Rhizosphere Soil Bacterial Communities Research Articles

Effects of Pruning on Growth, Rhizosphere Soil Physicochemical Indexes and Bacterial Community Structure of Tea Tree and Their Interaction

Pruning is an agronomic practice that contributes to tea tree yield during cultivation, but little is known about how pruning improves yield through shifting bacterial communities in rhizosphere soil. Therefore, Meizhan tea (Camellia sinensis) was used as the research object to analyze the effect of unpruning and pruning on the growth and rhizosphere soil physicochemical indexes of the tea tree, and sequencing technology was used to obtain the diversity of soil bacterial communities. The results showed that leaf area, hundred bud weight and yield of pruned tea trees increased by 1.32, 1.40, and 1.84 times, respectively, and pH and available N, available P, and available K contents increased by 1.10, 1.07, 1.30, and 1.07 times, respectively, compared with unpruned treatment, while total N, total P, and total K contents decreased by 1.20, 1.37, and 1.13 times, respectively. Analysis of the bacterial community structure showed that the key differential bacteria between pruned and unpruned tea trees were Candidatus Solibacter, Acidibacter, Rhizomicrobium, Bryobacter, Solanum torvum, Mizugakiibacter, Nitrospira, Sphingomonas, and Granulicella. Among them, the bacterial abundance of Candidatus Solibacter, Bryobacter, and Nitrospira showed an upward trend and the rest showed a downward trend after pruned treatment. Interaction network analysis showed that the correlation between the total key genera of microorganisms and organic matter, total N, total K, and total P content in rhizosphere soil did not reach a significant level, whereas the correlation with soil available N, available K, available P, pH, and tea tree growth indexes were all positively and significantly correlated. It can be seen that pruning changed the structure of the rhizosphere soil microbial community of tea trees, promoted soil nutrient transformation, increased the content of soil available nutrients, and promoted the growth of tea tree.

Arbuscular mycorrhizal fungi alter rhizosphere bacterial diversity, network stability and function of lettuce in barren soil

Arbuscular mycorrhizal fungi (AMF) play an important role in plant growth and rhizosphere microbiome composition. However, how the plant-AMF-rhizosphere microbiome continuum interacts in barren soils to efficiently promote the plant's growth is still an area of little research. Here, we present the results of a controlled environment experiment to reveal the effect of AMF on the rhizosphere bacterial community of lettuce. Compared with the control group, AMF significantly increased plant biomass, mycorrhizal colonization, and affected the rhizosphere microbial community composition. AMF inoculation changed the function of the rhizosphere bacterial community, reduced the complexity of the bacterial network, and improved its stability. In addition, SEM showed that the composition and structure of rhizosphere soil bacterial community were significantly positively correlated with soil carbon, nitrogen, and phosphorus content after adding AMF. Our findings provide new information for exploring the positive effects of plant-microbe interactions.

Control effect of root exudates from mycorrhizal watermelon seedlings on Fusarium wilt and the bacterial community in continuously cropped soil.

Watermelon (Citrullus lanatus) is susceptible to wilt disease caused by Fusarium oxysporum f. sp niveum (FON). AMF colonization alleviates watermelon wilt and regulates the composition of root exudates, but the effects of mycorrhizal watermelon root exudates on watermelon Fusarium wilt is not well understood. Root exudates of watermelon inoculated with AMF (Funeliformis mosseae or Glomus versiformme) were collected in this study. Then the root exudates of control plants and mycorrhizal plants were used to irrigate watermelon in continuous cropping soil, respectively. Meanwhile, the watermelon growth, antioxidant enzyme activity, rhizosphere soil enzyme activities and bacterial community composition, as well as the control effect on FON were analyzed. The results indicated that mycorrhizal watermelon root exudates promoted the growth of watermelon seedlings and increased soil enzyme activities, actinomyces, and the quantity of bacteria in rhizosphere soil. The proportion of Proteobacteria and Bacteroides was decreased, and the proportion of Actinobacteria, Firmicutes, and Chloroflexi in rhizosphere soil was increased when the seedlings were watered with high concentrations of mycorrhizal root exudates. The dominant bacterial genera in rhizosphere soil were Kaistobacter, Rhodanobacter, Thermomonas, Devosia, and Bacillus. The root exudates of mycorrhizal watermelon could reduce the disease index of Fusarium wilt by 6.7-30%, and five ml/L of watermelon root exudates inoculated with F. mosseae had the strongest inhibitory effect on watermelon Fusarium wilt. Our results suggest mycorrhizal watermelon root exudates changed the composition of bacteria and soil enzyme activities in rhizosphere soil, which increase the resistance of watermelon to Fusarium wilt and promoted the growth of plants in continuous cropping soil.

