Distinct effects of phyllosphere and rhizosphere microbes on invader Ageratina adenophora during its early life stages.

Microbes strongly affect invasive plant growth. However, how phyllosphere and rhizosphere soil microbes distinctively affect seedling mortality and growth of invaders across ontogeny under varying soil nutrient levels remains unclear. In this study, we used the invader Ageratina adenophora to evaluate these effects. We found that higher proportions of potential pathogens were detected in core microbial taxa in leaf litter than rhizosphere soil and thus leaf inoculation had more adverse effects on seed germination and seedling survival than soil inoculation. Microbial inoculation at different growth stages altered the microbial community and functions of seedlings, and earlier inoculation had a more adverse effect on seedling survival and growth. The soil nutrient level did not affect microbe-mediated seedling growth and the relative abundance of the microbial community and functions involved in seedling growth. The effects of some microbial genera on seedling survival are distinct from those on growth. Moreover, the A. adenophora seedling-killing effects of fungal strains isolated from dead seedlings by non-sterile leaf inoculation exhibited significant phylogenetic signals, by which strains of Allophoma and Alternaria generally caused high seedling mortality. Our study stresses the essential role of A. adenophora litter microbes in population establishment by regulating seedling density and growth.

Diverse Mycena Fungi and Their Potential for Gastrodia elata Germination.

It remains to be determined whether there is a geographical distribution pattern and phylogenetic signals for the Mycena strains with seed germination of the orchid plant Gastrodia elata. This study analyzed the community composition and phylogenetics of 72 Mycena strains associated with G. elata varieties (G. elata. f. glauca and G. elata. f. viridis) using multiple gene fragments (ITS+nLSU+SSU). We found that (1) these diverse Mycena phylogenetically belong to the Basidiospore amyloid group. (2) There is a phylogenetic signal of Mycena for germination of G. elata. Those strains phylogenetically close to M. abramsii, M. polygramma, and an unclassified Mycena had significantly higher germination rates than those to M. citrinomarginata. (3) The Mycena distribution depends on geographic site and G. elata variety. Both unclassified Mycena group 1 and the M. abramsii group were dominant for the two varieties of G. elata; in contrast, the M. citrinomarginata group was dominant in G. elata f. glauca but absent in G. elata f. viridis. Our results indicate that the community composition of numerous Mycena resources in the Zhaotong area varies by geographical location and G. elata variety. Importantly, our results also indicate that Mycena's phylogenetic status is correlated with its germination rate.

Fungal communities associated with early immature tubers of wild Gastrodia elata.

Full myco-heterotrophic orchid Gastrodia elata Bl. is widely distributed in Northeast Asia, and previous research has not fully investigated the symbiotic fungal community of its early immature tubers. This study utilized Illumina sequencing to compare symbiotic fungal communities in natural G. elata immature tubers and their habitats. LEfSe (Linear Discriminant Analysis Effect Size) was used to screen for Biomarkers that could explain variations among different fungal communities, and correlation analyses were performed among Biomarkers and other common orchid mycorrhizal fungi. Our results illustrate that the symbiotic fungal communities of immature G. elata tubers cannot be simply interpreted as subsets of the environmental fungal communities because some key members cannot be traced back to the environment. The early growth of G. elata was related to a small group of fungi, such as Sebacina, Thelephora, and Inocybe, which were also common mycorrhizal fungi from other orchids. In addition, Mycena, Auricularia, and Cryptococcus were unique fungal partners of G. elata, and many new species have yet to be discovered. Possible symbiotic Mycena should be M. plumipes and its sibling species in this case. Our results provide insight into the symbiotic partner switch and trophic pattern change during the development and maturation of G. elata.

Native plants change the endophyte assembly and growth of an invasive plant in response to climatic factors.

