Rhizosphere Environment Research Articles

Comparative analysis on root exudate and rhizosphere soil bacterial assembly between tomatoes and peppers infected by Ralstonia

BackgroundThe rhizosphere environment regulated by root secretory activity and rhizosphere microbial interactions plays an essential role in resisting soil-borne diseases, while the host species is an important factor that affects the composition of root exudates and rhizosphere microbiomes. However, few studies have been done on the characteristics of root exudates and bacterial communities in terms of composition, diversity, and functional potential when host plants of different species are subjected to the same disease.ResultsIn this study, we examined the rhizosphere soil bacteria and root exudates of both healthy and diseased tomatoes and peppers employing metabolomics and amplicon techniques. Our findings indicated that variations existed in both root exudates and the bacterial community among different host species and health states. The diversities of both rhizosphere metabolites and bacterial communities were significantly reduced in different diseased plants. Although pepper and tomato resisted the invasion of Ralstonia by recruiting different potentially beneficial bacteria, their rhizosphere bacterial communities had the same functional potential. In comparison to diseased rhizosphere soil, healthy rhizosphere soil had many more functional pathways associated with disease suppression and plant growth.ConclusionsThis study highlighted the crucial role of host plants in shaping the rhizosphere environment and revealed the variation characteristics of root exudates and rhizosphere bacteria of different host plants induced by the same disease.Graphical

Effect of Bacillus amyloliquefaciens QST713 on Inter-Root Substrate Environment of Cucumber under Low-Calcium Stress

(1) Background: Low-calcium stress can have adverse effects on the rhizosphere environment of cucumber, subsequently impacting cucumber growth. However, plant-growth-promoting rhizobacteria can directly or indirectly enhance plant growth and induce plant tolerance, thereby mitigating the detrimental effects of low-calcium stress on cucumber growth. This study aims to elucidate the role of Bacillus amyloliquefaciens QST713 in the rhizosphere environment of cucumber under low-calcium stress, providing a theoretical basis for the application and promotion of Bacillus amyloliquefaciens. (2) Methods: This study used the ‘JinYou NO.4′ cucumber variety as test material, setting four treatments of CK, CK+Q, LCa, LCa+Q. We conducted measurements of plant height and stem diameter for four groups of cucumber plants: before treatment (0 d), and at 10 d, 20 d, 30 d, and 60 d after treatment. Additionally, we determined the biomass of cucumber plants under different treatments during the peak fruiting period. Inter-root matrix samples of cucumber were collected during the fruiting late period, and the physical and chemical properties and nutrient contents of the inter-root matrix of cucumber were determined, and bacterial microbial diversity and bacterial microbial communities were analysed using Illumina-MiSeq high-throughput sequencing technology. (3) Results: Low-calcium stress significantly inhibits the growth of cucumber plants. However, the application of Bacillus amyloliquefaciens QST713 effectively mitigates the inhibitory effects of low-calcium stress on cucumber growth. The application of Bacillus amyloliquefaciens QST713 was able to improve the physicochemical environment of the matrix and enhanced the absorption and utilisation of matrix nutrients in cucumber. The high-throughput sequencing analysis showed that the richness and diversity of bacterial communities and the number of bacteria decreased significantly under low-calcium stress, and increased significantly after the application of Bacillus amyloliquefaciens QST713. The composition of the dominant bacterial groups of the inter-root matrix of cucumber was basically the same among the four treatments, and the main difference was in the abundance of bacteria. The application of Bacillus amyloliquefaciens QST713 increased the relative abundance of bacteria that decreased under low-calcium stress, and decreased the relative abundance of bacteria that increased under low-calcium stress. (4) Conclusions: The results of this study elucidated the positive effects of Bacillus amyloliquefaciens QST713 on the growth and inter-root environment of cucumber under low-calcium stress, and provided a theoretical basis for in-depth research on the resistance of Bacillus amyloliquefaciens and its popularised application.

