Rhizosphere Soil Of Plants Research Articles

Isolation of Clavibacter michiganensis subsp. michiganenesis-specific bacteriophages from tomato fields in Turkey and their biocontrol potential

BackgroundClavibacter michiganensis subsp. michiganensis (Cmm) is causing wilt and canker and significant economic losses in tomato production. Current control methods with conventional chemicals or antibiotics lost their effectiveness due to the development of bacterial resistance to this agent. Bacteriophages, viruses of bacteria, have been attracting increasing attention as an environmentally friendly means of controlling bacterial diseases. In this study, Cmm and Cmm-specific lytic bacteriophages were isolated from rhizosphere soil and phyllospheres of diseased tomato plants, and the biocontrol potential of bacteriophages was investigated.ResultsEight isolates that showed typical symptoms of Cmm infection in biochemical and pathogenicity tests contained the virulence gene pat-1 in the genome. Twenty-two native bacteriophages were isolated from 90 samples. As a result of the host range tests performed on the local Cmm isolates obtained in the study, temperature and pH tolerance tests were performed with ten phages with a wide host range. Phage24, Phage33 and Phage41, which have higher temperature and pH tolerance than other phages, were used to kill curve assay. Although the combined applications of phages were performed to increase efficacy, it was found that the application of Phage33 alone was more effective.ConclusionPhage33 may prove to be a suitable agent to be used as part of the microbial control strategy of Cmm. In further studies, Phage33 should be formulated to protect it from adverse environmental conditions and tested under field conditions to confirm the results obtained in this study.

Isolation, morphological characterization, and screening a virulence of Beauveria bassiana and Metarhizium robertsii as bioagents

Background: Entomopathogenic fungi exists naturally in plants as an asymptote and has the potential to reduce the population of insect pests through indirect interactions. This study was conducted to detect and characterize the endophytic fungi Beauveria bassiana and Metarhizium robertsii from the rhizosphere soil of tomato plants and their virulence effect on Galleria melonella. Methods: From the rhizosphere soil of 40 tomato fields, three Beauveria bassiana and seven Metarhizium robertsii isolates were identified using the galleria bait method. All fungi isolates were morphologically characterized by their colony color, shape, and surface texture. Isolates with the highest percentages of germination, conidial yield, and radial growth were selected, and their pathogenicity was evaluated on second instar larvae of Galleria melonella under laboratory conditions. Results: In this study, Beauveria bassiana showed white colony color and aseptate hyphae, whereas Metarhizium robertsii showed dark green to light green colony color and septate hyphal structures. Maximum spore production and conidial length were obtained by Beauveria bassiana isolate APPRC-27 with 2.67x107 spores ml-1 and 3.24 µm, respectively. Colony radial growth rates ranged from 1.73 to 3.24 mm day-1. The results revealed that the highest mortality rate of Galleria melonella (100%) was obtained by Metarhizium robertsii isolates K-61 and K-102 at a concentration of 1x108 conidial ml-1 at 7 days post-inoculation. The lowest mortality rate was registered by Metarhizium robertsii isolate RST-11. Conclusions: In the present study, isolates that produced the most spores and had the highest germination rates were the most virulent to Galleria mellonella second instar larvae. Therefore, virulent entomopathogenic fungi, Beauveria bassiana and Metarhizium robertsii, are promising bioagents for the control of pests.

Mixed oligosaccharides-induced changes in bacterial assembly during cucumber (Cucumis sativus L.) growth.

