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It is unknown whether soil microbiota and soil bacteria isolated from the rhizosphere of selenium hyperaccumulator plants can affect selenium absorption by selenium non-hyperaccumulator plants. Here, we used pot experiments and split root experiments to investigate the role of soil microbiota and isolated rhizosphere bacteria from a selenium hyperaccumulator plant (Cardamine violifolia) in affecting selenium absorption by a selenium non-hyperaccumulator plant (Brassica napus), combining root metabolism analysis, microbiome profiling, strain isolation and its selenium absorption functional validation. We found that soil microbiota of Cardamine violifolia significantly increased the root selenium content by 31.8% and regulated root exudation by Brassica napus. Additionally, the application of upregulated long-chain organic acids + amino acids, long-chain organic acids + short-chain organic acids, ethanolamine, and 2-ketobutyric acid increased the selenium contents in the roots of Brassica napus by 69.6%, 38.4%, 81.2%, and 48.8%, respectively. Further investigation revealed that dominant bacteria were significantly enriched in the rhizosphere of C. violifolia compared to B. napus. After that, we isolated the rhizosphere bacteria of Cardamine violifolia and observed that Bacillus sp.-2, Chryseobacterium sp., and Pseudomonas sp., as well as their combined communities, significantly improved selenium absorption in Brassica napus. Moreover, the combined bacterial communities significantly regulated specific-root metabolism, enhanced rhizosphere soil available selenium content, promoted root development, increased expression levels of genes encoding selenium transporter in root. These findings provide insights into utilizing rhizosphere bacteria of selenium hyperaccumulator plants to increase selenium absorption by non-hyperaccumulator plants. [ABSTRACT FROM AUTHOR]

Introduction: Thus far, the impact of kaolin mining activities on the surrounding native plants and rhizosphere microecology has not been fully understood. Methods: In this study, we used 16S rRNA high-throughput sequencing to examine the impact of kaolin mining on the rhizosphere bacterial communities and functions of three local plant species: Conyza bonariensis, Artemisia annua, and Dodonaea viscosa. Results: The results showed that kaolin mining significantly reduced the diversity of rhizosphere bacteria in these plants, as indicated by the Shannon, Simpson, Chao1, and observed species indices (p < 0.05). Kaolin mining had an impact on the recruitment of three rhizosphere bacteria native to the area: Actinoplanes, RB41, and Mycobacterium. These bacteria were found to be more abundant in the rhizosphere soil of three local plants than in bulk soil, yet the mining of kaolin caused a decrease in their abundance (p < 0.05). Interestingly, Ralstonia was enriched in the rhizosphere of these plants found in kaolin mining areas, suggesting its resilience to environmental stress. Furthermore, the three plants had different dominant rhizosphere bacterial populations in kaolin mining areas, such as Nocardioides, Pseudarthrobacter, and Sphingomonas, likely due to the unique microecology of the plant rhizosphere. Kaolin mining activities also caused a shift in the functional diversity of rhizosphere bacteria in the three local plants, with each plant displaying different functions to cope with kaolin mining-induced stress, such as increased abundance of the GlpM family and glucan-binding domain. Discussion: This study is the first to investigate the effects of kaolin mining on the rhizosphere microecology of local plants, thus contributing to the establishment of soil microecological health monitoring indicators to better control soil pollution in kaolin mining areas. [ABSTRACT FROM AUTHOR]

Biodegradable microplastics (Bio-MPs) are a hot topic in soil research due to their potential to replace conventional microplastics. Biofertilizers are viewed as an alternative to inorganic fertilizers in agriculture due to their potential to enhance crop yields and food safety. The use of both can have direct and indirect effects on rhizosphere microorganisms. However, the influence of the coexistence of "Bio-MPs and biofertilizers" on rhizosphere microbial characteristics remains unclear. We investigated the effects of coexisting biofertilizers and Bio-MPs on the structure, function, and especially the carbon metabolic properties of crop rhizosphere bacteria, using a pot experiment in which polyethylene microplastics (PE-MPs) were used as a reference. The results showed that the existence of both microplastics (MPs) changed the physicochemical properties of the rhizosphere soil. Exposure to MPs also remarkably changed the composition and diversity of rhizosphere bacteria. The network was more complex in the Bio-MPs group. Additionally, metagenomic analyses showed that PE-MPs mainly affected microbial vitamin metabolism. Bio-MPs primarily changed the pathways related to carbon metabolism, such as causing declined carbon fixation/degradation and inhibition of methanogenesis. After partial least squares path model (PLS-PM) analysis, we observed that both materials influenced the rhizosphere environment through the bacterial communities and functions. Despite the degradability of Bio-MPs, our findings confirmed that the coexistence of biofertilizers and Bio-MPs affected the fertility of the rhizosphere. Regardless of the type of plastic, its use in soil requires an objective and scientifically grounded approach. [ABSTRACT FROM AUTHOR]

Bacterial exopolysaccharides (EPS) are biopolymers of carbohydrates, often released from cells into the extracellular environment. Due to their distinctive physicochemical properties, biocompatibility, biodegradability, and non-toxicity, EPS finds applications in various industrial sectors. However, the need for alternative EPS has grown over the past few decades as lactic acid bacteria’s (LAB) low-yield EPS is unable to meet the demand. In this case, rhizosphere bacteria with the diverse communities in soil leading to variations in composition and structure, are recognized as a potential source of EPS applicable in various industries. In addition, media components and cultivation conditions have an impact on EPS production, which ultimately affects the quantity, structure, and biological functions of the EPS. Therefore, scientists are currently working on manipulating bacterial EPS by developing cultures and applying abiotic and biotic stresses, so that better production of exopolysaccharides can be attained. This review highlights the composition, biosynthesis, and effects of environmental factors on EPS production along with the potential applications in different fields of industry. Ultimately, an overview of potential future paths and tactics for improving EPS implementation and commercialization is pointed out. [ABSTRACT FROM AUTHOR]

Mine pollution causes a serious impact on the ecological environment surrounding the mine site. It provides great theoretical value to explore the effects of planting different plants on soil characteristics and bacterial community structure around the mine site for vegetation restoration. In this study, we mainly assessed the rhizosphere bacterial community structure and diversity of wheat and Chinese milk vetch seedlings in copper tailings by 16S rRNA high-throughput sequencing and also soil properties. The results showed that planting wheat and Chinese milk vetch seedlings led to a decrease in soil pH, but both could increase the content of total nitrogen, organic matter, and available nitrogen in the rhizosphere soil, as well as enhance the activities of urease and alkaline protease. In addition, a total of 1,133,919 active sequences and 13,199 operational taxonomic units were obtained. The microorganisms in the substrate samples belong to 34 phyla and 81 classes, Proteobacteria, Acidobacteria and Actinobacteria were the top three dominant group. In general, Chinese milk vetch or wheat enriched the diversity of bacterial community in rhizosphere soil, the results showed that the number of rhizosphere bacteria in Chinese milk vetch was higher than that in wheat. The structure of the rhizosphere bacterial community of wheat and Chinese milk vetch seedling was similar, but the bacterial abundance was different. Mantel tests showed that Chao index significantly correlated with ammonium nitrogen. These results not only expand our understanding of rhizosphere bacteriomes but also provide theoretical basis for improving the soil quality of industrial and crop yields. [ABSTRACT FROM AUTHOR]

This greenhouse study evaluated the effects of soil enrichment with Pteris vittata rhizosphere bacteria on the growth and accumulation of arsenic in P. vittata grown on a naturally As-rich soil. Inoculations were performed with a consortium of six bacteria resistant to 100 mM arsenate and effects were compared to those obtained on the sterilized soil. Selected bacteria from the consortium were also utilized individually: PVr_9 homologous to Agrobacterium radiobacter that produces IAA and siderophores and shows ACC deaminase activity, PVr_15 homologous to Acinetobacter schindleri that contains the arsenate reductase gene, and PVr_5 homologous to Paenarthrobacter ureafaciens that possesses all traits from both PVr_9 and PVr_15. Frond and root biomass significantly increased in ferns inoculated with the consortium only on non-sterilized soil. A greater increase was obtained with PVr_9 alone, while only an increased root length was found in those inoculated with either PVr_5 or PVr_15. Arsenic content significantly decreased only in ferns inoculated with PVr_9 while it increased in those inoculated with PVr_5 and PVr_15. In conclusion, inoculations with the consortium and PVr_9 alone increase plant biomass, but no increase in As phytoextraction occurs with the consortium and even a reduction is seen with PVr_9 alone. Conversely, inoculations with PVr_5 and PVr_15 have the capacity of increasing As phytoextraction. [ABSTRACT FROM AUTHOR]

