Highly Heterogeneous Soil Bacterial Communities around Terra Nova Bay of Northern Victoria Land,Antarctica

Given the diminished role of biotic interactions in soils of continental Antarctica, abiotic factors are believed to play a dominant role in structuring of microbial communities. However, many ice-free regions remain unexplored, and it is unclear which environmental gradients are primarily responsible for the variations among bacterial communities. In this study, we investigated the soil bacterial community around Terra Nova Bay of Victoria Land by pyrosequencing and determined which environmental variables govern the bacterial community structure at the local scale. Six bacterial phyla, Actinobacteria, Proteobacteria, Acidobacteria, Chloroflexi, Cyanobacteria, and Bacteroidetes, were dominant, but their relative abundance varied greatly across locations. Bacterial community structures were affected little by spatial distance, but structured more strongly by site, which was in accordance with the soil physicochemical compositions. At both the phylum and species levels, bacterial community structure was explained primarily by pH and water content, while certain earth elements and trace metals also played important roles in shaping community variation. The higher heterogeneity of the bacterial community structure found at this site indicates how soil bacterial communities have adapted to different compositions of edaphic variables under extreme environmental conditions. Taken together, these findings greatly advance our understanding of the adaption of soil bacterial populations to this harsh environment.     

Effects of ecological environment and host genotype on the phyllosphere bacterial communities of cigar tobacco (Nicotiana tabacum L.)

Microorganisms of plant phyllosphere play an important role in plant health and productivity and are influenced by abiotic and biotic factors. In this study, we investigated the phyllosphere bacterial communities of three cigar tobacco varieties cultivated in Guangcun (GC) and Wuzhishan (WZS), Hainan, China. Metagenomic DNA was extracted from tobacco leaf samples and sequenced by 16S rDNA amplicon sequencing. Our results showed that bacterial communities of cigar tobacco phyllosphere in GC exhibited remarkably higher alpha diversity than that in WZS. There was slight effect of tobacco genotype variations on the alpha diversity in both cultivation sites, and beta diversity and structure of bacterial community were not influenced significantly by the cultivation sites and tobacco varieties. Statistical analyses of species diversity unraveled that the dominant species in bacterial communities of cigar tobacco phyllosphere among all these samples were phylogenetically affiliated to Proteobacteria and Cyanobacteria. At the genus level, the most abundant microorganism was Limnobacter, followed by Brevundimonas, unidentified_Cyanobacteria, and Pseudomonas. Additionally, environmental conditions except for humidity were negatively correlated with the relative abundance of bacterial genera. Further analyses revealed that influence of site‐specific factors on tobacco bacterial community was relatively higher than genotype‐specific factors. In short, this study may contribute to the knowledge base of practical applications of bacterial inoculants for tobacco leaf production.     

盐城滨海滩涂湿地典型植物群落土壤微生物组成与结构特征

土壤微生物是生态系统维持正常结构与功能的重要组成部分,为探究盐城滩涂典型湿地土壤微生物群落结构特征,以江苏盐城滩涂互花米草、藨草、盐地碱蓬、芦苇及淤泥质光滩5种典型群落为对象,采用16S rRNA高通量测序技术分析0—10 cm(表层)、10—30 cm(中层)、30—60 cm(深层)土壤微生物多样性及群落结构。结果表明：(1)几种植物群落间,土壤微生物群落结构差异较大,主要体现在细菌群落结构的差异性,古菌群落结构差异相对较小。光滩与植物群落间,在土壤细菌种类及相对丰度上差异相对较大,互花米草群落与本土植物群落间,在微生物群落的细菌种类组成上存在较大差异;藨草群落土壤表层微生物群落结构与互花米草群落相似,深层与盐地碱蓬、芦苇群落相似。(2)同一群落不同层次土壤微生物群落结构相似,差异小于不同群落间土壤微生物群落的结构差异性;不同群落对应层次间,表深层土壤中五种群落土壤微生物多样性存在显著差异,中层土壤中五种群落微生物多样性差异不显著。总体上,植物群落类型对土壤微生物群落结构的影响大于土壤深度;与本土植物群落相比,互花米草群落土壤主要优势门微生物种类差异较小,但部分优势门微生物相对丰度...     