The application of oligosaccharides can promote plant growth by increasing photosynthesis or inducing plant innate immunity. However, the mechanisms by which oligosaccharides affect bacterial community diversity and abundance remain unclear. In this study, a mixed oligosaccharide was applied to the growth of cucumbers. The findings of the present study suggest that the application of MixOS has significant effects on the bacterial communities in the phyllosphere, rhizosphere, and bulk soil of cucumber plants. The treatment with MixOS resulted in delayed senescence of leaves, well-developed roots, and higher fruit production. The bacterial diversity and composition varied among the different ecological niches, and MixOS application caused significant shifts in the bacterial microbiome composition, particularly in the phyllosphere. Moreover, mixed oligosaccharides increased the abundance of potential growth-promoting bacteria such as Methylorubrum spp. and Lechevalieria spp., and more zOTUs were shared between the WM and MixOS treatments. Furthermore, the bacterial co-occurrence network analysis suggested that the modularity of the phyllosphere networks was the highest among all samples. The bacterial co-occurrence networks were altered because of the application of MixOS, indicating a greater complexity of the bacterial interactions in the rhizosphere and bulk soil. These findings suggest that mixed oligosaccharides has the potential to improve plant growth and yield by modulating the bacterial communities within and outside the plants and could provide a theoretical basis for future agricultural production.

Role of ACC deaminase-producing rhizobacteria in alleviation of water stress in watermelon

Owing to the increased global warming, drought severity has increased in many regions, threatening food security, especially in arid and semi-arid areas. Therefore, it is imperative to mitigate the impact of drought on plants in water-stressed areas. The utilization of plant-growth-promoting rhizobacteria (PGPRs) serves as an environmentally friendly approach to enhance the resilience of plants exposed to abiotic stress, specifically drought. This research focuses on examining the effects of 35 PGPR isolates, possessing significant ACC (1-aminocyclopropane-1-carboxylic acid) deaminase activity, which were obtained from diverse plant-rhizosphere soil samples encompassing approximately 17,000 km2 of semi-arid regions. The investigation was conducted on watermelon plants experiencing varying degrees of water stress (30% and 60% water stress). An increase in water stress exerted a detrimental effect on agro-morphological parameters, such as biomass (root + shoot), leaf number, and leaf area of non-inoculated plants. PGPRs stimulated plant growth and increased water use efficiency, especially under severe water-stress (60% water stress) conditions compared to non inoculated plants (control). Furthermore, some PGPRs such as B7, B22, B26 and B28 supported carotenoid synthesis, which plays an important role in photosynthesis, whereas some alleviated the effect of water stress in watermelon plants by stimulating the antioxidant defense system. The outcomes of principal component, where the data were collectively assessed, demonstrated the superior efficacy of certain PGPRs. Specifically, under water-stress conditions, PGPR isolates B31, B32, and B35 exhibited significant growth-promoting effects on watermelon. Additionally, isolates B13 and B15 demonstrated the activation of antioxidant defense mechanisms, including proline, catalase, and peroxidase. PGPRs showed considerable results on the agro-morphological, physiological, and biochemical properties of watermelon under 60% water-stress conditions compared with those under 30% water stress. In conclusion, PGPRs promoted growth and alleviated severe water stress in watermelon plants compared to their control. The results of this study elucidate PGPR-triggered response mechanisms in water-stressed watermelon plants.

Microbiome transplant can effectively manage root-knot nematode infectivity in tomato

A critical factor in alleviating nematode menace in horticultural crops is discerning the nature of microbial communities associated with roots and rhizosphere. Root-knot nematodes (Meloidogyne spp.) are one of the major constraints for obtaining high yields of vegetable crops. Root-knot nematode-infected and uninfected plants occur in agricultural fields. Most biocontrol strategies used for nematode management focus on introducing a single bioagent. Recently, microbiome transplant has been found effective in curing human diseases and is also used to cure animals. Here we evaluated the role played by the microbial communities in managing M. incognita infection on tomatoes grown in protected cultivation by transplanting the microbial slurry extracted from the rhizosphere soil of the healthy plants and those infected with the root-knot nematode. The relative abundance of Gram-negative bacteria (11.11 % and 16.08 %) and anaerobes (39.58 % and 16.59 %) phospholipid fatty acids (PLFA) was significantly higher in healthy roots and rhizosphere soil. In contrast, Gram-positive bacteria (21.52 % and 37.61 %) were comparatively higher in nematode-infected roots and rhizosphere soil. Nematode penetration and reproduction indices were significantly reduced (34–43 %) by inoculating the healthy plant's unfiltered microbial slurry. However, inoculation with unfiltered microbial slurry from the rhizosphere soil of infected plants increased (8–26 %) nematode penetration and reproduction. Plant growth and fruit yield (13.1 %) of tomatoes were positively influenced by unfiltered microbial slurry from the rhizosphere soil of healthy plants. The significant role of the healthy microbiome transplant in reducing nematode invasion and reproduction and increasing the crop yield of tomatoes grown in protected cultivation suggests that microbial transplants could be an approach to managing plant nematodes.

