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Arsenic contamination of soils threatens the health of millions globally through accumulation in crops. While plants detoxify arsenic via phytochelatin (PC) complexation and efflux of arsenite from roots, arsenite efflux mechanisms are not fully understood. Here, white lupin (Lupinus albus) was grown in semi-hydroponics and exudation of glutathione (GSH) derivatives and PCs in response to arsenic was scrutinised using LC-MS/MS. Inhibiting synthesis of PC precursor GSH with L-buthionine sulfoximine (BSO) or ABC transporters with vanadate drastically reduced (>22%) GSH-derivative and PC2 exudation, but not PC3 exudation. This was accompanied by arsenic hypersensitivity in plants treated with BSO and moderate sensitivity with vanadate treatment. Investigating arsenic-phytochelatin (As-PC) complexation revealed two distinct As-PC complexes, As bound to GSH and PC2 (GS-As-PC2) and As bound to PC3 (As-PC3), in exudates of As-treated lupin. Vanadate inhibited As-PC exudation, while BSO inhibited both the synthesis and exudation of As-PC complexes. These results demonstrate a role of GSH-derivatives and PC exudation in lupin arsenic tolerance and reveal As-PC exudation as a new potential mechanism contributing to active arsenic efflux in plants. Overall, this study uncovers insight into rhizosphere arsenic detoxification with potential to help mitigate pollution and reduce arsenic accumulation in crops.

Root exudation of N is a plant input to the soil environment and may be differentially regulated by the plant during drought. Organic N released by root systems has important implications in rhizosphere biogeochemical cycling considering the intimate coupling of C and N dynamics by microbial communities. Besides amino acids, diverse molecules exuded by root systems constitute a significant fraction of root exudate organic N but have yet to receive a metabolomic and quantitative investigation during drought. To observe root exudation of N during drought, mature cotton plants received progressive drought and recovery treatments in an aeroponic system throughout their reproductive stage and were compared to control plants receiving full irrigation. Root exudates were nondestructively sampled from the same plants at 9 timepoints over 18 days. Total organic C and N were quantified by combustion, inorganic N with spectrophotometric methods, free amino acids by high performance liquid chromatography (HPLC), and untargeted metabolomics by Fourier-transform ion cyclotron resonance-mass spectrometry (FT-ICR-MS). Results indicate that organic N molecules in root exudates were by far the greatest component of root exudate total N, which accounted for 20-30% of root exudate mass. Drought increased root exudation of organic N (62%), organic C (6%), and free amino acid-N (562%), yet free amino acids were <5% of the N balance. Drought stress significantly increased root exudation of serine, aspartic acid, asparagine, glutamic acid, tryptophan, glutamine, phenylalanine, and lysine compared to the control. There was a total of 3,985 molecules detected across root exudate samples, of which 41% contained N in their molecular formula. There were additionally 349 N-containing molecules unique to drought treatment and 172 unique to control. Drought increased the relative abundance and redistributed the molecular weights of low molecular weight N-containing molecules. Time-series analysis revealed root exudation of organic N was stimulated by drought and was sensitive to the degree of drought stress. [ABSTRACT FROM AUTHOR]

The soil redox potential in wetlands such as peatlands or salt marshes exerts a strong control over microbial decomposition processes and consequently soil carbon cycling. Wetland plants can influence redox by supplying both terminal electron acceptors (i.e. oxygen) and electron donors (i.e. organic matter) to the soil system. However, quantitative insight into the importance of plant effects on wetland soil redox and associated plant traits are scarce. In a combined mesocosm and field study we investigated the impact of plants on soil reduction using IRIS (Indicator of Reduction in Soils) sticks. Vegetated plots were compared to non-vegetated plots along an elevational gradient in a salt marsh of the Wadden Sea and along an artificially created gradient in a tidal tank mesocosm experiment. Our findings from the mesocosm experiment demonstrated that vegetation both enhanced and suppressed soil reduction relative to non-vegetated control pots. The direction of the plant effect (i.e., net oxidizing or net reducing) was inversely correlated with background redox conditions. Insights from high-resolution oxygen profiling via planar optode imaging corroborated these findings. In the field study, vegetation consistently reduced the comparatively well-aerated Wadden Sea salt marsh soil. Reduction correlated positively with soil organic matter content and belowground biomass, indicating that greater availability of plant-derived electron donors, in the form of organic matter, increased soil reduction. Challenging the dominant paradigm that wetland plants primarily act as soil oxidizers, our study reveals their potential to exert a net reducing effect. The documented impact of these plant-induced changes in soil redox conditions suggests a previously overlooked role in shaping the stability of soil organic carbon stocks in wetland ecosystems with variable water tables. [ABSTRACT FROM AUTHOR]