Bio-organic fertilizer facilitated phytoremediation of heavy metal(loid)s-contaminated saline soil by mediating the plant-soil-rhizomicrobiota interactions

Bio-organic fertilizer (BOF) was effective to promote the phytoremediation efficiency of heavy metal(loid)s-contaminated saline soil (HCSS) by improving rhizosphere soil properties, especially microbiome. However, there existed unclear impacts of BOF on plant metabolome and plant-driven manipulation on rhizosphere soil microbiota in HCSS, which were pivotal contributors to stress defense of plants trapped in adverse conditions. Here, a pot experiment was conducted to explore the mechanisms of BOF in improving alfalfa (Medicago sativa)-performing phytoremediation of HCSS. BOF application significantly increased the biomass (150.87–401.58 %) to support the augments of accumulation regarding heavy metal(loid)s (87.50 %–410.54 %) and salts (38.27 %–271.04 %) in alfalfa. BOF promoted nutrients and aggregates stability but declined pH of rhizosphere soil, accompanied by the boosts of rhizomicrobiota including increased activity, reshaped community structure, enriched plant growth promoting rhizobacteria (Blastococcus, Modestobacter, Actinophytocola, Bacillus, and Streptomyces), strengthened mycorrhizal symbiosis (Leohumicola, Funneliformis, and unclassified_f_Ceratobasidiaceae), optimized co-occurrence networks, and beneficial shift of keystones. The conjoint analysis of plant metabolome and physiological indices confirmed that BOF reprogrammed the metabolic processes (synthesis, catabolism, and long-distance transport of amino acid, lipid, carbohydrate, phytohormone, stress-resistant secondary metabolites, etc) and physiological functions (energy supply, photosynthesis, plant immunity, nutrients assimilation, etc) that are associated intimately. The consortium of root metabolome, soil metabolome, and soil microbiome revealed that BOF facilitated the exudation of metabolites correlated with rhizomicrobiota (structure, biomarker, and keystone) and rhizosphere oxidative status, e.g., fatty acyls, phenols, coumarins, phenylpropanoids, highlighting the plant-driven regulation on rhizosphere soil microbes and environment. By compiling various results and omics data, it was concluded that BOF favored the adaptation and phytoremediation efficiency of alfalfa by mediating the plant-soil-rhizomicrobiota interactions. The results would deepen understanding of the mechanisms by which BOF improved phytoremediation of HCSS, and provide theoretical guidance to soil amelioration and BOF application.

Effects of Different Agricultural Waste Composts on Cabbage Yield and Rhizosphere Environment

The return of agricultural waste to the field is one of the most effective strategies of increasing crop yield, improving the soil’s physicochemical properties, and improving the soil rhizosphere environment. In the present study, sheep manure (SM), cow manure (CM), tail vegetable (TV), mushroom residue (MR), and corn straw (CS) were used as raw materials, and no fertilization (CK1) and local commercial organic fertilizer (CK2) treatments were used as controls. Eight composts were set up using specific mass ratios of different compost materials. After fermentation, field experiments were conducted to determine the cabbage yield, soil’s physicochemical properties, and soil rhizosphere conditions. The eight composts increased the soil organic matter and nutrient contents significantly. Among the eight fermentation formulas, T6 (CM:CS:TV:SM = 1:1:2:6), T7 (MR:CS:TV:SM = 1:1:2:6), and T8 (CM:MR:CS:TV:SM = 1:1:1:2:5) were relatively effective. Therefore, high-throughput sequencing was performed on T6, T7, T8, CK1, and CK2. T6, T7, and T8 exhibited increased relative abundance of Proteobacteria, Actinomycetes, and Firmicutes, while the Acidobacteria abundance was decreased. In addition, Ascomycota’s and Basidiomycetes’ relative abundance decreased, and the oil chytrid and mortierella increased. The microbial community structure was affected significantly by pH, electrical conductivity, available potassium, available nitrogen, and organic matter. In general, the three composts increased yield by improving the soil’s physicochemical properties, fertility, and microbial community structure. Among them, T6 had the most significant effect and is the optimal formula for use as a local organic cabbage fertilizer, and it could facilitate sustainable agricultural development.

Plant root associated chitinases: structures and functions.

