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The changed phenolic acids (PAs) allelochemicals exuded by the roots induced by interspecific interactions is related to intercropping alleviates soil-borne disease. However, the presence of PAs in roots and root exudations and their rhizodeposition under intercropping are still unclear. Hydroponic and soil experiments of wheat, faba bean, and wheat intercropped with faba bean were conducted, and the major compositions and contents of PAs in roots, root exudations, and rhizospheric soil were determined. The results showed that ρ-hydroxybenzoic, vanillic, and syringic acids were the major components of PAs in roots, root exudations, and rhizospheric soil in a wheat and faba bean intercropping system. The compositions and percentages of PAs in roots of faba bean were altered when faba bean intercropped with wheat. The total exudation rate of PAs in root exudations was decreased by 30%–60% under the wheat and faba bean intercropping (W//F) system as compared to mono-cropped faba bean (MF). ρ-hydroxybenzoic acid was identified in the root exudation of both MF and mono-cropped wheat (MW), but not detected in the intercropping on 60 days after transplanting. Vanillic acid was only detected in the root exudation of MF on 30 days after transplanting. The rhizodepostion of vanillic and cumaric acid were decreased at both branching and pod setting stages in W//F as compared to MF. In conclusion, interspecific interaction changed the compositions and contents of PAs in faba bean roots and root exudations. W//F constrained vanillic acid exuded by roots and decreased vanillic and coumaric acid rhizodeposition by faba bean, which provides insight into root-soil interactions in the intercropping systems.

Western Ghats are designated as world heritage sites and global biodiversity hotspots. Microbial diversity in this forest area has been largely neglected and is getting attention since the end of the last millennium. In this review, we have studied and organized various microorganisms from Western Ghats and their diversity, important characteristics and potential biotechnological applications. Microorganisms from Western Ghats have been explored individually for potential bioactive molecules. While most of the microorganisms were analyzed for antimicrobial activities, there have been studies on microbial promotion of plant growth. The microbes analyzed included from aquatics, soil, rhizosphere, phyllosphere and even as endophytes. There have been microorganisms which have shown antioxidant and anti-cancerous activities. There are microorganisms capable of degrading plant wastes and also xenobiotics. Microorganisms capable of producing industrially important enzymes have also been reported. The present review explores largely neglected microbial diversity with respect to their ability to produce potential bioactive biomolecules.

Host genetic variation can shape the diversity and composition of associated microbiomes, which may reciprocally influence host traits and performance. While the genetic basis of phenotypic diversity of plant populations in nature has been studied, comparatively little research has investigated the genetics of host effects on their associated microbiomes. Switchgrass (Panicum virgatum) is a highly outcrossing, perennial, grass species with substantial locally adaptive diversity across its native North American range. Here, we compared 383 switchgrass accessions in a common garden to determine the host genotypic influence on rhizosphere bacterial composition. We hypothesized that the composition and diversity of rhizosphere bacterial assemblages would differentiate due to genotypic differences between hosts (potentially due to root phenotypes and associated life history variation). We observed higher alpha diversity of bacteria associated with upland ecotypes and tetraploids, compared to lowland ecotypes and octoploids, respectively. Alpha diversity correlated negatively with flowering time and plant height, indicating that bacterial composition varies along switchgrass life history axes. Narrow-sense heritability (h2) of the relative abundance of twenty-one core bacterial families was observed. Overall compositional differences among tetraploids, due to genetic variation, supports wide-spread genotypic influence on the rhizosphere microbiome. Lastly, a genome-wide association study identified 1,861 single-nucleotide polymorphisms associated with 110 families and genes containing them related to potential regulatory functions. Our findings suggest that switchgrass genomic and life-history variation influences bacterial composition in the rhizosphere, potentially due to host adaptation to local environments.

Root associated bacteria were isolated from Suaeda nudiflora and two isolates were selected for this study: rhizospheric Bacillus megaterium and endophytic Pseudomonas aeruginosa. These isolates were inoculated into maize variety Narmada Moti during its germination. TTC (2, 3, 5-triphenyl tetrazolium chloride) staining was used to confirm the association of the isolates with the maize root. The effects of these root associated bacteria were tested alone and in combinations for cell wall reinforcement and the induction of defense enzymes such as phenylalanine ammonia lyase (PAL) and β-1,3-glucanase in the presence of fungal pathogen Aspergillus niger in maize. The results indicated that the rhizospheric bacteria had a greater fight response to fungal infection than the endophhytic bacteria due to cell wall lignification as well as the rapid induction of higher concentrations of defense related enzymes.

Root-knot nematodes (Meloidogyne spp.) are obligate plant parasites that cause severe economic losses to agricultural crops worldwide. Because of serious health and environmental concerns related to the use of chemical nematicides, the development of efficient alternatives is of great importance. Biological control through exploiting the potential of rhizosphere microorganisms is currently accepted as an important approach for pest management in sustainable agriculture. In our research, during screening of rhizosphere bacteria against the root-knot nematodes Meloidogyne incognita, Ochrobactrum pseudogrignonense strain NC1 from the rhizosphere of healthy tomatoes showed strong nematode inhibition. A volatile nematicidal assay showed that the cell-free fermentation filtrate in the first-row wells of 12-well tissue culture plates caused M. incognita juvenile mortality in the second-row wells. Gas chromatography-mass spectrometry analysis revealed that dimethyl disulfide (DMDS) and benzaldehyde were the main volatile compounds produced by strain NC1. The nematicidal activity of these compounds indicated that the lethal concentration 50 against the M. incognita juveniles in the second-row wells and the fourth-row wells were 23.4 μmol/ml and 30.7 μmol/ml for DMDS and 4.7 μmol/ml and 15.2 μmol/ml for benzaldehyde, respectively. A greenhouse trial using O. pseudogrignonense strain NC1 provided management efficiencies of root-knot nematodes of 88 to 100% compared with the untreated control. This study demonstrated that nematode-induced root-gall suppression mediated by the bacterial volatiles DMDS and benzaldehyde presents a new opportunity for root-knot nematode management.

L-ASPARAGINASE is an anti-neoplasm agent. This agent is classified as an enzyme compound. L-asparaginase is used in medicine as well as in the food industry. Microbial strains that are producing L-Asparaginase can be found in many habitats such as soil. The aim of this study was to find isolates producing L-asparaginase enzyme with high ability to inhibit cancer cells. Bacteria of the Actinobacter family were isolated from the soil samples around the roots of the plants in the actinomycet isolation medium. Then, the bacteria were isolated and extracted by screening in M9 medium. Isolates were identified using16S PCR sequencing method. Three isolates of ASP and B and C showed the highest enzyme production, which showed a molecular weight of 43 kDa and in terms of enzymatic activity112. 572 IU/ml, 99.706 IU/ml, 138.572 IU/ml respectively. These three isolates with sequence analysis was similar to Streptomyces flavoviridis and Streptomyces griseus and Streptomyces hypolyticus respectively. Isolate C showed good effects in inhibiting cell MCF-7, HepG-2. There are various isolates enzyme production power in nature and Actinobacter family has shown more ability to produce various enzymes and metabolites and the isolates isolated in this study are used for industrial enzyme production.

Phyllosphere is an important reservoir of antibiotic resistance genes (ARGs), but the transfer mechanism of ARGs from soil and air to phyllosphere remains unclear. This study demonstrated that soil-air-phyllosphere was the dominant ARG transfer pathway, and blocking it by film mulching can reduce typical phyllosphere ARGs in lettuce by 80.7% - 98.7% (89.5% on average). To further eliminate phyllosphere ARGs in lettuce grown with film mulching, the internal soil-endosphere-phyllosphere transfer pathway deserves more attention. We analyzed the ARG hosts and the resistome in lettuce rhizosphere and phyllosphere with film mulching via hybrid Illumina-Nanopore sequencing. Pseudomonas sp. 7SR1 was more abundant than other ARG hosts, accounting for 1.0% and 47.1% of the total bacteria in rhizosphere and phyllosphere, respectively. The species has flagella that can promote mobility and can excrete extracellular polymeric substances and/or surfactant-like microbial products, which benefits its colonization in the phyllosphere. Impeding the migration of Pseudomonas sp. 7SR1 via the soil-endosphere-phyllosphere pathway would be effective to further reduce ARGs in phyllosphere. Multidrug resistant genes were predominant in phyllosphere (40.3% of the total), and 87.6% of the phyllosphere ARGs were located on chromosomes, indicating relatively low horizontal gene transfer (HGT) potentials. This study provides insights into the transfer mechanism, hosts, and control strategies of phyllosphere ARGs in typical plants.