Bacterial Community Assemblages Associated with the Phyllosphere,Dermosphere, and Rhizosphere of Tree Species of the Atlantic Forest are Host Taxon Dependent

Bacterial communities associated with tree canopies have been shown to be specific to their plant hosts, suggesting that plant species-specific traits may drive the selection of microbial species that comprise their microbiomes. To further examine the degree to which the plant taxa drive the assemblage of bacterial communities in specific plant microenvironments, we evaluated bacterial community structures associated with the phyllosphere, dermosphere, and rhizosphere of seven tree species representing three orders, four families and four genera of plants from a pristine Dense Ombrophilous Atlantic forest in Brazil, using a combination of PCR-DGGE of 16S rRNA genes and clone library sequencing. Results indicated that each plant species selected for distinct bacterial communities in the phyllosphere, dermosphere, and rhizosphere, and that the bacterial community structures are significantly related to the plant taxa, at the species, family, and order levels. Further characterization of the bacterial communities of the phyllosphere and dermosphere of the tree species showed that they were inhabited predominantly by species of Gammaproteobacteria, mostly related to Pseudomonas. In contrast, the rhizosphere bacterial communities showed greater species richness and evenness, and higher frequencies of Alphaproteobacteria and Acidobacteria Gp1. With individual tree species each selecting for their specific microbiomes, these findings greatly increase our estimates of the bacterial species richness in tropical forests and provoke questions concerning the ecological functions of the microbial communities that exist on different plant parts.     

Bacterial Communities Associated with Surfaces of Leafy Greens: Shift in Composition and Decrease in Richness over Time

The phyllosphere is colonized by a wide variety of bacteria and fungi; it harbors epiphytes, as well as plant-pathogenic bacteria and even human pathogens. However, little is known about how the bacterial community composition on leafy greens develops over time. The bacterial community of the leafy-green phyllosphere obtained from two plantings of rocket salad (Diplotaxis tenuifolia) and three plantings of lettuce (Lactuca sativa) at two farms in Norway were profiled by an Illumina MiSeq-based approach. We found that the bacterial richness of the L. sativa samples was significantly greater shortly (3 weeks) after planting than at harvest (5 to 7 weeks after planting) for plantings 1 and 3 at both farms. For the second planting, the bacterial diversity remained consistent at the two sites. This suggests that the effect on bacterial colonization of leaves, at least in part must, be seasonally driven rather than driven solely by leaf maturity. The distribution of phyllosphere communities varied between D. tenuifolia and L. sativa at harvest. The variability between these species at the same location suggests that the leaf-dwelling bacteria are not only passive inhabitants but interact with the host, which shapes niches favoring the growth of particular taxa. This work contributes to our understanding of host plant-specific microbial community structures and shows how these communities change throughout plant development.     

Effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on associated soil bacterial communities: A field‐based experiment

Loss of plant biodiversity can result in reduced abundance and diversity of associated species with implications for ecosystem functioning. In ecosystems low in plant species diversity, such as Neotropical mangrove forests, it is thought that genetic diversity within the dominant plant species could play an important role in shaping associated communities. Here, we used a manipulative field experiment to study the effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on the composition and richness of associated soil bacterial communities. Using terminal restriction fragment length polymorphism (T‐RFLP) community fingerprinting, we found that bacterial community composition differed among R. mangle maternal genotypes but not with genetic diversity. Bacterial taxa richness, total soil nitrogen, and total soil carbon were not significantly affected by maternal genotypic identity or genetic diversity of R. mangle. Our findings show that genotype selection in reforestation projects could influence soil bacterial community composition. Further research is needed to determine what impact these bacterial community differences might have on ecosystem processes, such as carbon and nitrogen cycling.     