Chitinases degrade chitin, a linear homopolymer of β-1,4-linked N-acetyl-D-glucosamine (GlcNAc) residues found in the cell walls of fungi and the exoskeletons of arthropods. They are secreted by the roots into the rhizosphere, a complex and dynamic environment where intense nutrient exchange occurs between plants and microbes. Here we modeled, expressed, purified, and characterized Zea mays and Oryza sativa root chitinases, and the chitinase of a symbiotic bacterium, Chitinophaga oryzae 1303 for their activities with chitin, di-, tri-, and tetra-saccharides and Aspergillus niger, with the goal of determining their role(s) in the rhizosphere and better understanding the molecular mechanisms underlying plant-microbe interactions. We show that Zea mays basic endochitinase (ZmChi19A) and Oryza sativa chitinase (OsChi19A) are from the GH19 chitinase family. The Chitinophaga oryzae 1303 chitinase (CspCh18A) belongs to the GH18 family. The three enzymes have similar apparent K M values of (20-40 µM) for the substrate 4-MU-GlcNAc3. They vary in their pH and temperature optima with OsChi19A activity optimal between pH 5-7 and 30-40°C while ZmChi19A and CspCh18A activities were optimal at pH 7-9 and 50-60°C. Modeling and site-directed mutation of ZmChi19A identified the catalytic cleft and the active residues E147 and E169 strategically positioned at ~8.6Å from each other in the folded protein. Cleavage of 4-MU-GlcNAc3 was unaffected by the absence of the CBD but diminished in the absence of the flexible C-terminal domain. However, unlike for the soluble substrate, the CBD and the newly identified flexible C-terminal domain were vital for inhibiting Aspergillus niger growth. The results are consistent with the involvement of the plant chitinases in defense against pathogens like fungi that have chitin exoskeletons. In summary, we have characterized the functional features and structural domains necessary for the activity of two plant root chitinases that are believed to be involved in plant defense and a bacterial chitinase that, along with the plant chitinases, may participate in nutrient recycling in the rhizosphere.

Inoculation with rhizospheric microorganisms in tropical dry forests restoration increased microbial diversity but had no effect on seedling growth

The diversity of soil microbial organisms is rarely considered in restoration scenarios, even though this diversity is an important component of the ecological complexity that we aim to understand. Plant growth promoting microorganisms can positively affect plants by providing nutrients regularly, producing phytohormones to stimulate root growth and development, and modifying the rhizosphere environment. The present study evaluated, over a 5‐month period, the effects of inoculation of Inga densiflora nurse seedlings with rhizospheric microorganisms taken from a neighbor forest habitat, in the context of an early‐stage ecological restoration project in a Tropical Dry Forest area invaded by Guinea grass (Panicum maximum). The inoculation's effect on two response variables was evaluated: (1) growth of the seedling (I. densiflora), and (2) the diversity of bacteria and fungi, with an emphasis on genera associated with rhizosphere that promote vegetation growth. Bacterial and fungal diversity were evaluated using the metabarcoding method and Hill numbers q = 0, 1, and 2. Significantly higher microorganism diversity was found in the rhizosphere of inoculated seedlings compared to non‐inoculated seedlings. However, no significant differences were found in the growth of inoculated versus non‐inoculated seedlings. This evidence suggests that, in the short term and through a restoration context, inoculating trees with microorganisms taken directly from a neighboring forest can increase bacterial diversity, and possibly also fungal diversity. While understanding the intricacies of these processes requires further study, this technique seems to be a promising approach for recovering the diversity of rhizosphere microbiomes during ecological restoration.

Above-and below-ground feedback loop of maize is jointly enhanced by plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi in drier soil