Abstract Background The plant roots excrete a large number of organic compounds into the soil. The rhizosphere, a thin soil zone around the roots, is a hotspot for microbial activity, making it a crucial component of the soil ecosystem. Secondary metabolites produced by rhizospheric Sphingomonas sanguinis DM have sparked significant curiosity in investigating their possible biological impacts. Methods A bacterial strain has been isolated from the rhizosphere of Datura metel. The bacterium’s identification, fermentation, and working up have been outlined. The ethyl acetate fraction of the propagated culture media of Sphingomonas sanguinis DM was fractioned and purified using various chromatographic techniques. The characterization of the isolated compounds was accomplished through the utilization of various spectroscopic techniques, such as UV, MS, 1D, and 2D-NMR. Furthermore, the evaluation of their antimicrobial activity was conducted using the agar well diffusion method, while cytotoxicity was assessed using the MTT test. Results The extract from Sphingomonas sanguinis DM provided two distinct compounds: n-dibutyl phthalic acid (1) and Bis (2-methyl heptyl) phthalate (2) within its ethyl acetate fraction. Furthermore, the 16S rRNA gene sequence of Sphingomonas sanguinis DM has been registered under the NCBI GenBank database with the accession number PP422198. The bacterial extract exhibited its effect against gram-positive bacteria, inhibiting Streptococcus mutans (12.6 ± 0.6 mm) and Staphylococcus aureus (10.6 ± 0.6 mm) compared to standard antibiotics. Conversely, compound 1 showed a considerable effect against phytopathogenic fungi such as Alternaria alternate (56.3 ± 10.6 mm) and Fusarium oxysporum (21.3 ± 1.5 mm) with a MIC value of 17.5 µg/mL. However, it was slightly active against Klebsiella pneumonia (11.0 ± 1.0 mm). Furthermore, compound 2 was the most active metabolite, having a significant antimicrobial efficacy against Rhizoctonia solani (63.6 ± 1.1 mm), Pseudomonas aeruginosa (16.7 ± 0.6 mm), and Alternaria alternate (20.3 ± 0.6 mm) with MIC value at 15 µg/mL. In addition, compound 2 exhibited the most potency against hepatocellular (HepG-2) and skin (A-431) carcinoma cell lines with IC50 values of 107.16 µg/mL and 111.36 µg/mL, respectively. Conclusion Sphingomonas sanguinis DM, a rhizosphere bacterium of Datura metel, was studied for its phytochemical and biological characteristics, resulting in the identification of two compounds with moderate antimicrobial and cytotoxic activities.

Background: The plant roots excrete a large number of organic compounds into the soil. The rhizosphere, a thin soil zone around the roots, is a hotspot for microbial activity, making it a crucial component of the soil ecosystem. Secondary metabolites produced by rhizospheric Sphingomonas sanguinis DM have sparked significant curiosity in investigating their possible biological impacts. Methods: A bacterial strain has been isolated from the rhizosphere of Datura metel. The bacterium's identification, fermentation, and working up have been outlined. The ethyl acetate fraction of the propagated culture media of Sphingomonas sanguinis DM was fractioned and purified using various chromatographic techniques. The characterization of the isolated compounds was accomplished through the utilization of various spectroscopic techniques, such as UV, MS, 1D, and 2D-NMR. Furthermore, the evaluation of their antimicrobial activity was conducted using the agar well diffusion method, while cytotoxicity was assessed using the MTT test. Results: The extract from Sphingomonas sanguinis DM provided two distinct compounds: n-dibutyl phthalic acid (1) and Bis (2-methyl heptyl) phthalate (2) within its ethyl acetate fraction. Furthermore, the 16S rRNA gene sequence of Sphingomonas sanguinis DM has been registered under the NCBI GenBank database with the accession number PP422198. The bacterial extract exhibited its effect against gram-positive bacteria, inhibiting Streptococcus mutans (12.6 ± 0.6 mm) and Staphylococcus aureus (10.6 ± 0.6 mm) compared to standard antibiotics. Conversely, compound 1 showed a considerable effect against phytopathogenic fungi such as Alternaria alternate (56.3 ± 10.6 mm) and Fusarium oxysporum (21.3 ± 1.5 mm) with a MIC value of 17.5 µg/mL. However, it was slightly active against Klebsiella pneumonia (11.0 ± 1.0 mm). Furthermore, compound 2 was the most active metabolite, having a significant antimicrobial efficacy against Rhizoctonia solani (63.6 ± 1.1 mm), Pseudomonas aeruginosa (16.7 ± 0.6 mm), and Alternaria alternate (20.3 ± 0.6 mm) with MIC value at 15 µg/mL. In addition, compound 2 exhibited the most potency against hepatocellular (HepG-2) and skin (A-431) carcinoma cell lines with IC50 values of 107.16 µg/mL and 111.36 µg/mL, respectively. Conclusion: Sphingomonas sanguinis DM, a rhizosphere bacterium of Datura metel, was studied for its phytochemical and biological characteristics, resulting in the identification of two compounds with moderate antimicrobial and cytotoxic activities. [ABSTRACT FROM AUTHOR]

Soil acidification represents a severe threat to tobacco cultivation regions in South China, exacerbating bacterial wilt caused by Ralstonia solanacearum. The comprehension of the underlying mechanisms that facilitate the restoration of rhizosphere microbial communities in “healthy soils” is imperative for ecologically managing tobacco bacterial wilt. This study focuses on acidified tobacco soils that have been subjected to continuous cultivation for 20 years. The experimental treatments included lime (L), biochar (B), and a combination of lime and biochar (L+B), in addition to a control group (CK). Utilizing rhizosphere biology and niche theory, we assessed disease suppression effects, changes in soil properties, and the co-evolution of the rhizosphere bacterial community. Each treatment significantly reduced tobacco bacterial wilt by 16.67% to 20.14% compared to the control group (CK) (p < 0.05) and increased yield by 7.86% to 27.46% (p < 0.05). The biochar treatment (B) proved to be the most effective, followed by the lime-biochar combination (L+B). The key factors controlling wilt were identified through random forest regression analysis as an increase in soil pH and exchangeable bases, along with a decrease in exchangeable acidity. However, lime treatment alone led to an increase in soil bulk density and a decrease in available nutrients, whereas both biochar and lime-biochar treatments significantly improved these parameters (p

Plant microbiota are an important factor impacting plant cadmium (Cd) uptake. However, little is known about how plant microbiota affects the Cd uptake by plants under the influence of microplastics (MPs) with different particle sizes. In this study, bacterial structure and assembly in the rhizosphere and endosphere in pakchoi were analyzed by amplicon sequencing of 16S rRNA genes under the influence of different particle sizes of polystyrene microplastics (PS-MPs) combined with Cd treatments. Results showed that there were no significant differences observed in the shoot endophytes among different treatments. However, compared to Cd treatment, larger-sized PS-MPs (2 and 20 μm) significantly increased community diversity and altered the structural composition of rhizosphere bacteria and root endophytes, while smaller-sized PS-MPs (0.2 μm) did not. Under the treatment of larger-sized PS-MPs, the niche breadth of rhizosphere bacteria and root endophytes were significantly increased. And larger-sized PS-MPs also maintained stability and complexity of bacterial co-occurrence networks, while smaller-sized PS-MPs reduced them. Furthermore, compared to Cd treatment, the addition of larger particle size PS-MPs decreased the proportion of homogeneous section, while increased the proportion of drift in root endophytic bacterial community assembly. The role of larger-sized MPs in the community assembly of rhizosphere bacteria was opposite. Using random forest and structural equation models, the study found that larger-sized PS-MPs can promote the colonization of specific bacterial taxa, such as Brevundimonas, AKAU4049, SWB02, Ellin6055, Porphyrobacter, Sphingorhabdus, Rhodobacter, Erythrobacter, Devosia and some other bacteria belonging to Alphaproteobacteria, in the rhizosphere and root endosphere. The colonization of these taxa can may induce the formation of biofilms in the roots, immobilize heavy metals through oxidation processes, and promote plant growth, thereby reducing Cd uptake by pakchoi. The findings of this study provide important insights into the microbial mechanisms underlying the influence of MPs with different particle sizes on plant Cd uptake.