The plant faces different pedological and climatic challenges that influence its growth and enhancement. While, plant-microbes interactions throught the rhizosphere offer several privileges to this hotspot in the service of plant, by attracting multi-beneficial mutualistic and symbiotic microorganisms as plant growth-promoting bacteria (PGPB), archaea, mycorrhizal fungi, endophytic fungi, and others…). Currently, numerous investigations showed the beneficial effects of these microbes on growth and plant health. Indeed, rhizospheric microorganisms offer to host plants the essential assimilable nutrients, stimulate the growth and development of host plants, and induce antibiotics production. They also attributed to host plants numerous phenotypes involved in the increase the resistance to abiotic and biotic stresses. The investigations and the studies on the rhizosphere can offer a way to find a biological and sustainable solution to confront these environmental problems. Therefore, the interactions between microbes and plants may lead to interesting biotechnological applications on plant improvement and the adaptation in different climates to obtain a biological sustainable agricultures without the use of chemical fertilizers.

Basal stem rot (BSR) is the most common disease of oil palm (Elaeis guineensis Jacq.) in Southeast Asia. BSR is caused by a white-rot fungus Ganoderma boninense. The disease is difficult to manage. Therefore, development of novel and environmentally safe approaches to control the disease is important. Species of Burkholderia are known to have diverse lifestyles, some of which can be beneficial to plants either by suppressing diseases or enhancing plant growth. In the present study, antifungal peptides (AFPs) produced by a bacterial strain isolated from the rhizosphere of an oil palm tree, namely Burkholderia sp. strain CP01, exhibited strong growth inhibition on G. boninense. A loss-of-function mutant of CP01 was generated, and it has enabled the identification of a 1.2 kDa peptide and its variants as the active antifungal compounds. High-resolution mass spectrometry revealed six analogous compounds with monoisotopic masses similar to the previously reported cyclic lipopeptides occidiofungin and burkholdine. The antifungal compounds of CP01 were secreted into media and we sought to use CP01 culture extract without living cells to control BSR disease. Glasshouse experiments showed that CP01 culture extract suppressed BSR disease in oil palm seedlings. The ability of CP01 to produce an antifungal substance and suppress plant disease suggests its potential application as a biofungicide in agriculture.

Pythium root rot (PRR) is a disease that can rapidly devastate large swaths of golf course putting greens, with little recourse once symptoms appear. Golf courses routinely apply preventive fungicides for root diseases, which may alter the rhizosphere microbiome, leading to unintended effects on plant health. A multiyear field trial was initiated on a ‘T-1’ creeping bentgrass (Agrostis stolonifera L. cultivar T-1) putting green in College Park, Maryland to evaluate preventive PRR management for disease suppression and effects on rhizosphere bacterial communities. Fungicides commonly used to prevent PRR and a biological fungicide were repeatedly applied to experimental plots throughout the growing season. Rhizosphere samples were collected twice annually from each plot for evaluation of rhizosphere bacterial communities through amplicon sequencing and monitoring of biological control organism populations via quantitative PCR. Cyazofamid was the only treatment to suppress PRR in both years compared with the control. Fosetyl-Al on a 14-day interval and Bacillus subtilis QST713 also reduced PRR severity in 2019 compared with the nontreated control. Treatments did not significantly affect bacterial diversity or relative abundances of bacterial classes; however, seasonal environmental changes did. Repeated rhizosphere-targeted applications of B. subtilis QST713 appear to have established the bacterium into the rhizosphere, as populations increased between samples, even after applications stopped. These findings suggest that QST713 may reduce pathogen pressure when repeatedly applied and can reduce fungicide usage during periods of low PRR pressure.

Maintaining a proper content of selenium (Se) in food is particularly important for human health. However, the mechanisms of uptake and enrichment of Se ENMs in crops are still unclear. Herein, Se engineered nanomaterials (Se ENMs) (size 62.3 ± 14.6 nm and surface charge −34.4 ± 1.4 mV) were synthesized and used as nanofertilizers for Se-fortified vegetables. The results demonstrated the Se content and yield were increased by 338.0% and 19.8% respectively in Brassica chinensis L. through soil application of Se ENMs (0.5 mg‧kg–1). The content of Se in vegetables increased up to 32.8 μg/100 g (7.5 μg/100 g for the control), which could provide the daily recommended Se intake (55–400 μg/day) for human. Amendments of the slightly alkaline soil with the Se ENMs improved beneficial rhizosphere microbiomes (Pseudomonas and Bacillus), and resulted in the plants accumulating more low molecular weight compounds (betaine, proline, glycine, norleucine, urocanic acid and indole-3-acrylic acid) with increases in the Se content of the plant by 264.9%. Moreover, the nutrient accumulation in leaves promoted the photosynthesis (16.7%) and increased carbohydrate content (6.5%). Also, the expression of carbohydrate transport-related genes (BnSUC1,1, BnSUC1,4, and BnSWEET10,2) were up-regulated by 52.2, 53.2 and 76.3-fold, respectively, promoting root growth, improving rhizosphere microbiome and nutrient availability. Therefore, such mutual benefits between leaves and roots using ENMs could provide an alternative model for cultivating Se-enriched crops.

Plant root exudates serve pivotal roles in supporting plant development and interactions with the physicochemical and biological factors in the rhizosphere. Under stress conditions, root exudation is involved in enhancing plant resource-use efficiency and facilitating the crosstalk between plant and soil microbes to ameliorate stress. Although there are a large number of root exudates that remain to be characterized, recent technological advancements have allowed for the function of many exudate compounds to be elucidated. In this review, we discuss current knowledge about the key root exudates that modulate plant resource-use efficiency under various abiotic stresses including drought, aluminum toxicity, phosphorus, nitrogen, and iron deficiency. The role that key root exudates play in shaping microbial communities in the rhizosphere under stress conditions is also an important consideration addressed in this review.

