Streptomyces Application Triggers Reassembly and Optimization of the Rhizosphere Microbiome of Cucumber

ABSTRACTDistinct plant associated microbiomes live in rhizosphere soil, roots, and leaves. However, the differences in community assembly of fungi and bacteria along soil-plant continuum are less documented in ecosystems. We examined fungal and bacterial communities associated with leaves, roots, and rhizosphere soil of the dominant arbuscular mycorrhizal (AM) plants Taraxacum mongolicum and Elymus nutans and non-AM plant Carex enervis in the Zoige Wetland by using high throughput sequencing techniques. The operational taxonomic unit (OTU) richness of fungi and bacteria was significantly higher in rhizosphere soil than in roots and leaves, and their community compositions were significantly different in the rhizosphere soil, roots, and leaves in each plant species. The co-occurrence network analysis revealed that the sensitive fungal and bacterial OTUs with various taxonomic positions were mainly clustered into different modules according to rhizosphere soil, roots, and leaves in each plant species. Along the soil-plant continuum, the rhizosphere soil pool contributed more source on bacterial than on fungal communities in roots and leaves of the three plant species, and more source on bacterial and fungal communities in leaves of T. mongolicum and E. nutans compared with C. enervis. Furthermore, the root pool contributed more source on bacterial than on fungal communities in leaves of T. mongolicum and E. nutans but not that of C. enervis. This study highlights that the host plant selection intensity is higher in fungal than in bacterial communities in roots and leaves from rhizosphere soil in each plant species, and differs in fungal and bacterial communities along the soil-plant continuum in AM plants T. mongolicum and E. nutans and non-AM plant C. enervis in the Zoige Wetland.IMPORTANCE Elucidating the community microbiome assemblage alone the soil-plant continuum will help to better understand the biodiversity maintenance and ecosystem functioning. Here, we examined the fungal and bacterial communities in rhizosphere soil, roots, and leaves of two dominant AM plants and a non-AM plant in Zoige Wetland. We found that along the soil – plant continuum, host plant selection intensity is higher in fungal than in bacterial communities in roots and leaves from rhizosphere soil in each plant species, and differs in fungal and bacterial communities in the AM- and non-AM plants. This is the first report provides evidence of different assembly patterns of fungal and bacterial communities along the soil-plant continuum in the AM- and non-AM plants in the Zoige Wetland.

The responses of soil microbes to climatic and anthropological factors in the Tibetan grasslands

Continuous cropping disorders of eggplants (Solanum melongena L.) and tomatoes (Solanum lycopersicum L.) in suburban agriculture: Microbial structure and assembly processes

Atmospheric nitrogen (N) deposition is known to alter soil microbial communities, but how canopy and understory N addition affects soil bacterial and fungal communities in different soil layers remains poorly understood. Conducting a 6-year canopy and understory N addition experiment in a temperate forest, we showed that soil bacterial and fungal communities in the organic layer exhibited different responses to N addition. The main effect of N addition decreased soil bacterial diversity and altered bacterial community composition in the organic layer, but not changed fungal diversity and community composition in all layers. Soil pH was the main factor that regulated the responses of soil bacterial diversity and community composition to N addition, whereas soil fungal diversity and community composition were mainly controlled by soil moisture and nutrient availability. In addition, compared with canopy N addition, the understory N addition had stronger effects on soil bacterial Shannon diversity and community composition but had a weaker effect on soil bacteria richness in the organic soil layer. Our study demonstrates that the bacterial communities in the organic soil layer were more sensitive than the fungal communities to canopy and understory N addition, and the conventional method of understory N addition might have skewed the effects of natural atmospheric N deposition on soil bacterial communities. This further emphasizes the importance of considering canopy processes in future N addition studies and simultaneously evaluating soil bacterial and fungal communities in response to global environmental changes.