Drought can seriously affect the yield and quality of tea. The interaction between rhizosphere microorganisms and tea plants could enhance the drought resistance of tea plants. However, there are few studies on the effects of abundant and rare microorganisms on tea plants. In this study, the contributions of abundant and rare bacteria in the rhizosphere microorganisms of 'FudingDabaicha' and 'Baiye No.1' to the resistance of tea plants to drought stress were studied using 16SrRNA sequencing, co-occurrence network analysis, and PLS-PM modeling analysis. By measuring the contents of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), malondialdehyde (MDA), proline, soluble sugar and soluble protein, it was found that the activity of antioxidant enzymes and the content of osmotic substances increased significantly after drought stress (p < 0.001). In the co-occurrence network of the two varieties, the average degree, clustering coefficient, and modularity index of the rare bacteria were greater than those of the abundant bacteria, and the path coefficient of the rare bacteria to drought was greater than that of the abundant bacteria. The contribution of rare microorganisms in 'FudingDabaicha' to drought stress was greater than that in 'Baiye No.1'. The rare bacteria of the two varieties were positively correlated with amino acids and negatively correlated with lipids. The results of this study will provide new insights for the use of rhizosphere microorganisms in improving the drought resistance of tea plants. [ABSTRACT FROM AUTHOR]

The rhizosphere, as the "frontline" of plant life, connects plant roots, rhizosphere microorganisms, and surrounding soil, plays a crucial role in plant growth and health, particularly in sustainable agriculture. Despite the well-established contribution of plant-microbe interactions to plant health, the specific molecular mechanisms remain insufficiently understood. This review aims to summarize the physiological adjustments and signal modulation that both plants and microorganisms undergo within this unique ecological niche to ensure successful colonization. By analyzing key processes such as chemotaxis, root attachment, immune evasion, and biofilm formation, we uncover how plants precisely modulate root exudates to either recruit or repel specific microorganisms, thereby shaping their colonization patterns. These findings provide new insights into the complexity of plant-microbe interactions and suggest potential directions for future research in sustainable agriculture. [ABSTRACT FROM AUTHOR]

Root exudates serve as a bridge connecting plant roots and rhizosphere microbes, playing a key role in influencing the assembly and function of the rhizobiome. Recent studies have fully elucidated the role of root exudates in recruiting rhizosphere microbes to enhance plant performance, particularly in terms of plant resistance to soil-borne pathogens; however, it should be noted that the composition and amount of root exudates are primarily quantitative traits regulated by a large number of genes in plants. As a result, there are knowledge gaps in understanding the contribution of the rhizobiome to soil-borne plant disease resistance and the ternary link of plant genes, root exudates, and disease resistance-associated microbes. Advancements in technologies such as quantitative trait loci (QTL) mapping and genome-wide association studies (GWAS) offer opportunities for the identification of genes associated with quantitative traits. In the present review, we summarize recent studies on the interactions of plant and rhizosphere microbes through root exudates to enhance soil-borne plant disease resistance and also highlight methods for quantifying the contribution of the rhizobiome to plant disease resistance and identifying the genes responsible for recruiting disease resistance-associated microbes through root exudates. [ABSTRACT FROM AUTHOR]