Agrobacterium tumefaciens is a bacterial pathogen that causes crown gall disease on a wide range of eudicot plants by genetic transformation. Besides T-DNA integrated by natural transformation of plant vegetative tissues by pathogenic Agrobacterium spp., previous reports have indicated that T-DNA sequences originating from an ancestral Agrobacterium sp. are present in the genomes of all cultivated sweet potato (Ipomoea batatas) varieties analyzed. Expression of an Agrobacterium-derived agrocinopine synthase (ACS) gene was detected in leaf and root tissues of sweet potato, suggesting that the plant can produce agrocinopine, a sugar-phosphodiester opine considered to be utilized by some strains of Agrobacterium spp. in crown gall. To validate the product synthesized by Ipomoea batatas ACS (IbACS), we introduced IbACS into tobacco under a constitutive promoter. High-voltage paper electrophoresis followed by alkaline silver nitrate staining detected the production of an agrocinopine-like substance in IbACS1-expressing tobacco, and further mass spectrometry and nuclear magnetic resonance analyses of the product confirmed that IbACS can produce agrocinopine A from natural plant substrates. The partially purified compound was biologically active in an agrocinopine A bioassay. A 16S ribosomal RNA amplicon sequencing and meta-transcriptome analysis revealed that the rhizosphere microbial community of tobacco was affected by the expression of IbACS. A new species of Leifsonia (actinobacteria) was isolated as an enriched bacterium in the rhizosphere of IbACS1-expressing tobacco. This Leifsonia sp. can catabolize agrocinopine A produced in tobacco, indicating that the production of agrocinopine A attracts rhizosphere bacteria that can utilize this sugar-phosphodiester. These results suggest a potential role of IbACS conserved among sweet potato cultivars in manipulating their microbial community. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Objective To find a suitable ecological cultivation measure to solve the problem of root-knot nematode disease of Panax quinquefolium (Panacis Quinquefolii Radix) and the heavy metals accumulating in its roots. Methods Three-year-old P. quinquefolium was treated with four different combinations of microbial inoculant (MI) and garbage fermentation liquid (GFL) [the joint application of ‘TuXiu’ MI and Fifty potassium MI (TF), the combination use of ‘No. 1’ MI and Fifty potassium MI (NF), ‘Gulefeng’ poly-γ-glutamic acid MI (PGA), GFL], and the untreated control (CK). Here, high-throughput sequencing, ICP-MS and UPLC were employed to systematically characterize changes of microbial diversity and structure composition, heavy metals (As, Cd and Pb) content and ginsenoside content among different treatments. Results The results revealed that different MIs and GFL could increase the root dry weight of P. quinquefolium, PGA enhanced it by 83.24%, followed by GFL (49.93%), meanwhile, PGA and GFL were able to lessen root-knot nematode disease incidence by 57.25% and 64.35%. The treatment of PGA and GFL can also effectively reduce heavy metals in roots. The As content in GFL and PGA was decreased by 52.17% and 43.48% respectively, while the Cd and Pb contents of GFL and PGA was decreased somewhat. Additionally, the content of total ginsenosides was increased by 42.14% and 42.07%, in response to TF and NF, respectively. Our metagenomic analysis showed that the relative abundance of particular soil microbial community members related to the biocontrol of root-knot nematode disease and plant pathogen (i.e., Chaetomium in NF, Xylari in GFL, and Microascus in PGA), heavy metal bioremediation (Hyphomacrobium in PGA and Xylaria in GFL), and nitrogen fixation (Nordella and Nitrospira in TF) was significantly increased; notably, potential harmful microflora, such as Plectosaphaerella and Rhizobacter, were more abundant in the control group. Conclusion MI and GFL could improve the quality of P. quinquefolium by modifying its rhizosphere microbial community structure and composition, both of them are beneficial to the development of ecological cultivation of P. quinquefolium.

Domestication and breeding have affected interactions between plants and their microbiomes in ways that are only beginning to be understood but may have important implications for recruitment of rhizosphere microorganisms, particularly under stress conditions. We investigated the responses of a modern maize (Zea mays subsp. mays) cultivar and its wild relative, teosinte (Z. mays subsp. parviglumis), to different phosphate availabilities. We appraised responses of the plant-microbial holobiont to phosphate stresses by profiling root exudate metabolomes, and microbial communities in the root endosphere and rhizosphere. We also performed plate assays to quantify phosphate-solubilizing microorganisms from the rhizosphere. Although root exudate metabolite profiles were distinct between the teosinte and modern maize under high phosphate, both plants shifted exudate compositions in response to phosphate stress toward a common metabolite profile. Root and rhizosphere microbial communities also responded significantly to both plant type and the phosphate availability. A subset of bacterial and fungal taxa were differentially abundant under the different phosphate conditions, with each of the three conditions favoring different taxa. Both teosinte and maize rhizospheres harbored phosphate-solubilizing microorganisms under all growth conditions. These results suggest that the root exudation response to phosphate stress was conserved through the domestication of maize from teosinte, shifting exudation levels of specific metabolites. Although microbial communities also shifted, plate-based assays did not detect selective recruitment of phosphate solubilizers in response to phosphate availability.

Thousand cankers disease (TCD) is hypothesized to have a greater impact on eastern black walnut (Juglans nigra) in urban forests and plantations compared with natural forest stands. Along with other factors such as resource availability, the phytobiome could partly account for observed differences in disease severity across management regimes. We investigated the extent to which J. nigra-associated soil microbiomes from plantations and natural forests modulate (i) the amount of necrosis caused by Geosmithia morbida in 1-year-old seedlings, and (ii) relative abundance of rhizosphere endophytes and opportunistic pathogens Fusarium and Rhizoctonia in response to aboveground inoculation with G. morbida. Our results suggest that the microbiome from natural forest soil in central Indiana suppresses Fusarium spp. and is indirectly suppressive of G. morbida. Natural forest soil had a greater ability to reduce the size of necrotic area caused by G. morbida compared with steam-treated soil. Inoculating stems of seedlings with G. morbida induced a shift in fungal community composition in the rhizosphere, including Fusarium and Rhizoctonia spp.; however, the direction and magnitude of the shift depended on whether seedlings were amended with forest, plantation, or steam-treated soil. In a companion experiment, necrotic area in G. morbida-inoculated seedlings was twice as high in seedlings grown from seeds that were treated with Fusarium solani relative to those grown from seed treated with water. Our findings support the hypothesis that TCD severity can be modulated by host-mediated feedback between above- and belowground pathogens, as well as by microbial interactions in the rhizosphere.

s Plant-parasitic nematodes infect the roots of crops which bring rigorous economic loss to food industry across the globe. Several plant protection agents are being used but they cause severe negative environmental and health impacts. Recently, organic matter has become an important green alternative for several pesticides including nematicides. In the present study, identification and management of stylet bearing nematodes associated with Malus pumila from different locations of Khanpur, Pakistan, have been presented. Soil samples were collected from the rhizosphere of infected M. pumila and isolated using Baermann funnel extraction technique. Collected specimens were killed, fixed and mounted. After identification, cow dung (organic) and carbofuran (inorganic) were applied after taking the first soil samples and soil samples were recollected and analyzed after 3 months of applications. Ten species of nematodes; Helicotylenchus pseudorobustus, Helicotylenchus dihystera, Helicotylenchus vulgaris, Meloidogyne javanica, Meloidogyne incognita, Aphelenchus avenae, Pratylenchus penetrans, Filenchus sheri, Psilenchus hilarulus and Tylenchus semipenetrans were identified from different locations. Results of amendments revealed that carbofuran was found more effective because of its intense toxic properties, whereas nematode decline rate was slow in case of organic amendments. Being an insecticide, carbofuran killed maximum nematodes but it is highly toxic. If the time period is increased, comparable results can be achieved by applying cow dung, which makes it an environmentally friendly option for the protection of plants against nematodes.

An important number of Micromonospora strains have been reported from nitrogen-fixing root nodules of legume and actinorhizal plants. However, the question of whether this bacterium can also be found in other parts of these plants remains unanswered. More than 150 strains were recovered from different Lupinus angustifolius and Pisum sativum tissues, including leaves, stems, roots, and nodules. In all, 97% of the isolates were identified by 16S ribosomal RNA gene sequence in the target genus and were associated with 27 different Micromonospora spp. Plant-polymer-degrading enzymes are suspected to play a role in the colonization of plants. To this end, bacterial enzymatic activity assays for amylases, cellulases, chitinases, pectinases, and xylanases were determined. All strains produced xylanases and pectinases, while 98.6, 98, and 94.6% of them produced amylases, cellulases, and chitinases, respectively. The most productive strains included seven isolates from P. sativum and one from L. angustifolius. Strain Micromonospora lupini ML01-gfp was used to determine its capacity to reach and colonize different plant organs using P. sativum as the plant model. Stem and leaf samples were monitored by optical and fluorescence microscopy to locate the tagged strain. These results strongly suggest that Micromonospora is able not only to infect nitrogen-fixing nodules but also to reach other parts of the host plant, especially the leaves.