Climate change, microbial endophytes, and local plants can affect the establishment and expansion of invasive species, yet no study has been performed to assess these interactions. Using a growth chamber, we integrated the belowground (rhizosphere soils) and aboveground (mixture of mature leaf and leaf litter) microbiota into an experimental framework to evaluate the impacts of four native plants acting as microbial inoculation sources on endophyte assembly and growth of the invasive plant Ageratina adenophora in response to drought stress and temperature change. We found that fungal and bacterial enrichment in the leaves and roots of A. adenophora exhibited distinct patterns in response to climatic factors. Many fungi were enriched in roots in response to high temperature and drought stress; in contrast, many bacteria were enriched in leaves in response to low temperature and drought stress. Inoculation of microbiota from phylogenetically close native plant species (i.e., Asteraceae Artemisia atrovirens) causes the recipient plant A. adenophora (Asteraceae) to enrich dominant microbial species from inoculation sources, which commonly results in a lower dissimilar endophytic microbiota and thus produces more negative growth effects when compared to non-Asteraceae inoculations. Drought, microbial inoculation source, and temperature directly impacted the growth of A. adenophora. Both drought and inoculation also indirectly impacted the growth of A. adenophora by changing the root endophytic fungal assembly. Our data indicate that native plant identity can greatly impact the endophyte assembly and host growth of invasive plants, which is regulated by drought and temperature.IMPORTANCEThere has been increasing interest in the interactions between global changes and plant invasions; however, it remains to quantify the role of microbial endophytes in plant invasion with a consideration of their variation in the root vs leaf of hosts, as well as the linkages between microbial inoculations, such as native plant species, and climatic factors, such as temperature and drought. Our study found that local plants acting as microbial inoculants can impact fungal and bacterial enrichment in the leaves and roots of the invasive plant Ageratina adenophora and thus produce distinct growth effects in response to climatic factors; endophyte-mediated invasion of A. adenophora is expected to operate more effectively under favorable moisture. Our study is important for understanding the interactions between climate change, microbial endophytes, and local plant identity in the establishment and expansion of invasive species.

Assembly and Function of Seed Endophytes in Response to Environmental Stress.

Seeds are colonized by diverse microorganisms that can improve the growth and stress resistance of host plants. Although understanding the mechanisms of plant endophyte-host plant interactions is increasing, much of this knowledge does not come from seed endophytes, particularly under environmental stress that the plant host grows to face, including biotic (e.g., pathogens, herbivores and insects) and abiotic factors (e.g., drought, heavy metals and salt). In this article, we first provided a framework for the assembly and function of seed endophytes and discussed the sources and assembly process of seed endophytes. Following that, we reviewed the impact of environmental factors on the assembly of seed endophytes. Lastly, we explored recent advances in the growth promotion and stress resistance enhancement of plants, functioning by seed endophytes under various biotic and abiotic stressors.

Two Novel Species of Mesophoma gen. nov. from China.

During an investigation of the fungal pathogens associated with the invasive weed Ageratina adenophora from China, some interesting isolates were obtained from healthy leaf, leaf spot, and roots of this weed. Among them, a novel genus Mesophoma, containing two novel species M. speciosa and M. ageratinae, was found. Phylogenetic analysis of the combined, the internal transcribed spacer (ITS), large nuclear subunit ribosomal DNA (LSU), the RNA polymerase II second largest subunit (rpb2), and the partial ß-tubulin (tub2) sequences, showed that M. speciosa and M. ageratinae formed a distinct clade far from all genera previously described in the family Didymellaceae. Combined distinctive morphological characters, including smaller and aseptate conidia when comparing with nearby genera Stagonosporopsis, Boeremia, and Heterphoma, allowed us to describe them as novel species belonging to a novel genus Mesophoma. The full descriptions, illustrations, and a phylogenetic tree showing the position of both M. speciosa and M. ageratinae are provided in this paper. Moreover, the potential for two strains belonging to these two species to be developed into a biocontrol for the spread of the invasive weed Ag. adenophora is also discussed.

Artificial Cultivation Changes Foliar Endophytic Fungal Community of the Ornamental Plant Lirianthe delavayi.