SUMMARY: The domestication process progressively differentiated wild relatives from modern cultivars, thus impacting plant‐associated microorganisms. Endophytic bacterial communities play vital roles in plant growth, development, and health, which contribute to the crop's sustainable development. However, how plant domestication impacts endophytic bacterial communities and relevant root exudates in wheat remains unclear. First, we have observed that the domestication process increased the root endophytic microbial community diversity of wheat while decreasing functional diversity. Second, domestication decreased the endophytic bacterial co‐occurrence network stability, and it did significantly alter the abundances of core microorganisms or potential probiotics. Third, untargeted LC–MS metabolomics revealed that domestication significantly altered the metabolite profiles, and the abundances of various root exudates released were significantly correlated with keystone taxa including the Chryseobacterium, Massilia, and Lechevalieria. Moreover, we found that root exudates, especially L‐tyrosine promote the growth of plant‐beneficial bacteria, such as Chryseobacterium. Additionally, with L‐tyrosine and Chryseobacterium colonized in the roots, the growth of wild wheat's roots was significantly promoted, while no notable effect could be found in the domesticated cultivars. Overall, this study suggested that wild wheat as a key germplasm material, and its native endophytic microbes may serve as a resource for engineering crop microbiomes to improve the morphological and physiological traits of crops in widely distributed poor soils. Significant Statement: Building on previous research, our study further investigates the significant effects of long‐term domestication, which has played a crucial role in the development of human civilization, on the communities of endophytic bacteria and root exudates in wheat. Our findings indicate that wild wheat, along with its naturally occurring endophytic microbes, could be valuable resources for manipulating crop microbiomes and improving the overall characteristics of crops in nutrient‐depleted soils. [ABSTRACT FROM AUTHOR]

Intercropping can enable more efficient resource use and increase yield. Most current studies focus on the correlation between soil nutrients and crop yield under intercropping conditions. However, the mechanisms related to root exudates and soil nutrients remain unclear. Therefore, this study explored the correlation between rhizosphere soil nutrients and root exudates in sugarcane/peanut intercropping. Root extracts, root exudates, rhizosphere soil enzyme activities, and soil nutrients were analyzed and compared in monocultured and intercropped peanut and sugarcane at different growth stages. The root metabolites were annotated using the Kyoto Encyclopedia of Genes and Genomes pathways to further identify the connection between soil nutrients and root exudates. The effects of intercropping differed in peanut and sugarcane at different growth stages, and the difference between podding and pod-filling stages was significant. Intercropping generally had a great effect on peanut; it not only significantly increased the organic acid, soluble sugars, and phenolic acids in root exudates and extracts from peanuts, but also significantly increased rhizosphere soil enzyme activities and soil nutrient levels. Intercropping peanuts promoted fumaric acid secretion from roots and significantly affected the metabolic pathways of alanine, aspartate, and glutamate. Sugarcane/peanut intercropping can increase root exudates and effectively improve soil nutrients. The changes in soil nutrients are closely related to the effects of fumaric acid on alanine, aspartate, and glutamate metabolism. [ABSTRACT FROM AUTHOR]

Microbes such as bacteria and fungi play important roles in nutrient cycling in soils, often leading to the bioavailability of metabolically important mineral elements such as nitrogen (N), phosphorus (P), iron (Fe), and zinc (Zn). Examples of microbes with beneficial traits for plant growth promotion include mycorrhizal fungi, associative diazotrophs, and the N2-fixing rhizobia belonging to the α, β and γ class of Proteobacteria. Mycorrhizal fungi generally contribute to increasing the surface area of soil-root interface for optimum nutrient uptake by plants. However, when transformed into bacteroids inside root nodules, rhizobia also convert N2 gas in air into ammonia for use by the bacteria and their host plant. Thus, nodulated legumes can meet a high proportion of their N requirements from N2 fixation. The percentage of legume N derived from atmospheric N2 fixation varies with crop species and genotype, with reported values ranging from 50–97%, 24–67%, 66–86% 27–92%, 50–92%, and 40–75% for soybean (Gycine max), groundnut (Arachis hypogea), mung bean (Vigna radiata), pigeon pea (Cajanus cajan), cowpea (Vigna unguiculata), and Kersting's groundnut (Macrotyloma geocarpum), respectively. This suggests that N2-fixing legumes require little or no N fertilizer for growth and grain yield when grown under field conditions. Even cereals and other species obtain a substantial proportion of their N nutrition from associative and endophytic N2-fixing bacteria. For example, about 12–33% of maize N requirement can be obtained from their association with Pseudomonas, Hebaspirillum, Azospirillum, and Brevundioronas, while cucumber can obtain 12.9–20.9% from its interaction with Paenebacillus beijingensis BJ-18. Exploiting the plant growth-promoting traits of soil microbes for increased crop productivity without any negative impact on the environment is the basis of green agriculture which is done through the use of biofertilizers. Either alone or in combination with other synergistic rhizobacteria, rhizobia and arbuscular mycorrhizal (AM) fungi have been widely used in agriculture, often increasing crop yields but with occasional failures due to the use of poor-quality inoculants, and wrong application techniques. This review explores the literature regarding the plant growth-promoting traits of soil microbes, and also highlights the bottle-necks in tapping this potential for sustainable agriculture. [ABSTRACT FROM AUTHOR]