Unraveling the functional genes present in rhizosphere microbiomes of Solanum lycopersicum.

The microbiomes living in the rhizosphere soil of the tomato plant contribute immensely to the state of health of the tomato plant alongside improving sustainable agriculture. With the aid of shotgun metagenomics sequencing, we characterized the putative functional genes (plant-growth-promoting and disease-resistant genes) produced by the microbial communities dwelling in the rhizosphere soil of healthy and powdery mildew-diseased tomato plants. The results identified twenty-one (21) plant growth promotion (PGP) genes in the microbiomes inhabiting the healthy rhizosphere (HR) which are more predomiant as compared to diseased rhizosphere (DR) that has nine (9) genes and four (4) genes in bulk soil (BR). Likewise, we identified some disease-resistant genes which include nucleotide binding genes and antimicrobial genes. Our study revealed fifteen (15) genes in HR which made it greater in comparison to DR that has three (3) genes and three (3) genes in bulk soil. Further studies should be conducted by isolating these microorganisms and introduce them to field experiments for cultivation of tomatoes.

Effects of Septoglomus constrictum and Bacillus cereus on the competitive growth of Ageratina adenophora.

Beneficial microorganisms play a pivotal role in the invasion process of exotic plants, including arbuscular mycorrhizal fungi (AMF) and Bacillus. However, limited research exists on the synergistic influence of AMF and Bacillus on the competition between both invasive and native plants. In this study, pot cultures of Ageratina adenophora monoculture, Rabdosia amethystoides monoculture, and A. adenophora and R. amethystoides mixture were used to investigate the effects of dominant AMF (Septoglomus constrictum, SC) and Bacillus cereus (BC), and the co-inoculation of BC and SC on the competitive growth of A. adenophora. The results showed that inoculation with BC, SC, and BC + SC significantly increased the biomass of A. adenophora by 14.77, 112.07, and 197.74%, respectively, in the competitive growth between A. adenophora and R. amethystoides. Additionally, inoculation with BC increased the biomass of R. amethystoides by 185.07%, while inoculation with SC or BC + SC decreased R. amethystoides biomass by 37.31 and 59.70% compared to the uninoculated treatment. Inoculation with BC significantly increased the nutrient contents in the rhizosphere soil of both plants and promoted their growth. Inoculation with SC or SC + BC notably increased the nitrogen and phosphorus contents of A. adenophora, therefore enhancing its competitiveness. Compared with single inoculation, dual inoculation with SC and BC increased AMF colonization rate and Bacillus density, indicating that SC and BC can form a synergistic effect to further enhance the growth and competitiveness of A. adenophora. This study reveals the distinct role of S. constrictum and B. cereus during the invasion of A. adenophora, and provide new clues to the underlying mechanisms of interaction between invasive plant, AMF and Bacillus.

Inoculation with Bacillus cereus DW019 Modulates Growth, Yield and Rhizospheric Microbial Community of Cherry Tomato

Plant growth-promoting rhizobacteria (PGPR) play an important role in promoting plant growth and increasing crop yield. Bacillus cereus DW019, which was previously isolated from an ion-absorbed rare-earth ore of Ganzhou in Southeastern China, has been considered as a PGPR due to its production of indole-3-acetic acid (IAA), ammonia and siderophore, but its promoting effect on plants remains poorly understood. In this study, autoclaved dead cells and viable cells of Bacillus cereus DW019 at different concentrations were inoculated into pot-cultivated cherry tomato (Lycopersicon esculentum) to investigate the promoting effect on plant growth and yield. A total of 70 days after inoculation, the plants and fruits of cherry tomato were harvested, and their growth indicators, yields, and nutrients were measured. The results showed that biomass, stem thickness, plant height and root length were significantly promoted and that the vitamin C, soluble sugar and soluble protein were significantly increased. Inoculation with Bacillus cereus also modulated the rhizospheric microbial community diversity and structure, especially the proportions of Proteobacteria and Actinobacteriota, which in turn improved the plant height, fresh weight, nutritional quality and rhizosphere soil bacterial diversity of cherry tomato. All the findings suggest that Bacillus cereus DW019 is beneficial to the growth of crops and improves the yield of cherry tomato, suggesting that Bacillus cereus DW019 could be developed into a potential biofertilizer to be used as an agricultural inoculant to increase crop yield and improve the soil ecosystem.