Drought is a potent abiotic stressor that arrests crop growth, significantly affecting crop health and yields. The arbuscular mycorrhizal fungi (AMF), and plant growth-promoting rhizobacteria (PGPR) can offer to protect plants from stressful environments through improving water, and nutrient use efficiency by strengthening plant root structure and harnessing favorable rhizosphere environments. When Acaulospora laevis (AMF) and Bacillus subtilus (PGPR) are introduced in combination, enhanced root growth and beneficial microbial colonization can mitigate drought stress. To assess this potential, a pot experiment was done with maize (Zea mays L.) to explore the effects of A. laevis and B. subtilus under different water levels (well-watered = 80 %; moderate water stress = 55 %; and severe water stress = 35 %) on maize yield, soil microbial activities, nutrients contents, root, and leaf functioning. Plants exposed to severe drought stress hampered their root and leaf functioning, and reduced grain yield compared with control plants. Combined use of AMF and PGPR increased root colonization (104.6 %–113.2 %) and microbial biomass carbon (36.38 %–40.23 %) under moderate to severe drought conditions over control. Higher root colonization was strongly linked with elevated ACC (aminocyclopropane-1-carboxylic acid) production, subsequently enhancing water use efficiency (21.62 %–12.77 %), root hydraulic conductivity (1.9 %–1.4 %) and root nutrient uptake under moderate to severe drought conditions. Enhanced nutrient uptake further promoted leaf photosynthetic rate by 27.3 %–29.8 % under moderate and severe drought stress. Improving leaf and root physiological functioning enhanced maize grain yield under stressful environments. Furthermore, co-inoculation with AMF-PGPR reduced cellular damage by lowering oxidative enzyme levels and increasing antioxidative enzyme activities, improving plant performance and grain yield under stressful environments. Conclusively, the synergistic interaction of AMF with PGPR ensured plant stress tolerance by reducing cellular injury, facilitating root-leaf functioning, enhancing nutrient-water-use-efficiencies, and increasing yield under drought stress.

Role of extracellular matrix components in biofilm formation and adaptation of Pseudomonas ogarae F113 to the rhizosphere environment

Regulating the transition of bacteria from motile to sessile lifestyles is crucial for their ability to compete effectively in the rhizosphere environment. Pseudomonas are known to rely on extracellular matrix (ECM) components for microcolony and biofilm formation, allowing them to adapt to a sessile lifestyle. Pseudomonas ogarae F113 possesses eight gene clusters responsible for the production of ECM components. These gene clusters are tightly regulated by AmrZ, a major transcriptional regulator that influences the cellular levels of c-di-GMP. The AmrZ-mediated transcriptional regulation of ECM components is primarily mediated by the signaling molecule c-di-GMP and the flagella master regulator FleQ. To investigate the functional role of these ECM components in P. ogarae F113, we performed phenotypic analyses using mutants in genes encoding these ECM components. These analyses included assessments of colony morphology, dye-staining, static attachment to abiotic surfaces, dynamic biofilm formation on abiotic surfaces, swimming motility, and competitive colonization assays of the rhizosphere. Our results revealed that alginate and PNAG polysaccharides, along with PsmE and the fimbrial low molecular weight protein/tight adherence (Flp/Tad) pilus, are the major ECM components contributing to biofilm formation. Additionally, we found that the majority of these components and MapA are needed for a competitive colonization of the rhizosphere in P. ogarae F113.

Evaluation of Fine Root Morphology and Rhizosphere Environmental Characteristics of the Dioecious Idesia polycarpa Maxim

To explore the differences in the fine root characteristics and rhizosphere environment of male and female Idesia polycarpa Maxim at different stages, 7-year-old male and female I. polycarpa were used as plant materials. The fine root characteristics were measured with a root scanner, and rhizosphere soil was collected at the flowering stage (May), fruit accumulation stage (July), and fruit maturity stage (October). In addition, this study analyzed the soil nutrient characteristics of these conditions at different stages. At the same time, Illumine high-throughput sequencing technology and gas chromatography–tandem mass spectrometry (GC–MS) technology were used to analyze the rhizosphere microbes and metabolites of male and female plants at different stages. The results showed that the total root length, surface area, total volume, root tip number, and total average diameter of the fine root of female plants were larger than those of male plants, and the difference reached its maximum in the fruit material accumulation stage. Total carbon (TC) and total nitrogen (TN) content in the rhizosphere soil of male and female plants significantly differed over multiple stages, while available soil nitrogen and potassium content significantly differed during fruit ripening. The rhizosphere microbial composition of male and female plants was similar, and the dominant bacteria in the rhizosphere soil of each stage were Proteobacteria, Acidobacteria, Ascomycota, and Mortierellomycota. The relative abundance of Bacillus, Arthrobacter, Volutella, and Neocosmospora in rhizosphere soil at different stages differed between male and female plants. Combined with the OPLS-DA model and database retrieval, 29 significantly different metabolites, most of which were carbohydrates, were detected in the rhizosphere soil of male and female plants. Moreover, there were more significant metabolites in the rhizosphere soil at the flowering stage than in the fruit ripening stage. Through RDA analysis, available potassium (AK), Pedomicrobium, Chaetomium, and Glucose 1 had the greatest influence on fine root traits of I. polycarpa. The results indicated that the fine root traits were negatively correlated with AK and rhizosphere metabolites. Moreover, positive correlations were found with rhizosphere microorganism traits. The above results laid a foundation for the field management of I. polycarpa and the screening and application of rhizosphere growth-promoting bacteria resources.