Pine wilt disease (PWD), caused by pinewood nematodes, is highly destructive to pine forests in Asia and Europe, including Korean white pine (Pinus koraiensis). The microbiome in the needles and trunk of Pinus spp. are recognized to play key roles in resistance against PWD. However, the role of root and soil microbiomes in the resistance remains unclear. This study compares bacterial and fungal communities in the root endosphere, rhizosphere soil, and bulk soil of diseased versus healthy P. koraiensis. Results showed that PWD increased the α-diversity of fungi in rhizosphere soil but did not affect the microbial diversity in the root endosphere or bulk soil. The composition of bacterial and fungal communities in rhizosphere and bulk soils was significantly altered by PWD. Specifically, the relative abundance of Planctomycetes decreased, and the relative abundance of Tremellomycetes increased, while Agaricomycetes decreased in both rhizosphere and bulk soils after infestation with PWD, respectively. Relative abundances of Chloroflexi and Verrucomicrobia increased, while Proteobacteria decreased in bulk soil following PWD. Relative abundances of Leotiomycetes and Eurotiomycetes increased in the rhizosphere soil and bulk soil following PWD, respectively. Furthermore, with the host plant infestation by PWD, the relative abundance of ectomycorrhizal fungi decreases, while that of saprotrophic fungi increases in both rhizosphere and bulk soils. Our results revealed that PWD significantly affects the soil microbiomes of P. koraiensis, with varying impacts across different plant-soil compartments. This study provides insights into how root and soil microbiomes respond to PWD, enhancing our understanding of the disease's ecological consequences.IMPORTANCEThe belowground microbiome is often sensitive to infection of forest diseases and is also recognized as a potential reservoir for selection of microbial agents against PWD. Our study demonstrates that the dynamics of belowground microbiome following natural infection of PWD are compartment and taxa specific, with varying degrees of responses in both diversity and composition of bacterial or fungal communities across the root endosphere, rhizosphere soil, and bulk soil. The results highlight the importance of utilizing appropriate plant-soil compartments and microbial taxa to understand the ecological consequences of the destructive PWD.

To evaluate the micro-ecological effects of tetracycline residues on tobacco soil, high-throughput sequencing technology was used to study the effects of the addition of different concentrations (0, 5, 50, and 500 mg·kg−1) of tetracycline on the abundance, diversity, and structure of bacterial and fungal communities in the rhizosphere and non-rhizosphere soil of flue-cured tobacco in China. Results showed that the presence of tetracycline had an important but varying effect on soil bacterial and fungal community richness, diversity, and structure. Changes in the diversity indices (Chao index and Shannon index) of soil bacterial and fungal communities showed a similar pattern after the addition of tetracycline; however, a few differences were found in the effects of tetracycline in the rhizosphere and non-rhizosphere soil, suggesting an evident rhizosphere-specific effect. The bacterial community at the phylum level in the rhizosphere closely clustered into one group, which might be the result of tobacco root secretions and rhizodeposition. Tetracycline showed a concentration-dependent effect on the soil bacterial community structure. The soil bacterial community structures observed after treatments with higher concentrations of tetracycline (50 and 500 mg·kg−1) were found to be closely related. Moreover, the effects of the treatments with higher concentrations of tetracycline, on the soil bacterial community at the phylum level, were different from those with lower concentrations of tetracycline (5 mg·kg−1), and CK treatments. This might have resulted from the induction of increasing selective pressure with increasing antibiotic concentration. Tetracycline continued to affect the soil bacterial community throughout the experiment. Tetracycline was found to have a varying impact on the community structure of soil fungi compared to that of soil bacteria, and the addition of an intermediate concentration of tetracycline (50 mg·kg−1) significantly increased the soil fungal diversity in the non-rhizosphere soil. The biological effects of tetracycline on the soil fungal community and the fungal-bacterial interactions, therefore, require further elucidation, warranting further research.

Seed-associated microbiomes can impact the later colonization of a plant rhizosphere microbiome. However, there remains little insight into the underlying mechanisms concerning how alterations in the composition of the seed microbiome may intervene in the assembly of a rhizosphere microbiome. In this study, the fungus Trichoderma guizhouense NJAU4742 was introduced to both maize and watermelon seed microbiomes by seed coating. Application was found to significantly promote seed germination and improve plant growth and rhizosphere soil quality. The activities of acid phosphatase, cellulase, peroxidase, sucrase, and α-glucosidase increased significantly in two crops. The introduction of Trichoderma guizhouense NJAU4742 also led to a decrease in the occurrence of disease. Coating with T. guizhouense NJAU4742 did not alter the alpha diversities of the bacterial and fungal communities but formed a key network module that contained both Trichoderma and Mortierella. This key network module comprised of these potentially beneficial microorganisms was positively linked with the belowground biomass and activities of rhizosphere soil enzymes but negatively correlated with disease incidence. Overall, this study provides insights into plant growth promotion and plant health maintenance via seed coating in order to influence the rhizosphere microbiome. IMPORTANCE Seed-associated microbiomes can impact the rhizosphere microbiome assembly and function display. However, there remains little insight into the underlying mechanisms concerning how alterations in the composition of the seed microbiome with the beneficial microbes may intervene in the assembly of a rhizosphere microbiome. Here, we introduced T. guizhouense NJAU4742 to the seed microbiome by seed coating. This introduction led to a decrease in the occurrence of disease and an increase in plant growth; furthermore, it formed a key network module that contained both Trichoderma and Mortierella. Our study provides insights into plant growth promotion and plant health maintenance via seed coating in order to influence the rhizosphere microbiome.