Responses of bulk and rhizosphere soil microbiomes to different cover crop inputs and their connection and contribution to soil fertility and plant growth

Bulk and rhizosphere soil microbiomes may be naturally linked and exhibit unique responses to different cover crop inputs during the early decomposition process. However, their relationship and contribution to soil carbon and nitrogen levels and plant growth during the decomposition process remain unclear. Herein, we performed a pot-based experiment to investigate the interactive effects of cover crops (rye, hairy vetch [HV], and a mixture of rye and HV [mix]) and soil microbial habitats (bulk and rhizosphere soils) on the microbial community. Additionally, we identified the hub taxa and evaluated their contributions to the microbial community, soil fertility, and plant growth. Lettuce was grown in soil exposed to control, rye, HV, or mixed cover crops. Bacterial 16S rRNA) and fungal (ITS) community structures were characterized in bulk and rhizosphere soils of lettuce plants using a DNA-based molecular approach. The results showed that cover crops and soil microbial habitats independently affected microbial community structures; the relative abundances of fungi and bacteria, known as decomposers in bulk soil and plant growth-promoting bacteria in rhizosphere soil, increased. The hub taxa under each treatment represented specific groups that connect bulk and rhizosphere microbiomes. Based on Mantel statistical analysis, hub taxa may maintain the bulk soil microbiome, within which the bacterial community in HV and mix treatments may contribute to the nitrogen supply from cover crop residues. Additionally, the bacterial community in rhizosphere soil in HV and mix treatments may contribute to nitrogen absorption by lettuce plants. These results add to the understanding of the early process of sustainable agriculture using cover crops.

Effect of Chemical Fertilizer and Manure Combined with Biochar on Denitrification Potential and Denitrifying Bacterial Community in Rhizosphere Soil

To clarify the effect of chemical fertilizer and manure combined with biochar on denitrifying microorganisms and denitrification potential of rhizosphere soil, a pot experiment growing lemon was conducted involving five treatments, namely no fertilization (CK), chemical fertilizer (CF), manure (M), chemical fertilizer combined with biochar (CFBC), and manure combined with biochar (MBC). We determined the characteristics of the rhizosphere soil nirS-, nirK-, and nosZ-type denitrifying bacteria populations; denitrification potential; and soil environmental factors to clarify the effects of chemical and manure combined with biochar on denitrification. Our results showed that compared with that in CK, the CF treatment reduced the rhizosphere soil denitrification potential by 47.7%, whereas the M and MBC treatments increased the denitrification potential by 2192.7% and 1989.9%, respectively. The M and MBC treatments increased the gene copy number of nirS and nosZ, the CF and CFBC treatments decreased the gene copy number of nirS and nosZ, and all four fertilization treatments increased the gene copy number of nirK. Stepwise regression analysis showed that pH was the main factor for the abundance of nirS-type denitrifying bacteria and SOM and NH+4-N were the main factors for the abundance of nirK-type denitrifying bacteria, whereas pH, NO-3-N, and N/P were main factors for the abundance of nosZ-type denitrifying bacteria. The results of partial least squares analysis indicated that the abundance of nirS-and nosZ-type denitrifying bacteria, pH, TN, and N/P were the main factors affecting rhizosphere denitrification potential. Therefore, in acidic purple soil, nirS- and nosZ-type denitrifying bacteria were the main drivers of the soil denitrification process in lemon rhizospheres under chemical fertilizer and pig manure combined with biochar, whereas fertilizer affected the rhizosphere soil denitrification process by regulating soil pH, TN, and N/P.