Asarum is a traditional Chinese medicinal plant, and its dried roots are commonly used as medicinal materials. Research into the traits of the bacteria and fungus in the Asarum rhizosphere and how they relate to the potency of medicinal plants is important. During four cropping years and collecting months, we used ITS rRNA gene amplicon and sequencing to assess the population, diversity, and predominant kinds of bacteria and fungus in the rhizosphere of Asarum. HPLC was used to determine the three bioactive ingredients, namely asarinin, aristolochic acid I, and volatile oil. The mainly secondary metabolites of Asarum, relationships between microbial communities, soil physicochemical parameters, and possible influences on microbial communities owing to various cropping years and collecting months were all statistically examined. The cropping years and collecting months affected the abundance and diversity of rhizosphere bacteria and fungi, but the cropping year had a significant impact on the structures and compositions of the bacterial communities. The rhizosphere microorganisms were influenced by both the soil physicochemical properties and enzyme activities. Additionally, this study revealed that Trichoderma was positively correlated with the three bioactive ingredients of Asarum, while Tausonia showed entirely opposite results. Gibberella and Leptosphaeria demonstrated a significantly negative correlation with asarinin and violate oil, but they were weakly correlated with the aristolochic acid I content. This study revealed variations in the Asarum rhizosphere microorganism population, diversity, and dominant types across four cropping years and collecting months. The relationship between Asarum secondary metabolites, the soil physicochemical properties, enzyme activities, and rhizosphere microorganisms was discussed. Our results will guide the exploration of the soil characteristics and rhizosphere microorganisms' structures by regulating the microbial community to enhance Asarum quality. [ABSTRACT FROM AUTHOR]

[Objective] To study the growth-promoting characteristics of a strain of Bacillus amyloliquefaciens SQ-2 isolated and screened in the laboratory, and to determine the concentration range, mechanism of action, and changes in soil microbiota induced by this strain to promote rice growth. [Method] The phosphorus solubility and nitrogenase activity of strain SQ-2 were detected using the molybdenum blue colorimetric method and ELISA nitrogenase kit. Inoculating10², 104, 106, 108, and 3×108 CFU/mL bacterial suspension into hydroponic and soil cultured rice, the dry and fresh weight, length, and thickness of the roots and stems of hydroponic and soil cultured rice were measured, respectively after 14 and 20 d of cultivation. Meanwhile, the activities of urease, protease, and sucrase in soil cultured rice were determined using the phenol sodium hypochlorite colorimetric method, the ninhydrin detection method, and the 3,5-dinitrosalicylic acid colorimetric method. Besides, the soil pH value was determined using the pH meter potential method and the content of nitrogen, phosphorus, and potassium available in soil and the activity of acid phosphatase were detected by utilizing the corresponding reagent kit. Analysis of rhizosphere bacterial community structure in soil cultured rice soil was inoculated with 3×108 CFU/mL components. [Result] The dissolution of tricalcium phosphate by strain SQ-2 was 229.63 mg/L, and the nitrogenase activity was 55.07 U/L. Compared with the control, the dry and fresh weight of hydroponic rice roots showed the most significant increase at an inoculum suspension concentration of 104 CFU/mL. At a vaccination concentration of 3×108 CFU/mL, the dry and fresh weight of soil cultivated rice rhizomes increased most significantly. As the concentration of the inoculum suspension increased, the activities of various enzymes and the concentration of available nitrogen, phosphorus, and potassium in the soil increased to varying degrees, the soil pH value while inoculating strain 3×108 CFU/mL decreased from 7.83 to 7.26. The inoculant strain SQ-2 changed the colony composition in the rice rhizosphere soil and significantly increased Ace, Chao, Sobs and Shannon indices of soil α-diversity. [Conclusion] B. amyloliquefaciens SQ-2 had different growth promotion effects on soil culture and hydroculture rice. In soil culture experiments, the growth-promoting effect is notably pronounced through the augmentation of soil enzyme activity, rapid increases in available nitrogen, phosphorus, and potassium levels, and alterations in the soil microbial community structure. Overall, these experimental findings offer valuable insights into new strain resources for the development of bacterial fertilizer. [ABSTRACT FROM AUTHOR]

Microalgae are an effective soil biostimulant. However, pathways for the enhancement of plant growth are still unclear. In this study, the effects of Chlorella vulgaris (C. vulgaris) on wheat growth promotion and its direct and indirect mechanisms were investigated under hydroponic experiment condition in pots in a constant temperature indoor laboratory. Living C. vulgaris showed significant promoting effect on wheat growth in terms of root length (52.41%), shoot length (44.44%) and dry weight (13.86%). Besides the function of supplying inorganic nutrient, the organic molecules in the culture supernatant and cell extract of C. vulgaris promoted wheat growth directly through interaction with the plant roots. The culture supernatant fraction increased root length, shoot length and dry weight of wheat by 27.59%. 11.84%, 16.53%, respectively. The cell extract fraction had a larger effect with the increase in root length, shoot length and dry weight by 33.10%, 20.86% and 27.10%, respectively. Changes in the bacterial community in the rhizosphere under co-culturing of bacteria and microalgae was also investigated to determine indirect mechanisms on plant growth promotion. The results showed living C. vulgaris and rhizosphere bacteria had a synergistic interaction. Compared with initial rhizosphere bacterial community at genus level, the number of beneficial rhizosphere bacteria such as Sphingobacterium, Comamonas, Acetobacter and Mucilaginibacter significantly increased when co-cultured with the supernatant of C. vulgaris. In conclusion, considering the presence of bacteria in the soil environment, it is important to maintain the activity of microalgal cells to release extracellular polymer substances sustainably to promote plant growth. [ABSTRACT FROM AUTHOR]

Biodegradable microplastics (Bio-MPs) are a hot topic in soil research due to their potential to replace conventional microplastics. Biofertilizers are viewed as an alternative to inorganic fertilizers in agriculture due to their potential to enhance crop yields and food safety. The use of both can have direct and indirect effects on rhizosphere microorganisms. However, the influence of the coexistence of “Bio-MPs and biofertilizers” on rhizosphere microbial characteristics remains unclear. We investigated the effects of coexisting biofertilizers and Bio-MPs on the structure, function, and especially the carbon metabolic properties of crop rhizosphere bacteria, using a pot experiment in which polyethylene microplastics (PE-MPs) were used as a reference. The results showed that the existence of both microplastics (MPs) changed the physicochemical properties of the rhizosphere soil. Exposure to MPs also remarkably changed the composition and diversity of rhizosphere bacteria. The network was more complex in the Bio-MPs group. Additionally, metagenomic analyses showed that PE-MPs mainly affected microbial vitamin metabolism. Bio-MPs primarily changed the pathways related to carbon metabolism, such as causing declined carbon fixation/degradation and inhibition of methanogenesis. After partial least squares path model (PLS-PM) analysis, we observed that both materials influenced the rhizosphere environment through the bacterial communities and functions. Despite the degradability of Bio-MPs, our findings confirmed that the coexistence of biofertilizers and Bio-MPs affected the fertility of the rhizosphere. Regardless of the type of plastic, its use in soil requires an objective and scientifically grounded approach.

Changes in the soil environment in the root zone will affect the growth, development and resistance of plants. The mechanism underlying the effect of drought and flood stress on rhizosphere bacterial diversity, soil metabolites and soil enzyme activity is not clear and needs further study. To analyze the dynamic changes in bacteria, metabolites and enzyme activities in the rhizosphere soil of maize under different drought-flood abrupt alternation (DFAA) stresses, the barrel test method was used to set up the ‘sporadic light rain’ to flooding (referring to trace rainfall to heavy rain) (DFAA1) group, ‘continuous drought’ to flooding (DFAA2) group and normal irrigation (CK) group from the jointing to the tassel flowering stage of maize. The results showed that Actinobacteria was the most dominant phylum in the two DFAA groups during the drought period and the rewatering period, and Proteobacteria was the most dominant phylum during the flooding period and the harvest period. The alpha diversity index of rhizosphere bacteria in the DFAA2 group during the flooding period was significantly lower than that in other stages, and the relative abundance of Chloroflexi was higher. The correlation analysis between the differential genera and soil metabolites of the two DFAA groups showed that the relative abundance of Paenibacillus in the DFAA1 group was higher during the drought period, and it was significantly positively correlated with the bioactive lipid metabolites. The differential SJA-15 bacterium was enriched in the DFAA2 group during the flooding period and were strongly correlated with biogenic amine metabolites. The relative abundances of Arthrobacter, Alphaproteobacteria and Brevibacillus in the DFAA2 group were higher compared with DFAA1 group from rewatering to harvest and were significantly positively correlated with hydrocarbon compounds and steroid hormone metabolites. The acid phosphatase activity of the DFAA1 group was significantly higher than that of the DFAA2 group during the flooding period. The study suggests that there is a yield compensation phenomenon in the conversion of ‘continuous drought’ to flooding compared with ‘sporadic light rain’, which is related to the improvement in the flooding tolerance of maize by the dominant bacteria Chloroflexi, bacterium SJA-15 and biogenic amine metabolites. These rhizosphere bacteria and soil metabolites may have the potential function of helping plants adapt to the DFAA environment. The study revealed the response of the maize rhizosphere soil environment to DFAA stress and provided new ideas for exploring the potential mechanism of crop yield compensation under DFAA. [ABSTRACT FROM AUTHOR]