Assembly and enrichment of rhizosphere and bulk soil microbiomes in Robinia pseudoacacia plantations during long-term vegetation restoration

Agriophara rhombata is a tea leaf moth that is considered one of the most destructive pests of Camellia sinensis (tea plant). Several recent studies have shown that many insects acquire part of the microbiome from their host and soil, but the pattern and diversity of their microbiome have not been clearly demonstrated. The present study aimed to investigate the bacterial and fungal communities present in the rhizospheric soil and leaf of tea plant compared to the gut of tea moth at different developmental stages (larvae, pupae, adult female and male) using Illumina MiSeq technology. Alpha diversity (Shannon index) showed higher (p < 0.05) bacterial and fungal diversity in soil samples than in leaf and tea moth larvae, pupae, and adult gut samples. However, during different developmental stages of tea moth, bacterial and fungal diversity did not differ (p > 0.05) between larvae, pupae, female, and male guts. Beta diversity also revealed more distinct bacterial and fungal communities in soil and leaf samples compared with tea moth gut samples, which had a more similar microbiome. Furthermore, Proteobacteria, Firmicutes, and Tenericutes were detected as the dominant bacterial phyla, while Ascomycota, Basidiomycota, and Mortierellomycota were the most abundant fungal phyla among all groups, but their relative abundance was comparatively higher (p < 0.05) in soil and leaf samples compared to tea moth gut samples. Similarly, Klebsiella, Streptophyta, and Enterococcus were the top three bacterial genera, while Candida, Aureobasidium, and Strelitziana were the top three fungal genera, and their relative abundance varied significantly (p < 0.05) among all groups. The KEGG analysis also revealed significantly higher (p < 0.5) enrichment of the functional pathways of bacterial communities in soil and leaf samples than in tea moth gut samples. Our study concluded that the bacterial and fungal communities of soil and tea leaves were more diverse and were significantly different from the tea moth gut microbiome at different developmental stages. Our findings contribute to our understanding of the gut microbiota of the tea moth and its potential application in the development of pest management techniques.

Scutellaria baicalensis is an important medicinal plant, and the diversity of its rhizosphere microbiota may influence its growth, development, and yield. Numerous studies have reported that warming associated with global climate change significantly altered plant-associated soil microbial diversity. To reveal the effects of night-time warming on the rhizosphere microbial community of S. baicalensis, soil microbial diversity in the rhizosphere (RS) and bulk soil (BS) of S. baicalensis were analyzed by employing bacterial 16S rRNA and fungal ITS sequencing technology. Warming significantly altered both bacterial and fungal communities in the rhizosphere and bulk soils of S. baicalensis, with pronounced changes in OTU composition, relative abundances at both phylum and species levels. The analysis of alpha and beta diversity showed that warming significantly altered the fungal community structure in the rhizosphere soil (R2 = 0.423, p &lt; 0.05) and significantly reduced the species richness in the bulk soil of S. baicalensis (Shannon and Simpson index, p &lt; 0.05). LEfSe and functional prediction analyses revealed that warming altered the taxonomic composition of both bacterial (35 taxa, LDA &gt; 3) and fungal (24 taxa, LDA &gt; 4) communities in rhizosphere and bulk soils of S. baicalensis, with multiple bacterial and fungal taxa serving as treatment-specific biomarkers. Functional predictions indicated that fungal functional groups, including saprotrophic and mycorrhizal guilds, were more strongly affected by warming than bacteria. Overall, warming has a significantly stronger impact on fungal communities in the rhizosphere and bulk soils of S. baicalensis than on bacteria, and has a significantly greater effect on the diversity of microbial communities in bulk soils than that in rhizosphere soils. This study provides important data for understanding the impact of global climate change on the rhizosphere microbial communities of cultivated plants.