Response of bacterial community characteristics in the rhizosphere soil of Stellera chamaejasme L. to its expansion on the Qinghai‐Tibet Plateau

AbstractQinghai‐Tibet Plateau is facing a serious environmental and ecological problem of Meadow degradation. Toxic weed invasion is a typical characteristic of grassland degradation. Soil microbial community composition is sensitive to environmental changes; however, the effects of poisonous weed expansion on soil bacterial communities are unclear. Here, we investigated the effects of Stellera chamaejasme L. expansion on the rhizosphere soil bacterial community structure and function using high‐throughput sequencing. The results showed that expansion of Stellera chamaejasme L. changed soil nitrogen(e.g., total nitrogen [TN, −39.02%], available nitrogen [AN, −32.95%]) and other soil nutrients. Redundancy analysis (RDA) and Variance partitioning analysis (VPA) showed that soil nutrients changed, leading to significant changes in the bacterial community structure. The expansion of Stellera chamaejasme L significantly reduced its rhizosphere bacterial alpha diversity, and the beta diversity had significant differences (p < 0.05). Principal coordinates analysis (PCoA) and analysis of similarity (ANOSIM) indicated that the expansion caused significant variations in the rhizosphere bacterial community (R = 0.7037, p < 0.01). The linear discriminant analysis (LDA) effect size (LEfSe) analysis identified 23 biomarkers, most of which were Proteobacteria, indicating that bacteria involved in soil nutrient cycling were better able to survive in the alpine grassland. The Biolog EcoPlate method was used to determine the soil microbial metabolic capacity in different S. chamaejasme expansions. The result showed that heavy expansion had higher carbon source usage ability and microbial diversity index values. Furthermore, it was also found that heavy expansion improved the usage rate of amino acid carbon sources. Tax4Fun prediction analysis further indicated that carbohydrate metabolism, amino acid metabolism, and membrane transport were central metabolic pathways of rhizosphere soil bacteria. Our study found that Stellera chamaejasme L. changed rhizosphere soil nutrient and bacterial community structure during expansion and helped it tolerate harsh conditions by enriching bacterial communities actively involved in carbon and nitrogen metabolism and promoting plant growth. These findings provided evidence to propose effective restoration measures for poisonous grassland degradation.

Assembly and co-occurrence patterns of rhizosphere bacterial communities are closely linked to soil fertility during continuous cropping of cut chrysanthemum (Chrysanthemum morifolium Ramat).

Continuous cropping is known to have profound effects on the soil microbial community in different planting systems. However, we lack an understanding of how different years of continuous cropping affects rhizosphere soil bacterial community co-occurrence pattern and assembly processes in the cut chrysanthemum (Chrysanthemum morifolium Ramat.) field. We collected the soils from cut chrysanthemum rhizospheres with planting for 1 year (PY1) and continuous cropping for 6 years (CY6) and 12 years (CY12). Real-time quantitative PCR and flow cytometry (FCM) techniques were used to test the 16S rRNA gene copy number and bacterial cell count, respectively. The bacterial community structure was analysed by using high-throughput sequencing technology. The CY12 had a significantly decreased soil fertility index and rhizosphere bacterial living cell counts and gene copy numbers compared to CY6 and PY1 (P <0.05). The rhizosphere bacterial community dissimilarity increased as the continuous cropping years increased. Three main ecological clusters (modules #1, #2, and #3) were observed in the bacterial co-occurrence network across all samples, and only the relative abundance of module #1 (enriched in the CY12) was significantly correlated with soil fertility (P <0.05). Moreover, the rhizosphere bacterial community assembly was primarily governed by the deterministic process under 12 years of continuous cropping. Soil fertility decline correlates with ecological network modularization and the deterministic assembly process of the rhizosphere bacterial community of cut chrysanthemum during continuous cropping.