Salt stress detrimentally impacts plant growth, imperiling crop yield and food quality. Ameliorating plant resilience and productivity in saline environments is critical for global food security. Here, we report the positive effect of Arthrospira (Spirulina) on plant growth and salt tolerance in Arabidopsis and sweet sorghum. Arthrospira application greatly promotes seed germination and seedling growth in both species under salt stress conditions in a dosage-dependent manner. Application of 6 mg Arthrospira per plate significantly enhances K+/Na+ equilibrium and reactive oxygen species (ROS) scavenging in Arabidopsis, reducing salt-induced toxicity. The primary root length, survival rate, chlorophyll content, photosynthesis, plant height, biomass and yield were all improved in both species. Concurrently, Arthrospira demonstrated the synthesis of compatible solutes, such as trehalose (Tre) and glucosylglycerol (GG), contributing to heightened stress tolerance when co-cultivated with Arabidopsis on plates. Transcriptome analysis revealed dramatic up-/downregulation of genes involved in phytohormone signal transduction, chlorophyll and photosynthesis metabolism, and phenylpropanoid metabolism in Arabidopsis. Furthermore, the application of Arthrospira exerted a positive influence on the rhizosphere bacteriome structure in sweet sorghum, crucial for nutrient cycling and soil health enhancement. Our findings uncovered the underlying mechanisms of algae-plants interaction in saline soil, proposing strategies to enhance crop productivity and soil quality, thereby addressing the urgent need for sustainable agriculture practices to mitigate salinity's repercussions amidst climate change challenges. [ABSTRACT FROM AUTHOR]

This review covers the literature data on plant growth-promoting bacteria in soil, which can fix atmospheric nitrogen, solubilize phosphates, produce and secrete siderophores, and may exhibit several different behaviors simultaneously. We discuss perspectives for creating bacterial consortia and introducing them into the soil to increase crop productivity in agrosystems. The application of rhizosphere bacteria—which are capable of fixing nitrogen, solubilizing organic and inorganic phosphates, and secreting siderophores, as well as their consortia—has been demonstrated to meet the objectives of sustainable agriculture, such as increasing soil fertility and crop yields. The combining of plant growth-promoting bacteria with mineral fertilizers is a crucial trend that allows for a reduction in fertilizer use and is beneficial for crop production. [ABSTRACT FROM AUTHOR]

Soil salinization has become an ecological and environmental problem that cannot be ignored. Tetraploid black locust (Robinia pseudoacacia L.) is a leguminous tree with characteristics of drought and saline-alkali tolerance. Rhizosphere bacteria are the primary functional microorganisms within the plant root system, and they play a crucial role in regulating plant growth and enhancing stress tolerance. However, there is still a lack of research on the effect of saline-alkali stress on the bacterial community structure in the rhizosphere of black locusts. In this study, we applied 0, 50, 100, and 150 mM NaHCO3 stress to diploid (2×) and tetraploid (4×) black locusts for 16 days. We used 16S rDNA sequencing to investigate the changes in the rhizosphere bacterial communities. Furthermore, we evaluated soil enzyme activity and plant physiological characteristics to explore the response of rhizosphere bacteria to NaHCO3 stress. The results demonstrated that the 4× plant exhibited superior alkali resistance compared to its 2× plant counterpart under NaHCO3 stress. Simultaneously, it was observed that low concentrations of NaHCO3 stress notably increased the abundance of rhizosphere bacteria in both plant types, while reducing their diversity. The impact of stress on the rhizosphere bacterial community weakened as the stress concentration increased. The application of NaHCO3 stress caused a significant change in the composition of the bacterial community in the rhizosphere. Additionally, alkaline salt stress influences the diversity of rhizosphere bacterial communities, which are linked to soil enzyme activities. These data will help us better understand the relationship between the dominant rhizosphere bacterial community and black locust. They will also provide a reference for further improving the alkali resistance of black locust by enhancing the soil bacterial community. [ABSTRACT FROM AUTHOR]

The rhizobial inoculation effects on the peanut rhizosphere bacterial community and metabolites were studied under different N availability following the five N application rates without rhizobial inoculation (N1–N5; 0, 40, 80, 110, 170 kg N ha−1) or with rhizobial inoculation (RN1–RN5) in a 3-year field trial. The effects of rhizobia on peanut growth, the rhizobacterial community, and root metabolites differed depending on the N availability. Plant height and nodule number were significantly increased by rhizobial inoculation, especially in RN3. Rhizobacterial abundance and richness were increased by rhizobial inoculation, except in RN1 (no N added). The number of 16S rRNA gene copies was higher in RN1–RN3 than in N1–N3 in both years. The largest number of differential bacterial genera between an inoculated treatment and its corresponding uninoculated treatment was in RN1 vs. N1. The beneficial bacteria Saccharimonadales and c_JG30-KF-CM66 (Chloroflexi) were most abundant in RN3. The concentrations of organic acids (3-methylglutaric acid, adipic acid, 3-hydroxyoctanoic acid, and octenedioic acid) were significantly increased in RN3 and were positively correlated with c_JG30-KF-CM66 (Chloroflexi), soil available N, and biomass. No metabolic pathways were significantly enriched by rhizobial inoculation at the highest N application rate (RN5). These results demonstrate that rhizobia positively affect peanut growth and yield under the best N availability via their ability to reshape the soil microbiome and metabolites. [ABSTRACT FROM AUTHOR]

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BACKGROUND: Plant growth-promoting rhizobacteria (PGPR) are the rhizosphere bacteria that can enhance plant growth by a wide variety of mechanisms. This study was conducted to assess the effects of plant growth-promoting rhizobacteria on growth and nutrient assimilation of rice. METHODOLOGY: Seeds of transplant Aman rice (cv. BRRI dhan49) were collected from Bangladesh Rice Research Institute (BRRI). Pot experiment was conducted with rice plant inoculated with two PGPR isolates MQ1 (Zinc solubilizing, IAA producing, phosphate solubilizing and N2-fixing) and MQ2 (Zinc solubilizing, phosphate solubilizing and N2-fixing) with addition of three different levels of chemical fertilizers (FR0.0 no fertilizer, FR0.5 half of the recommended dose, FR1.0 full of the recommended dose of fertilizers) following Completely Randomized Design with three replications. Plant height at different days after transplanting, number of tillers hill-1 and biomass yield were recorded. Plant samples were analyzed for N, P, Ca, Mg, S, Fe, Zn, Mn, Cu and Cd contents. KEY FINDINGS: Rice plants inoculated with the PGPR both individually or in consortium along with different doses of fertilizers showed an improved plant growth and increased biomass production. Highest plant height (74.057±3.164 cm) and maximum number of tillers hill-1 (13.000±2.082) were recorded in PGPRMQ1RF1.0 treatment and the highest biomass production (10.275±0.541 t ha-1) was recorded in PGPRCONS.RF1.0. Nitrogen content and uptake of the individual PGPR treated rice plants was also found to be higher in comparison with the uninoculated control plants. Besides these iron and zinc content of the treated rice plants was also found to be higher in comparison with the uninoculated control plants. N (0.268±0.046), P (0.626±0.095), Fe (6.062094±A), Zn (1.237±0.197) and Mn (11.908±1.879) uptake were observed higher in PGPRMQ1RF1.0 treatment. CONCLUSION: PGPR inoculation has immense potential to be used as agricultural crop inoculants as they promote plant growth as well as nutrient assimilation of rice. [Fundam Appl Agric 2023; 8(3.000): 507-523]

This greenhouse study evaluated the effects of soil enrichment with Pteris vittata rhizosphere bacteria on the growth and accumulation of arsenic in P. vittata grown on a naturally As-rich soil. Inoculations were performed with a consortium of six bacteria resistant to 100 mM arsenate and effects were compared to those obtained on the sterilized soil. Selected bacteria from the consortium were also utilized individually: PVr_9 homologous to Agrobacterium radiobacter that produces IAA and siderophores and shows ACC deaminase activity, PVr_15 homologous to Acinetobacter schindleri that contains the arsenate reductase gene, and PVr_5 homologous to Paenarthrobacter ureafaciens that possesses all traits from both PVr_9 and PVr_15. Frond and root biomass significantly increased in ferns inoculated with the consortium only on non-sterilized soil. A greater increase was obtained with PVr_9 alone, while only an increased root length was found in those inoculated with either PVr_5 or PVr_15. Arsenic content significantly decreased only in ferns inoculated with PVr_9 while it increased in those inoculated with PVr_5 and PVr_15. In conclusion, inoculations with the consortium and PVr_9 alone increase plant biomass, but no increase in As phytoextraction occurs with the consortium and even a reduction is seen with PVr_9 alone. Conversely, inoculations with PVr_5 and PVr_15 have the capacity of increasing As phytoextraction.

