Rhizosphere Soil Bacterial Communities Research Articles

Black shank-mediated alteration of the community assembly of rhizosphere soil bacteria in tobacco.

There is a close and complex interaction between the elements in the aboveground-underground ecosystem during the growth and development of plants. Specifically, when the aboveground part of plants is infected by pathogens, it induces the plant rhizosphere to synthesize specific root exudates. Consequently, a group of beneficial rhizosphere soil bacteria is recruited to help plants resist diseases. However, the changes in the rhizosphere soil bacterial community of plants under infection by oomycete pathogens remain unknown. Three experimental treatments were set up in this experiment: soils inoculated with P. nicotianae, no-inoculation with P. nicotianae, and a control. The control treatment was composed of soils without transplanted tobacco plants, with the pathogen inoculated twice at an interval of eight days to ensure a successful P. nicotianae infection. P. nicotianae inoculation treatments were designed using the hyphal block inoculation method. In the non-inoculation treatment, tobacco plants were grown normally without pathogen inoculation. The tobacco plants were grown in a greenhouse. This study demonstrates that tobacco plants recruit microorganisms at the rhizosphere level as a defense mechanism against disease after infection by the oomycete pathogen Phytophthora nicotianae. Specific rhizosphere soil bacteria were screened in vitro to promote tobacco growth in a biofilm-forming manner, which induced the systemic resistance of the plants to P. nicotianae. The recruitment of rhizosphere soil bacteria to the inter-root zone of tobacco plants after infection by P. nicotianae can help subsequently cultivated tobacco plants in the same soil resist pathogen infestation. In conclusion, the present study confirms that infestation caused by oomycete pathogens alters the composition of the plant rhizosphere soil bacterial community and recruits a specific group of beneficial microorganisms that induce disease resistance and promote plant growth, thereby maximizing the protection of progeny grown in the same soil against the disease.

Mangrove afforestation as an ecological control of invasive Spartina alterniflora affects rhizosphere soil physicochemical properties and bacterial community in a subtropical tidal estuarine wetland

Background The planting of mangroves is extensively used to control the invasive plant Spartina alterniflora in coastal wetlands. Different plant species release diverse sets of small organic compounds that affect rhizosphere conditions and support high levels of microbial activity. The root-associated microbial community is crucial for plant health and soil nutrient cycling, and for maintaining the stability of the wetland ecosystem. Methods High-throughput sequencing was used to assess the structure and function of the soil bacterial communities in mudflat soil and in the rhizosphere soils of S. alterniflora, mangroves, and native plants in the Oujiang estuarine wetland, China. A distance-based redundancy analysis (based on Bray–Curtis metrics) was used to identify key soil factors driving bacterial community structure. Results S. alterniflora invasion and subsequent mangrove afforestation led to the formation of distinct bacterial communities. The main soil factors driving the structure of bacterial communities were electrical conductivity (EC), available potassium (AK), available phosphorus (AP), and organic matter (OM). S. alterniflora obviously increased EC, OM, available nitrogen (AN), and NO3−-N contents, and consequently attracted copiotrophic Bacteroidates to conduct invasion in the coastal areas. Mangroves, especially Kandelia obovata, were suitable pioneer species for restoration and recruited beneficial Desulfobacterota and Bacilli to the rhizosphere. These conditions ultimately increased the contents of AP, available sulfur (AS), and AN in soil. The native plant species Carex scabrifolia and Suaeda glauca affected coastal saline soil primarily by decreasing the EC, rather than by increasing nutrient contents. The predicted functions of bacterial communities in rhizosphere soils were related to active catabolism, whereas those of the bacterial community in mudflat soil were related to synthesis and resistance to environmental factors. Conclusions Ecological restoration using K. obovata has effectively improved a degraded coastal wetland mainly through increasing phosphorus availability and promoting the succession of the microbial community.

Intercropping of tobacco and maize at seedling stage promotes crop growth through manipulating rhizosphere microenvironment.