Drive soil nitrogen transformation and improve crop nitrogen absorption and utilization - a review of green manure applications.

Green manure application presents a valuable strategy for enhancing soil fertility and promoting ecological sustainability. By leveraging green manures for effective nitrogen management in agricultural fields can significantly reduce the dependency of primary crops on chemical nitrogen fertilizers, thereby fostering resource efficiency. This review examines the current advancements in the green manure industry, focusing on the modulation of nitrogen transformation in soil and how crops absorb and utilize nitrogen after green manure application. Initially, the influence of green manure on soil nitrogen transformation is delineated, covering processes such as soil nitrogen immobilization, and mineralization, and losses including NH3, N2O, and NO3 --N leaching. The review then delves into the effects of green manure on the composition and function of soil microbial communities, highlighting their role in nitrogen transformation. It emphasizes the available nitrogen content in the soil, this article discussing nitrogen uptake and utilization by plants, including aspects such as nitrogen translocation, distribution, the root system, and the rhizosphere environment of primary crops. This provides insights into the mechanisms that enhance nitrogen uptake and utilization when green manures are reintroduced into fields. Finally, the review anticipates future research directions in modulating soil nitrogen dynamics and crop nitrogen uptake through green manure application, aiming to advance research and the development of the green manure sector.

Triple interactions for induced systemic resistance in plants.

Induced systemic resistance (ISR) is a crucial concept in modern agriculture, explaining plant defense mechanisms primed by rhizosphere stimuli and activated by subsequent infections. Biological factors contributing to ISR generally include plant growth-promoting microbes3 (PGPM). Bacillus spp., Pseudomonas spp., and Trichoderma spp. have been extensively studied for their plant growth-promoting characteristics and ISR effect against above-ground pathogens and insect infestations. These phenomena elucidate the bottom-up effects of how beneficial rhizosphere microbes help plants resist above-ground attacks. Conversely, soil microbiome analysis in the rhizosphere of plants infected by above-ground pathogens has shown increased beneficial microbes in the soil, a phenomenon termed 'soil legacy effects'. This represents the top-down effects of above-ground attackers on plants' rhizosphere environments. Interestingly, recent studies have shown that above-ground stimuli not only recruit PGPM in the rhizosphere but also that these PGPM influence plant defense responses against subsequent pathogen infections. This can be seen as a four-step plant defense mechanism involving above-ground attackers, host plants, rhizosphere microbes, and subsequent attacks. This represents an active defense mechanism that overcomes the limitations of sessile plants. This review summarizes plant ISR mechanisms in terms of triple inter-organism interactions and provides molecular evidence for each step.

Metagenomics and vegetative growth of Salvia hispanica inoculated with Trichoderma harzianum.

The soil is a dynamic environment, influenced by abiotic and biotic factors, which can result in changes in plant development. This study aimed to assess the impact on vegetative growth of chia (Salvia hispanica L) inoculated with Trichoderma harzianum and on the rhizosphere microbiome. The experimentation was conducted in a greenhouse under controlled conditions growing chia plants in pots containing soil with a clayey texture. Different concentrations of T. harzianum (0; 2.5; 5.0; 10.0; 20.0 µL. g-1 of seed) were applied to the chia seeds before planting. Morphological parameters, including plant height (cm), number of branches, stem diameter (mm), number of days to flowering and shoot and root dry masses (g) were quantitatively assessed. After the cultivation period, soil samples from the rhizosphere region were collected for subsequent chemical and metagenomic analyses. These samples were also compared with the control soil, collected before installing the experiment. The results showed that increasing doses of T. harzianum promoted a significant increase in the diameter of the stem, number of branches, dry biomass of the root system and the number of days to flowering, without modifying the overall height of the plants. Soil metagenomics indicated that T. harzianum inoculation modified the microbial diversity of the rhizosphere environment, with more pronounced effects observed in samples treated with higher concentrations of the inoculant. Furthermore, there were changes in the chemical composition and enzymes related to soil quality in correlation with the concentrations of the applied inoculant. This study demonstrated that inoculating chia seeds with T. harzianum not only promotes specific morphogenetic characteristics of the plant, but it also has a significant impact on the microbial diversity and biochemical functionality of the soil, including an observed increase in the populations of T. harzianum and T. asperellum.