Microplastics (MPs) can serve as bearers of microorganisms and additional contaminants. However, the functional composition and assembly processes of plastisphere bacteria in co-contaminated soil–plant systems are not yet well understood. Using a pot experiment, we examined the effects of both individual and combined cadmium (Cd) and polypropylene (PP) MP contamination on the development of the bioenergy plant sorghum. The bacterial community, co-occurrence networks, and assembly processes in the rhizosphere soil and PP plastisphere were investigated using high-throughput sequencing. Compared with contamination by a single compound, combined contamination with Cd and PP had a more potent inhibitory effect on the development of sorghum. PCoA and diversity indices indicate that the bacterial community on PP plastics is structurally simpler than that in rhizosphere soil. The PP plastisphere could recruit bacteria from the genera Sphingomonas, Rhizobium, and Bacillus. The bacterial communities in the soil and the PP plastisphere were mostly formed by stochastic processes, with diffusion limitation playing a greater role in the bacterial community in the PP plastisphere. Co-occurrence network analysis revealed differences between the bacterial communities in the soil and in the PP plastisphere, with the network in the PP plastisphere showing lower complexity and connectivity. Functional prediction revealed that the prevalence of nitrogen cycling genes was greater in the PP plastisphere than in the dirt and that the PP plastisphere presented greater metabolic activity. The relative prevalence of metabolic pathways associated with human diseases was markedly elevated in the PP plastisphere, which may be correlated with the dissemination of pathogenic microorganisms. These findings indicate that the PP plastisphere, as a distinct microbial niche, might attract certain bacteria, consequently affecting the functional characteristics of cocontaminated soil–plant systems.

Triple-transgenic soybean in conjunction with glyphosate drive patterns in the rhizosphere microbial community assembly

Effects of grassland afforestation on structure and function of soil bacterial and fungal communities

The rhizosphere microbiome is considered to play a key role in determining crop health. However, current understanding of the factors which shape assembly and composition of the microbiome is heavily biased toward bacterial communities, and the relevance for other microbial groups is unclear. Furthermore, community assembly is determined by a variety of factors, including host genotype, environment and agricultural management practices, and their relative importance and interactions remain to be elucidated. We investigated the impact of nitrogen fertilization on rhizosphere bacterial, fungal, nematode and protist communities of 10 contrasting oilseed rape genotypes in a field experiment. We found significant differences in the composition of bacteria, fungi, protist and nematode communities between the rhizosphere and bulk soil. Nitrogen application had a significant but weak effect on fungal, bacterial, and protist community composition, and this was associated with increased relative abundance of a complex of fungal pathogens in the rhizosphere and soil, including Mycosphaerella sp. and Leptosphaeria sp. Network analysis showed that nitrogen application had different effects on microbial community connectivity in the soil and rhizosphere. Crop genotype significantly affected fungal community composition, with evidence for a degree of genotype specificity for a number of pathogens, including L. maculans, Alternaria sp., Pyrenopeziza brassicae, Olpidium brassicae, and L. biglobosa, and also potentially beneficial Heliotales root endophytes. Crop genotype had no significant effect on assembly of bacteria, protist or nematode communities. There was no relationship between genetic distance of crop genotypes and the extent of dissimilarity of rhizosphere microbial communities. Field disease assessment confirmed infection of crops by Leptosphaeria sp., P. brassicae, and Alternaria sp., indicating that rhizosphere microbiome sequencing was an effective indicator of plant health. We conclude that under field conditions soil and rhizosphere nutrient stoichiometry and crop genotype are key factors determining crop health by influencing the infection of roots by pathogenic and mutualistic fungal communities, and the connectivity and stability of rhizosphere microbiome interaction networks.

Soil microorganisms are essential for the long-term sustainability of agricultural ecosystems. However, continuous grapevine replanting can disrupt the stability of soil microbial communities. We investigated the bacterial and fungal abundance, diversity, and community composition in rhizosphere soils with continuous grapevine replanting for 5, 6, 7 (Y5, Y6, and Y7; short-term), and 20 (Y20; long-term) years with high-throughput sequencing. Results showed that diversities and abundances of bacterial and fungal communities in Y20 were significantly lower than in other samples. The bacterial and fungal community compositions were markedly affected by the replanting time and planting year. After short-term grapevine replanting, relative abundances of potential beneficial bacteria and harmful fungi in rhizosphere soils were higher compared to long-term planting. Bacterial and fungal communities were significantly correlated with available nitrogen (AN), available phosphorus, available potassium (AK), and pH. AK and AN were the primary soil factors related to the shift of bacterial and fungal communities. Bacterial and fungal co-occurrence patterns were remarkably affected by replanting time, showing that fallow land harbored co-occurrence networks more complex than those in other groups, with the Y20 group showing the lowest complexity. Then, we isolated the dominant fungi in grapevine rhizosphere soil after continuous replanting and verified the harmful effects of three candidate strains through pot experiments. The results showed that 12days post-treating the soil with fungal spore suspensions significantly inhibited grapevine seedlings' growth, whereas Fusarium solani inhibited plant growth. Overall, we showed that F. solani might be a potentially harmful fungus related to grapevine replant diseases. KEY POINTS: • Continuous grapevine planting reduced soil microbe diversities/abundances. • Beneficial bacteria and harmful fungi increased after short-term replanting. • F. solani may be a harmful fungus related to grapevine replant diseases.