Changes in the rhizosphere microbiome and metabolites resulting from crop intercropping can significantly enhance crop growth. While there has been an increasing number of studies on various crop combinations, research on the intercropping of tobacco and maize at seedling stage remains limited. This study is the first to explore rhizosphere effects of intercropping between tobacco and maize seedling stages, we analyzed the nitrogen, phosphorus and potassium nutrients in the soil, and revealed the important effects on soil microbial community composition and metabolite profiles, thereby regulating crop growth and improving soil balance. Compared with mono-cropping, intercropping increased the biomass of the two crops and promoted the nutrient absorption of nitrogen, phosphorus and potassium. Under intercropping conditions, the activities of sucrase, catalase and nitrate reductase in tobacco rhizosphere soil and the content of available potassium, the activities of nitrate reductase and acid phosphatase in maize rhizosphere soil were significantly increasing. Rhizosphere soil bacterial and fungal communities such as Sphingomonas, Massilia, Humicola and Penicillium respond differently to crop planting patterns, and soil dominant microbial communities are regulated by environmental factors such as pH, Organic Matter, Available Potassium, Nitrate Reductase, and Urease Enzyme. Network analysis showed that soil microbial communities were more complex after intercropping, and the reciprocal relationship between bacteria and fungi was enhanced. The difference of metabolites in soil between intercropping and monocropping system was mainly concentrated in galactose metabolism, starch and sucrose metabolism pathway, and the content of carbohydrate metabolites was significantly higher than that of monocropping soil. Key metabolites such as D-Sucrose, D-Fructose-6-Phosphate, D-Glucose-1-Phosphatel significantly influence the composition of dominant microbial communities such as Sphingomonas and Penicillium. This study explained the effects of intercropping between flue-cured tobacco and maize on the content of soil metabolites and soil microbial composition in rhizosphere soil, and deepened the understanding that intercropping system can improve the growth of flue-cured crops seedlings through rhizosphere effects.

Reclamation of co-pyrolyzed dredging sediment as soil cadmium and arsenic immobilization material: Immobilization efficiency, application safety, and underlying mechanisms

The safe management of toxic metal-polluted dredging sediment (DS) is imperative owing to its potential secondary hazards. Herein, the co-pyrolysis product (DS@BC) of polluted DS was creatively applied to immobilize soil Cd and As to achieve DS resource utilization, and the efficiency, safety, and mechanism were investigated. The results revealed that the DS@BC was more effective at reducing soil Cd bioavailability than the DS was (58.9–73.2% vs. 21.8–27.4%), except for the dilution effect, whereas the opposite phenomenon occurred for soil As (25.5–35.7% vs. 35.7–42.8%). The DS@BC immobilization efficiency was dose-dependent for both Cd and As. Soil labile Cd and As were transformed to more stable fractions after DS@BC immobilization. DS@BC immobilization inhibited the transfer of soil Cd and As to Brassica chinensis L. and did not cause excessive accumulation of other toxic metals in the plants. The appropriate addition of the DS@BC (8%) sufficiently alleviated the oxidative stress response of the plants and enhanced their growth. These findings indicate that the DS@BC was safe and effective for soil Cd and As immobilization. DS@BC immobilization decreased the diversity and richness of the rhizosphere soil bacterial community because of the dilution effect. The DS@BC immobilized soil Cd and As via direct adsorption, and indirect increasing soil pH, and regulating the abundance of specific beneficial bacteria (e.g., Bacillus). Therefore, the use of co-pyrolyzed DS as a soil Cd and As immobilization material is a promising resource utilization method for DS. Notably, to verify the long-term effects and safety of DS@BC immobilization, field trials should be conducted to explore the effectiveness and risk of harmful metal release from DS@BC immobilization under real-world conditions.

Carbendazim adsorption on polyethylene microplastics and the toxicity mechanisms on cotton plants, soil enzyme activity and rhizosphere bacterial community under combined stress conditions