Many wild ornamental plant species have been introduced to improve the landscape of cities; however, until now, no study has been performed to explore the composition and function of foliar endophytes associated with cultivated rare plants in cities after their introduction. In this study, we collected the leaves of the healthy ornamental plant Lirianthe delavayi from wild and artificially cultivated habitats in Yunnan and compared their diversity, species composition, and functional predictions of their foliar endophytic fungal community based on high-throughput sequencing technology. In total, 3125 ASVs of fungi were obtained. The alpha diversity indices of wild L. delavayi populations are similar to those of cultivated samples; however, the species compositions of endophytic fungal ASVs were significantly varied in the two habitats. The dominant phylum is Ascomycota, accounting for more than 90% of foliar endophytes in both populations; relatively, artificial cultivation trends to increase the frequency of common phytopathogens of L. delavayi, such as Alternaria, Erysiphe. The relative abundance of 55 functional predictions is different between wild and cultivated L. delavayi leaves (p < 0.05); in particular, chromosome, purine metabolism, and peptidases are significantly increased in wild samples, while flagellar assembly, bacterial chemotaxis, and fatty acid metabolism are significantly enhanced in cultivated samples. Our results indicated that artificial cultivation can greatly change the foliar endophytic fungal community of L. delavayi, which is valuable for understanding the influence of the domestication process on the foliar fungal community associated with rare ornamental plants in urban environments.

Coordinative Changes in Metabolites in Grape Cells Exposed to Endophytic Fungi and Their Extracts.

Endophytes and their elicitors can all be utilized in regulating crop biochemical qualities. However, living endophytes and their derived elicitors are always applied separately; little is known about the similarities and differences of their effects. To increase the efficiency of this system when applied in practice, the present work profiled simultaneously the metabolomes in grape cells exposed to endophytic fungi (EF) and their corresponding fungal extracts (CFE). As expected, grape cells exposed separately to different fungi, or to different fungi derived extracts, each exhibited different modifications of metabolite patterns. The metabolic profiles of certain EF- and CFE-exposed grape cells were also differently influenced to certain degrees, owing to the presence of differentially responding metabolites (DRMs). However, the detected majority proportions of coordinately responding metabolites (CRMs) in both the EF- and the CFE-exposed grape cells, as well as the significantly influenced metabolites (SIMs) which are specific to certain fungal strains, clearly indicate coordinative changes in metabolites in grape cells exposed to EF and CFEs. The coordinative changes in metabolites in EF- and CFE-treated grape cells appeared to be fungal strain-dependent. Notably, several of those fungal strain-specific CRMs and DRMs are metabolites and belong to amino acids, lipids, organic acids, phenolic acids, flavonoids, and others, which are major contributors to the biochemistry and sensory qualities of grapes and wines. This research clarifies the detailed responses of metabolites in grape cells exposed to EF and CFEs. It also demonstrates how endophytes can be selectively used in the form of extracts to produce functions as CRMs of the living fungus with increased eco-safety, or separately applied to the living microbes or elicitors to emphasize those effects related to their specifically initiated SIMs and DRMs.

Virulence and Host Range of Fungi Associated With the Invasive Plant Ageratina adenophora.

To determine whether disease-mediated invasion of exotic plants can occur and whether this increases the risk of disease transmission in local ecosystems, it is necessary to characterize the species composition and host range of pathogens accumulated in invasive plants. In this study, we found that Didymellaceae, a family containing economically important plant fungal pathogens, is commonly associated with the invasive plant Ageratina adenophora. Accordingly, we characterized its phylogenetic position through multi-locus phylogenetic analysis, as well as its environmental distribution, virulence, and host range. The results indicated that 213 fungal collections were from 11 genera in Didymellaceae, ten of which are known, and one is potentially new. Didymella, Epicoccum, Remotididymella, and Mesophoma were the dominant genera, accounting for 93% of total isolates. The virulence and host ranges of these fungi were related to their phylogenetic relationship. Boeremia exigua, Epicoccum latusicollum, and E. sorghinum were found to be strongly virulent toward all tested native plants as well as toward A. adenophora; M. speciosa and M. ageratinae were weakly virulent toward native plants but strongly virulent toward A. adenophora, thus displaying a narrow host range. Co-evolution analysis showed no strong phylogenetical signal between Didymellaceae and host plants. Isolates S188 and Y122 (belonging to M. speciosa and M. ageratinae, respectively) showed strong virulence toward A. adenophora relative to native plants, highlighting their potential as biocontrol agents for A. adenophora invasion. This study provides new insights into the understanding of the long-term ecological consequences of disease transmission driven by plant invasion.