Interactions between plants and microbiomes play a key role in ecosystem functioning and are of broad interest due to their influence on nutrient cycling and plant protection. However, we do not yet have a complete understanding of how plant microbiomes are assembled. Here, we tested and quantified the effect of different factors driving the diversity and composition of plant-associated microbial communities. We manipulated soil microbial diversity (high or low diversity), plant species ('Solanum tuberosum' or 'S. vernei'), and herbivory (presence or absence of a phloem-feeding insect, 'Macrosiphum euphorbiae') and found that soil microbial diversity influenced the herbivore-associated microbiome composition but also plant species and herbivory influenced the soil microbiome composition. We quantified the relative strength of these effects and demonstrated that the initial soil microbiome diversity explained the most variation in plant- and herbivore-associated microbial communities. Our findings strongly suggest that soil microbial community diversity is a driver of the composition of multiple associated microbiomes (plant and insect), and this has implications for the importance of management of soil microbiomes in multiple systems., Finanziert durch den Open-Access-Publikationsfonds der Westfälischen Wilhelms-Universität Münster (WWU Münster).

La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research CentreMDFRC item.Rate studies of orthophosphate removal from wastewater in Schoenoplectus validus Vahl. (A Love and D Love) planted bucket-sized vertical upflow wetlands occurs simultaneously through three removal processes. In order of decreasing rate, these are reversible sorption to the gravel substratum, reversible conversion to complex phosphorus compounds, and irreversible uptake by plant roots. Mixing the rhizosphere liquid, using forced convection, accelerated orthophosphate removal; concentrations falling from ≈10 mg litre−1 to < 0.2 mg litre−1 in < 48 h. The rate determining step in systems without rhizosphere liquid mixing appears to be diffusive transport of phosphate. Over two years, initial removal rates, and minimum reactive phosphorus concentrations changed little, but aged or high BOD systems sometimes released reactive phosphorus or tannins holding large amounts of phosphorus. The relevance of these mechanisms to total wetland assimilative capacity, and effluent quality, are evaluated.

Publisher Summary The release of easily decomposable root exudates leads to higher microbial density and activity in the rhizosphere compared to bulk soil, and this high density of microorganisms, in turn, attracts predators such as nematodes and protozoa. This chapter focuses on the colonization of the roots by microorganisms and discusses how these microorganisms can both enhance and reduce nutrient availability to plants. As the root grows through the soil, the new root surface just behind the meristematic tissue is colonized by microorganisms that are attracted to the root surface. Root exudates released in the zone immediately behind the root tip and in the distal elongation zone stimulate microbial growth and attract more soil microorganisms to the root surface. Mycorrhiza is the most widespread association between microorganisms and higher plants, and for plants, mycorrhizal associations are either mutualistic, neutral or parasitic. The two major mycorrhizal groups based on differential morphology and physiology are endomycorrhiza and ectomycorrhiza. There are several types of endomycorrhiza, the best known being arbuscular mycorrhiza (AM), ericoid and orchid mycorrhiza. Root colonization by mycorrhizal fungi is initiated either from soil-borne propagules (spores, colonized root residues) or from neighboring roots of the same or different plants and plant species. The most distinct effect of AM on plant growth is the improved supply of nutrients of low mobility in the soil solution, particularly P. Some ericoid and ECM fungi release proteinases and thereby provide the host plant with an access to complex organic sources of N such as proteins. Mycorrhizal colonization can also induce systemic resistance, that is, even roots not colonized by the fungus become resistant to pathogen attack.

Accurate predictions of plant responses to elevated CO2 (eCO2) levels require a better understanding of uptake and allocation of resources that affect growth. While it is well-established that plants can increase C transfer belowground to increase access to nutrients in N-limited environments, there is less studies investigating the role of these adaptations in P-limited systems. In this study, we aimed to characterise plant nutrient use and acquisition strategies under future atmospheric [CO2] scenarios, under P-limited conditions and determine how different levels of water availability regulate these strategies. We exposed four grass species commonly found in the understory of P-limited Australian Eucalyptus woodlands to eCO2 over a period of 14 weeks, under two contrasting water levels. We assessed a suite of root morphological and chemical traits and the rhizosphere activity of extracellular enzymes related to C, N and P cycles, along with changes in plant allocation patterns and use efficiency of these nutrients. Elevated CO2 effects on root functional attributes were species-specific, but clear trends towards increased phosphatase activity were observed across species, leading to a lower C:P ratio. In contrast, water supply affected root morphological attributes, but interactions between CO2 and water levels on functional traits were minor. Greater water availability also stimulated microbial activity in the rhizosphere, but without observable changes in the relative demand for N and P relative to C. Despite changes in rhizosphere processes, eCO2 did not lead to increased plant biomass regardless of water supply, suggesting primary nutrient limitation and a lack of positive rhizosphere feedbacks to plant growth.

Microbial activity in the soil of wetlands is responsible for the emission of more methane to the atmosphere than all other natural sources combined. This microbial activity is heavily impacted by plant roots, which influence the microbial community by exuding organic compounds and by leaking oxygen into an otherwise anoxic environment. This study compared the microbial communities of planted and unplanted wetland soil from an Alaskan bog to elucidate how plant growth influences populations and metabolisms of methanogens and methanotrophs. A common boreal wetland sedge, Carex aquatilis, was grown in the laboratory and DNA samples were sequenced from the rhizosphere, unplanted bulk soil, and a simulated rhizosphere with oxygen input but no organic carbon. The abundance of both methanogens and methanotrophs were positively correlated with methane emissions. Among the methanotrophs, both aerobic and anaerobic methane oxidizing microbes were more common in the rhizosphere of mature plants than in unplanted soil, while facultative methanotrophs capable of utilizing either methane or other molecules became relatively less common. These trends indicate that the roots in this experiment created an environment which favored highly specialized microbial metabolisms over generalist approaches. One aspect of this specialized microbiome is the presence of both aerobic and anaerobic metabolisms, which indicates that oxygen is present but is a limiting resource controlling competition.

Rhizosphere bacterial communities (‘rhizobacteria’) can mediate plant-soil feedbacks that enhance plant drought tolerance, but the composition and ecological characteristics of these populations are poorly understood. We investigated the impact of drought on rhizobacteria communities and the effect of propagating drought-impacted communities on the drought tolerance of naive plants in a two-phase experiment. We tested whether propagating rhizosphere soils from drought-stressed shrub willow (Salix purpurea), or continuously watered controls, affected the performance of a subsequent generation of droughted plants. The impacts of drought on rhizobacteria and plant fitness were evaluated using 16S rRNA gene sequencing and measures of plant growth (root mass and stem length etc.) and stress (abscisic acid, osmolality). Uninoculated reference plants were used to isolate the effects of inoculation. Drought had a significant and lasting impact on the structure of rhizobacterial communities, characterized by increased populations of Actinobacteria (Acidimicrobiia, Thermoleophilia and Micrococcaceae). Foliar osmolality was significantly higher in plants receiving drought-selected communities relative to uninoculated controls, but no significant differences in plant growth were observed. Inoculation with rhizosphere soil from watered controls significantly reduced plant growth. The rhizosphere of watered control plants was dominated by Proteobacteria and Bacteroidetes. Our findings demonstrate that plants are affected by the legacy effects of drought on the rhizosphere microbiome. This drought legacy was propagated and persisted throughout nine weeks of plant growth, independent of prevailing water stress. Drought-impacted rhizospheres had larger populations of desiccation-tolerant (ex. Arthrobacter) and putatively endophytic taxa (ex. Rhizobium) with established plant growth promoting capabilities.