Polyethylene (PE) and carbendazim are common pollutants in soil, and their individual toxicities have been widely studied. However, there are few reports on PE as a carrier for carbendazim and their combined toxicity to plants and soil. Therefore, in this study, we focused on the adsorption effects of different PE particle sizes (25 μm, 150 μm) at different concentrations (1 %, 5 %, m/m) on carbendazim (2.0 mg·kg−1, 5.0 mg·kg−1) and the combined toxicity to cotton and soil microbiota. The results showed that the carbendazim adsorption by PE followed secondary kinetics and was consistent with the Freundlich model. Due to adsorption, the half-life of carbendazim in soil was extended (from 6.31 d to 14.20 d), and the capacity of carbendazim to control cotton Verticillium wilt was weakened. Combined stress exacerbated the inhibitory effects on cotton biomass, chlorophyll content, soil enzyme activity compared to the individual carbendazim or PE treatments. The high-throughput sequencing analysis indicated that combined stress (5.0 mg·kg−1 carbendazim, 5 % 25 μm PE) significantly reduced the richness and diversity, changed the structural composition of rhizosphere soil bacterial community, and greatly increased the abundance of bacteria with potential degrading functions, such as Marmoricola. Functional and network analysis showed that combined stress altered the soil microbial function and abundance, as well as the network structure and key bacterial groups, decreased the number of positively correlated connections. This study provides a theoretical basis for evaluating the effects of combined PE and carbendazim stress on crops and soils.

Oat/Soybean Intercropping Reshape the Soil Bacterial Community for Enhanced Nutrient Cycling

ABSTRACTIntercropping, particularly within legume‐based systems, has been shown to enhance yields and optimize resource use efficiency. Yet, the potential contribution of intercropping on soil microbial communities and functions to soil nutrients cycling are not fully understood. We conducted the same field experiments at Youyu (Site1) and Zhangbei (Site2) in Northern China to evaluate the impact of oat/soybean intercropping on the rhizosphere soil bacterial community structure, composition, and co‐occurrence networks. Our results indicated that intercropping significantly modified the bacterial community structure for both oat and soybean at Site1, with changes observed only in the oat community at Site2. Specifically, intercropping led to a substantial increase in the relative abundance of Bacteroidetes and Patescibacteria in the oat rhizosphere by 48.3% and 65.4% (Site1), respectively. Conversely, in the soybean rhizosphere at Site1, there was a notable decrease in the abundance of Patescibacteria and Nitrospirae by 32.4% and 40.0%, respectively. The soil bacterial functional groups demonstrated robust positive correlations with key soil parameters such as available nitrogen (Nmin), available phosphorus (Avail‐P), and the activities of nitrogen‐ and phosphorus‐acquiring enzymes in the rhizosphere. In conclusion, intercropping is an effective agricultural practice for enhancing nitrogen and phosphorus cycling by reshaping the soil bacterial community, offering a distinct advantage over monoculture practices. This insight underscores the potential of intercropping to foster sustainable soil nutrient management, highlighting the importance of integrating such practices into modern agricultural strategies to ensure long‐term productivity and environmental sustainability.

Impact of a Potent Strain of Plant Growth-Promoting Bacteria (PGPB), Bacillus subtilis S1 on Bacterial Community Composition, Enzymatic Activity, and Nitrogen Content in Cucumber Rhizosphere Soils.

Antagonistic bacterial strains from Bacillus spp. have been widely studied and utilized in the biocontrol of phytopathogens and the promotion of plant growth, but their impacts on the rhizosphere microecology when applied to crop plants are unclear. Herein, the effects of applying the antagonistic bacterium Bacillus subtilis S1 as a biofertilizer on the rhizosphere microecology of cucumbers were investigated. In a pot experiment on cucumber seedlings inoculated with S1, 3124 bacterial operational taxonomic units (OTUs) were obtained from the rhizosphere soils using high-throughput sequencing of 16S rRNA gene amplicons, and the most abundant phylum was Proteobacteria that accounted for 49.48% in the bacterial community. S1 treatment significantly reduced the abundances of soil bacterial taxa during a period of approximately 30days but did not affect bacterial diversity in the rhizosphere soils of cucumbers. The enzymatic activities of soil nitrite reductase (S-Nir) and dehydrogenase (S-DHA) were significantly increased after S1 fertilization. However, the activities of soil urease (S-UE), cellulase (S-CL), and sucrase (S-SC) were significantly reduced compared to the control group. Additionally, the ammonium- and nitrate-nitrogen contents of S1-treated soil samples were significantly lower than those of the control group. S1 fertilization reshaped the rhizosphere soil bacterial community of cucumber plants. The S-CL activity and nitrate-nitrogen content in rhizosphere soil affected by S1 inoculation play important roles in altering the abundance of rhizosphere soil microbiota.