Introduction: The rhizosphere is the zone of soil surrounding plant roots that is directly influenced by root exudates released by the plant, which select soil microorganisms. The resulting rhizosphere microbiota plays a key role in plant health and development by enhancing its nutrition or immune response and protecting it from biotic or abiotic stresses. In particular, plant growth-promoting rhizobacteria (PGPR) are beneficial members of this microbiota that represent a great hope for agroecology, since they could be used as bioinoculants for sustainable crop production. Therefore, it is necessary to decipher the molecular dialog between roots and PGPR in order to promote the establishment of bioinoculants in the rhizosphere, which is required for their beneficial functions. Methods: Here, the ability of root exudates from rapeseed (Brassica napus), pea (Pisum sativum), and ryegrass (Lolium perenne) to attract and feed three PGPR (Bacillus subtilis, Pseudomonas fluorescens, and Azospirillum brasilense) was measured and compared, as these responses are directly involved in the establishment of the rhizosphere microbiota. Results: Our results showed that root exudates differentially attracted and fed the three PGPR. For all beneficial bacteria, rapeseed exudates were the most attractive and induced the fastest growth, while pea exudates allowed the highest biomass production. The performance of ryegrass exudates was generally lower, and variable responses were observed between bacteria. In addition, P. fluorescens and A. brasilense appeared to respond more efficiently to root exudates than B. subtilis. Finally, we proposed to evaluate the compatibility of each plant–PGPR couple by assigning them a “love match” score, which reflects the ability of root exudates to enhance bacterial rhizocompetence. Discussion: Taken together, our results provide new insights into the specific selection of PGPR by the plant through their root exudates and may help to select the most effective exudates to promote bioinoculant establishment in the rhizosphere. [ABSTRACT FROM AUTHOR]

Background: Soybean seeds are rich in protein and oil. The selection of varieties that produce high-quality seeds has been one of the priorities of soybean breeding programs. However, the influence of improved seed quality on the rhizosphere microbiota and whether the microbiota is involved in determining seed quality are still unclear. Here, we analyzed the structures of the rhizospheric bacterial communities of 100 soybean varieties, including 53 landraces and 47 modern cultivars, and evaluated the interactions between seed quality traits and rhizospheric bacteria. Results: We found that rhizospheric bacterial structures differed between landraces and cultivars and that this difference was directly related to their oil content. Seven bacterial families (Sphingomonadaceae, Gemmatimonadaceae, Nocardioidaceae, Xanthobacteraceae, Chitinophagaceae, Oxalobacteraceae, and Streptomycetaceae) were obviously enriched in the rhizospheres of the high-oil cultivars. Among them, Oxalobacteraceae (Massilia) was assembled specifically by the root exudates of high-oil cultivars and was associated with the phenolic acids and flavonoids in plant phenylpropanoid biosynthetic pathways. Furthermore, we showed that Massilia affected auxin signaling or interfered with active oxygen-related metabolism. In addition, Massilia activated glycolysis pathway, thereby promoting seed oil accumulation. Conclusions: These results provide a solid theoretical basis for the breeding of revolutionary soybean cultivars with desired seed quality and optimal microbiomes and the development of new cultivation strategies for increasing the oil content of seeds. 7196FtKvsnPuUrhB77D9vL Video Abstract [ABSTRACT FROM AUTHOR]