Diversity and pathogenicity of Alternaria species associated with the invasive plant Ageratina adenophora and local plants.

Pathogen accumulation after introduction is unavoidable for exotic plants over a long period of time. Therefore, it is important to understand whether plant invasion promotes novel pathogen emergence and increases the risk of pathogen movement among agricultural, horticultural, and wild native plants. In this study, we used multiple gene analysis to characterize the species composition of 104 isolates of Alternaria obtained from the invasive plant Ageratina adenophora and native plants from Yunnan, Hubei, Guizhou, Sichuan, and Guangxi in China. Phylogenetically, these strains were from A. alternata (88.5%), A. gossypina (10.6%) and A. steviae (0.9%). There was a high amount of sharing between strains associated with A. adenophora and with local plants. Pathogenicity tests indicated that most of these Alternaria strains are generalists; the isolates with a wider host range were more virulent to the plant. Woody plants were more resistant to these strains than herbaceous plants and vines. However, the invasive plant A. adenophora was highly sensitive to these strains. Our data are valuable for understanding how A. adenophora invasion impacts the Alternaria species composition of the native plant and whether A. adenophora invasion causes potential disease risks in invaded ecosystems.

Virulence and community dynamics of fungal species with vertical and horizontal transmission on a plant with multiple infections.

The virulence evolution of multiple infections of parasites from the same species has been modeled widely in evolution theory. However, experimental studies on this topic remain scarce, particularly regarding multiple infections by different parasite species. Here, we characterized the virulence and community dynamics of fungal pathogens on the invasive plant Ageratina adenophora to verify the predictions made by the model. We observed that A. adenophora was highly susceptible to diverse foliar pathogens with mixed vertical and horizontal transmission within leaf spots. The transmission mode mainly determined the pathogen community structure at the leaf spot level. Over time, the pathogen community within a leaf spot showed decreased Shannon diversity; moreover, the vertically transmitted pathogens exhibited decreased virulence to the host A. adenophora, but the horizontally transmitted pathogens exhibited increased virulence to the host. Our results demonstrate that the predictions of classical models for the virulence evolution of multiple infections are still valid in a complex realistic environment and highlight the impact of transmission mode on disease epidemics of foliar fungal pathogens. We also propose that seedborne fungi play an important role in structuring the foliar pathogen community from multiple infections within a leaf spot.

Evaluation of foliar fungus-mediated interactions with below and aboveground enemies of the invasive plant Ageratina adenophora.

Plant-fungal associations are frequently key drivers of plant invasion success. Foliar fungi can benefit their invasive hosts by enhancing growth promotion, disease resistance and environmental stress tolerance. However, the roles of foliar fungi may vary when a given invasive plant faces different stresses. In this study, we designed three independent experiments to evaluate the effects of a foliar fungus, Colletotrichum sp., on the growth performance of the invasive plant Ageratina adenophora under different soil conditions, as well as the responses of A. adenophora to the foliar fungal pathogen Diaporthe helianthi and to herbivory. We found that the soil type was the most influential factor for the growth of A. adenophora. The role of the foliar fungus Colletotrichum sp. varied in the different soil types but generally adversely affected leaf development in A. adenophora. Colletotrichum sp. may be a weak latent foliar pathogen that can enhance the pathogenicity of D. helianthi on leaves of A. adenophora and marginally reduce signs of herbivory by natural insects in the wild on A. adenophora seedlings. In general, the benefits of the foliar fungus Colletotrichum to the fitness of A. adenophora are not significant in the context of this experimental design. However, our data highlight the need to consider both aboveground and belowground biota in different soil habitats when evaluating the effects of foliar fungi.