Bacillus licheniformisYB06: A Rhizosphere-Genome-Wide Analysis and Plant Growth-Promoting Analysis of a Plant Growth-Promoting Rhizobacterium Isolated from Codonopsis pilosula.

Codonopsis pilosula, commonly known as Dangshen, is a valuable medicinal plant, but its slow growth and susceptibility to environmental stress pose challenges for its cultivation. In pursuit of sustainable agricultural practices to enhance the yield and quality of Dangshen, the present study isolated a bacterial strain exhibiting plant growth-promoting potential from the rhizosphere of C. pilosula. This strain was subsequently identified as Bacillus licheniformisYB06. Assessment of its plant growth-promoting attributes revealed the potential of B. licheniformis YB06 as a biofertilizer. Whole-genome sequencing of B. licheniformis YB06 revealed a genome size of 4,226,888 bp with a GC content of 46.22%, harboring 4325 predicted protein-coding sequences. Genomic analysis of B. licheniformis YB06 revealed a diverse array of genes linked to induced systemic resistance (ISR) and plant growth-promoting (PGP) traits, encompassing phytohormone production, nitrogen assimilation and reduction, siderophore biosynthesis, phosphate solubilization, biofilm formation, synthesis of PGP-related amino acids, and flagellar motility. Seed germination assays demonstrated the positive effects of B. licheniformis YB06 on the germination and growth of C. pilosula seedlings. Furthermore, we explored various fertilization regimes, particularly the B. licheniformis YB06-based biofertilizer, were investigated for their impact on the structure and diversity of the C. pilosula rhizosphere soil bacterial community. Our findings revealed that fertilization significantly impacted soil bacterial composition and diversity, with the combined application of B. licheniformis YB06-based biofertilizer and organic fertilizer exhibiting a particularly pronounced enhancement of rhizosphere bacterial community structure and diversity. This study represents the first report on the beneficial effects of B. licheniformis YB06 on both the growth of C. pilosula and the composition of its rhizosphere soil microbial community. These findings provide a theoretical foundation and practical guidance for the development of novel bio-organic compound fertilizers, thereby contributing to the sustainable cultivation of C. pilosula.

Impact of Transgenic Maize Ruifeng125 on Diversity and Dynamics of Bacterial Community in Rhizosphere Soil.

With the development of commercialized planting of genetically modified crops, their ecological security risks remain a key topic of public concern. Insect-resistant genetically modified maize, Ruifeng125, which expresses a fusion Bt protein (Cry1Ab-Cry2Aj), has obtained the application safety certificate issued by the Chinese government. To determine the effects of Ruifeng125 on the diversity and dynamics of bacterial communities, the accumulation and degradation pattern of the fusion Bt protein in the rhizosphere soil of transgenic maize were detected. Results showed that the contents of Bt protein varied significantly at different developmental stages, but after straw was returned to the field, over 97% of Bt proteins were degraded quickly at the early stages (≤10 d) and then they were degraded at a relatively slow rate. In addition, the variations in bacterial community diversity in the rhizosphere soil were detected by 16S ribosomal RNA (Rrna) high-throughput sequencing technology. A total of 44 phyla, 435 families, and 842 genera were obtained by 16S rRNA sequencing, among which Proteobacteria, Actinobacia, Acidobacter Acidobacterium, and Chloroflexi were the dominant taxa. At the same developmental stage, no significant differences in soil bacterial diversity were detected between Ruifeng125 and its non-transgenic control variety. Further analysis revealed that developmental stage, rather than the transgenic event, made the greatest contribution to the changes in soil microbial diversity. This research provides important information for evaluating the impacts of Bt crops on the soil microbiome and establishes a theoretical foundation for their environmental safety assessment.