Summary: Bacteria colonize plant roots and engage in reciprocal interactions with their hosts. However, the contribution of individual taxa or groups of bacteria to plant nutrition and fitness is not well characterized due to a lack of in situ evidence of bacterial activity.To address this knowledge gap, we developed an analytical approach that combines the identification and localization of individual bacteria on root surfaces via gold‐based in situ hybridization with correlative NanoSIMS imaging of incorporated stable isotopes, indicative of metabolic activity.We incubated Kosakonia strain DS‐1‐associated, gnotobiotically grown rice plants with 15N–N2 gas to detect in situ N2 fixation activity. Bacterial cells along the rhizoplane showed heterogeneous patterns of 15N enrichment, ranging from the natural isotope abundance levels up to 12.07 at% 15N (average and median of 3.36 and 2.85 at% 15N, respectively, n = 697 cells).The presented correlative optical and chemical imaging analysis is applicable to a broad range of studies investigating plant–microbe interactions. For example, it enables verification of the in situ metabolic activity of host‐associated commercialized strains or plant growth‐promoting bacteria, thereby disentangling their role in plant nutrition. Such data facilitate the design of plant–microbe combinations for improvement of crop management. [ABSTRACT FROM AUTHOR]

The bacteria that dominate and become enriched in the rhizosphere during continuous cropping are of increasing interest, as they can greatly adapt to the rhizosphere. However, there are still little knowledge about the general composition and function of these bacteria. In this study, we planted tomatoes in three different soils for three planting cycles and used both high-throughput sequencing and culture-dependent workflows. Despite significant differences in bacterial communities from the initial soils, we observed a similar succession in the rhizosphere bacterial community compositions. We identified certain bacteria that were gradually enriched and potentially beneficial, such as Rhizobium and Flavobacterium. However, some other potentially beneficial bacteria, such as Massilia and Lysobacter, were gradually depleted. Additionally, we found that predicted functions related to xenobiotic biodegradation, nutrient metabolism and antibiotic biosynthesis were enriched in different rhizosphere soils. Beijerinckia fluminensis GR2, which was gradually enriched in all tested soils, significantly inhibited the growth of Ralstonia solanacearum and protected the host from infection. Our study provides new insights into the assembly mechanism of gradually enriched bacteria and their role as plant-beneficial microbes that adapt well to the rhizosphere. [ABSTRACT FROM AUTHOR]

Maize has the largest cultivation area of any crop in the world and plays an important role in ensuring food security. High-density planting is essential for maintaining high maize yields in modern intensive agriculture. Nonetheless, how high-density planting and the tolerance of individual genotypes to such planting shape the root-associated microbiome of maize is still unknown. In this study, we analyzed the root and rhizosphere bacterial communities of two maize accessions with contrasting shoot architectures grown under high- and low-density planting conditions. Our results suggested that maize hosted specific, distinct bacterial communities in the root endocompartment and that the maize genotype had a significant effect on the selection of specific microbes from the rhizosphere. High-density planting also had significant effects on root-associated bacterial communities. Specifically, genotype and high-density planting coordinated to shape the structure, composition, and function of root and rhizosphere bacterial communities. Taken together, our results provide insights into how aboveground plant architecture and density may alter the belowground bacterial community in root-associated compartments of maize. [ABSTRACT FROM AUTHOR]

Qinghai‐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. [ABSTRACT FROM AUTHOR]

Tartary buckwheat (Fagopyrum tataricum Gaertn.) is an important pseudocereal crop with excellent edible, nutritional and medicinal values. However, the yield of Tartary buckwheat (TB) is very low due to old-fashioned cultivation techniques, particularly unreasonable application of nitrogen fertilizer. To improve the understanding on the theories of nitrogen use in TB, the effects of nitrogen application on growth, as well as chemical properties and microbial community of rhizosphere soil were investigated in this study. Nitrogen application could promote the plant height, stem diameter, nitrogen accumulation and yield of TB. The relative abundance and diversity of bacteria and fungi in the rhizosphere soil of TB were improved by nitrogen fertilizer. Nitrogen application increased the abundance of beneficial bacteria such as Lysobacter and Sphingomonas in rhizosphere soil, and decreased the abundance of pathogenic fungi such as Fusarium and Plectosphaerella. The results indicated that nitrogen application changed the distribution of microbial communities in TB rhizosphere soil. Furthermore, the specific enriched or depleted microorganisms in the rhizosphere soil of four TB varieties were analyzed at OTU level. 87 specific nitrogen-responsive genes with sequence variation were identified in four varieties by integrating genomic re-sequencing and transcriptome analysis, and these genes may involve in the recruitment of specific rhizosphere microorganisms in different TB varieties. This study provided new insights into the effects of nitrogen application on TB growth and rhizosphere microbial community, and improved the understanding on the mechanisms of TB root-microbe interactions. [ABSTRACT FROM AUTHOR]

Agricultural Jiaosu (AJ) is a method of recycling agricultural wastes for improving soil properties, promoting plant growth, and enhancing plant stress resistance. However, the underlying mechanism by which AJ improves plant stress resistance needs to be determined. Therefore, in this study, two treatments of AJ spraying and water spraying were set up to determine the enzyme activities related to the stress resistance of pak choi after 30 days of growth, and the potential mechanism of AJ's influence on the stress resistance of pak choi was revealed by transcriptome, metabolome, and rhizome microbiome analyses. Microbial community analysis revealed that the application of AJ does not alter microbial abundance in the rhizosphere; however, it can improve microbial diversity and enrich Actinobacteriota, Proteobacteria, and Firmicutes in the pak choi rhizosphere. Metabolomic analysis revealed that these phyla were significantly positively correlated, with highly upregulated metabolites. Our findings suggest that AJ recruits beneficial microorganisms (BMs) in the rhizosphere and stimulates the expression of genes and metabolites involved in phenylpropanoid and glucosinolate biosynthesis, as well as glutathione and alpha-linolenic acid metabolism pathways. The use of AJ could considerably minimise the use of pesticides and fertilisers and improve the quality of the ecological environment. [ABSTRACT FROM AUTHOR]

Rhizosphere microorganisms and the volatile organic compounds (VOCs) produced by them take part in the regulation of the chemotaxis of nematodes. A total of 150 strains of rhizosphere bacteria were screened via a chemotaxis experiment with Meloidogyne incognita. Some isolates affected the behavior of the nematodes, including attraction, randomness, and repulsion. Volatile metabolites produced via the selected bacteria were associated with the chemotaxis of nematodes. M. incognita was highly attracted to decanal. In addition, dimethyl disulfide, 2,5-dimethylpyrazine, pentadecanoic acid, and palmitic acid were found to attract weakly M. incognita. Furthermore, the chemotaxis of M. incognita was tested in a pot experiment. The bacteria Bacillus sp. 1-50, Brevibacillus brevis 2-35, B. cereus 5-14, Chryseobacterium indologens 6-4, and VOC decanal could regulate the movement of M. incognita in the pot with or without plants. The results provide insights into rhizosphere microorganisms and their VOCs and how they regulate the chemotaxis of the nematodes. [ABSTRACT FROM AUTHOR]

Background: Rhizosphere bacteria play important roles in plant growth and secondary metabolite accumulation. Moreover, only with favorable production areas and desirable germplasm can high-yield and high-quality medicinal materials be produced. However, whether origin and germplasm indirectly affect the yield and quality of Angelica dahurica var. formosana through rhizosphere bacterial effects are not known. Methods: In this study, a high-throughput sequencing strategy was used to explore the relationship between the rhizosphere bacterial community and the cultivation of A. dahurica var. formosana from different production areas and germplasm for the first time. Results: (1) Proteobacteria was the dominant bacterial phylum in the rhizosphere soil of A. dahurica var. formosana, and these bacteria were stable and conserved to a certain extent. (2) High abundance of Proteobacteria was an important rhizospheric indicator of high yield, and high abundance of Firmicutes was an important indicator of high quality. Proteobacteria and Firmicutes might have an important relationship with the yield and quality of A. dahurica var. formosana, respectively. (3) PCoA cluster analysis demonstrated that both production area and germplasm affected the bacterial community structure in the rhizosphere of A. dahurica var. formosana to a certain extent, and production area had the greatest effect. In addition to available potassium, the rhizosphere soil nutrient levels of different production areas strongly affected the bacterial diversity and community. These findings provide a theoretical basis for the exploitation and utilization of rhizosphere microbial resources of A. dahurica var. formosana and offer a novel approach for increasing the yield and quality of this crop. [ABSTRACT FROM AUTHOR]

Asarum is a traditional Chinese medicinal plant, and its dried roots are commonly used as medicinal materials. Research into the traits of the bacteria and fungus in the Asarum rhizosphere and how they relate to the potency of medicinal plants is important. During four cropping years and collecting months, we used ITS rRNA gene amplicon and sequencing to assess the population, diversity, and predominant kinds of bacteria and fungus in the rhizosphere of Asarum. HPLC was used to determine the three bioactive ingredients, namely asarinin, aristolochic acid I, and volatile oil. The mainly secondary metabolites of Asarum, relationships between microbial communities, soil physicochemical parameters, and possible influences on microbial communities owing to various cropping years and collecting months were all statistically examined. The cropping years and collecting months affected the abundance and diversity of rhizosphere bacteria and fungi, but the cropping year had a significant impact on the structures and compositions of the bacterial communities. The rhizosphere microorganisms were influenced by both the soil physicochemical properties and enzyme activities. Additionally, this study revealed that Trichoderma was positively correlated with the three bioactive ingredients of Asarum, while Tausonia showed entirely opposite results. Gibberella and Leptosphaeria demonstrated a significantly negative correlation with asarinin and violate oil, but they were weakly correlated with the aristolochic acid I content. This study revealed variations in the Asarum rhizosphere microorganism population, diversity, and dominant types across four cropping years and collecting months. The relationship between Asarum secondary metabolites, the soil physicochemical properties, enzyme activities, and rhizosphere microorganisms was discussed. Our results will guide the exploration of the soil characteristics and rhizosphere microorganisms’ structures by regulating the microbial community to enhance Asarum quality.