Responses of Phragmites communis and its rhizosphere bacteria to different exposure sequences of molybdenum disulfide and levofloxacin

The effect of the molybdenum disulfide (MoS2)/levofloxacin (LVF) co-exposure was explored on Phragmites communis and rhizosphere soil bacterial communities. The sequence of MoS2/LVF exposure and the different MoS2 dosages (10 mg/kg and 100 mg/kg) contributed to different degrees of effect on the plant after 42 days of exposure. The treatment with priority addition of low dosage MoS2 significantly ameliorated P. communis growth, with root length growing up to 532.22 ± 46.29 cm compared to the sole LVF stress (200.04 ± 29.13 cm). Besides, MoS2 served as an alleviator and reduced the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) in P. communis under LVF stress, and activated bacteria in rhizosphere soil. These rhizosphere soil microbes assisted in mitigating toxic pollution in the soil and inducing plant resistance to external stress, such as bacteria genera Bacillus, Microbacterium, Flavihumibacter and altererythrobacter. Potential functional profiling of bacterial community indicated the addition of MoS2 contributed to relieve the reduction in functional genes associated with amino acid metabolism and the debilitation of gram_negative and aerobic phenotypic traits caused by LVF stress. This finding reveals the effect of different exposure sequences of MoS2 nanoparticles and antibiotic for plant-soil systems.

Fertilizer management methods affect bacterial community structure and diversity in the maize rhizosphere soil of a coal mine reclamation area

BackgroundThe filling or mixed stack mode is a frequently used coal mine reclamation engineering technique that results in changes in soil microbial community structure and nutrient content, which lead to considerable deviations from the characteristics of restored coal mine reclamation areas that can be used for farming. Fertilization is an effective strategy for improving soil fertility in such areas; however, the response of soil bacterial communities, especially in the crop rhizosphere soil, to different fertilization techniques in such soils remains unclear. Therefore, we investigated the effects of different fertilization management methods, including no fertilizer, farmers' practice, inorganic fertilizer, organic fertilizer, and organic–inorganic fertilizer, on maize yield, rhizosphere soil bacterial community and diversity, soil physicochemical properties, and nitrogen cycle-related gene abundance (nifH, AOB, and nirS).ResultsThe results showed that organic–inorganic fertilizer treatment significantly improved maize yield. The relative abundance of the dominant phyla did not significantly differ between the treatment groups. However, the Chao 1 and Shannon indices of the bacterial community significantly changed between the no fertilizer and organic–inorganic fertilizer treatments. Notably, organic–inorganic fertilizer application significantly increased the copy numbers of nifH and nirS. Further, moisture, bulk density, and available phosphorus content were identified as the major driving factors responsible for the changes in bacterial community structure, diversity, and copy numbers of nifH, nirS, and AOB.ConclusionsThe results of this study revealed that organic–inorganic fertilizer application improved soil bacterial diversity and the copy numbers of nifH and nirS in maize rhizosphere soil. Therefore, we concluded that organic–inorganic fertilizer is an effective strategy for the restoration of maize rhizosphere soil properties and bacterial communities in coal mine reclamation areas.