Microbial Assemblages Associated with the Soil-Root Continuum of an Endangered Plant, Helianthemum songaricum Schrenk.

The microbial network of the soil-root continuum plays a key role in plant growth. To date, limited information is available about the microbial assemblages in the rhizosphere and endosphere of endangered plants. We suspect that unknown microorganisms in roots and soil play an important role in the survival strategies of endangered plants. To address this research gap, we investigated the diversity and composition of the microbial communities of the soil-root continuum of the endangered shrub Helianthemum songaricum and observed that the microbial communities and structures of the rhizosphere and endosphere samples were distinguishable. The dominant rhizosphere bacteria were Actinobacteria (36.98%) and Acidobacteria (18.15%), whereas most endophytes were Alphaproteobacteria (23.17%) as well as Actinobacteria (29.94%). The relative abundance of rhizosphere bacteria was higher than that in endosphere samples. Fungal rhizosphere and endophyte samples had approximately equal abundances of the Sordariomycetes (23%), while the Pezizomycetes were more abundant in the soil (31.95%) than in the roots (5.70%). The phylogenetic relationships of the abundances of microbes in root and soil samples also showed that the most abundant bacterial and fungal reads tended to be dominant in either the soil or root samples but not both. Additionally, Pearson correlation heatmap analysis showed that the diversity and composition of soil bacteria and fungi were closely related to pH, total nitrogen, total phosphorus, and organic matter, of which pH and organic matter were the main drivers. These results clarify the different patterns of microbial communities of the soil-root continuum, in support of the better conservation and utilization of endangered desert plants in Inner Mongolia. IMPORTANCE Microbial assemblages play significant roles in plant survival, health, and ecological services. The symbiosis between soil microorganisms and these plants and their interactions with soil factors are important features of the adaptation of desert plants to an arid and barren environment. Therefore, the profound study of the microbial diversity of rare desert plants can provide important data to support the protection and utilization of rare desert plants. Accordingly, in this study, high-throughput sequencing technology was applied to study the microbial diversity in plant roots and rhizosphere soils. We expect that research on the relationship between soil and root microbial diversity and the environment will improve the survival of endangered plants in this environment. In summary, this study is the first to study the microbial diversity and community structure of Helianthemum songaricum Schrenk and compare the diversity and composition of the root and soil microbiomes.

Impact of Insect-Resistant Transgenic Maize 2A-7 on Diversity and Dynamics of Bacterial Communities in Rhizosphere Soil.

Artificial modification of Bacillus thuringiensis (Bt) proteins can effectively improve their resistance to target pests, but the effect of such modification on the diversity of rhizosphere microorganisms remains unclear. Transgenic maize 2A-7 contains two artificially modified Bt proteins, mCry1Ab and mCry2Ab. These proteins can enter soil and pose a potential threat to soil microbial diversity. To assess their impacts on rhizosphere bacteria communities, the contents of the two Bt proteins and changes in bacterial community diversity in the rhizosphere soils of transgenic maize 2A-7 and its control variety were analyzed at different growth stages in 2020. The results showed that the two Bt proteins were detected at low levels in the rhizosphere soils of 2A-7 plants. No significant differences in soil bacterial diversity were detected between 2A-7 and its control variety at any of the growth stages. Bioinformatics analysis indicated that the growth stage, rather than the cultivar, was the main factor causing changes in bacterial communities. This research provides valuable data for understanding the impact of Bt crops on the soil microbiome, and establishes a theoretical basis for evaluation of their safety.