Analysis of Bacterial Community Characteristics in Maize Root Zones Under Maize-soybean Compound Planting Mode

Maize-soybean compound intercropping has the potential to increase yield and is being tested for spreading in Huang-Huai-hai Plain. However, the main regulatory regions of this cropping pattern on soil microbial communities have not been clarified. In the present study, the tested samples were collected from three maize root zones of bulk soil, rhizosphere soil, and roots under mono- and intercropping planting modes, respectively. The non-rhizosphere soil chemical properties and enzyme activities were determined, and bacterial communities were characterized using high-throughput sequencing of the 16S rRNA gene V3-V4 region. Compared with monocropping, the maize bulk soil electric conductivity （EC）, soil organic matter （SOM）, available potassium （AK）, available phosphorus （AP）, total nitrogen （TN）, and enzyme activities of intercropping were significantly increased. The α diversities and β diversity of the bacterial community in rhizosphere soil were significantly different between the two planting modes. There were 11 bacteria genera with significantly higher abundance in the rhizosphere soil of compound planting than that of monoculture, and TN, AP, and catalase were the three most important factors contributing to their distribution. The abundances of 8 genera among the 11 genera mentioned above, unclassified Vicinamibacterales, unclassified Geminicoccaceae, MND1, unclassified Gemmatimonadaceae, Acidibacter, unclassified Vicinamibacteraceae, Sphingomonas, and unclassified Comamonadaceae were significantly positively correlated with TN. As for the bacteria distribution in maize root, AK contributed the most and had a significantly negative correlation with unclassified Rhizobiaceae and unclassified Microscillaceae and a positive correlation with Haliangium. Maize-soybean compound intercropping affected mainly the bacterial community of maize rhizosphere and had an evident effect on soil fertilizer cultivation and microbial diversity regulation, which provides a theoretical basis and practical guidance for rational intercropping to maintain agroecosystem biodiversity.

Fertilization regime changes rhizosphere microbial community assembly and interaction in Phoebe bournei plantations

Fertilizer input is one of the effective forest management practices, which improves soil nutrients and microbial community compositions and promotes forest productivity. However, few studies have explored the response of rhizosphere soil microbial communities to various fertilization regimes across seasonal dynamics. Here, we collected the rhizosphere soil samples from Phoebe bournei plantations to investigate the response of community assemblages and microbial interactions of the soil microbiome to the short-term application of four typical fertilizer practices (including chemical fertilizer (CF), organic fertilizer (OF), compound microbial fertilizer (CMF), and no fertilizer control (CK)). The amendments of organic fertilizer and compound microbial fertilizer altered the composition of rhizosphere soil bacterial and fungal communities, respectively. The fertilization regime significantly affected bacterial diversity rather than fungal diversity, and rhizosphere fungi responded more sensitively than bacteria to season. Fertilization-induced fungal networks were more complex than bacterial networks. Stochastic processes governed both rhizosphere soil bacterial and fungal communities, and drift and dispersal limitation dominated soil fungal and bacterial communities, respectively. Collectively, these findings demonstrate contrasting responses to community assemblages and interactions of rhizosphere bacteria and fungi to fertilizer practices. The application of organic fertilization strengthens microbial interactions and changes the succession of key taxa in the rhizosphere habitat.Key points• Fertilization altered the key taxa and microbial interaction• Organic fertilizer facilitated the turnover of rhizosphere microbial communities• Stochasticity governed soil fungal and bacterial community assembly

Differential regulation of belowground rhizospheric ecosystem by biological and chemical nitrogen supplies: implications for maize yield enhancement mechanisms.

Nitrogen (N) content affects aboveground maize growth and nutrient absorption by altering the belowground rhizospheric ecosystem, impacting both yield and quality. However, the mechanisms through which different N supply methods (chemical and biological N supplies) regulate the belowground rhizospheric ecosystem to enhance maize yield remain unclear. To address this issue, we conducted a field experiment in northeast China, comprising three treatments: maize monocropping without N fertilizer application (MM), maize/alfalfa intercropping without N fertilizer application (BNF), and maize monocropping with N fertilizer application (CNS). The MM treatment represents the control, while the BNF treatment represents the biological N supply form, and CNS treatment represents the chemical N supply form. In the autumn of 2019, samples of maize and rhizospheric soil were collected to assess parameters including yield, rhizospheric soil characteristics, and microbial indicators. Both BNF and MM significantly increased maize yield and different yield components compared with MM, with no statistically significant difference in total yield between BNF and CNS. Furthermore, BNF significantly improved N by 12.61% and available N (AN) by 13.20% compared with MM. Furthermore, BNF treatment also significantly increased the Shannon index by 1.90%, while the CNS treatment significantly increased the Chao1 index by 28.1% and ACE index by 29.49%, with no significant difference between CNS and BNF. However, CNS had a more pronounced impact on structure of the rhizosphere soil bacterial community compared to BNF, inducing more significant fluctuations within the microbial network (modularity index and negative cohesion index). Regarding N transformation pathways predicted by bacterial functions, BNF significantly increased the N fixation pathway, while CNS significantly increased assimilatory nitrate reduction. In CNS, AN, NO3-N, NH4-N, assimilatory nitrate reduction, and community structure contributed significantly to maize yield, whereas in BNF, N fixation, community structure, community stability, NO3-N, and NH4-N played significant roles in enhancing maize yield. While CNS and BNF can achieve comparable maize yields in practical agricultural production, they have significantly different impacts on the belowground rhizosphere ecosystem, leading to different mechanisms of yield enhancement.