To better conserve the ecology of the wild Rhododendron mucronulatum range, we studied the rhizosphere microenvironment of R. mucronulatum in Beijing's Yunmeng Mountain National Forest Park. R. mucronulatum rhizosphere soil physicochemical properties and enzyme activities changed significantly with temporal and elevational gradients. The correlations between soil water content (SWC), electrical conductivity (EC), organic matter content (OM), total nitrogen content (TN), catalase activity (CAT), sucrose-converting enzyme activity (INV), and urease activity (URE) were significant and positive in the flowering and deciduous periods. The alpha diversity of the rhizosphere bacterial community was significantly higher in the flowering period than in the deciduous period, and the effect of elevation was insignificant. The diversity of the R. mucronulatum rhizosphere bacterial community changed significantly with the change in the growing period. A network analysis of the correlations revealed stronger linkages between the rhizosphere bacterial communities in the deciduous period than in the flowering period. Rhizomicrobium was the dominant genus in both periods, but its relative abundance decreased in the deciduous period. Changes in the relative abundance of Rhizomicrobium may be the main factor influencing the changes in the R. mucronulatum rhizosphere bacterial community. Moreover, the R. mucronulatum rhizosphere bacterial community and soil characteristics were significantly correlated. Additionally, the influence of soil physicochemical properties on the rhizosphere bacterial community was larger than that of enzyme activity on the bacterial community. We mainly analyzed the change patterns in the rhizosphere soil properties and rhizosphere bacterial diversity of R. mucronulatum during temporal and spatial variation, laying the foundation for further understanding of the ecology of wild R. mucronulatum. [ABSTRACT FROM AUTHOR]

Simple Summary: An increasing diversity of bacteria with medically relevant biological properties is being discovered in natural environments where extreme physical conditions can select for unique chemistry. This research has allowed us to discover, in the desert region of the Chilean highlands in the province of Parinacota (3681–5104 m high), bacterial strains that live in the roots of an Aymara medicinal plant with impressive biological activities, such as hydrolytic enzymes, plant-growth-promoting traits, and antibacterial and antifungal properties. These discoveries have great value for society and medicine and should be further investigated for the benefit of global public health. Endemic medicinal plants that grow at altitudes in northern Chile have been traditionally used for therapeutic applications by Aymara doctors. Several studies have analyzed the biological properties of these plants for therapeutic purposes. The aim was to characterize at molecular and biochemical levels the bacteria that live in the rhizosphere and roots from endemic medicinal plants that grow between 3681–5104 m.a.s.l. in the province of Parinacota. Thirty-nine bacteria were isolated from nine medicinal plants under our laboratory conditions. These bacteria were characterized by Gram stain, hydrolase production, plant-growth promotion, anti-fungal and antibacterial activities, and 16S rDNA sequencing. A phylogenetic study revealed the presence of three major phyla, Actinomycetota (46.2%), Bacillota (43.6%), and Pseudomonadota (10.3%). The rhizobacteria strains associated with the Aymara medicinal plant exhibited several interesting biological activities, such as hydrolytic enzymes, plant-growth-promoting traits, and antibacterial and antifungal properties, indicating their potential for developing new bio-based products for agricultural or clinical applications. These results are promising and highlight the need to point toward the search for explanations of the bio-molecular basis of the therapeutic effects of medicinal plants. [ABSTRACT FROM AUTHOR]

Introduction: Root-knot nematodes (RKN) disease is a devastating disease in Cucumis crops production. Existing studies have shown that resistant and susceptible crops are enriched with different rhizosphere microorganisms, and microorganisms enriched in resistant crops can antagonize pathogenic bacteria. However, the characteristics of rhizosphere microbial communities of Cucumis crops after RKN infestation remain largely unknown. Methods: In this study, we compared the changes in rhizosphere bacterial communities between highly RKN-resistant Cucumis metuliferus (cm3) and highly RKN-susceptible Cucumis sativus (cuc) after RKN infection through a pot experiment. Results: The results showed that the strongest response of rhizosphere bacterial communities of Cucumis crops to RKN infestation occurred during early growth, as evidenced by changes in species diversity and community composition. However, the more stable structure of the rhizosphere bacterial community in cm3 was reflected in less changes in species diversity and community composition after RKN infestation, forming a more complex and positively co-occurrence network than cuc. Moreover, we observed that both cm3 and cuc recruited bacteria after RKN infestation, but the bacteria enriched in cm3 were more abundant including beneficial bacteria Acidobacteria, Nocardioidaceae and Sphingomonadales. In addition, the cuc was enriched with beneficial bacteria Actinobacteria, Bacilli and Cyanobacteria. We also found that more antagonistic bacteria than cuc were screened in cm3 after RKN infestation and most of them were Pseudomonas (Proteobacteria, Pseudomonadaceae), and Proteobacteria were also enriched in cm3 after RKN infestation. We hypothesized that the cooperation between Pseudomonas and the beneficial bacteria in cm3 could inhibit the infestation of RKN. Discussion: Thus, our results provide valuable insights into the role of rhizosphere bacterial communities on RKN diseases of Cucumis crops, and further studies are needed to clarify the bacterial communities that suppress RKN in Cucumis crops rhizosphere. [ABSTRACT FROM AUTHOR]

Copyright of Acta Agriculturae Zhejiangensis is the property of Acta Agriculturae Zhejiangensis Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Drought is a major abiotic stress that threatens crop production. Soil microbiomes are thought to play a role in enhancing plant adaptation to various stresses. However, it remains unclear whether soil microbiomes play a key role when plants are challenged by drought and whether different varieties are enriched with specific bacteria at the rhizosphere. In this study, we measured changes in growth phenotypes, physiological and biochemical characteristics of droughttolerant alfalfa (AH) and drought-sensitive (QS) under sterilized and unsterilized soil conditions with adequate watering and with drought stress, and analyzed the rhizosphere bacterial community composition and changes using 16S rRNA highthroughput sequencing. We observed that the unsterilized treatment significantly improved the growth, and physiological and biochemical characteristics of alfalfa seedlings under drought stress compared to the sterilized treatment. Under drought stress, the fresh and dry weight of seedlings increased by 35.24, 29.04, and 11.64%, 2.74% for unsterilized AH and QS, respectively, compared to sterilized treatments. The improvement was greater for AH than for QS. AH and QS recruited different rhizosphere bacteria when challenged by drought. Interestingly, under well-watered conditions, the AH rhizosphere was already rich in drought-tolerant bacterial communities, mainly Proteobacteria and Bacteroidetes, whereas these bacteria started to increase only when QS was subjected to drought. When drought stress was applied, AH was enriched with more drought-tolerant bacteria, mainly Acidobacteria, while the enrichment was weaker in QS rhizosphere. Therefore, the increase in drought tolerance of the drought-tolerant variety AH was greater than that of the drought-sensitive variety QS. Overall, this study confirmed the key role of drought-induced rhizosphere bacteria in improving the adaptation of alfalfa to drought stress, and clarified that this process is significantly related to the variety (genotype). The results of this study provide a basis for improving drought tolerance in alfalfa by regulating the rhizosphere microbiome. [ABSTRACT FROM AUTHOR]

Soil salinization has become an ecological and environmental problem that cannot be ignored. Tetraploid black locust (Robinia pseudoacacia L.) is a leguminous tree with characteristics of drought and saline-alkali tolerance. Rhizosphere bacteria are the primary functional microorganisms within the plant root system, and they play a crucial role in regulating plant growth and enhancing stress tolerance. However, there is still a lack of research on the effect of saline-alkali stress on the bacterial community structure in the rhizosphere of black locusts. In this study, we applied 0, 50, 100, and 150 mM NaHCO3 stress to diploid (2×) and tetraploid (4×) black locusts for 16 days. We used 16S rDNA sequencing to investigate the changes in the rhizosphere bacterial communities. Furthermore, we evaluated soil enzyme activity and plant physiological characteristics to explore the response of rhizosphere bacteria to NaHCO3 stress. The results demonstrated that the 4× plant exhibited superior alkali resistance compared to its 2× plant counterpart under NaHCO3 stress. Simultaneously, it was observed that low concentrations of NaHCO3 stress notably increased the abundance of rhizosphere bacteria in both plant types, while reducing their diversity. The impact of stress on the rhizosphere bacterial community weakened as the stress concentration increased. The application of NaHCO3 stress caused a significant change in the composition of the bacterial community in the rhizosphere. Additionally, alkaline salt stress influences the diversity of rhizosphere bacterial communities, which are linked to soil enzyme activities. These data will help us better understand the relationship between the dominant rhizosphere bacterial community and black locust. They will also provide a reference for further improving the alkali resistance of black locust by enhancing the soil bacterial community.