Learning from Seed Microbes: Trichoderma Coating Intervenes in Rhizosphere Microbiome Assembly.

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.

Phosphatase activity of Phosphate Solubilizing Fungi Isolation from Rhizosphere Soil of Medicinal Plants of Shivamogga District

Phosphatases are a group of enzymes which significantly accelerate the release of inorganic phosphate from organically bound phosphate and return to the soil by phosphate solubilizing fungi. Hence for the present study, we focused on the activity of phosphatase. Total 46 fungi were isolated from 55 rhizosphere soils of medicinal plants at Malnad regions of Shivamogga district. Among them, 10 isolates were selected by screening them using their solubilization index ranging from 3.02 to 3.96 and they were further evaluated. The selected 10 isolates showed good results in phosphate solubilization parameters. Decreased pH was observed in culture broth (4.3 to 3.0) from initial pH of 6.89. Amount of acid present in the culture broth (30.01 - 38.08g/L) and concentration of phosphate (70 - 20μg/ml) were recorded. The phosphatases activity was determined on 7th, 14th, 21st and 28th days after incubation at room temperature. Among them, PSF 44 (Aspergillus awamori) showed maximum alkaline phosphatase activity of 0.81, 1.53, 2.15 and 2.38μg PNP liberated/ml/min and acid phosphatases activity of 0.71, 1.34, 2.30 and 2.34μg PNP liberated/ml/min on 7th, 14th, 21st and 28th day respectively after incubation. Hence due to the maximum phosphatase activity and phosphate solubilization capacity of Aspergillus awamori, they can be recommended as phospho-fungal bioinoculum for agricultural field.

Bacterial Communities Structure and Diversity in Rhizosphere Soil of Dominant Plants in Riparian Wetlands of Reservoir in Zhejiang Province, China

Soil bacterial play special roles in the maintenance and stabilization of wetland ecosystem. To investigate bacterial community structure and diversity in rhizosphere soils of four dominant plants in riparian wetlands of mountain reservoir in Zhejiang province, the V4+V5 areas of 16S rDNA gene of bacteria were sequenced and analyzed by the Illumina HiSeq 2500 high-throughput sequencing technology. The results indicated that 27 phylums, 70 classes, 144 orders, 218 families, and 370 genuses of bacteria were achieved, with Proteobacteria, Acidobacteria,Actinobacteria and Bacteroidetes being the dominant phylum and Gammaproteobacteria, Deltaproteobacteria, Acidobacteria, Actinobacteria, Betaproteobacteria and Thermoleophilia being the main class in the soils of riparian wetlands in this areas. The Shannon index and chao1 index of the rhizosphere soil bacteria of Salix babylonica were 8.64 and 585.58, respectively, which were the highest among the four plants, and that of Pterocarya stenoptera were the lowest, with 7.71 and 289.63, respectively. Soil pH, total nitrogen and organic matter were the main factors affecting the soil bacterial community structure in the soil rhizosphere of four dominant plants species in wetlands of riparian zone of reservoir in Zhejiang province.

Plant Rhizospheres Harbour Specific Fungal Groups and Form a Stable Co-Occurrence Pattern in the Saline-Alkali Soil

Soil salinisation has been considered a substantial ecosystem issue with negative effects on sustainable agricultural practices. Practices of vegetation restoration are widely conducted for coping with saline soil degradation, especially in saline-alkali abandoned farmland. Compared with bulk soils, the rhizosphere soils of plants have different microbial community structures. However, how associations and functions of microbes vary in the rhizosphere and bulk soils of salt-tolerant plants remains unclear, limiting the successful implementation and efficacy of vegetation in restoring saline-alkali lands. Here, we analysed the fungal community composition, functional guilds, and co-occurrence networks in both rhizosphere and bulk soils of typical plant species in the abandoned farmland of the Yellow River Delta, China. Not all plant species had significantly different fungal community compositions and relative functional guild abundances between the rhizosphere and bulk soil. Soil nutrient concentrations explained more variance in the soil fungal community. Network analyses indicated that the rhizosphere fungal network had more nodes and links, more negative links, and higher modularity; however, fewer species were involved in the meta-module than those in the bulk soil network, indicating a more complex topology and niche differentiation therein. More generalist species and indicator taxa essential for carbon and nitrogen cycling (e.g., Sordariomycetes and Dothideomycetes) were identified in the salt-tolerant plant rhizosphere network. Overall, the salt-tolerant plants’ rhizosphere had a more stable fungal co-occurrence network and recruited more keystone species compared to the bulk soil, which could benefit soil nutrient cycling and soil restoration in abandoned farmlands.