Nano- and Microplastics Increase the Occurrence of Bacterial Wilt in Tomato (Solanum lycopersicum L.).

Concern over nano- and microplastic contamination of terrestrial ecosystems has been increasing. However, little is known about the effect of nano- and microplastics on the response of terrestrial ecosystems already under biotic stress. Here, nano- and microplastics at 150-500 mg·kg-1 were exposed to tomatoes (Solanum lycopersicum L.), and the results demonstrate that the presence of nano- and microplastics increased the occurrence of bacterial wilt caused by Ralstonia solanacearum in tomatoes as a function of contaminant concentration, surface modification, and size. Our work shows that nanoplastics (30 nm, 250 mg·kg-1) increased the disease incidence by 2.19-fold. The disease severities in amino- and carboxyl-modified nanoplastic treatments were 30.4 and 21.7% higher than that in unmodified nanoplastic treatment, respectively. The severity of disease under the influence of different-sized nano- and microplastic treatments followed the order 30 > 100 nm > 1 > 50 μm. Mechanistically, nanoplastics disrupted the structure of the tomato rhizosphere soil bacterial community and suppressed the induced systemic resistance in tomato; nanoplastics in planta decreased the salicylic acid and jasmonic acid content in tomatoes, thus inhibiting systemic acquired resistance; and microplastics increased the soil water retention, leading to increased pathogen abundance in the rhizosphere. Additionally, the leachates from nano- and microplastics had no effect on disease occurrence or the growth of tomatoes. Our findings highlight a potential risk of nano- and microplastic contamination to agriculture sustainability and food security.

Recruitment and Aggregation Capacity of Tea Trees to Rhizosphere Soil Characteristic Bacteria Affects the Quality of Tea Leaves.

There are obvious differences in quality between different varieties of the same plant, and it is not clear whether they can be effectively distinguished from each other from a bacterial point of view. In this study, 44 tea tree varieties (Camellia sinensis) were used to analyze the rhizosphere soil bacterial community using high-throughput sequencing technology, and five types of machine deep learning were used for modeling to obtain characteristic microorganisms that can effectively differentiate different varieties, and validation was performed. The relationship between characteristic microorganisms, soil nutrient transformation, and tea quality formation was further analyzed. It was found that 44 tea tree varieties were classified into two groups (group A and group B) and the characteristic bacteria that distinguished them came from 23 genera. Secondly, the content of rhizosphere soil available nutrients (available nitrogen, available phosphorus, and available potassium) and tea quality indexes (tea polyphenols, theanine, and caffeine) was significantly higher in group A than in group B. The classification result based on both was consistent with the above bacteria. This study provides a new insight and research methodology into the main reasons for the formation of quality differences among different varieties of the same plant.