Drought induces substitution of bacteria within taxonomic groups in the rhizosphere of native maize from arid and tropical regions

In Mexico, maize landraces are usually cultivated in milpa polyculture agroecosystems, which are maintained with ancestral practices, i.e. with very low external inputs such as chemicals and without irrigation systems. Several studies have characterized soil and maize-root microbiota from different milpas, however, robust experimental approaches are necessary to understand the relationship between a healthy microbial community structure and the health of milpa plants. We tested the hypothesis that different maize varieties not only differ in the microorganisms enriched in their rhizospheric environment, but also in the responses of these communities to drought. By suspending irrigation, we induced drought experimentally in three varieties of maize: one landrace from an arid milpa, one from a tropical milpa, and a commercial hybrid. The treatment elicited stress symptoms and growth declines in all three maize varieties. Nevertheless, the maize landrace from arid milpa displayed a better performance in biomass accumulation. The drought treatment did not significantly affect bulk soil bacterial communities; in contrast, all three varieties had shifts in their rhizospheric microbiomes, indicating that these responses were related to the presence of plant roots. The varieties differed in their changes of root-associated microbiota in response to drought, with only Paenarthrobacter genus increasing in all three. Responses mainly consisted of increases in the abundance of certain groups (e.g. Verrucomicrobiota) and substitution of strains within groups (e.g. Group 6 Acidobacteriota, family Streptomycetacea, and many others). The landrace from an arid region had the most bacteria substituted under drought, suggesting that a more stringent selection of microorganisms in roots could be part of the response of this landrace to drought. We propose that drought-tolerant maize landraces from arid milpas could be the source of bacterial strains or communities that aid drought-sensitive varieties in coping with reduced water availability expected due to climate change.

Characterization of the Microbial Community Structures, Soil Chemical Properties, and Enzyme Activity of Stellera chamaejasme (Thymelaeaceae) and Its Associated Forages in Alpine Grassland of Northwestern China.

The invasion of toxic weeds was detrimental to the growth of original vegetation and speed up the degraded grasslands. The purpose of this study was to explore the difference in microbial community, soil physicochemical properties, and enzyme activity in the rhizosphere of Stellera chamaejasme and its associated forages (Stipa purpurea and Polygonum viviparum). The rhizosphere soil microbial communities of S. chamaejasme and its associated forages were determined by high-throughput sequencing technology, the physicochemical properties, and enzyme activities were also measured using soil chemical methods. We performed biological statistical analyses to explore the correlation of rhizosphere micro-ecological environment between the invading poisonous herb S. chamaejasme and its associated forages. The Ascomycota community in the rhizosphere soil of S. chamaejasme was significantly decreased when compared with its associated forages. S. chamaejasme and S. purpurea had a similar bacterial composition, while the rhizosphere of P. viviparum was associated with more Acidobacteria and Bacteroidetes. The RDA analysis showed S. chamaejasme had highly correlated with acid proteinase, invertase, polyphenol oxidase, cellulose, and neutral protease and S. purpurea had highly associated with N-acetyl-beta-D-glucosaminidase, β-D-Glucosidase, and the P. viviparum had highly associated with total phosphorus, total nitrogen, ammonium nitrogen, soil organic matter, pH, acid phosphatase, and catalase. Along with the invasion of S. chamaejasme, the microbial composition, soil physicochemical properties, and enzyme activity of the growing area changed considerably compared with the associated forages. Taken together, our results suggested that the composition and diversity of microbial communities associated with S. chamaejasme and its associated forages exhibited different patterns, and the rhizosphere soil microbial communities in different plants were regulated by different environmental factors in this alpine grassland ecosystem.