Annual and Seasonal Variation in the Phyllosphere Bacterial Community Associated with Leaves of the Southern Magnolia (Magnolia grandiflora)

The phyllosphere contains a diverse bacterial community that can be intimately associated with the host plant; however, few studies have examined how the phyllosphere community changes over time. We sampled replicate leaves from a single magnolia (Magnolia grandiflora) tree in the winter of three consecutive years (2007?C2009) as well as during four seasons of 1?year (2008) and used molecular techniques to examine seasonal and year-to-year variation in bacterial community structure. Multivariate analysis of denaturing gradient gel electrophoresis profiles of 16S rRNA gene fragments revealed minimal leaf to leaf variation and much greater temporal changes, with the summer (August 2008) leaf community being most distinct from the other seasons. This was confirmed by sequencing and analysis of 16S rRNA gene clone libraries generated for each sample date. All phyllosphere communities were dominated by Alphaproteobacteria, with a reduction in the representation of certain Beijerinckiaceae during the summer and a concurrent increase in the Methylobacteriaceae being the most significant seasonal change. Other important components of the magnolia phyllosphere included members of the Bacteroidetes, Acidobacteria, and Actinobacteria, with the latter two lineages also showing differences in their representation in samples collected at different times. While the leaf-associated bacterial community sampled at the same time of year in three separate years showed some similarities, generally these communities were distinct, suggesting that while there are seasonal patterns, these may not be predictable from year to year. These results suggest that seasonal differences do occur in phyllosphere communities and that broad-leafed evergreen trees such as M. grandiflora may present interesting systems to study these changes in the context of changing environmental conditions.     

Variability of Bacterial Community Composition on Leaves Between and Within Plant Species

The phyllosphere is one of the largest habitats for terrestrial microorganisms. To gain a better insight into the factors underlying the composition of bacterial communities inhabiting leaf surfaces we performed culture-dependent and independent (Denaturing Gradient Gel Electrophoresis) analyses on the bacteria associated with the leaves of three plant species: Amygdalus communis, Citrus paradisi, and Nicotiana glauca. We found that the culturable classes Bacilli and Actinobacteria were the predominant classes on the phyllosphere of all three plant species. In contrast to this consistency on the bacterial class level, we found a significant variation on the bacterial species-level based on the culturable methods. Although some variation was detected among individual plants within one plant species, the inter-specific variability exceeded the intra-specific variability. C. paradisi leaf surface had the highest predicted total species richness (Chao 2 and ICE) and the highest species diversity (βw) among the three plant species. Our findings demonstrate that environmental conditions, mainly the plant species within a site, govern the bacterial community composition on leaf surfaces.     

Normal Operating Range of Bacterial Communities in Soil Used for Potato Cropping

In this study, the impacts of six potato (Solanum tuberosum) cultivars with different tuber starch allocations (including one genetically modified [GM] line) on the bacterial communities in field soil were investigated across two growth seasons interspersed with 1 year of barley cultivation, using quantitative PCR, clone library, and PCR-denaturing gradient gel electrophoresis (DGGE) analyses. It was hypothesized that the modifications in the tuber starch contents of these plants, yielding changed root growth rates and exudation patterns, might have elicited altered bacterial communities in the soil. The data showed that bacterial abundances in the bulk soil varied over about 2 orders of magnitude across the 3 years. As expected, across all cultivars, positive potato rhizosphere effects on bacterial abundances were noted in the two potato years. The bulk soil bacterial community structures revealed progressive shifts across time, and moving-window analysis revealed a 60% change over the total experiment. Consistent with previous findings, the community structures in the potato rhizosphere compartments were mainly affected by the growth stage of the plants and, to a lesser extent, by plant cultivar type. The data from the soil under the non-GM potato lines were then taken to define the normal operating range (NOR) of the microbiota under potatoes. Interestingly, the bacterial communities under the GM potato line remained within this NOR. In regard to the bacterial community compositions, particular bacterial species in the soil appeared to be specific to (i) the plant species under investigation (barley versus potato) or, with respect to potatoes, (ii) the plant growth stage. Members of the genera Arthrobacter, Streptomyces, Rhodanobacter, and Dokdonella were consistently found only at the flowering potato plants in both seasons, whereas Rhodoplanes and Sporosarcina were observed only in the soil planted to barley.     