The rhizosphere soil properties and bacteria community of poplar are affected by magnetic field under salt condition

Magnetic fields (MFs) are konwn to affect plant growth, but their effects on soil conditions remain obscure. In this study, poplar seedlings (Populus×euramericana 'Neva') were subjected to a MF under saline conditions, and the rhizosphere soil properties and bacterial communities were then examined. Salt stress detrimentally influenced rhizosphere soil nutrients availability and bacterial community structure. However, MF treatments showed several positive effects, such as increasing the ammonium nitrogen (NH4+-N), amorphous iron oxide (Feo) and available phosphorus (AP) contents in the soil. Moreover,. soil urease and acid phosphatase activity increased by 59% and 63%, respectively. Meanwhile, MF treatments significantly improved the contents of extracellular polymeric substances (EPS) in rhizosphere soils and increased the relative abundance of dominant bacteria phyla (e.g., Actinobacteria, Gemmatimonadetes, and Proteobacteria). Furthermore, a co-occurrence network analysis revealed greater modular clustering in the MF treatments, however, the network stability did not improve. In conclusion, MFs increased rhizobacterial community modularity and promoted the production of bacterial EPS, these effects that then enhanced soil nutirent availability and poplar salt tolerance.

Microbial interactions and metabolisms in response to bacterial wilt and black shank pathogens in the tobacco rhizosphere.

Tobacco bacterial wilt (TBW) and black shank (TBS) are responsible for substantial economic losses worldwide; however, microbial interactions and metabolisms in response to TBW and TBS pathogens in the tobacco rhizosphere remain unclear. We explored and compared the response of rhizosphere microbial communities to these two plant diseases with the incidences in moderate and heavy degrees by sequencing of 16S rRNA gene amplicons and bioinformatics analysis. We found that the structure of rhizosphere soil bacterial communities was significantly (p < 0.05) changed from the incidences of TBW and TBS, which also led to decreased Shannon diversity and Pielou evenness. Compared with the healthy group (CK), the OTUs with significantly (p < 0.05) decreased relative abundances were mostly affiliated with Actinobacteria (e.g., Streptomyces and Arthrobacter) in the diseased groups, and the OTUs with significantly (p < 0.05) increased relative abundances were mainly identified as Proteobacteria and Acidobacteria. Also, molecular ecological network analysis showed that the nodes (<467) and links (<641) were decreased in the diseased groups compared with the control group (572; 1056), suggesting that both TBW and TBS weakened bacterial interactions. In addition, the predictive functional analysis indicated that the relative abundance of genes related to the biosynthesis of antibiotics (e.g., ansamycins and streptomycin) was significantly (p < 0.05) decreased due to incidences of TBW and TBS, and antimicrobial tests showed that some Actinobacteria strains (e.g., Streptomyces) and their secreted antibiotics (e.g., streptomycin) could effectively inhibit the growth of these two pathogens.

Changes in rice rhizosphere and bulk soil bacterial communities in the Doñana wetlands at different growth stages

The Doñana wetlands comprise an emblematic Mediterranean landscape protected as a UNESCO World Heritage Site. Some parts of these wetlands have been transformed into intensive rice cultivation areas, which are currently the most productive rice-growing areas in Europe. We examined the bacterial communities in these domesticated soils as they are key for plant health and productivity and have a strong influence on biochemical cycles. To identify the bacteria, we used metabarcoding analysis coupled with metabolic predictions and co-occurrence networks. This analysis was performed in the bulk and rhizosphere soils during different stages in the growing season. These soil compartments had a greater effect on the bacterial communities than the plant phenological stages. The diversity and richness of the bacterial population inhabiting the rhizosphere was much lower than that in the bulk soil, comprising taxa that were significantly more represented in this soil compartment, such as bacteria from the genus Hydrogenophaga, three genera from the order Rhizobiales, and unclassified genera from the families Desulfocapsaceae and Actinobacteria. Rhizosphere co-occurrence networks revealed a high number of negative connections, indicating unstable bacterial communities that may be highly influenced by biotic and abiotic factors. Rhizosphere networks mostly rely on two taxa belonging to the phyla Proteobacteria and Cyanobacteria, which are the predicted network hubs in this soil compartment. The bulk soil conserved high bacterial diversity and richness that was stable throughout the growth period of rice. Anaerobic bacteria from genera Marmoricola, the uncultured Gemmatimonadota bacteria SDR1034 terrestrial group, Anaerolinea, and the sulphur oxidizer, Thiobacillus were highly represented. This analysis provides valuable information for understanding bacterial diversity in the rhizosphere of rice cultivated in this region, which is critical for enhancing plant growth and productivity.