Diversity and Distribution of Arbuscular Mycorrhizal Fungi in Selected Medicinal Plants

Background: Tha Arbuscular Mycorrhizal Fungi (AMF) association previously known as VAM belongs to an ancient fungal group known as Glomeromycota. In this study five commonly used medicinal plants viz., Eclipta prostrata, Mentha arvensis, Elettaria cardamomum, Bacopa monneri and Mimosa pudica were investigated for AMF colonization in the form of arbuscules, vesicles and hyphae from their roots and their rhizospheric soil was isolated for AMF spores. Majorly two genera of AMF dominated the rhizospheric soil of the plants investigated which were Acaulospora and Glomus. Altogether 12 AMF spores were isolated from the rhizospheric environment of the plants and they belonged to six different genera of AMF. Methods: In this field-laboratory investigation during 2022-23, different localities of Banaras Hindu University was surveyed. 5 different plants were selected for investigation on the diversity and distribution of AMF colonisation found in their rhizospheric soil. Result: Our investigation on the diversity and distribution of AMF of few selected plants from BHU have allowed us to isolate and morphologically identify 12 different species of AMF from 6 different genera. The geographical distribution of the collected species was discussed. The present work will be a complementary contribution to the comprehensive study of the identification and utility of AMF in plant growth and sust.

New Barrier Role of Iron Plaque: Producing Interfacial Hydroxyl Radicals to Degrade Rhizosphere Pollutants.

Iron plaque, as a natural barrier between rice and soil, can reduce the accumulation of pollutants in rice by adsorption, contributing to the safe production of rice in contaminated soil. In this study, we unveiled a new role of iron plaque, i.e., producing hydroxyl radicals (·OH) by activating root-secreted oxygen to degrade pollutants. The ·OH was produced on the iron plaque surface and then diffused to the interfacial layer between the surface and the rhizosphere environment. The iron plaque activated oxygen via a successive three-electron transfer to produce ·OH, involving superoxide and hydrogen peroxide as the intermediates. The structural Fe(II) in iron plaque played a dominant role in activating oxygen rather than the adsorbed Fe(II), since the structural Fe(II) was thermodynamically more favorable for oxygen activation. The oxygen vacancies accompanied by the structural Fe(II) played an important role in oxygen activation to produce ·OH. The interfacial ·OH selectively degraded rhizosphere pollutants that could be adsorbed onto the iron plaque and was less affected by the rhizosphere environments than the free ·OH. This study uncovered the oxidative role of iron plaque mediated by its produced ·OH, reshaping our understanding of the role of iron plaque as a barrier for rice.

Warm Temperature Increments Strengthen the Crosstalk between Roots and Soil in the Rhizosphere of Soybean Seedlings.

The plant rhizosphere underlies the crosstalk between plant and soil and has a crucial role in plant growth and development under various environments. We examined the effect of temperature rise on the rhizosphere environment of soybean roots to clarify the rhizosphere crosstalk between roots and soil in response to warm temperature rises in a global warming background. The in situ results of root enzyme activity revealed that soybean roots secrete β-glucosidase, and enzyme spectrum imaging demonstrated different enzymatic activities under different temperature environments. The soil enzyme kinetics results showed that soil enzymatic activity increased with increasing temperature, and soybean rhizosphere soil enzymatic activity was higher than that of non-rhizosphere soil. Rhizosphere soil and non-rhizosphere soil showed that the dominant bacterial phylum in soybean rhizosphere soil was Acidobacteria, and the dominant bacterial genus was JG30-KF-AS9. Compared with non-rhizosphere soil, rhizosphere soil was more nutrient-rich, and root secretions provided abundant carbon sources and other nutrients for soil microorganisms in the rhizosphere. Rhizosphere microorganisms affect plant growth by influencing the decomposition of soil organic carbon. The organic carbon content of rhizosphere soil was higher than that of non-rhizosphere soil under high temperatures.

Diversity and composition of active and total bacteria in rhizospheric soil in response to continuous cropping years of Panax notoginseng.