Nitrogen (N) deep placement has been found to reduce N leaching and increase N use efficiency in paddy fields. However, relatively little is known how bacterial consortia, especially abundant and rare taxa, respond to N deep placement, which is critical for understanding the biodiversity and function of agricultural ecosystem. In this study, Illumina sequencing and ecological models were conducted to examine the diversity patterns and underlying assembly mechanisms of abundant and rare taxa in rice rhizosphere soil under different N fertilization regimes at four rice growth stages in paddy fields. The results showed that abundant and rare bacteria had distinct distribution patterns in rhizosphere samples. Abundant bacteria showed ubiquitous distribution; while rare taxa exhibited uneven distribution across all samples. Stochastic processes dominated community assembly of both abundant and rare bacteria, with dispersal limitation playing a more vital role in abundant bacteria, and undominated processes playing a more important role in rare bacteria. The N deep placement was associated with a greater influence of dispersal limitation than the broadcast N fertilizer (BN) and no N fertilizer (NN) treatments in abundant and rare taxa of rhizosphere soil; while greater contributions from homogenizing dispersal were observed for BN and NN in rare taxa. Network analysis indicated that abundant taxa with closer relationships were usually more likely to occupy the central position of the network than rare taxa. Nevertheless, most of the keystone species were rare taxa and might have played essential roles in maintaining the network stability. Overall, these findings highlighted that the ecological mechanisms and co-occurrence patterns of abundant and rare bacteria in rhizosphere soil under N deep placement.

Tomato vine decline (TVD) disease complex results in fruit yield loss, but what soil management strategies might mitigate it? In commercial fields with a history of TVD, five approaches (soil organic amendments and transplant treatments) were evaluated for their impact on fruit yield, fruit quality, and microbial abundance or diversity at four site-years. One site-year had very high TVD pressure and high variability with no yield differences, thus efforts focused on the remaining site-years. Marketable yield was not different among treatments but numerically followed a trend similar to total yield. Amending soil with poultry manure delayed maturity (i.e., increased proportion of green fruit) and had the greatest total yield increases of 17.2%, congruent with decreased abundance of root pathogens (Verticillium dahliae, Rhizopicnis vagum). Microbial DNA fingerprinting data of rhizospheres, roots and (or) stems suggested treatments did not significantly shift the total diversity fungal nor bacterial populations, but the aforementioned pathogen loads were reduced with the application of organic amendments relative to the untreated control. While drenching tomato transplants with pseudomonad culture increased their presence in roots, pathogen load was not reduced relative to the untreated control. Overall, these results show that soil organic amendments were able to improve tomato total yield in two of four site-years without reducing fruit quality (i.e., soluble solids, pH, colour), perhaps, in part, due to their ability to suppress specific root pathogens in commercial fields.

Nematode damage to coffee poses a serious threat to coffee production all over the world, including Vietnam. Accordingly, the nematode community composition could be a reliable indicator of ecological shifts that affect coffee plants' health. Here, we analysed the nematode communities in the rhizosphere of a monoculture Robusta coffee plantation in Dak Lak of the Central Highlands, Vietnam. We found changes in the community composition of nematodes in an age gradient of replanting coffee plants and revealed distinct patterns of nematode distribution in the soils of healthy and diseased plant groups. Further analyses indicate the impact of intensive farming and inefficient nematode controls, which caused disturbances and a gradual decrease of the nematode fauna diversity in the plantation soil. These results can add to a complete prediction model for plant fitness using nematode community composition.

Pseudomonas spp., a ubiquitous biocontrol agent, protects the plants from phytopathogens by suppressing them directly by reinforcing the plant’s intrinsic defense mechanism. Root exudated phenolics play an important role in establishing the rhizobacteria population and cross the host boundaries in beneficial plant–microbe interaction. In this study, Pseudomonas spp. HU-8 & HU-9 antagonized the sugarcane red rot pathogen (C. falcatum) and showed a positive chemotactic response against different concentrations (10–30 µM) of synthetic phenolic acids like p-coumaric, vanillic, and 3,4 di-hydroxybenzoic acid. In a pot experiment, they effectively colonized the sugarcane rhizosphere and mediated defense response in sugarcane plants challenged with red rot pathogen C. falcatum by regulating the exudation of root phenolics under hydroponic conditions. They significantly induced the activity of the antioxidant enzymes CAT (1.24–1.64 fold), PO (0.78–1.61 fold), PAL (0.77–0.97 fold), and PPO (3.67–3.73 fold) over untreated plants in sugarcane. They also induced the total phenolic contents (TPC) in sugarcane in the presence (6.56–10.29 mg/g GAE) and absence (2.89–4.16 mg/g GAE) of the pathogen quantified through the Folin-Ciocalteu (FC) method. However, their effect was lower than that of the pathogen (4.34–8 mg/g GAE). The Pseudomonas spp. significantly colonized the sugarcane rhizosphere by maintaining a cell population of (1.0E + 07–1.3E + 08 CFU/mL). A significant positive Pearson’s correlation was observed between the root exudated total phenolic contents, antioxidant enzymatic activities, and rhizospheric population of inoculated bacteria. The 16S rRNA and rpoD gene analysis showed sequence conservation (C: 0.707), average number of nucleotide differences (k: 199.816), nucleotide diversity, (Pi): 0.09819), average number of informative nucleotide sites per site (Psi: 0.01275), GC content (0.57), and polymorphic sites (n = 656). These diverse Pseudomonas spp. could be an ideal bio-inoculants for a broad range of hosts especially graminaceous crops.

Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is one of the most important pests causing considerable damage to soybean (Glycine max (L.) Merr.) around the world. Biocontrol provides a strategy for sustainable nematode control. Previously, Aspergillus niger NBC001 was isolated from the cysts of Heterodera spp. and able to control H. glycines and promote the growth of soybean in a pot experiment. In this study, the effects of NBC001 on H. glycines density and on the soybean rhizosphere microbial community in a soybean cyst nematode-infested field were studied. The results showed that NBC001 could suppress H. glycines by 31.7% in the field. High-throughput sequencing analysis showed that NBC001 had no significant influence on soybean rhizosphere microbial community structure, indicating that seed coat-dressing with the concentrated culture filtrate of NBC001 was safe for the soil ecological environment. In addition, high-throughput sequencing results demonstrated that at 10 days post transplantation, NBC001 increased the abundances of Actinobacteria and Acidobacteria, but decreased the abundances of Bacteroidetes and Gemmatimonadetes at the phylum level. Meanwhile, the abundances of Phyllobacterium, Ralstonia and H16 were increased, while the abundances of Adhaeribacter, Gemmatimonas, Sphingomonas, Flavisolibacter were suppressed by application of NBC001. However, at 90 days post transplantation, NBC001 only increased the abundances of Aeromicrobium and RB41 whereas it decreased the abundance of H16. The results indicated that application of NBC001 increased the relative abundances of the beneficial microorganisms such as Actinobacteria, Acidobacteria, Aeromicrobium and Phyllobacterium in the soil. In summary, NBC001 is an eco-friendly biocontrol agent for H. glycines control.

The biostimulant BC204 is a commercially available biostimulant based on an extract from Citrus aurantium, comprising a mixture of bioflavonoids, other plant extracts and organic acids. In this study, the potential of BC204 to cause positive effects on plant growth and overall plant health by altering the rhizosphere microbial community of Solanum lycopersicum L. was investigated. Mycorrhizal colonization of plant roots was analysed by trypan blue-staining and light microscopy, followed by polymerase chain reaction (PCR) amplification of a region of the 18S rRNA gene conserved among arbuscular mycorrhizal fungi. No difference in mycorrhizal colonization of roots was observed between control and treated plants. The structural and functional diversity of rhizosphere bacteria between different treatment groups was assessed using 16S rRNA gene restriction fragment length polymorphism (RFLP) analysis and community-level physiological profiling (CLPP), respectively. Nearest sequence matches for three isolates from the rhizosphere of plants treated with BC204 as a soil drench in soil supplemented with Mycoroot™ revealed bacterial genera which play a role in promoting plant growth. Furthermore, the microbial community from this treatment group showed increased richness of substrate utilization on Biolog EcoPlates™. These results indicate some form of interaction between BC204 and Mycoroot™ which causes a shift in the structural and functional diversity of the rhizosphere bacterial community.