Remotididymella ageratinae sp. nov. and Remotididymella anemophila sp. nov., two novel species isolated from the invasive weed Ageratina adenophora in PR China.

To determine if Ageratina adenophora can accumulate diverse pathogens from surrounding native plants, we intensively sampled fungal communities, including endophytes, leaf spot pathogens and canopy air fungi, associated with Ag. adenophora as well as native plants in its invasive range. In total, we collected 4542 foliar fungal strains from 10 geographic sites, including 1340 from healthy leaves of Ag. adenophora, 2051 from leaf spots of Ag. adenophora and 1151 from leaf spots of 56 species of native plants and crops. Taxonomically, the common fungal genera included Colletotrichum, Diaporthe, Alternaria, Nemania, Xylaria, Neofusicoccum, Nigrospora, Epicoccum, Gibberella, Pestalotiopsis, Irpex, Schizophyllum and Clonostachys. We also isolated the cultivable fungi from 12 air samples collected from six areas in Yunnan Province, PR China. Among the total of 1255 air fungal isolates, the most common genera were Cladosporium, Trichoderma and Epicoccum. Among them, two new Remotididymella species, Remotididymella ageratinae from leaf spot of Ag. adenophora and Remotididymella anemophila from canopy air of Ag. adenophora were found. The two species showed both asexual and sexual reproductive structures. The conidia of R. ageratinae and R. anemophila are larger than those of R. anthropophila and R. destructiva. The size of ascospores of R. ageratinae and R. anemophila also differ from R. bauhiniae. Phylogenetic analysis of the combined ITS, LSU rRNA, rpb2 and tub2 sequences showed that R. ageratinae and R. anemophila each formed a distinct clade, separated from all species previously described in Remotididymella and confirmed them as new species belonging to Remotididymella. Full descriptions of R. ageratinae and R. anemophila are provided in this study.

Quantifying the sharing of foliar fungal pathogens by the invasive plant Ageratina adenophora and its neighbours.

Local pathogens can accumulate as asymptomatic endophytes, making it difficult to detect the impacts of invasive species as propagators of disease in the invaded range. We used the invasive plant Ageratina adenophora to assess such accumulation. We intensively collected foliar fungal endophytes and leaf spot pathogens of A. adenophora and co-occurring neighbours and performed an inoculation experiment to evaluate their pathogenicity and host range. Ageratina adenophora harboured diverse necrotrophic pathogens; its communities of endophytes and leaf spot pathogens were different in composition and shared only a small number of fungal species. In the pathogen communities of local plant hosts, 21% of the operational taxonomic units (OTUs), representing 50% of strains, also occurred as leaf spot pathogens and/or endophytes of A. adenophora. The local pathogen community was more similar to the endophytes than to the pathogens of A. adenophora. The inoculation experiment showed that local pathogens could infect A. adenophora leaves asymptomatically and that local plant hosts were susceptible to both A. adenophora endophytes and pathogens. Ageratina adenophora is a highly competent host for local pathogens, and its asymptomatic latent pathogens are fungi primarily shared with local neighbours. This poses challenges for understanding the long-term ecological consequences of plant invasion.

Characterization of the fungal community in the canopy air of the invasive plant Ageratina adenophora and its potential to cause plant diseases.

Airborne fungi and their ecological functions have been largely ignored in plant invasions. In this study, high-throughput sequencing technology was used to characterize the airborne fungi in the canopy air of the invasive weed Ageratina adenophora. Then, representative phytopathogenic strains were isolated from A. adenophora leaf spots and their virulence to A.adenophora as well as common native plants in the invaded range was tested. The fungal alpha diversities were not different between the sampling sites or between the high/low part of the canopy air, but fungal co-occurrences were less common in the high than in the low part of the canopy air. Interestingly, we found that the phytopathogenic Didymellaceae fungi co-occurred more frequently with themselves than with other fungi. Disease experiments indicated that all 5 Didymellaceae strains could infect A. adenophora as well as the 16 tested native plants and that there was large variation in the virulence and host range. Our data suggested that the diverse pathogens in the canopy air might be a disease infection source that weakens the competition of invasive weeds, a novel phenomenon that remains to be explored in other invasive plants.