Insight into the mechanisms of plant growth promoting strain ZY2 in improving phytoremediation efficiency in perfluorooctanoic acid (PFOA)-contaminated soil

Perfluorooctanoic acid (PFOA) is an anthropogenic perfluorinated alkyl substance which can enter the food chain and pose health risks. The hydrophilic carboxyl head of PFOA enhances its solubility in water, making it easier for PFOA to migrate with soil water and be absorbed by plants from the soil. Plant growth promoting bacteria (PGPR) have the ability to compensate for plant growth disadvantage under unfavorable conditions and are therefore likely to reduce the negative effects of PFOA phytotoxicity on plant growth. However, the effectiveness of the PGPR-assisted plant systems for remediation of PFOA-contaminated soil has not yet been demonstrated. To this end, a novel strain of Rhizobium sp. was isolated and named as ZY2, which is tolerant to PFOA and exhibits significant plant growth-promoting trains. The results indicated that inoculation with strain ZY2 significantly increased the biomass of oilseed rape. Notably, the accumulation content of PFOA in oilseed rape roots increased significantly by 89.0 % and the removal of PFOA from the soil increased over 3 times after inoculation with ZY2. In addition, inoculated ZY2 also altered the rhizosphere soil bacterial community structure which might correlate with the production of a series of hydrolases and reductases involved in soil carbon and nitrogen cycling processes. Generally, this study offered a novel approach for establishing an effective phytoremediation system in PFOA-contaminated soil.

Combined contamination of microplastic and antibiotic alters the composition of microbial community and metabolism in wheat and maize rhizosphere soil

The widespread application of antibiotics and plastic films in agriculture has led to new characteristics of soil pollution. The impacts of combined contamination of microplastics and antibiotics on plant growth and rhizosphere soil bacterial community and metabolisms are still unclear. We conducted a pot experiment to investigate the effects of polyethylene (0.2%) and norfloxacin/doxycycline (5 mg kg–1), as well as the combination of polyethylene and antibiotics, on the growth, rhizosphere soil bacterial community and metabolisms of wheat and maize seedlings. The results showed that combined contamination caused more serious damage to plant growth than individual contamination, and aggravated root oxidative stress responses. The diversity and structure of soil bacterial community were not markedly altered, but the composition of the bacterial community, soil metabolisms and metabolic pathways were altered. The co-occurrence network analysis indicated that combined contamination may inhibit the growth of wheat and maize seedings by simplifying the interrelationships between soil bacteria and metabolites, and altering the relative abundance of specific bacteria genera (e.g. Kosakonia and Sphingomonas) and soil metabolites (including sugars, organic acids and amino acids). The results help to elucidate the potential mechanisms of phytotoxicity of the combination of microplastic and antibiotics.

Effects of soil microbial ecology on ginsenoside accumulation in Panax ginseng across different cultivation years

The quality of ginseng is greatly influenced by ecological factors, especially soil factors. However, there are few reports on the association between the physicochemical properties of ginseng rhizosphere soil, enzyme activity, microbial bacterial community, and ginsenoside content accumulation in ginseng planted at different ages. In order to investigate the relationship between the soil microbial ecology of ginseng and the content of ginsenosides, this study compared the differences in the rhizosphere soil microecological environment and ginsenoside accumulation between ginseng planted for one, two, and three years, using soil without ginseng cultivation as a control. The results showed that monomer saponins Ro, Re, Rf, Rb1, and total ginsenoside content increased significantly (P < 0.05), while monomer saponins Rb2, Rd, Rh2, and Rg3 content decreased significantly in three-year-old ginseng, (P < 0.05). And soil pH, soil bulk weight and soil enzyme activity in ginseng rhizosphere soils altered the abundance and diversity of rhizosphere soil bacterial community. Redundancy analysis and Pearson correlation analysis revealed that soil pH, soil bulk density, soil urease, and protease were the primary factors influencing the bacterial community in the soil around roots of one, two, three years old ginseng. Co-occurrence network visualization analysis indicated that seven bacterial communities, Planctomycetota, Methylomirabilota, Verrucomicrobiota and Acidobacteriota at the phylum level, Vicinamibacterales_unclassified, Vicinamibacteraceae_unclassified and Candidatus_Udaeobacter at the genus level, had a significant effect on the synthesis of ginsenosides. In summary, soil urease, pH, and soil bulk density in agricultural soils can regulate soil physicochemical properties, soil enzymatic activities, and soil bacterial community abundance. These factors are key drivers of the ginseng soil microbial ecology in ginseng cultivation. These studies will provide a scientific basis for subsequent optimization of soil improvement techniques for cultivated ginseng in farmland by improving the soil microbial ecology.