Belowground facilitation of plant mixtures on rhizosphere soil of Commelina communis grown on extremely Cu- and Cd-contaminated mine: From soil quality to bacterial community

Plant–plant interactions exert positive effects under stress conditions, but their impact on heavy metal-contaminated rhizosphere soil quality and bacterial community remains unclear. In this work, the rhizospheric soil of Cu-accumulator Commelina communis and neighboring plants grown in a heavily contaminated copper mine was analyzed to elucidate such belowground facilitation. Physicochemical properties and microbial characteristics of rhizospheric soil of control C. communis (far from neighboring plants), facilitated C. communis (near neighboring plants), and neighboring plants were compared. The average values of total organic carbon, NH4+-N, NO2−-N, NO3−-N, available phosphorus, urease, and phosphatase in the C. communis rhizosphere increased by 0.82-, 0.64-, 0.44-, 0.06-, 0.10-, 0.36-, and 0.30-fold in the presence of surrounding plants, respectively. The relative abundance of oligotrophic bacteria (Chloroflexi) decreased, whereas copiotrophic bacteria (Proteobacteria) increased in plant species mixtures. Venn graph and partial least squares discriminant analysis indicated that the composition of the bacterial community in the facilitated C. communis rhizosphere showed higher similarity to neighboring plants than to control C. communis. Among 49 predicted functional groups analyzed by FAPROTAX analysis, chemoheterotrophy (36.04 %) involved in carbon cycles had the highest relative abundance and increased in the facilitated C. communis rhizosphere due to the positive response of 193 OTUs (mainly belonging to Proteobacteria and Actinobacteriota) under plant–plant interactions. The increased relative abundance of Methylocella and Bradyrhizobium resulted in improved nitrogen fixation in the C. communis rhizosphere, whereas nitrate reduction with its main performer Rubrobacter was inhibited. The ecological function of rhizobiomes of the facilitated C. communis and neighbors also showed higher similarity compared with that of the control C. communis. These results show the role of neighboring plants in modulating soil quality and rhizobiomes of plant remediators under stress and more indoor garden experiments need to be conducted to verify such belowground facilitation.

The diversity and abundance of bacterial and fungal communities in the rhizosphere of Cathaya argyrophylla are affected by soil physicochemical properties.

Cathaya argyrophylla is an ancient Pinaceae species endemic to China that is listed on the IUCN Red List. Although C. argyrophylla is an ectomycorrhizal plant, the relationship between its rhizospheric soil microbial community and soil properties related to the natural habitat remains unknown. High-throughput sequencing of bacterial 16S rRNA genes and fungal ITS region sequences was used to survey the C. argyrophylla soil community at four natural spatially distributed points in Hunan Province, China, and functional profiles were predicted using PICRUSt2 and FUNGuild. The dominant bacterial phyla included Proteobacteria, Acidobacteria, Actinobacteria, and Chloroflexi, and the dominant genus was Acidothermus. The dominant fungal phyla were Basidiomycota and Ascomycota, while Russula was the dominant genus. Soil properties were the main factors leading to changes in rhizosphere soil bacterial and fungal communities, with nitrogen being the main driver of changes in soil microbial communities. The metabolic capacities of the microbial communities were predicted to identify differences in their functional profiles, including amino acid transport and metabolism, energy production and conversion, and the presence of fungi, including saprotrophs and symbiotrophs. These findings illuminate the soil microbial ecology of C. argyrophylla, and provide a scientific basis for screening rhizosphere microorganisms that are suitable for vegetation restoration and reconstruction for this important threatened species.