Seasonal variations in the composition and diversity of rhizosphere soil microbiome of bamboo plants as infected by soil-borne pathogen and screening of associated antagonistic strains

As the occurrence and severity of soil-borne diseases are strongly season-dependent, the ecological processes that shift plant microbiome compositions and functions upon pathogen infection in different seasons are rarely studied. In this study, we compared the differences in fungal and bacterial communities in rhizosphere soil between healthy and diseased bamboo plants throughout the four seasons at the main bamboo production site in China and investigated how basal rot disease caused by Fusarium proliferatum affected the composition, structure and ecological functions of rhizosphere-associated microorganisms. The results showed that diseased bamboo plants enriched the highest abundance of Fusarium genus in rhizosphere soil while receiving largely increased stem lesion area in summer. Microbiome analysis further proved that healthy bamboo plants harbored more ecologically beneficial microbial taxa that might function as biological protectants in their rhizosphere soil than diseased plants at the same season. Three individual strains with biocontrol potentials were further isolated and identified as Trichoderma spirale, Bacillus velezensis and Streptomyces mirabilis. The antagonistic tests further demonstrated their inhibition effects on the growth and pathogenicity of the pathogenic fungus F. proliferatum in vitro and in vivo. This study advances our understanding of soil-borne pathogen mediated changes in microbiome structure and function in plant rhizosphere soil and provides potential biocontrol strains for increasing plant resistance against basal rot disease.

Effects of short‐term nitrogen addition on rhizosphere and bulk soil bacterial community structure of three halophytes in the Yellow River Delta

AbstractThe total amount and rate of atmospheric nitrogen (N) deposition are constantly increasing, which substantially influences the soil microbial community structure and function. However, it is still unclear whether the responses of different plant rhizosphere soil bacterial community to short‐term N addition was consistent. Based on 16s rRNA sequencing, we investigated the responses of rhizosphere and bulk soil bacterial community of halophytes (salt‐absorbing, salt‐rejecting, and salt‐secreting plant) to short‐term N addition in the Yellow River Delta. The bacterial community α‐diversity of Suaeda salsa (salt‐absorbing plant) was significantly higher in rhizosphere soil than in bulk soil, while no significant difference between Phragmites communis (salt‐rejecting plant) rhizosphere and bulk soil bacterial community α‐diversity was found. The differences were mainly ascribed to the higher N uptake capacity of P. communis, which resulted in no difference in N content between rhizosphere and bulk soil. The short‐term N addition significantly increased the α‐diversity of bacterial community in the rhizosphere soil of Aeluropus sinensis (salt‐secreting plant), but there was no effect on the α‐diversity of bacterial community in the rhizosphere soil of P. communis. Nitrogen addition enhances the salt uptake capacity of A. sinensis and alleviates the salt stress of bacterial growth. The relative abundance of Bacteroidetes for S. salsa and A. sinensis was significantly higher in rhizosphere soil than in bulk soil, and the relative abundance of Actinobacteria for P. communis and S. salsa was higher and lower in rhizosphere soil than in bulk soil, respectively. Salt‐absorbing of S. salsa leads to elevated rhizosphere soil salinity. Higher salinity and abundant carbon promote the Bacteroidetes and inhibit the Actinobacteria. Short‐term N addition caused an increase in the relative abundance of Gemmatimonadetes in halophyte rhizosphere soil and a decrease in the relative abundance of Firmicutes in S. salsa and A. sinensis bulk soil, which may be due to the different response of C:N of root secretions to N addition in halophytes. The relative abundance of rhizosphere soil denitrifying bacteria was higher in S. salsa and A. sinensis than in P. communis, while the reverse was observed for N‐fixing bacteria. The relative abundance of denitrifying bacteria decreased in P. communis and increased in S. salsa and A. sinensis. The low N soil environment of P. communis promotes the activity of N‐fixing bacteria, and the abundant N content of S. salsa and A. sinensis soil promotes the denitrification process. The research clarified that the response of soil bacterial community to short‐term N addition Treatment differed due to the influence of plant species and that N additions had smaller effects on the bacterial community than plant species.