Exposure to endophytic fungi quantitatively and compositionally alters anthocyanins in grape cells.

Anthocyanins contribute greatly to the organoleptic and biochemical properties of grapes and wines. Although there are broadly documented factors involved in grape anthocyanin synthesis, the present work focused on fungal endophytes and their possible role in grape coloration. Our results showed that exposure to endophytic fungi within a dual culture system differentially affected total anthocyanin concentrations and PAL activities in grape cells. Grape cells dual cultured with fungal strains XH-2, R2-21 and B2-17 showed significant differences of their anthocyanin concentrations were subjected to further analysis of their anthocyanidin compositions. Compared to the no-fungus controls, grape cells exposed to fungal strains XH-2 and R2-21 exhibited quantitative promotion of their total anthocyanidin concentrations by 74% and 28%, respectively, whereas treatment with the fungus B2-17 reduced the anthocyanidin content by 19%. A total of 14 species of anthocyanidins were detected from the grape cells in these experiments. Most interestingly, exposure to any of these fungal strains differentially modified the compositional patterns of grape cellular anthocyanidins. The obvious upregulation of the transcription of VvMYB in grape cells treated with fungal strains XH-2 and R2-21 implies that the increased anthocyanin levels in these grape cells may be due to the activated transcriptional factors. In addition, the exposure of grape cells to extracts of these fungi initiated similar responses of anthocyanin contents and PAL activities to exposure to the living fungi and appeared obvious dosage effects. The influence of fungal endophytes on the coloration of grape berries was also examined in this study.

Plant-soil-foliage feedbacks on seed germination and seedling growth of the invasive plant Ageratina adenophora.

Some exotic plants become invasive because they partially release from soil-borne enemies and thus benefit from positive plant-soil feedbacks (PSFs) in the introduced range. However, reports that have focused only on PSFs may exaggerate the invader's competitiveness. Here, we conducted three experiments to characterize plant-soil-foliage feedbacks, including mature leaves (ML), leaf litter (LL), rhizosphere soil (RS) and leaves plus soil (LS), on the early growth stages of the invasive plant Ageratina adenophora. In general, the feedbacks from aboveground (ML, LL) adversely affected A. adenophora by delaying germination time, inhibiting germination rate and reducing seedling growth. The increased invasion history exacerbated the adverse effects of LL and LS feedbacks on seedling growth. These adverse effects were partially contributed by more abundant fungi (e.g. Didymella) or/and more virulent fungi (e.g. Fusarium) developed in the aboveground part of A. adenophora during the invasion. Interestingly, the aboveground adverse effects can be weakened by microbes from RSs. Our novel findings emphasize the important role of aboveground feedbacks in the evaluation of plant invasiveness, and their commonness and significance remain to be explored in other invasive systems.

Dynamics of fungal communities during Gastrodia elata growth.

BACKGROUND: Gastrodia elata is a widely distributed achlorophyllous orchid and is highly valued as both medicine and food. Gastrodia elata produces dust-like seeds and relies on mycorrhizal fungi for its germination and growth. In its life cycle, G. elata is considered to switch from a specific single-fungus relationship (Mycena) to another single-fungus relationship (Armillaria). However, no studies have investigated the changes in the plant-fungus relationship during the growth of G. elata in the wild. In this study, high-throughput sequencing was used to characterize the fungal community of tubers in different growth phases as well as the soils surrounding G. elata. RESULTS: The predominant fungi were Basidiomycota (60.44%) and Ascomycota (26.40%), which exhibited changes in abundance and diversity with the growth phases of G. elata. Diverse basidiomycetes in protocorms (phase P) were Hyphodontia, Sistotrema, Tricholoma, Mingxiaea, Russula, and Mycena, but the community changed from a large proportion of Resinicium bicolor (40%) in rice-like tubers (phase M) to an unidentified Agaricales operational taxonomic unit 1(OTU1,98.45%) in propagation vegetation tubers (phase B). The soil fungi primarily included Simocybe, Psathyrella, Conocybe, and Subulicystidium. Three Mycena OTUs obtained in this study were differentially distributed among the growth phases of G. elata, accounting for less than 1.0% of the total reads, and were phylogenetically close to Mycena epipterygia and M. alexandri. CONCLUSIONS: Our data indicated that G. elata interacts with a broad range of fungi beyond the Mycena genus. These fungi changed with the growth phases of G. elata. In addition, these data suggested that the development of the fungal community during the growth of G. elata was more complex than previously assumed and that at least two different fungi could be involved in development before the arrival of Armillaria.