Rhizosphere Soil Bacterial Communities and Bacterial Root Endophytes in Cotton farming is Influence by Cultivation of Transgenic Bt and non-Bt Cotton Crop Varieties

Rhizosphere Soil Bacterial Communities and Bacterial Root Endophytes in Cotton farming is Influence by Cultivation of Transgenic Bt and non-Bt Cotton Crop Varieties

Rhizosphere and bulk soil bacterial community succession is influenced more by changes in soil properties than in rhizosphere metabolites across a maize growing season

The rhizosphere microbiome composition shifts across plant developmental stages. In addition, the bulk soil microbiome also changes during the growing season. However, the factors governing the rhizosphere and bulk soil microbiome succession across plant development are still not well identified. In this study we analyzed the changes in rhizosphere and bulk soil bacterial community structure through 16S rRNA amplicon sequencing across three maize growth stages (vegetative leaf 5 [V5], vegetative leaf 10 [V10] and reproductive stage 2 [R2]), as well as their correlations with temporal shifts in soil physicochemical properties and in root metabolites quantified in rhizosphere soils by LC/GC–MS. Twelve maize genotypes were used in a replicated field experiment for a comprehensive study. Results indicated significant correlations between the rhizosphere and bulk soil bacterial community succession with the temporal changes in rhizosphere metabolites and soil physicochemical properties. The changes in soil properties (mainly soil N and moisture) across stages explained more of the variation in the rhizosphere and bulk soil bacterial communities than the rhizosphere metabolites. However, shifts in rhizosphere metabolites (mainly sugars and gibberellins) across stages also strongly affected the rhizosphere bacterial community succession, but this effect was weaker on the bulk soil bacterial community. In addition to the changes in microbiome composition and diversity, we also detected changes in soil microbial respiration between plant developmental stages, with greater microbial activity at the V10 stage. In sum, our study showed that changes in soil properties have a great influence on both rhizosphere and bulk soil bacterial community succession across a growing season. The changes in plant root metabolites across the cropping season also affected the succession of the belowground bacterial communities, but the impact was much larger on the rhizosphere than on the bulk soil microbiome. Understanding the ecological processes shaping the belowground microbiomes through time is pivotal to develop future strategies for the most appropriate crop management across the whole growing season.

Schizotrophic Sclerotinia sclerotiorum-Mediated Root and Rhizosphere Microbiome Alterations Activate Growth and Disease Resistance in Wheat.

Sclerotinia sclerotiorum, a widespread pathogen of dicotyledons, can grow endophytically in wheat, providing protection against Fusarium head blight and stripe rust and enhancing wheat yield. In this study, we found that wheat seed treatment with strain DT-8, infected with S. sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV-1) and used as a "plant vaccine" for brassica protection, could significantly increase the diversity of the fungal and bacterial community in rhizosphere soil, while the diversity of the fungal community was obviously decreased in the wheat root. Interestingly, the relative abundance of potential plant growth-promoting rhizobacteria (PGPR) and biocontrol agents increased significantly in the DT-8-treated wheat rhizosphere soil. These data might be responsible for wheat growth promotion and disease resistance. These results may provide novel insights for understanding the interaction between the schizotrophic microorganism and the microbiota of plant roots and rhizosphere, screening and utilizing beneficial microorganisms, and further reducing chemical pesticide utilization and increasing crop productivity. IMPORTANCE Fungal pathogens are seriously threatening food security and natural ecosystems; efficient and environmentally friendly control methods are essential to increase world crop production. S. sclerotiorum, a widespread pathogen of dicotyledons, can grow endophytically in wheat, providing protection against Fusarium head blight and stripe rust and enhancing wheat yield. In this study, we discovered that S. sclerotiorum treatment increased the diversity of the soil fungal and bacterial community in rhizosphere soil, while the diversity of the fungal community was obviously decreased in the wheat root. More importantly, the relative abundance of potential PGPR and bio-control agents increased significantly in the S. sclerotiorum-treated wheat rhizosphere soil. The importance of this work is that schizotrophic S. sclerotiorum promotes wheat growth and enhances resistance against fungal diseases via changes in the structure of the root and rhizosphere microbiome.

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.