The ecology of the phyllosphere: geographic and phylogenetic variability in the distribution of bacteria on tree leaves

Large populations of bacteria live on leaf surfaces and these phyllosphere bacteria can have important effects on plant health. However, we currently have a limited understanding of bacterial diversity on tree leaves and the inter‐ and intra‐specific variability in phyllosphere community structure. We used a barcoded pyrosequencing technique to characterize the bacterial communities from leaves of 56 tree species in Boulder, Colorado, USA, quantifying the intra‐ and inter‐individual variability in the bacterial communities from 10 of these species. We also examined the geographic variability in phyllosphere communities on Pinus ponderosa from several locations across the globe. Individual tree species harboured high levels of bacterial diversity and there was considerable variability in community composition between trees. The bacterial communities were organized in patterns predictable from the relatedness of the trees as there was significant correspondence between tree phylogeny and bacterial community phylogeny. Inter‐specific variability in bacterial community composition exceeded intra‐specific variability, a pattern that held even across continents where we observed minimal geographic differentiation in the bacterial communities on P. ponderosa needles.     

Conversion from natural wetlands to paddy field alters the composition of soil bacterial communities in Sanjiang Plain,Northeast China

The Sanjiang Plain is the largest freshwater wetlands in Northeast China. In order to feed the growing population, about 84 % of the wetlands in this area have been converted to farmland, especially to paddy fields, since the 1950s. However, little is known about the influence of this conversion on soil microbial community composition. In this study, soil samples were collected from two natural wetlands dominated by plant species Carex lasiocarpa and Deyeuxia angustifolia and from a neighboring paddy field that was changed from wetland more than 10 years ago. The composition and diversity of bacterial communities in the soils were estimated by clone library analysis of nearly full length of 16S rDNA sequences. The results revealed that bacterial diversity was higher in paddy fields, and that the composition of bacterial communities differed among the three samples; the difference was more notable between the paddy field and two natural wetlands than between two natural wetlands. The distribution of clones into different bacterial phyla differed among soil samples, and the conversion from natural wetlands to paddy field increased the abundance of Proteobacteria and Firmicutes but decreased the abundance of Chloroflexi. About 63 % and 71 % of clones from two natural wetlands and 49 % of clones from the paddy field had <93 % similarity with known bacteria, suggesting that the majority of bacteria in natural wetland soils in the Sanjiang Plain are phylogenetically novel. In general, this study demonstrated that long-term conversion from natural wetlands to paddy field changes soil bacterial communities in the Sanjiang Plain.     

Local soil characteristics determine the microbial communities under forest understorey plants along a latitudinal gradient

The soil microbial community is essential for maintaining ecosystem functioning and is intimately linked with the plant community. Yet, little is known on how soil microbial communities in the root zone vary at continental scales within plant species. Here we assess the effects of soil chemistry, large-scale environmental conditions (i.e. temperature, precipitation and nitrogen deposition) and forest land-use history on the soil microbial communities (measured by phospholipid fatty acids) in the root zone of four plant species (Geum urbanum, Milium effusum, Poa nemoralis and Stachys sylvatica) in forests along a 1700 km latitudinal gradient in Europe.Soil microbial communities differed significantly among plant species, and soil chemistry was the main determinant of the microbial community composition within each plant species. Influential soil chemical variables for microbial communities were plant species-specific; soil acidity, however, was often an important factor. Large-scale environmental conditions, together with soil chemistry, only explained the microbial community composition in M. effusum and P. nemoralis. Forest land-use history did not affect the soil microbial community composition.Our results underpin the dominant role of soil chemistry in shaping microbial community composition variation within plant species at the continental scale, and provide insights into the composition and functionality of soil microbial communities in forest ecosystems.     