The cape gooseberry (Physalis peruviana) is a Solanaceae species with enormous economic importance in Colombia; it is the second most exported fruit, after bananas. Vascular wilt caused by Fusarium oxysporum f. sp. physali (Fox) is the most limiting factor of this crop, with losses of up to 80% of production. Biological control is a promising alternative for controlling this pathogen. Bacteria and fungi, originally isolated from potentially suppressive soils of cape gooseberry crops in Nariño, Colombia with different management (organic and conventional), were evaluated as biocontrol agents of Fox using a gnotobiotic model (seedlings cultured under axenic conditions with defined microbial strains). Of the 64 isolated microorganisms, 37.5% (15 bacteria and 9 fungi) were discarded because of toxicological risks and an unknow potential biological control. The remaining 62.5% of the microorganisms, 14 bacteria and 26 fungi, were evaluated to assess their potential as biological control agents against Fox. The gnotobiotic model system evaluated the protection and plant growth promotion characteristics. Response variables were used to group the microorganism using a principal component analysis (PCA), and five clusters were obtained. Cluster number four concentrated the 10 microorganisms (three bacteria and seven fungi) with the highest protection values against Fox, with a positive effect on growth. The isolates were identified as two Bacillus subtilis strains, Rhodococcus sp., Podospora setosa, Debaryomyces vindobonensis, Plectosphaerella plurivora, Acinetobacter rhizosphaerae, Umbelopsis sp. and two strains of Trichoderma koningiopsis. The gnobiotic system offered clear advantages for evaluating and selecting microorganisms with a biological control potential against Fusarium oxysporum f. sp. physalis. RESUMEN La uchuva (Physalis peruviana) es Solanaceae de enorme importancia económica en Colombia ya que es la segunda fruta más exportada después del banano. La marchitez vascular causada por Fusarium oxysporum f. sp. physali (Fox) es el factor más limitante de este cultivo, que ocasiona pérdidas de hasta el 80% de su producción. El control biológico se ha convertido en una alternativa prometedora para controlar este patógeno. Bacterias y hongos, originalmente aislados de suelos potencialmente supresores de cultivos de uchuva de Nariño, Colombia con diferente manejo (orgánico y convencional) fueron evaluados como agentes de control de Fox utilizando un modelo gnotobiótico (plántulas cultivadas en condiciones axiológicas con cepas microbianas definidas). A partir de los 64 microorganismos aislados, 37.5% (15 bacterias y nueve hongos) fueron descartados debido a su riesgo toxicológico y a un control biológico potencial desconocido, el 62.5% restante de microorganismos, 14 bacterias y 26 hongos, se evaluaron para evaluar su potencial como agentes de control biológico contra Fox. El sistema de modelos gnotobióticos nos permitió evaluar las características de protección y promoción del crecimiento vegetal, estas variables de respuesta se utilizaron para agrupar el microorganismo utilizando un análisis de componentes principales (PCA) y se obtuvieron cinco clústeres. El clúster número cuatro concentró 10 microorganismos (tres bacterias y siete hongos) con los valores de protección más altos contra Fox y con un efecto positivo en la promoción del crecimiento. Los aislados fueron identificados como dos cepas de Bacillus subtilis, Rhodococcus sp., Podospora setosa, Debaryomyces vindobonensis, Plectosphaerella plurivora, Acinetobacter rhizosphaerae, Umbelopsis sp. y dos cepas de Trichoderma koningiopsis. El sistema gnobiótico presentado ofrece claras ventajas para evaluar y seleccionar microorganismos con un potencial de control biológico contra Fusarium oxysporum f. sp. fisalis.

Less attention has been given to soil enzymes that contribute to beneficial rhizosphere interactions in intercropping systems. Therefore, we performed a field experiment by growing faba bean, lupine, and maize in mono and mixed cultures in a moderately fertile soil. We measured shoot biomass and the kinetic parameters (maximal velocity (Vmax) and Michaelis-constant (Km)) of three key enzymes in the rhizosphere: Leucine-aminopeptidase (LAP), β-1,4-N-acetylglucosaminidase (NAG), and phosphomonoesterase (PHO). Faba bean benefitted in mixed cultures by greater shoot biomass production with both maize and lupine compared to its expected biomass in monoculture. Next, LAP and NAG kinetic parameters were less responsive to mono and mixed cultures across the crop species. In contrast, both the Vmax and Km values of PHO increased in the faba bean rhizosphere when grown in mixed cultures with maize and lupine. A positive relative interaction index for shoot P and N uptake for faba bean showed its net facilitative interactions in the mixed cultures. Overall, these results suggest that over-productivity in intercropping is crop-specific and the positive intercropping effects could be modulated by P availability. We argue that the enzyme activities involved in nutrient cycling should be incorporated in further research.

The role of multi-heavy metal tolerant bacteria isolated from the rhizosphere of Eichhornia crassipes in the phytoremediation of Cu and Pb under laboratory conditions was investigated. The heavy metal tolerant rhizosphere bacteria were identified as Bacillus cereus, Paenibacillus alvei, Aeromonas caviae, Paenibacillus taiwanensis, and Achromobacter spanius. Results showed a significant variation in wet weight, Heterotrophic Plate Count (HPC) of the rhizosphere, HPC of water, removal and uptake of Cu and Pb by E. crassipes, either alone or in association with the rhizosphere bacteria. The removal of Cu by E. crassipes in different experimental conditions showed that OTC (Oxytetracycline) untreated E. crassipes with rhizosphere bacteria has maximum removal with 95%, followed by E. crassipes alone with 84%. The OTC treated E. crassipes with rhizosphere bacteria could remove 81% of Cu. The maximum Pb removal efficiency of 93.4% was shown by OTC untreated E. crassipes with rhizosphere bacteria, followed by E. crassipes alone with 86.8%. The OTC treated E. crassipes with rhizosphere bacteria showed the least removal efficiency with 82.32%. The translocation factor (TF) values for Cu and Pb were lower than 1 indicated that the absorption was mainly accomplished in the roots of E. crassipes. The order of accumulation of Cu and Pb in E. crassipes was noted as root > leaf > petiole.

BACKGROUND Excessive nitrogen (N) fertilization in glasshouse fields greatly increases N loss and fossil-fuel energy consumption resulting in serious environmental risks. Microbial inoculants are strongly emerging as potential alternatives to agrochemicals and offer an eco-friendly fertilization strategy to reduce our dependence on synthetic chemical fertilizers. Effects of a N-fixing strain Pseudomonas protegens CHA0-ΔretS-nif on ginger plant growth, yield, and nutrient uptake, and on earthworm biomass and the microbial community were investigated in glasshouse fields in Shandong Province, northern China. RESULTS Application of CHA0-ΔretS-nif could promote ginger plant development, and significantly increased rhizome yields, by 12.93% and 7.09%, respectively, when compared to uninoculated plants and plants treated with the wild-type bacterial strain. Inoculation of CHA0-ΔretS-nif had little impact on plant phosphorus (P) acquisition, whereas it was associated with enhanced N and potassium (K) acquisition by ginger plants. Moreover, inoculation of CHA0-ΔretS-nif had positive effects on the bacteria population size and the number of earthworms in the rhizosphere. Similar enhanced performances were also found in CHA0-ΔretS-nif-inoculated ginger plants even when the N-fertilizer application rate was reduced by 15%. A chemical N input of 573.8 kg ha-1 with a ginger rhizome yield of 1.31 × 105 kg ha-1 was feasible. CONCLUSIONS The combined application of CHA0-ΔretS-nif and a reduced level of N-fertilizers can be employed in glasshouse ginger production for the purpose of achieving high yields while at the same time reducing the inorganic-N pollution from traditional farming practices. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Terpenes constitute a major part of secondary metabolites secreted by plants in the rhizosphere. However, their specific functions in fungal–plant interactions have not been investigated thoroughly. In this study we investigated the role of monoterpenes in interactions between oilseed rape (Brassica napus) and the soilborne pathogen Verticillium longisporum. We identified seven monoterpenes produced by B. napus, and production of α‐pinene, β‐pinene, 3‐carene, and camphene was significantly increased upon fungal infection. Among them, β‐pinene was chosen for further analysis. Transcriptome analysis of V. longisporum on exposure to β‐pinene resulted in identification of two highly expressed pleotropic drug transporters paralog genes named VlAbcG1a and VlAbcG1b. Overexpression of VlAbcG1a in Saccharomyces cerevisiae increased tolerance to β‐pinene, while deletion of the VlAbcG1a homologous gene in Verticillium dahliae resulted in mutants with increased sensitivity to certain monoterpenes. Furthermore, the VlAbcG1a overexpression strain displayed an increased tolerance to β‐pinene and increased virulence in tomato plants. Data from this study give new insights into the roles of terpenes in plant–fungal pathogen interactions and the mechanisms fungi deploy to cope with the toxicity of these secondary metabolites., A pleotropic drug transporter VIAbcG1 is required for tolerance to the plant host β‐pinene monoterpene and virulence in the soilborne plant pathogen Verticillium longisporum.