The Effects of Coexisting Elements (Zn and Ni) on Cd Accumulation and Rhizosphere Bacterial Community in the Soil-Tomato System

The increasing cadmium (Cd) levels in agricultural soils have become a worldwide concern for food crop security. Cd accumulation in the soil-plant system is closely related to other coexisting factors. In this study, the effects of different levels of Zn or Ni on Cd accumulation in tomato plants and on the rhizosphere soil bacterial community structure were analyzed by coupling pot experiments with high-throughput sequencing. The results demonstrated that tomato plants (Lycopersicon esculentum) in Zn-Cd and Ni-Cd co-contaminated soils exhibited lower relative growth rates. Co-contamination at low levels tended to reduce the bioaccumulation of heavy metals in the roots of plants, whereas increased contaminant concentrations produced the opposite effect. In the presence of 200 mg/kg Zn or 20 mg/kg Ni, the biomass of plant roots increased by 4.95–23.16% and the Cd content of the plant roots decreased by 17.36–68.93% due to the antagonistic effects between Cd and Zn/Ni. In addition, the richness and diversity of the bacterial community were significantly altered under HMs co-contamination, and the number of special bacteria was positively correlated with the level of heavy metals in the rhizosphere soil. The relative abundance of Proteobacteria increased and that of Actinobacteria decreased in soils with low levels of heavy metals. This may improve the tolerance of plant roots to heavy metals and reduce the accumulation of Cd in plant roots. These findings highlight the important role of coexisting elements in the inhibition of Cd accumulation in tomatoes and offer important information for the production of safe crops.

Effects of Microplastic High-density Polyethylene on Cotton Growth, Occurrence of Fusarium wilt, and Rhizosphere Soil Bacterial Community

Plastic mulch, especially polyethylene mulch, is widely used in agricultural production in China, but the microplastics formed by its degradation gradually have accumulated in soil, causing a series of environmental problems. At present, there have been many reports on the environmental biological effects of microplastics in farmland soil, but studies on the effects of microplastics on crop growth, disease occurrence, and rhizosphere soil bacterial communities are still lacking. In the previous study, it was found that 1% high-density polyethylene (HDPE, 500 mesh) could increase the incidence rate of cotton Fusarium wilt (33.3%) and inhibit growth, but this phenomenon was not found after soil sterilization. It was speculated that HDPE could affect the growth and occurrence of Fusarium wilt by regulating the soil microbial community. Therefore, high-throughput sequencing technology, combined with network and FAPROTAX function analysis, were used to investigate the effects of HDPE on the bacterial community structure, interaction network, and soil function in cotton rhizosphere in order to analyze the mechanism of HDPE. NovaSeq sequencing showed that the bacterial community of HDPE-treated cotton rhizosphere soil was composed of 54 phyla and 472 genera; the number of phyla and genera was higher than that in untreated soil. The α and β diversity and ANOSIM/Adonis analyses showed that HDPE significantly reduced the richness of the bacterial community and changed the composition of the community structure. Based on a T-test species difference analysis, HDPE significantly reduced the relative abundance of bacteria with biological control, pollutant degradation, and antifungal drug synthesis (such as Kribbella, Massiliam, Hailiangium, and Ramlibacter).The change in the bacterial community will lead to the change in soil bacterial function. Further analysis of FAPROTAX function revealed that HDPE weakened some biochemical functions of bacteria in the cotton rhizosphere soil, such as aerobic chemoheterotrophy, fermentation, and nitrate reduction. The correlation network at the genus level showed that HDPE treatment weakened the interaction between rhizosphere bacteria, reduced the number of positive correlation connections, increased the number of negative correlation connections, simplified network structure, and changed the key flora. The above results showed that HDPE could reduce the cotton growth and the occurrence of Fusarium wilt by changing the bacterial community, interaction, and functional metabolism in rhizosphere soil, which can provide guidance for evaluating the ecological risk of polyethylene microplastics and the remediation of contaminated soil.