The Soil Bacterial Communities of South African Fynbos Riparian Ecosystems Invaded by Australian Acacia Species

Riparian ecosystem along rivers and streams are characterised by lateral and longitudinal ecological gradients and, as a result, harbour unique biodiversity. Riparian ecosystems in the fynbos of the Western Cape, South Africa, are characterised by seasonal dynamics, with summer droughts followed by high flows during winter. The unique hydrology and geomorphology of riparian ecosystems play an important role in shaping these ecosystems. The riparian vegetation in the Western Cape has, however, largely been degraded due to the invasion of non-indigenous plants, in particular Acacia mearnsii, A. saligna and A. dealbata. This study investigated the effect of hydrology and invasion on the bacterial communities associated with fynbos riparian ecosystems. Bacterial communities were characterised with automated ribosomal intergenic spacer analysis (ARISA) and 454 16S rDNA pyrosequencing. Chemical and physical properties of soil within sites were also determined and correlated with community data. Sectioning across the lateral zones revealed significant differences in community composition, and the specific bacterial taxa influenced. Results also showed that the bacterial community structure could be linked to Acacia invasion. The presence of invasive Acacia was correlated with specific bacterial phyla. However, high similarity between cleared and pristine sites suggests that the effect of Acacia on the soil bacterial community structure may not be permanent. This study demonstrates how soil bacterial communities are influenced by hydrological gradients associated with riparian ecosystems and the impact of Acacia invasion on these communities.     

Comparison of Soil Bacterial Communities in Rhizospheres of Three Plant Species and the Interspaces in an Arid Grassland

Soil bacteria are important contributors to primary productivity and nutrient cycling in arid land ecosystems, and their populations may be greatly affected by changes in environmental conditions. In parallel studies, the composition of the total bacterial community and of members of the Acidobacterium division were assessed in arid grassland soils using terminal restriction fragment length polymorphism (TRF, also known as T-RFLP) analysis of 16S rRNA genes amplified from soil DNA. Bacterial communities associated with the rhizospheres of the native bunchgrasses Stipa hymenoides and Hilaria jamesii, the invading annual grass Bromus tectorum, and the interspaces colonized by cyanobacterial soil crusts were compared at three depths. When used in a replicated field-scale study, TRF analysis was useful for identifying broad-scale, consistent differences in the bacterial communities in different soil locations, over the natural microscale heterogeneity of the soil. The compositions of the total bacterial community and Acidobacterium division in the soil crust interspaces were significantly different from those of the plant rhizospheres. Major differences were also observed in the rhizospheres of the three plant species and were most apparent with analysis of the Acidobacterium division. The total bacterial community and the Acidobacterium division bacteria were affected by soil depth in both the interspaces and plant rhizospheres. This study provides a baseline for monitoring bacterial community structure and dynamics with changes in plant cover and environmental conditions in the arid grasslands.     

Dominance of Candidatus Scalindua species in anammox community revealed in soils with different duration of rice paddy cultivation in Northeast China

The anaerobic ammonium-oxidizing (anammox) bacteria play an important role in the oxygen-limited zone for nitrogen cycling, but their roles in agricultural ecosystems are still poorly understood. In this study, soil samples were taken from the rhizosphere and non-rhizosphere and from surface (0–5 cm) and subsurface (20–25 cm) layers with 1, 4, and 9 years of rice cultivation history on the typical albic soil of Northeast China to examine the diversity and distribution of anammox bacteria based on 16S rRNA gene and hydrazine oxidoreductase encoding gene (hzo). By comparing these soil samples, no obvious difference was observed in community composition between the rhizosphere and non-rhizosphere or the surface and subsurface layers. Surprisingly, anammox bacterial communities of these rice paddy soils were consisted of mainly Candidatus Scalindua species, which are best known to be dominant in marine and pristine environments. The highest diversity was revealed in the 4-year paddy soil based on clone library analysis. Phylogenetic analysis of 16S rRNA gene and deduced HZO from the corresponding encoding gene showed that most of the obtained clones are grouped together with Candidatus Scalindua sorokinii, Candidatus Scalindua brodae, and Candidatus Scalindua spp. of seawater. The obtained clone sequences from all samples are distributed in two subclusters that contain sequences from environmental samples only. Tentative new species were also discovered in this paddy soil. This study provides the first evidence on the existence of anammox bacteria with limited diversity in agricultural ecosystems in Northern China.     