Growth-promoting characteristics of potential nitrogen-fixing bacteria in the root of an invasive plant Ageratina adenophora.

Root endophytic nitrogen-fixing bacteria (reNFB) have been proposed as important contributors to the invasiveness of exotic legumes; however, the reNFB of invasive nonlegumes has received less attention. In particular, the growth-promoting effect of reNFB on invasive plants remains unknown. In this study, 131 strains of potential nitrogen-fixing bacteria were isolated and purified from the roots of the invasive plant, Ageratina adenophora, in Southwest China. Phylogenetically, these reNFB were categorized into three phyla at 97% sequence identity that included Proteobacteria (92.4%), Actinobacteria (4.6%), and Firmicutes (3.1%). The dominant isolates ranked by number were Pseudomonas (80 isolates, 61.1%), Rhizobium (12 isolates, 9.2%), and Duganella (11 isolates, 8.4%). The community composition and diversity of A. adenophora reNFB were markedly different across study regions. The capacity of these reNFB to accumulate indolyl-3-acetic acid (IAA), solubilize phosphate, and produce siderophores was determined. All 131 isolates of reNFB accumulated IAA, 67 isolates solubilized phosphate, and 108 isolates produced siderophores. Among the three dominant genera of reNFB, Pseudomonas had the highest phosphorus solubilization and siderophore production, while the accumulation of IAA in the genus Duganella was the lowest. Interestingly, the calculated reNFB Shannon diversity index of each A. adenophora individual was negatively correlated with the capacity of reNFB to produce growth-promoting products. Six randomly selected isolates from three dominant genera were further used to conduct inoculation experiments, and all isolates showed significant positive growth-promoting effects on A. adenophora seedlings. The contribution of reNFB to the root biomass was higher than that to the shoot biomass. Our results suggest that reNFB, similar to soil or nodular nitrogen-fixing bacteria, can potentially promote plant growth and may play an important role in the invasion of nonleguminous plants. More detailed studies on the correlation between reNFB and invasive plants are necessary.

Enrichment of soil rare bacteria in root by an invasive plant Ageratina adenophora.

The assembly of the root-associated microbiome provides mutual benefits for the host plant and bacteria in soils. It is interesting how invasive plants interact with the local soil microbial community and establish the soil bacterial community in the endosphere of these plants in the short term. In this study, we compared the bacterial community in the rhizosphere with that in the root endosphere of an invasive plant, Ageratina adenophora, using high-throughput sequencing. The results showed that the roots of A. adenophora selectively accumulated the genera Clostridium and Enterobacter, which are rarely distributed in the rhizosphere. This selective accumulation caused a switch in the bacterial composition at the phylum level from Bacteroidetes predominant in the rhizosphere to Proteobacteria dominant in the root endosphere of A. adenophora. Our data indicated the potential existence of a highly conserved signal recognition in which hosts, either invasive or native, enrich the endosphere bacteria, such as Clostridium, Enterobacter, etc., from the rhizosphere. Moreover, the accumulated bacteria were physiologically and genetically different at the strain level and displayed distinct roles in growth between invasive and native plants. The assembly of the bacterial community in the roots may be an advantageous strategy for A. adenophora in competition with native plants.