Phthalate ester (PAEs) accumulation in wheat tissues and dynamic changes of rhizosphere microorganisms in the field with plastic-film residue

Phthalates acid esters (PAEs) have accumulated in soil and crops like wheat as a result of the widespread usage of plastic films. It is yet unclear, nevertheless, how these dynamic variations in PAE accumulation in wheat tissues relate to rhizosphere bacteria in the field. In this work, a field root-bag experiment was conducted to examine the changes of PAEs accumulation in the rhizosphere soil and wheat tissues under film residue conditions at four different growth stages of wheat, and to clarify the roles played by the microbial community in the alterations. Results showed that the plastic film residues significantly increased the concentrations of PAEs in soils, wheat roots, straw and grains. The maximum ΣPAEs concentration in soils and different wheat tissues appeared at the maturity, with the ΣPAEs concentration of 1.57 mg kg−1, 4.77 mg kg−1, 5.21 mg kg−1, 1.81 mg kg−1 for rhizosphere soils, wheat roots, straw and grains, respectively. The plastic film residues significantly changed the functions and components of the bacterial community, increased the stochastic processes of the bacterial community assembly, and reduced the complexity and stability of the bacterial network. In addition, the present study identified some bacteria associated with plastic film residues and PAEs degradation in key-stone taxa, and their relative abundances were positive related to the ΣPAEs concentration in soils. The PAEs content and key-stone taxa in rhizosphere soil play a crucial role in the formation of rhizosphere soil bacterial communities. This field study provides valuable information for better understanding the role of microorganisms in the complex system consisting of film residue, soil and crops.

Diversity and growth-promoting characteristics of rhizosphere bacteria of three naturally growing plants at the sand iron ore restoration area in Qinghe County

It is a great challenge to restore northern mines after mining and achieve optimal results due to the extremely harsh environment and climate, as in Qinghe County of Xinjiang Province, China. Qinghe County has a climate of drought, cold, strong winds, and high altitude. After sand and iron mining, the soil in this area contains a large amount of sand and gravel with extremely low organic matter, nitrogen deficiency, and a high pH of 9.26. Our preliminary studies disclosed that only three plants, including Caligonum junceum, Atraphaxis virgata, and Melilotus albus Medic, can grow naturally in this environment without any artificial management. For effective ecology restoration, this study explored the mechanism of plant-microbial interaction and stress resistance in this environment. It was found that although the soil condition in the sand iron ore landfill area is extreme, the bacterial diversity remained high, with Shannon and Simpson indices reaching 9.135 and 0.994, respectively. The planting of three types of remediation plants did not significantly improve, or even decreased, the soil bacterial diversity index, but greatly changed the composition of dominant bacterial genera. Significant differences in the composition of rhizosphere soil bacterial communities among these three remediation plants were observed. Potential new bacterial species accounted for 9.8 %, and the proportion of unique genera reached 30 % or 50 %, respectively. Among all the isolated strains, 74 % had nitrogen fixation and other growth-promoting properties. In summary, the soil microbial community structure in this extreme environment is unique and diverse. The types of remediation plants play a major role in the composition of the rhizosphere bacterial community structure, and the recruited growth-promoting bacteria are diverse and functional. This study may offer valuable information for further studies in vegetation restoration and aid in ecology restoration, especially under extreme conditions.

Impacts of AlaAT3 transgenic poplar on rhizosphere soil chemical properties, enzyme activity, bacterial community, and metabolites under two nitrogen conditions

ABSTRACT Poplar stands as one of the primary afforestation trees globally. We successfully generated transgenic poplar trees characterized by enhanced biomass under identical nutrient conditions, through the overexpression of the pivotal nitrogen assimilation gene, pxAlaAT3. An environmental risk assessment was conducted for investigate the potential changes in rhizosphere soil associated with these overexpressing lines (OL). The results show that acid phosphatase activity was significantly altered under ammonium in OL compared to the wild-type control (WT), and a similar difference was observed for protease under nitrate. 16SrDNA sequencing indicated no significant divergence in rhizosphere soil microbial community diversity between WT and OL. Metabolomics analysis revealed that the OL caused minimal alterations in the metabolites of the rhizosphere soil, posing no potential harm to the environment. With these findings in mind, we anticipate that overexpressed plants will not adversely impact the surrounding soil environment.