could drive plant-microbe interactions facing challenges of the Anthropocene.

Exploring the Diversity and Aromatic Hydrocarbon Degrading Potential of Epiphytic Fungi on Hornbeams from Chronically Polluted Areas

Plants can ‘catch’ and mitigate airborne pollutants and are assisted by fungi inhabiting their leaves. The structure and function of the fungal communities inhabiting the phyllosphere of hornbeam trees growing in two chronically polluted areas, the oilfield of Bóbrka and the city center of Warsaw, were compared to the ones growing in one nature reserve, the Białowieża National Park. Fungi were isolated and characterized both phylogenetically and functionally for their potential role in air pollution mitigation. Both culture-dependent (e.g., enzyme assays and tolerance tests) and culture-independent methods (e.g., ITS and shotgun sequencings) were used. Furthermore, the degradation potential of the fungi was assessed by gas chromatography mass spectrometry (GC-MS). Shotgun sequencing showed that the phyllosphere fungal communities were dominated by fungi belonging to the phylum Ascomycota. Aureobasidium was the only genus detected at the three locations with a relative abundance ≥1.0%. Among the cultivated epiphytic fungi from Bóbrka, Fusarium sporotrichioides AT11, Phoma herbarum AT15, and Lophiostoma sp. AT37 showed in vitro aromatic hydrocarbon degradation potential with laccase activities of 1.24, 3.62, and 7.2 μU L⁻¹, respectively, and peroxidase enzymes with activities of 3.46, 2.28, and 7.49 μU L⁻¹, respectively. Furthermore, Fusarium sporotrichioides AT11 and Phoma herbarum AT15 tolerated exposure to airborne naphthalene and benzene. Lophiostoma sp. AT37 was the most tolerant to exposure to these pollutants, in line with being the best potential aromatic hydrocarbon degrader isolated in this study.

Ambient Air Pollution Shapes Bacterial and Fungal Ivy Leaf Communities

Ambient air pollution exerts deleterious effects on our environment. Continuously exposed to the atmosphere, diverse communities of microorganisms thrive on leaf surfaces, the phylloplane. The composition of these communities is dynamic, responding to many environmental factors including ambient air pollution. In this field study, over a 2 year period, we sampled Hedera helix (ivy) leaves at six locations exposed to different ambient air pollution conditions. Daily, we monitored ambient black carbon (BC), PM_2.5, PM₁₀, nitrogen dioxide, and ozone concentrations and found that ambient air pollution led to a 2–7-fold BC increase on leaves, the phylloplane BC load. Our results further indicated that the phylloplane BC load correlates with the diversity of bacterial and fungal leaf communities, impacting diversity more than seasonal effects. The bacterial genera Novosphingobium, Hymenobacter, and Methylorubrum, and the fungal genus Ampelomyces were indicators for communities exposed to the highest phylloplane BC load. Parallel to this, we present one fungal and two bacterial phylloplane strains isolated from an air-polluted environment able to degrade benzene, toluene, and/or xylene, including a genomics-based description of the degradation pathways involved. The findings of this study suggest that ambient air pollution shapes microbial leaf communities, by affecting diversity and supporting members able to degrade airborne pollutants.

Canopy Position Has a Stronger Effect than Tree Species Identity on Phyllosphere Bacterial Diversity in a Floodplain Hardwood Forest

The phyllosphere is a challenging microbial habitat in which microorganisms can flourish on organic carbon released by plant leaves but are also exposed to harsh environmental conditions. Here, we assessed the relative importance of canopy position-top, mid, and bottom at a height between 31 and 20 m-and tree species identity for shaping the phyllosphere microbiome in a floodplain hardwood forest. Leaf material was sampled from three tree species-maple (Acer pseudoplatanus L.), oak (Quercus robur L.), and linden (Tilia cordata MILL.)-at the Leipzig canopy crane facility (Germany). Estimated bacterial species richness (Chao1) and bacterial abundances approximated by quantitative PCR of 16S rRNA genes exhibited clear vertical trends with a strong increase from the top to the mid and bottom position of the canopy. Thirty operational taxonomic units (OTUs) formed the core microbiome, which accounted for 77% of all sequence reads. These core OTUs showed contrasting trends in their vertical distribution within the canopy, pointing to different ecological preferences and tolerance to presumably more extreme conditions at the top position of the canopy. Co-occurrence analysis revealed distinct tree species-specific OTU networks, and 55-57% of the OTUs were unique to each tree species. Overall, the phyllosphere microbiome harbored surprisingly high fractions of Actinobacteria of up to 66%. Our results clearly demonstrate strong effects of the position in the canopy on phyllosphere bacterial communities in a floodplain hardwood forest and-in contrast to other temperate or tropical forests-a strong predominance of Actinobacteria.

Cryphonectria carpinicola sp. nov. Associated with hornbeam decline in Europe

Since the early 2000s, reports on declining hornbeam trees (Carpinus betulus) are spreading in Europe. Two fungi are involved in the decline phenomenon: One is Anthostoma decipiens, but the other etiological agent has not been identified yet. We examined the morphology, phylogenetic position, and pathogenicity of yellow fungal isolates obtained from hornbeam trees from Austria, Georgia and Switzerland, and compared data with disease reports from northern Italy documented since the early 2000s. Results demonstrate distinctive morphology and monophyletic status of Cryphonectria carpinicola sp. nov. as etiological agent of the European hornbeam decline. Interestingly, the genus Cryphonectria splits into two major clades. One includes Cry. carpinicola together with Cry. radicalis, Cry. decipiens and Cry. naterciae from Europe, while the other comprises species known from Asia-suggesting that the genus Cryphonectria has developed at two evolutionary centres, one in Europe and Asia Minor, the other in East Asia. Pathogenicity studies confirm that Car. betulus is a major host species of Cry. carpinicola. This clearly distinguished Cry. carpinicola from other Cryphonectria species, which mainly occur on Castanea and Quercus.