This review covers the literature data on plant growth-promoting bacteria in soil, which can fix atmospheric nitrogen, solubilize phosphates, produce and secrete siderophores, and may exhibit several different behaviors simultaneously. We discuss perspectives for creating bacterial consortia and introducing them into the soil to increase crop productivity in agrosystems. The application of rhizosphere bacteria—which are capable of fixing nitrogen, solubilizing organic and inorganic phosphates, and secreting siderophores, as well as their consortia—has been demonstrated to meet the objectives of sustainable agriculture, such as increasing soil fertility and crop yields. The combining of plant growth-promoting bacteria with mineral fertilizers is a crucial trend that allows for a reduction in fertilizer use and is beneficial for crop production.

ABSTRACT Near-natural forest management plays an important role in the maintenance of the long-term productivity and soil fertility of plantations. We conducted high-throughput absolute quantitative sequencing of 16S rRNA genes to compare the structures and diversity of rhizosphere soil bacterial communities among a pure Chinese fir (Cunninghamia lanceolata) plantation (S), a Cunninghamia lanceolata-Castanopsis hystrix-Michelia hedyosperma mixed plantation (SHX), and a Cunninghamia lanceolata-Castanopsis fissa mixed plantation (SD). The results revealed that near-natural forest management improved the rhizosphere soil properties of Chinese fir, especially the phosphorus content. Rhizosphere soil bacterial communities of Chinese fir in SHX and SD contained higher total absolute abundances and more unique operational taxonomic units (OTUs) than the pure plantation forest. Planctomycetes and Actinobacteria were abundant in SD, and Actinobacteria were enriched in SHX. The tree species also had an impact on the rhizosphere soil bacterial communities. For the rhizosphere soils of different tree species of SHX, the available phosphorus (AP) content of the rhizosphere of Chinese fir significantly surpassed those of Castanopsis hystrix and Michelia hedyosperma. Bacteria related to nitrogen fixing, such as Burkholderiales and Rhizobiales, were more abundant in Chinese fir in SD than in Castanopsis fissa. Acdiobacteria and Proteobacteria underpinned the differences found in the compositions of soil bacteria. The pH and soil organic matter were key variables influencing the rhizosphere soil bacterial communities. Our results demonstrated that in Chinese fir plantations, 12 years of near-natural management of introduced broad-leaved tree species can drive alterations of the physicochemical characteristics, bacterial community structure, and composition of rhizosphere soil, with tree species identity further influencing the rhizosphere soil bacterial community. IMPORTANCE Near-natural forest management is an important way to change the soil fertility decline and productivity reduction of pure Chinese fir plantations. At present, many detailed studies have been carried out on the impact of near-natural forest management on Chinese fir plantations at home and abroad. However, there are still few studies on the response of rhizosphere bacterial communities to near-natural forest management. Our study determined absolute quantities of Chinese fir rhizosphere bacterial communities in different mixed patterns. The results underscore the importance of near-natural forest management for Chinese fir plantation rhizosphere bacterial communities and provide new information on soil factors that affect rhizosphere bacterial communities in South China.

Kiwifruit bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) is a severe global disease. However, effective biological control agents for controlling Psa are currently unavailable. This study aimed to screen potential biological control agents against Psa from the kiwifruit rhizosphere. In this study, a total of 722 isolates of bacteria were isolated from the rhizosphere of kiwifruit orchards in five regions of China. A total of 82 strains of rhizosphere bacteria showed antagonistic effects against Psa on plates. Based on amplified ribosomal DNA restriction analysis (ARDRA), these antagonistic rhizosphere bacteria were grouped into 17 clusters. BLAST analyses based on 16S rRNA gene sequence revealed 95.44%–100% sequence identity to recognized species. The isolated strains belonged to genus Acinetobacter, Bacillus, Chryseobacterium, Flavobacterium, Glutamicibacter, Lysinibacillus, Lysobacter, Pseudomonas, Pseudarthrobacter , and Streptomyces , respectively. A total of four representative strains were selected to determine their extracellular metabolites and cell-free supernatant activity against Psa in vitro. They all produce protease and none of them produce glucanase. One strain of Pseudomonas sp. produces siderophore. Strains of Bacillus spp. and Flavobacteria sp. produce cellulase, and Flavobacteria sp. also produce chitinase. Our results suggested that the kiwifruit rhizosphere soils contain a variety of antagonistic bacteria that effectively inhibit the growth of Psa. [ABSTRACT FROM AUTHOR]

Rhizobacteria have been studied for carrying out important processes in plants generating benefits, among which are activities such as biological nitrogen fixation, phosphate solubilization, production of indoleacetic acid, production of ACC deaminase and siderophores promoting plant growth. The aim of this study was to identify in vitro plant growth promoting rhizobacteria associated with avocado crops. For this purpose, rhizobacteria were isolated from soils from Salitral, Ovejas (Mountain of the María), department of Sucre, Colombia. In vitro phosphate solubilization, nitrogen fixation, siderophore production and ACC deaminase tests were carried out to finally identify them molecularly by amplification and subsequent analysis of 16S rDNA sequences. The highest population densities were 2.95 x 107, 2.19 x 107, 1.91 x 107, 1.64 x 107, 1.50 x 107, 1.39 x107 and 1. 30 x 107 CFU/g of soil for the farms Florida S, Sector 2, El Ojito, Sector 1R, Sector 1D, Florida N and Villa Esperanza respectively, a total of 35 morphotypes of rhizosphere bacteria were isolated, only five isolates showed the ability to promote plant growth identifying them as Burkholderia cepacia, Pseudomona aureginosa, Burkholderia cepacea, Bacillus cereus and Bacillus megaterium. These results show the importance of microorganisms as agents of biotechnological value in the search for alternatives to agricultural and environmental problems in crops of agricultural interest. [ABSTRACT FROM AUTHOR]

Plant rhizosphere microbes are closely related to plant growth, whereas how the rhizosphere microbial community affects root development remains poorly understood. In this study, 16S rRNA gene high-throughput sequencing technology was used to detect the bacterial community of tobacco rhizosphere, and to explore the association mechanism between different developmental conditions of tobacco roots and differences in rhizosphere microbial community. The results showed that the species richness and diversity of rhizosphere bacteria in the well-developed root system (WDR) were higher than those in the undeveloped root system (UDR), with the genera Gallionella and Luteimona significantly increased, while the genera Edaphobaculum, PLTA13 and Rhodobacter significantly increased. Abundance significantly reduced (P<0.05). The molecular ecological network of UDR is more complex, and the interaction between species is strong, especially the cooperative behavior. The number of key nodes in the WDR network is more, and its carbon cycle related network modules increase. In addition, the WDR rhizosphere bacterial community assembly tends to be more developmentally aggregated, and environmental filtering plays a more important role in it. Overall, the results of this study emphasize that the structural composition, network changes and community assembly of the rhizosphere microbial community play an important role in the development of plant roots, and provide a theoretical basis for regulating the rhizosphere microbial community to promote plant root growth. [ABSTRACT FROM AUTHOR]