Effect of arbuscular mycorrhizal fungi inoculation on revegetation at Nukui Dam site, Japan

The establishment of the surviving arbuscular mycorrhizal (AM) fungi, Gigaspora margarita Becker & Hall, inoculated in revegetation at the Nukui Dam was studied. The population of AM fungi and AM colonization of three plant species Japanese hill cherry (Prunus jamasakura Sieb. ex Koidz, yamazakura-inoculated plant), eulalia (Miscanthus sinensis Anderss, susuki), and mugwort (Artemisia vulgaris Pampan, yomogi) were investigated to compare inoculated and non-inoculated treatments. The AM colonisation was enhanced in inoculated plots although natural or accidental AM fungi were involved in non-inoculated plots and successfully colonised. Coverage of soil surface was more than 80% and even reached nearly 100% in summer regardless of the soil amendment type.The number of spores and the percentage of colonisation of investigated plant roots, as well as the density of typical AM structures such as arbuscules, auxiliary cells, vesicles, and coiling hyphae by AM fungi in inoculated plots were higher than those in non-inoculated ones. Some spores were Gigaspora andGlomus-inoculated species and were relatively rich in inoculated plots of Yamazakura. There was a significant increase in the number of AM spores in inoculated treatments at a 5% confidence level (ANOVA, p<0.05) in Susuki and Yamazakura. Much more spores of Gigaspora sp.occurred in the rhizosphere soil of Yamazakura and Susuki plants in inoculated plots than in non-inoculated plots (2.33 and 3.73 times, respectively).The colonisation intensity and spore number in the rhizosphere were positively correlated. Therefore, inoculation at an early establishment should be important for the successive development of AM-plant symbiosis formation.

Differences in Soil Microbial Communities between Healthy and Diseased Lycium barbarum cv. Ningqi-5 Plants with Root Rot.

For a long time, the development of the Lycium barbarum industry has been seriously restricted by root rot disease. In general, the occurrence of plant root rot is considered to be closely related to the composition and diversity of the soil microbial community. It is critical to understand the relationship between the occurrence of root rot in L. barbarum and the soil microbial composition. In this study, samples of the rhizosphere, rhizoplane, and root zone were collected from diseased and healthy plants. The V3-V4 region of bacterial 16S rDNA and the fungal ITS1 fragment of the collected samples were sequenced using Illumina MiSeq high-throughput sequencing technology. The sequencing results were first quality controlled and then aligned with the relevant databases for annotation and analysis. The richness of fungal communities in the rhizoplane and root zone of the healthy plants was significantly higher than that of the diseased plants (p < 0.05), and the community evenness and diversity of all the rhizoplane samples were significantly different from those of the rhizosphere and root zone. The richness of the bacterial communities in the rhizosphere and root zone of healthy plants was significantly greater than those of diseased plants (p < 0.05). The community composition of the rhizoplane was quite different from the other parts. The abundance of Fusarium in the rhizoplane and rhizosphere soil of diseased plants was higher than that in the corresponding parts of healthy plants. The abundances of Mortierella and Ilyonectria in the three parts of the healthy plants were correspondingly higher than those in the three parts of the diseased plants, and Plectosphaerella was the most abundant in the rhizoplane of diseased plants. There was little difference in the composition of the dominant bacteria at the phylum and genus levels between healthy plants and diseased plants, but the abundances of these dominant bacteria were different between healthy and diseased plants. Functional prediction showed that the bacterial community had the largest proportion of functional abundance belonging to metabolism. The functional abundances of the diseased plants, such as metabolism and genetic information processing, were lower than those of the healthy plants. The fungal community function prediction showed that the Animal Pathogen-Endophyte-Lichen Parasite-Plant Pathogen-Soil Saprotroph-Wood Saprotroph group had the largest functional abundance, and the corresponding fungi were Fusarium. In this study, we mainly discussed the differences in the soil microbial communities and their functions between the healthy and diseased L. barbarum cv. Ningqi-5, and predicted the functional composition of the microbial community, which is of great significance to understanding the root rot of L. barbarum.