Metagenome-assembled genome distribution and key functionality highlight importance of aerobic metabolism in Svalbard permafrost

Permafrost underlies a large portion of the land in the Northern Hemisphere. It is proposed to be an extreme habitat and home for cold-adaptive microbial communities. Upon thaw permafrost is predicted to exacerbate increasing global temperature trend, where awakening microbes decompose millennia old carbon stocks. Yet our knowledge on composition, functional potential and variance of permafrost microbiome remains limited. In this study, we conducted a deep comparative metagenomic analysis through a 2 m permafrost core from Svalbard, Norway to determine key permafrost microbiome in this climate sensitive island ecosystem. To do so, we developed comparative metagenomics methods on metagenomic-assembled genomes (MAG). We found that community composition in Svalbard soil horizons shifted markedly with depth: the dominant phylum switched from Acidobacteria and Proteobacteria in top soils (active layer) to Actinobacteria, Bacteroidetes, Chloroflexi and Proteobacteria in permafrost layers. Key metabolic potential propagated through permafrost depths revealed aerobic respiration and soil organic matter decomposition as key metabolic traits. We also found that Svalbard MAGs were enriched in genes involved in regulation of ammonium, sulfur and phosphate. Here, we provide a new perspective on how permafrost microbiome is shaped to acquire resources in competitive and limited resource conditions of deep Svalbard soils.

Ozone affects plant, insect, and soil microbial communities: A threat to terrestrial ecosystems and biodiversity

Elevated tropospheric ozone concentrations induce adverse effects in plants. We reviewed how ozone affects (i) the composition and diversity of plant communities by affecting key physiological traits; (ii) foliar chemistry and the emission of volatiles, thereby affecting plant-plant competition, plant-insect interactions, and the composition of insect communities; and (iii) plant-soil-microbe interactions and the composition of soil communities by disrupting plant litterfall and altering root exudation, soil enzymatic activities, decomposition, and nutrient cycling. The community composition of soil microbes is consequently changed, and alpha diversity is often reduced. The effects depend on the environment and vary across space and time. We suggest that Atlantic islands in the Northern Hemisphere, the Mediterranean Basin, equatorial Africa, Ethiopia, the Indian coastline, the Himalayan region, southern Asia, and Japan have high endemic richness at high ozone risk by 2100.

Drivers of Foliar Fungal Endophytic Communities of Kudzu (Pueraria montana var. lobata) in the Southeast United States

Fungal endophytes play important roles in plant fitness and plant–microbe interactions. Kudzu (Pueraria montana var. lobata) is a dominant, abundant, and highly aggressive invasive plant in the Southeast United States. Kudzu serves as a pathogen reservoir that impacts economically important leguminous crops. We conducted the first investigations on kudzu fungal endophytes (Illumina MiSeq—ITS2) to elucidate drivers of endophytic communities across the heart of the invasive range in the Southeast United States (TN, MS, AL, GA). We tested the impacts of multiple environmental parameters (Chlorophyll, NO3−, K+, soil pH, leaf area, host genotype, traffic intensity, and geographic location) on foliar endophyte communities. Endophytic communities were diverse and structured by many factors in our PerMANOVA analyses, but location, genotype, and traffic (proxy for pollution) were the strongest drivers of community composition (R2 = 0.152, p < 0.001, R2 = 0.129, p < 0.001, and R2 = 0.126, p < 0.001, respectively). Further, we examined the putative ecological interactions between endophytic fungi and plant pathogens. We identify numerous OTUs that are positively and strongly associated with pathogen occurrence, largely within the families Montagnulaceae and Tremellales incertae sedis. Taken together, these data suggest location, host genetics and local pollution play instrumental roles in structuring communities, and integrative plant management must consider these factors when developing management strategies.

Plant-microorganisms interaction promotes removal of air pollutants in Milan (Italy) urban area

Plants and phyllosphere microorganisms may effectively contribute to reducing air pollution in cities through the adsorption and biodegradation of pollutants onto leaves. In this work, during all seasons, we sampled atmospheric particulate matter (PM₁₀) and leaves of southern magnolia Magnolia grandiflora and deodar cedar Cedrus deodara, two evergreen plant species widespread in the urban area of Milan where the study was carried out. We then quantified Polycyclic Aromatic Hydrocarbons (PAHs) both in PM₁₀ and on leaves and used sequencing of 16S rRNA gene, shotgun metagenomics and qPCR analyses to investigate the microbial communities hosted by the sampled leaves. Taxonomic and functional profiles of epiphytic bacterial communities differed between host plant species and seasons and the microbial communities on leaves harboured genes involved in the degradation of hydrocarbons. Evidence collected in this work also suggested that the abundance of hydrocarbon-degrading microorganisms on evergreen leaves increased with the concentration of hydrocarbons when atmospheric pollutants were deposited at high concentration on leaves, and that the biodegradation on the phyllosphere can contribute to the removal of PAHs from the urban air.