To highlight the importance of the soil-root interface in bacterial root colonization, we performed 16S rRNA gene amplicon sequencing on the Illumina MiSeq platform to characterize the bacterial endophytes of rice plants grown by two experiments – soil and hydroponic, considering their soil, solution, and endosphere compartments. We hypothesized that rice plants from both experiments would exhibit dissimilar endophytic bacterial communities. Alpha-diversity (richness (ASVs), Shannon index, Faith’s phylogenetic diversity, and Pielou’s evenness) for bacterial endophytes was lower in the soil experiment than in the hydroponic experiment. However, the rhizospheric soil exhibited higher microbial diversity and richness than the hydroponic solution after 6 weeks. Proteobacteria and Firmicutes were the most dominant phyla in both experiments, while several other bacterial taxa showed major differences at genus levels. A Venn diagram revealed that 5 overlapping bacterial genera were shared by the endosphere and rhizosphere/solution compartments of both experiments. Principal coordinate analysis (PCoA) based on weighted UniFrac distances showed a clear distinction between microbial communities of all sampled compartments. Furthermore, PERMANOVA results showed that the endophyte communities of both experiments differed significantly (p

Cadmium’s presence in agricultural soils resulting from industrial activities, factories, fertilizers, and pesticides is an environmental challenge threatening public health. Therefore, this study was carried out to assess Trichoderma harzianum and indigenous rhizosphere soil microbes’ ability on cadmium absorption, translocation, and tolerance in barley. A pot experiment was conducted in a full factorial randomized design with three replicates. Treatments were T. harzianum (Tri) and rhizosphere soil (Rhi) and Cd at seven levels (0, 1.54, 3.84, 9.6, 24, 60, and 150 mg kg−1). We found that simultaneous application of T. harzianum and indigenous soil microorganisms had positive effects on barley tolerance index (TI), Cd uptake efficiency, shoot dry weight, and plant uptake. Co-inoculation of T. harzianum and soil microorganisms resulted in significantly higher chlorophyll content as compared to plants inoculated only with only T. harzianum or soil microorganisms. The maximum root uptake obtained at 150 mg kg−1 Cd added was in plants also co-inoculated with Tri and Rhi. Also, the Cd uptake efficiency was lower in plants inoculated with Tri and Rhi compared to non-inoculated plants. Meanwhile, Cd uptake efficiency increased with soil Cd up to 133 mg kg−1. The lowest Cd phytoextraction efficiency was observed with Tri and Rhi co-inoculated plants. The obtained results suggest that co-inoculation of T. harzianum and soil microbes ameliorates the negative effects of Cd contamination and could then be used as an option to remediate Cd-contaminated soils even in higher levels than this study.

The comparative study of soil bacteria from the rhizosphere was carried out using samples obtained from the soil (rhizospheres) of Anogeissus leiocarpa and Pterocarpus erinaceus using purposive sampling method. The soil samples were collected at a depth of 0-30cm and 30-60cm around the rhizosphere of the studied tree species and away from the rhizosphere used as a control. The method by Ibitoye (2008) was used to test for physico-chemical properties and method by Cheesborough (2006) was used for stocking, culturing, incubating and gram staining. Result for the mean physical properties shows, P. erinaceus had highest mean values for clay and silt which wasn’t significant (p= 0.067 and 0.381 respectively). A. leiocarpus had the second highest clay and silt. Sand and bulk density was highest for the control which was highly significant (p = 0.000 and p=0.044 respectively). For mean chemical properties among plant species, pH, EC, OC, OM, N, Na, Ca and CEC were highly significant (p

Intercropping or assistant endophytes promote phytoremediation capacities of hyperaccumulators and enhance their tolerance to heavy metal (HM) stress. Findings from a previous study showed that intercropping the hyperaccumulator Sonchus asper (L.) Hill grown in HM-contaminated soils with maize improved the remediating properties and indicated an excluder-to-hyperaccumulator switched mode of action towards lead. In the current study, RNA-Seq analysis was conducted on Sonchus roots grown under intercropping or monoculture systems to explore the molecular events underlying this shift in lead sequestering strategy. The findings showed that intercropping only slightly affects S. asper transcriptome but significantly affects expression of root-associated microbial genomes. Further, intercropping triggers significant reshaping of endophytic communities associated with a ‘root-to-shoot’ transition of lead sequestration and improved phytoremediation capacities of S. asper. These findings indicate that accumulator activities of a weed are partially attributed to the root-associated microbiota, and a complex network of plant–microbe-plant interactions shapes the phytoremediation potential of S. asper. Analysis showed that intercropping may significantly change the structure of root-associated communities resulting in novel remediation properties, thus providing a basis for improving phytoremediation practices to restore contaminated soils.

Effects of hydrogen concentrations on the diversity and changes of bacterial community structure, soybean rhizosphere soil samples were investigated. The high-throughput sequencing technology of illumina was adopted to determine the bacterial 16S rRNA V3+V4 region series. Data processing such as splicing, filtering, removing chimeric sequences, and cluster analysis was then performed based on the raw data, and the tax was annotated with OTU. When the air-treated soil samples were compared with the ones treated with hydrogen at a concentration of 1100 ppm and 1300 ppm, the abundance of Proteobacteria increased and Actinobacteria decreased for the later. In addition the Simpson index decreased and the Shannon index increased significantly for both hydrogen-treated samples. However, for the soil sample treated with 1500 ppm of hydrogen, the above-mentioned two indexes didnot vary obviously compared with the air-treated sample. The results demonstrated that the rhizosphere bacterial structure diversity of soybean was significantly increased after hydrogen treatment at the concentration of 1100 and 1300 ppm. Bangladesh J. Bot. 50(3): 775-780, 2021 (September) Special

It is becoming increasingly evident about interactions between plant hosts and their microbiotas, while the effects of plant communities on microbial communities in different geographic environments are poorly understood. Here, the differentiation of licorice plant ecotypes and the distribution of root-associated microbiotas were investigated across five sampling sites in northwest China. The interactions between the environment, plant and microbial communities, and their effects on licorice root secondary metabolites, were elucidated. The plant community was clearly differentiated into distinct ecotypes based on genotyping-by-sequencing and was primarily driven by geographic distance and soil available nitrogen. The bulk soil and root-associated microbiotas (rhizosphere soil and root endosphere) partially correlated with plant community, but all were significantly discriminated by plant clade. Moreover, these microbiotas were explained to different extents by distinct combinations of environment, geography and plant community. Similarly, three structural equation models showed that licorice root secondary metabolites were complicatedly modulated by multiple abiotic and biotic factors; and were mostly explained by these factors in the rhizosphere model. Collectively, the results provide novel insights into the role of environment-plant-microbiotas interactions in regulating root secondary metabolites. That should be accounted for when selecting appropriate licorice planting sites and management measures. This article is protected by copyright. All rights reserved.