Phytophthora pseudocryptogea, P. nicotianae and P. multivora Associated to Cycas revoluta: First Report Worldwide.

A dieback was observed on three-year-old pot-grown plants of Cycas revoluta in Sicily (Italy). Symptoms, including stunting, yellowing and blight of the leaf crown, root rot and internal browning and decay of the basal stem, closely resembled the Phytophthora root and crown rot syndrome, common in other ornamentals. Isolations from rotten stem and roots, using a selective medium, and from rhizosphere soil of symptomatic plants, using leaf baiting, yielded three Phytophthora species, P. multivora, P. nicotianae and P. pseudocryptogea, were obtained. Isolates were identified by both morphological characters and DNA barcoding analysis, using three gene regions: ITS, β-tub and COI. Phytophthora pseudocryptogea was the sole species isolated directly from the stem and roots. The pathogenicity of the isolates of the three Phytophthora species was tested on one-year-old potted plants of C. revoluta, using both stem inoculation by wounding, and root inoculation through infested soil. Phytophthora pseudocryptogea was the most virulent and, like P. nicotianae, reproduced all the symptoms of natural infections, while P. multivora was the least virulent and induced solely very mild symptoms. Phytophthora pseudocryptogea was identified as the causal agent of the decline of C. revoluta, as it was re-isolated from both the roots and stems of artificially infected symptomatic plants, thus fulfilling Koch's postulates.

Arbuscular mycorrhizal fungi alter rhizosphere bacterial community characteristics to improve Cr tolerance of Acorus calamus

Arbuscular mycorrhizal fungi (AMF) can improve plant tolerance to heavy metal stress in terrestrial ecosystems. However, in wetland ecosystems, AMF can improve the tolerance of wetland plants to heavy metals by changing the structure and composition of rhizosphere bacterial communities, which is still rarely studied. In this study, we investigated the effects of AMF on the structure and composition of bacterial communities in the rhizosphere of plants under different chromium concentrations. The results showed that Cr(Ⅵ) concentration in Acorus calamus. rhizosphere soil decreased by 12.6 % (5.6–21.7 %) on average after AMF inoculation, At the same time, it promoted the uptake of nutrients by A. calamus and increased soil carbon input. In addition, Cr stress decreased the bacterial community diversity and abundance index by 9.8 % (1.6–18.1 %) and 24.5 % (17.3–27.6 %) on average. On the contrary, the rhizosphere soil bacterial diversity and abundance index increased by 7.3 % (2.2–19.1 %) and 13.9 % (6.0–20.9 %) on average after AMF inoculation. Moreover, compared with the non-inoculated AMF group, the bacterial community structure of A. calamus rhizosphere changed by 24.6 % under Cr stress, The common number of species increased by 6.4 %. In addition, after inoculation of AMF significantly promote the growth of a large number of bacteria related to organic degradation, plant growth, and oxidative stress, increased soil carbon input improved the soil microenvironment. Meanwhile, After AMF inoculation, the Number of edges, Number of Nodes, Average degree, and Average Path length in the symbiotic network of rhizosphere soil bacterial community increased by 34.6 %, 10 %, 44.3 %, and 26.4 %, respectively. Therefore, it offers a possibility that AMF can enhance the tolerance of wetland plants to soil Cr pollution by improving the structure and composition of bacterial communities in the rhizosphere soils of wetland plants, which provide a basis for wetland plants to repair soil Cr pollution.