Patterns of Bacterial Diversity Along a Long-Term Mercury-Contaminated Gradient in the Paddy Soils

Mercury (Hg) pollution is usually regarded as an environmental stress in reducing microbial diversity and altering bacterial community structure. However, these results were based on relatively short-term studies, which might obscure the real response of microbial species to Hg contamination. Here, we analysed the bacterial abundance and community composition in paddy soils that have been potentially contaminated by Hg for more than 600 years. Expectedly, the soil Hg pollution significantly influenced the bacterial community structure. However, the bacterial abundance was significantly correlated with the soil organic matter content rather than the total Hg (THg) concentration. The bacterial alpha diversity increased at relatively low levels of THg and methylmercury (MeHg) and subsequently approached a plateau above 4.86 mg kg^?1 THg or 18.62 ng g^?1 MeHg, respectively. Contrasting with the general prediction of decreasing diversity along Hg stress, our results seem to be consistent with the intermediate disturbance hypotheses with the peak biological diversity under intermediate disturbance or stress. This result was partly supported by the inconsistent response of bacterial species to Hg stress. For instance, the relative abundance of Nitrospirae decreased, while that of Gemmatimonadetes increased significantly along the increasing soil THg and MeHg concentrations. In addition, the content of SO₄ ^2?, THg, MeHg and soil depth were the four main factors influencing bacterial community structures based on the canonical correspondence analysis (CCA). Overall, our findings provide novel insight into the distribution patterns of bacterial community along the long-term Hg-contaminated gradient in paddy soils.     

Diversity and Activity of PAH-Degrading Bacteria in the Phyllosphere of Ornamental Plants

Phyllosphere bacteria on ornamental plants were characterized based on their diversity and activity towards the removal of polycyclic aromatic hydrocarbons (PAHs), the major air pollutants in urban area. The amounts of PAH-degrading bacteria were about 1–10% of the total heterotrophic phyllosphere populations and consisted of diverse bacterial species such as Acinetobacter, Pseudomonas, Pseudoxanthomonas, Mycobacterium, and uncultured bacteria. Bacterial community structures analyzed by polymerase chain reaction–denaturing gradient gel electrophoresis from each plant species showed distinct band patterns. The uniqueness of these phyllosphere bacterial communities was partly due to the variation in leaf morphology and chemical properties of ornamental plants. The PAH degradation activity of these bacteria was monitored in gas-tight systems containing sterilized or unsterilized leaves. The results indicated that phyllosphere bacteria on unsterilized leaves were able to enhance the activity of leaves for phenanthrene removal. When compared between plant species, phenanthrene removal efficiency corresponded to the size of phenanthrene-degrading bacteria. In addition, phyllosphere bacteria on Wrightia religiosa were able to reduce other PAHs such as acenaphthylene, acenaphthene, and fluorine in 60-ml glass vials and in a 14-l glass chamber. Thus, phyllosphere bacteria on ornamental plants may play an important role in natural attenuation of airborne PAHs in urban areas.     