The synchronous research and analysis of total and active soil microbial communities can provide insight into how these communities are impacted by continuous cropping years and pathogen infection. The diversity of total and active bacteria in rhizospheric soil of 2-year-old and 3-year-old healthy and diseased Panax notoginseng can comprehensively reveal the bacterial response characteristics in continuous cropping practice. The results showed that 4916 operational taxonomic units (OTUs) were found in the rhizospheric soil bacterial community of P. notoginseng at the DNA level, but only 2773 OTUs were found at the RNA level. The rhizospheric environment had significant effects on the active and bacterial communities, as indicated by the number of OTUs, Shannon, Chao1, Faith's phylogenetic diversity (Faith's PD), and Simpson's diversity indexes. The DNA level can better show the difference in diversity level before and after infection with root rot. The bacterial Chao1 and Faith's PD diversity indexes of 2-year-old root rot-diseased P. notoginseng rhizospheric soil (D2) were higher than that of healthy plants, while the bacterial Shannon diversity index of 3-year-old root rot-diseased P. notoginseng rhizospheric soil (D3) was the lowest in the total bacteria. Principal coordinate analysis (PCoA) illustrated that the total bacterial species composition changed markedly after root rot disease. There were significant differences in the composition of active bacterial species between the 2-year and 3-year rhizospheres. In conclusion, the total and active edaphic rhizospheric bacterial communities could provide important opportunities to understand the responses of bacteria to continuous cropping of P. notoginseng.

Harnessing root exudates for plant microbiome engineering and stress resistance in plants

A wide range of abiotic and biotic stresses adversely affect plant's growth and production. Under stress, one of the main responses of plants is the modulation of exudates excreted in the rhizosphere, which consequently leads to alterations in the resident microbiota. Thus, the exudates discharged into the rhizospheric environment play a preponderant role in the association and formation of plant-microbe interactions. In this review, we aimed to provide a synthesis of the latest and most pertinent literature on the diverse biochemical and structural compositions of plant root exudates. Also, this work investigates into their multifaceted role in microbial nutrition and intricate signaling processes within the rhizosphere, which includes quorum-sensing molecules. Specifically, it explores the contributions of low molecular weight compounds, such as carbohydrates, phenolics, organic acids, amino acids, and secondary metabolites, as well as the significance of high molecular weight compounds, including proteins and polysaccharides. It also discusses the state-of-the-art omics strategies that unveil the vital role of root exudates in plant-microbiome interactions, including defense against pathogens like nematodes and fungi. We propose multiple challenges and perspectives, including exploiting plant root exudates for host-mediated microbiome engineering. In this discourse, root exudates and their derived interactions with the rhizospheric microbiota should receive greater attention due to their positive influence on plant health and stress mitigation.

α-Tomatine gradient across artificial roots recreates the recruitment of tomato root-associated Sphingobium.

α-Tomatine is a major saponin that accumulates in tomatoes (Solanum lycopersicum). We previously reported that α-tomatine secreted from tomato roots modulates root-associated bacterial communities, particularly by enriching the abundance of Sphingobium belonging to the family Sphingomonadaceae. To further characterize the α-tomatine-mediated interactions between tomato plants and soil bacterial microbiota, we first cultivated tomato plants in pots containing different microbial inoculants originating from three field soils. Four bacterial genera, namely, Sphingobium, Bradyrhizobium, Cupriavidus, and Rhizobacter, were found to be commonly enriched in tomato root-associated bacterial communities. We constructed a pseudo-rhizosphere system using a mullite ceramic tube as an artificial root to investigate the influence of α-tomatine in modifying bacterial communities. The addition of α-tomatine from the artificial root resulted in the formation of a concentration gradient of α-tomatine that mimicked the tomato rhizosphere, and distinctive bacterial communities were observed in the soil close to the artificial root. Sphingobium was enriched according to the α-tomatine concentration gradient, whereas Bradyrhizobium, Cupriavidus, and Rhizobacter were not enriched in α-tomatine-treated soil. The tomato root-associated bacterial communities were similar to the soil bacterial communities in the vicinity of artificial root-secreting exudates; however, hierarchical cluster analysis revealed a distinction between root-associated and pseudo-rhizosphere bacterial communities. These results suggest that the pseudo-rhizosphere device at least partially creates a rhizosphere environment in which α-tomatine enhances the abundance of Sphingobium in the vicinity of the root. Enrichment of Sphingobium in the tomato rhizosphere was also apparent in publicly available microbiota data, further supporting the tight association between tomato roots and Sphingobium mediated by α-tomatine.