Biochar and bioorganic fertilizers (BOF) that are used in agriculture can, both directly and indirectly, impact rhizosphere soil microorganisms. However, changes to the halophyte rhizosphere bacterial community after applying biochar and BOF to saline–alkali soil have not been thoroughly described. This study has investigated the bacterial communities of halophytes in saline–alkali soil through the addition of different biochar and BOF formulas using Illumina-based sequencing of the 16S rRNA gene fragment. B_BOF (biochar and BOF combined application) had the best effect, either by promoting the plant growth or by improving the physical and chemical properties of the soil. The concentration of the rhizosphere bacterial communities correlated with the changes in soil organic matter (OM) and organic carbon (OC). Proteobacteria, Actinobacteria, Chloroflexi, and Acidobacteria accounted for >80% of the total bacteria in each treatment. In addition, the abundance of Micromonospora was much higher in response to B_BOF than to the other treatments. BOF, with or without biochar, significantly influenced the bacterial community composition in the saline–alkali soil. The OC, OM, total nitrogen, and the available phosphorus had significant effects on the bacterial structure of this soil. The complex correlation of the bacterial communities between CK and B_BOF was higher compared to that between CK and FB or between CK and BOF. These findings suggested that the plant growth, the soil characteristics, and the diversity or community composition of the rhizosphere bacteria in saline–alkali soil were significantly influenced by B_BOF, followed by BOF, and then biochar; fine biochar had a stronger effect than medium or coarse biochar. This study provides an insight into the complex microbial compositions that emerge in response to biochar and BOF. [ABSTRACT FROM AUTHOR]

Deciphering responses of bacterial communities to environmental change, and understanding how communities assemble in response to environmental change, are important subjects. The assembly processes governing the rhizosphere bacterial communities of minor grain crops are rarely explored based on regional scales, especially in terms of the environmental adaptation. Here, we investigated the environmental thresholds and phylogenetic signals for ecological preferences of rhizosphere bacterial communities of three minor grain crop taxa across complex environmental gradients to reflect their environmental adaptation. Additionally, we reported environmental factors affecting their community assembly processes based on a large‐scale soil survey in agricultural fields across northern China using high‐throughput sequencing. The results demonstrated a narrower range of environmental thresholds and weaker phylogenetic signals for the ecological traits of rhizosphere bacteria in proso millet than in foxtail millet and sorghum fields. The proso millet rhizosphere community was the most phylogenetically clustered. Null model analysis indicated that homogeneous selection belonging to deterministic processes governed the sorghum rhizosphere community, whereas dispersal limitation belonging to stochastic processes was the critical assembly process in the foxtail millet and proso millet. Mean annual temperature was the decisive factor for adjusting the balance between stochasticity and determinism of the foxtail millet, proso millet and sorghum rhizosphere communities. A higher temperature resulted in stochasticity in the proso millet and sorghum communities. For the foxtail millet community, the deterministic assembly increased with an increase in temperature. These results contribute to the understanding of rhizosphere‐associated bacterial community assembly processes in agro‐ecosystems on a large scale. Highlights: Proso millet rhizosphere bacterial taxa exhibited weaker environmental adaptation than foxtail millet and sorghum taxa.Determinism governed the sorghum rhizosphere community, whereas stochasticity was the critical assembly process in the foxtail and proso millet.Mean annual temperature mediated balance between stochastic and deterministic processes. [ABSTRACT FROM AUTHOR]

Rhizosphere bacteria are critical for supporting plant performance in stressful environments. Understanding the assembly and co-occurrence of rhizosphere bacterial communities contributes significantly to both plant growth and heavy metal accumulation. In this study, Ligustrum lucidum and Melia azedarach were planted in soils with simulated varying levels of Pb-Zn contamination. The Rhizosphere bacterial communities were investigated by using 16S rRNA gene sequencing. The impacts of Pb-Zn contamination on the diversity and structure of the rhizosphere bacterial community were found to be greater than those of both tree species. The variation in bacterial community structure in both trees was mainly driven by the combinations of Pb-Zn and soil properties. Deterministic processes (non-planted, 82 %; L. lucidum , 73 %; M. azedarach , 55 %) proved to be the most important assembly processes for soil bacterial communities, but both trees increased the importance of stochastic processes (18 %, 27 %, 45 %). The rhizosphere co-occurrence networks exhibited greater stability compared to the non-planted soil networks. Rare taxa played a dominant role in maintaining the stability of rhizosphere networks, as most of the keystone taxa within rhizosphere networks belonged to rare taxa. Dissimilarities in the structure and network complexity of rhizosphere bacterial communities were significantly associated with differences in tree biomass and metal accumulation. These variations in response varied between both trees, with L. lucidum exhibiting greater potential for phytoremediation in its rhizosphere compared to M. azedarach. Our results offer valuable insights for designing effective microbe-assisted phytoremediation systems. [Display omitted] • The effect of Pb-Zn contamination on bacteria was greater than that of both trees. • Pb-Zn and soil properties jointly shaped bacterial community structure in trees. • L. lucidum and M. azedarach increased the importance of stochastic processes. • Trees contributed to the intensity of bacterial interactions and network complexity. • Rare taxa played a dominating role for stability of rhizosphere networks. [ABSTRACT FROM AUTHOR]

[Display omitted] • Larger-sized MPs altered community composition in rhizosphere and root endosphere. • Community assembly was influenced by the MPs with different particle size. • Cd concentrations in pakchoi were decreased by larger-sized MPs. • Larger-sized PS-MPs inhibit Cd uptake through the recruitment of specific taxa. Plant microbiota are an important factor impacting plant cadmium (Cd) uptake. However, little is known about how plant microbiota affects the Cd uptake by plants under the influence of microplastics (MPs) with different particle sizes. In this study, bacterial structure and assembly in the rhizosphere and endosphere in pakchoi were analyzed by amplicon sequencing of 16S rRNA genes under the influence of different particle sizes of polystyrene microplastics (PS-MPs) combined with Cd treatments. Results showed that there were no significant differences observed in the shoot endophytes among different treatments. However, compared to Cd treatment, larger-sized PS-MPs (2 and 20 μm) significantly increased community diversity and altered the structural composition of rhizosphere bacteria and root endophytes, while smaller-sized PS-MPs (0.2 μm) did not. Under the treatment of larger-sized PS-MPs, the niche breadth of rhizosphere bacteria and root endophytes were significantly increased. And larger-sized PS-MPs also maintained stability and complexity of bacterial co-occurrence networks, while smaller-sized PS-MPs reduced them. Furthermore, compared to Cd treatment, the addition of larger particle size PS-MPs decreased the proportion of homogeneous section, while increased the proportion of drift in root endophytic bacterial community assembly. The role of larger-sized MPs in the community assembly of rhizosphere bacteria was opposite. Using random forest and structural equation models, the study found that larger-sized PS-MPs can promote the colonization of specific bacterial taxa, such as Brevundimonas, AKAU4049, SWB02, Ellin6055, Porphyrobacter, Sphingorhabdus, Rhodobacter, Erythrobacter, Devosia and some other bacteria belonging to Alphaproteobacteria, in the rhizosphere and root endosphere. The colonization of these taxa can may induce the formation of biofilms in the roots, immobilize heavy metals through oxidation processes, and promote plant growth, thereby reducing Cd uptake by pakchoi. The findings of this study provide important insights into the microbial mechanisms underlying the influence of MPs with different particle sizes on plant Cd uptake. [ABSTRACT FROM AUTHOR]

Maize has the largest cultivation area of any crop in the world and plays an important role in ensuring food security. High-density planting is essential for maintaining high maize yields in modern intensive agriculture. Nonetheless, how high-density planting and the tolerance of individual genotypes to such planting shape the root-associated microbiome of maize is still unknown. In this study, we analyzed the root and rhizosphere bacterial communities of two maize accessions with contrasting shoot architectures grown under high- and low-density planting conditions. Our results suggested that maize hosted specific, distinct bacterial communities in the root endocompartment and that the maize genotype had a significant effect on the selection of specific microbes from the rhizosphere. High-density planting also had significant effects on root-associated bacterial communities. Specifically, genotype and high-density planting coordinated to shape the structure, composition, and function of root and rhizosphere bacterial communities. Taken together, our results provide insights into how aboveground plant architecture and density may alter the belowground bacterial community in root-associated compartments of maize.

Agricultural Jiaosu (AJ) is a method of recycling agricultural wastes for improving soil properties, promoting plant growth, and enhancing plant stress resistance. However, the underlying mechanism by which AJ improves plant stress resistance needs to be determined. Therefore, in this study, two treatments of AJ spraying and water spraying were set up to determine the enzyme activities related to the stress resistance of pak choi after 30 days of growth, and the potential mechanism of AJ’s influence on the stress resistance of pak choi was revealed by transcriptome, metabolome, and rhizome microbiome analyses. Microbial community analysis revealed that the application of AJ does not alter microbial abundance in the rhizosphere; however, it can improve microbial diversity and enrich Actinobacteriota, Proteobacteria, and Firmicutes in the pak choi rhizosphere. Metabolomic analysis revealed that these phyla were significantly positively correlated, with highly upregulated metabolites. Our findings suggest that AJ recruits beneficial microorganisms (BMs) in the rhizosphere and stimulates the expression of genes and metabolites involved in phenylpropanoid and glucosinolate biosynthesis, as well as glutathione and alpha-linolenic acid metabolism pathways. The use of AJ could considerably minimise the use of pesticides and fertilisers and improve the quality of the ecological environment.