A mosaic community of macrophytes for the ecological remediation of eutrophic shallow lakes

The restoration of macrophytes in eutrophic shallow lakes has been the focus of active research in the past decade. The approach of building up a mosaic community of macrophytes (MCMs) to improve water quality and remediate the ecosystems of lakes is proposed in this paper. Several species of floating, floating-leaved, and submerged macrophytes were introduced in experimental enclosures in eutrophic shallow lakes. These macrophytes were intercropped in small patches and formed mosaic communities of spatial and temporal combinations (spatial and seasonal mosaic patterns) in the lakes. Macrophytes can improve water transparency quickly and the MCM system can stabilize this clear water state over a long time in turbid eutrophic shallow lakes. The constructed MCM created heterogeneous habitats that are favourable for different macrophytes and for the growth and succession of other organisms, as well as for removing water pollutants. When the eutrophic water flowed through the MCM system at a retention time of 7 days, the removal efficiency rates of the MCM system for algae biomass, NH₄⁺–N, TN, TP and PO₄^3?–P were 58%, 66%, 60%, 72% and 80%, respectively.     

Responses of Bacterial Communities to Simulated Climate Changes in Alpine Meadow Soil of the Qinghai-Tibet Plateau

The soil microbial community plays an important role in terrestrial carbon and nitrogen cycling. However, microbial responses to climate warming or cooling remain poorly understood, limiting our ability to predict the consequences of future climate changes. To address this issue, it is critical to identify microbes sensitive to climate change and key driving factors shifting microbial communities. In this study, alpine soil transplant experiments were conducted downward or upward along an elevation gradient between 3,200 and 3,800 m in the Qinghai-Tibet plateau to simulate climate warming or cooling. After a 2-year soil transplant experiment, soil bacterial communities were analyzed by pyrosequencing of 16S rRNA gene amplicons. The results showed that the transplanted soil bacterial communities became more similar to those in their destination sites and more different from those in their “home” sites. Warming led to increases in the relative abundances in Alphaproteobacteria, Gammaproteobacteria, and Actinobacteria and decreases in Acidobacteria, Betaproteobacteria, and Deltaproteobacteria, while cooling had opposite effects on bacterial communities (symmetric response). Soil temperature and plant biomass contributed significantly to shaping the bacterial community structure. Overall, climate warming or cooling shifted the soil bacterial community structure mainly through species sorting, and such a shift might correlate to important biogeochemical processes such as greenhouse gas emissions. This study provides new insights into our understanding of soil bacterial community responses to climate warming and cooling.     

Changes amid constancy: Flower and leaf microbiomes along land use gradients and between bioregions

Microbial communities inhabiting above-ground parts of plants affect their host's development, fitness and function. Although studies on plant-associated microbes are of growing interest, environmental drivers of flower microbiomes in particular are poorly characterized. In this study, we investigated flower and leaf epiphytic bacterial microbiomes of Ranunculus acris and Trifolium pratense using metabarcoding of 16S ribosomal DNA in three German bioregions and along land-use intensity gradients. Our data suggests that the structures of bacterial communities clearly differed between plant species and tissue types. Also, floral bacterial communities of R. acris showed higher variability in comparison to T. pratense. Bacteria usually associated with pollinators were found solely in flower samples, while bacteria usually associated with the rhizosphere were only present in high abundances on leaves. We identified Pseudomonadaceae, Enterobacteriaceae and Sphingomonadaceae as the most abundant taxa on flowers, while Sphingomonadaceae, Methylobacteriaceae and Cytophagaceae dominated bacterial communities on leaves. We found that bacterial communities did not differ between long-distant regions. However, there was a turnover within each bioregion between short-distant locations. High land use intensity caused phylogenetically less diverse and more homogenous bacterial communities with an exception of T. pratense flowers. This was associated with a loss of rare bacterial families. Intensification of mowing affected the bacterial communities associated with leaves of T. pratense and fertilization led to more homogenous flower and leaf communities of R. acris, while grazing had no effects on the bacterial community composition. However, dominant taxa were not affected by land use intensification. Despite that, we identified indicator taxa for regularly disturbed environments in flower microbiomes. In conclusion, our study contributes to the knowledge about microbial community structures of the phyllosphere and extends the understanding of their community dynamics with respect to biogeographical separation and anthropogenic changes of the environment.