As rizobactérias promotoras do crescimento de plantas (RPCP) são capazes de proporcionar o melhor desenvolvimento vegetal por meio de diversos mecanismos. Um desses mecanismos trata da produção de reguladores de crescimento vegetal, como por exemplo, o ácido indolacético (AIA). Com isso, o objetivo do presente trabalho foi o isolamento, a caracterização fenotípica e a avaliação do potencial de produção de AIA de rizobactérias, obtidas da rizosfera de oliveiras (Olea europaea L.), visando a sua aplicação na indução do enraizamento durante a produção de mudas. Para isso, amostras de rizosfera de 17 diferentes cultivares de oliveira, do banco de germoplasma da Empresa de Pesquisa Agropecuária de Minas Gerais (EPAMIG), em Maria da Fé - MG, foram utilizadas para o isolamento de RPCP em meios de cultura JNFb, NFb e LGI, posteriormente caracterizadas fenotipicamente em meio batata-dextrose-ágar e submetidas ao teste de produção de AIA. Pôde-se observar efeito das cultivares no número de RPCP nos diferentes meios de cultura. Na caracterização fenotípica, os isolados de RPCP apresentaram alta similaridade entre si (93% a 100%). Quanto à produção de AIA, esses isolados apresentaram índices relevantes (0,16 e 29,08 μg mL-1) quando comparados a outros estudos, sendo aqueles obtidos no meio JNFb os maiores produtores. Pôde-se concluir que 11 isolados (KRJ2, GLJ2, G57J2, MFJ1, ADJ2, G57N1, AUSAL3, FTJ1, AUSAN1, AUSAJ2, KRN1), com produção acima de 20 μg mL-1 de AIA, apresentam potencial de utilização em futuros testes na indução de enraizamento de estacas de plantas de oliveira.

Rhizospheric soils and corms of Crocus sativus L. accommodate 13 different nematode taxa in the saffron fields of Kishtwar, Jammu and Kashmir, India. Out of which, three are identified as free-living, two predatory and eight plant-parasitic. Among free-living, predatory and plant-parasitic nematodes Acrobeles spp., Mononchus spp. and Helicotylenchus spp. respectively were the most frequently and densely available nematodes with high prominence value. Shannon diversity index (H′ = 2.43) and evenness index (J = 0.95) determined that Crocus sativus L. rhizosphere in Kishtwar is rich in terms of nematode diversity.

In a model study, we analysed the impact of humic acids (HAs, 500 ppm) on the accumulation of heavy metals (HMs; Pb, Cu, Ni and Zn) in roots and aboveground organs of the annual ornamental plant Tagetes patula (Scarlet variety) cultivated on the Terra Vita nutritive substrate used in modern cultural landscape mulching to imitate the upper fertile root layer (UR-RAT) of contaminated urban soils in megacities. Plants were grown in full photoculture (at no sunlight) in pots placed in a closed grow box, maintaining internal microclimate. A modern HLG Quantum Board QB288 V2 Rspec LED panel enabled with vegetation modes was used as light source. HMs were introduced in substrate as aqueous saline. Each setting was quadruplicated. Total experiment duration was 30 days. Tagetes patula was proved a particularly effective phytoextractor of Zn applied at 40 mg/kg (pPb>Ni. Ni at 30 mg/kg had a major impact on plant weight and length, which sets off the variety as a sensitive phytoexcluder for this metal. HAs increased aboveground mass in all settings and decreased the HM mass impact. A sharp root mass reduction was observed in combinations of the two factors (HMs+HAs), which was clearly reflected in impaired root mass in zinc settings. A single metal addition reduced the mass by average 12.0 % (p

Plant growth promoting microorganisms (PGPMs) are inhabitants of the rhizosphere that are able to provide better growth and biomass accumulation. Current agronomic practices have depleted these communities, which has created the opportunity for the development of commercial inoculants. These products use strains that are able to interact with a wide range of plant species and survive in diverse environments. The use of these generalist strains is required for providing a widespread solution that aggregates enough demand to reach market scale. Growth promotion by generalist strains may be suboptimal in comparison to the effect provoked by native and host-specific populations, but these specialist strains are not a market-available solution. In this work, we assess the nitrogen, phosphorus and potassium (NPK) use efficiency provided by commercial inoculants to cassava plants using Data Envelopment Analysis (DEA) to demonstrate the advantages of conceiving nutrient-limited yield as a production function. We also estimate the prospective production frontier that commercial inoculants can provide to cassava plants. Our results suggest that commercial inoculants have potential for improving cassava yields via improved NPK use efficiency. The methods presented here offer an ecological/economic production framework for the assessment of PGPMs and PGPMs-based commercial inoculants that can be extended to other laboratory, greenhouse or field situations. The simple, intuitive and graphical approximation that DEA offers will facilitate the understanding of the concept of technical efficiency and the role of commercial inoculants on closing yield gaps.

The microbial community within the root system, the rhizosphere closely connected to the root, and their symbiotic relationship with the host are increasingly seen as possible drivers of natural pathogen resistance. Resistant cultivars have the most effective strategy in controlling the Chinese wheat yellow mosaic disease, but the roles of the root and rhizosphere microbial interactions among different taxonomic levels of resistant cultivars are still unknown. Thus, we aimed to investigate whether these microbial community composition and network characteristics are related to disease resistance and to analyze the belowground plant-associated microflora. Relatively high microbial diversity and stable community structure for the resistant cultivars were detected. Comparison analysis showed that some bacterial phyla were significantly enriched in the wheat root or rhizosphere of the resistant wheat cultivar. Furthermore, the root and rhizosphere of the resistant cultivars greatly recruited many known beneficial bacterial and fungal taxa. In contrast, the relative abundance of potential pathogens was higher for the susceptible cultivar than for the resistant cultivar. Network co-occurrence analysis revealed that a much more complex, more mutually beneficial, and a higher number of bacterial keystone taxa in belowground microbial networks were displayed in the resistant cultivar, which may have been responsible for maintaining the stability and ecological balance of the microbial community. Overall, compared with the susceptible cultivar, the resistant cultivar tends to recruit more potential beneficial microbial groups for plant and rhizosphere microbial community interactions. These findings indicate that beneficial rhizosphere microbiomes for cultivars should be targeted and evaluated using community compositional profiles. KEY POINTS: • Different resistance levels in cultivars affect the rhizosphere microbiome.. • Resistant cultivars tend to recruit more potential beneficial microbial groups. • Bacteria occupy a high proportion and core position in the microflora network.

The application of biochar and plant‐growth‐promoting bacteria (PGPBs) in biocontrol soil‐borne pathogens has garnered worldwide interest recently. However, how agricultural replanting disease is alleviated by a combination of biochar and PGPBs treatment (SYBB) remains largely unexplored. In this study, we investigated the beneficial effects of single biochar addition and the combination of biochar and PGPBs on alleviating replanting disease by altering the rhizosphere microbiome and metabolites. Our field experiment showed that the SYBB treatment had a better alleviating effect on replanting disease than the single biochar addition. The study indicated the dominant effect of deterministic processes on the bacterial community and of stochastic processes on the fungal community under biochar and PGPBs treatment. The combination of biochar and PGPBs tended to convert the stochastic processes of fungal community assembly into deterministic processes. We found SYBB treatment increased the abundance of potentially beneficial Pseudomonas, Lysobacter, Gemmatimonadetes and Nitrospira, and decreasing the abundance of potentially pathogenic Fusarium, Talaromyces and Fusarium oxysporum. Moreover, the SYBB treatment increased the abundances of carbohydrates, fatty acids and plant hormones, and decreased the abundances of amino acids in the rhizosphere soil. Co‐occurrence network analysis indicated that SYBB treatment increased the connections within the microbial communities and drove the alteration of co‐occurrence network among the microbial communities and metabolites, which increased positive correlations in bacteria‐metabolite networks and decreased positive correlations in fungi‐metabolite networks. Spearman correlation analysis showed the abundances of beneficial Streptomyces, Pseudomonas and Lysobacter were significantly and positively correlated to the metabolites most increased under SYBB treatment. The combination of biochar and PGPBs alleviated replanting disease by mediating the change of rhizosphere soil metabolites, and stimulating the proliferation of indigenous and beneficial soil microbes. The research results are intended to provide the basis for new strategies for green and sustainable remediation of soil‐borne pathogens.