Understanding the interactions between fungal plant pathogens and host roots is crucial for developing effective disease management strategies. This study investigates the molecular mechanisms underpinning the chemotropic responses of the maize anthracnose fungus Colletotrichum graminicola to maize root exudates. Combining the generation of a deletion mutant with monitoring of disease symptom development and detailed analysis of chemotropic growth using a 3D-printed device, we identify the 7-transmembrane G-protein coupled receptor (GPCR) CgSte3 as a key player in sensing both plant-derived class III peroxidases and diterpenoids. Activation of CgSte3 initiates signaling through CgSo, a homolog to the Cell Wall Integrity Mitogen-Activated Protein Kinase (CWI MAPK) pathway scaffold protein identified in other filamentous fungi, facilitating the pathogen's growth towards plant defense molecules. The NADPH oxidase CgNox2 is crucial for peroxidase sensing but not for diterpenoid detection. These findings reveal that CgSte3 and CWI MAPK pathways are central to C. graminicola's ability to hijack plant defense signals, highlighting potential targets for controlling maize anthracnose. [ABSTRACT FROM AUTHOR]

Introduction: Root exudates act as the "language" of plant-soil communication, facilitating crucial interactions, information exchange, and energy transfer between plants and soil. The interactions facilitated by root exudates between plants and microorganisms in the rhizosphere are crucial for nutrient uptake and stress resilience in plants. However, the mechanism underlying the interaction between root exudates and rhizosphere microorganisms in desert plants under drought conditions remains unclear, especially among closely related species. Methods: To reveal the ecological strategies employed by the genus Haloxylon in different habitats. Using DNA extraction and sequencing and UPLC-Q-Tof/MS methods, we studied root exudates and soil microorganisms from two closely related species, Haloxylon ammodendron (HA) and Haloxylon persicum (HP), to assess differences in their root exudates, soil microbial composition, and interactions. Results: Significant differences were found in soil properties and root traits between the two species, among which soil water content (SWC) and soil organic carbon (SOC) in rhizosphere and bulk soils (P < 0.05). While the metabolite classification of root exudates was similar, their components varied, with terpenoids being the main differential metabolites. Soil microbial structure and diversity also exhibited significant differences, with distinct key species in the network and differential functional processes mainly related to nitrogen and carbon cycles. Strong correlations were observed between root exudatemediated root traits, soil microorganisms, and soil properties, although the complex interactions differed between the two closely relative species. The primary metabolites found in the network of HA include sugars and fatty acids, while HP relies on secondary metabolites, steroids and terpenoids. Discussion: These findings suggest that root exudates are key in shaping rhizosphere microbial communities, increasing microbial functionality, fostering symbiotic relationships with hosts, and bolstering the resilience of plants to environmental stress. [ABSTRACT FROM AUTHOR]

Purpose: Grafting is a commonly used technique in horticulture and agriculture. The rhizosphere microbiome is critical for plant growth and performance, however, knowledge of the effect of grafting on rhizosphere microbial assemblages is still limited. Here, we use grafting systems of common beans (Phaseolus vulgaris) to study the effects of scion cultivar and grafting on rhizomicrobiome and root exudates. Methods: Grafting systems were constructed by using two cultivars of common bean. The rhizomicrobiome of intercultivar grafts (wherein different cultivars used as the scion and the rootstock) and intracultivar grafts (wherein same cultivar used as the scion and the rootstock) were analyzed by high-throughput sequencing of the bacterial 16S rRNA gene and fungal internal transcribed spacer region. Root exudates of intercultivar and intracultivar grafts were analyzed by ultra-high performance liquid chromatography-mass spectrometry analyses. Results: The rhizomicrobiome and root exudate profiles of common bean were significantly different between two cultivars. Scion cultivar significantly influenced the composition of rhizomicrobiome and root exudate profiles. Intercultivar grafts narrowed the differences of rhizomicrobiome between two cultivars. Pseudomonas and Talaromyces were highly accumulated in intercultivar grafts relative to those in intracultivar grafts. m-Coumaric acid, methyl jasmonate, and sebacic acid were increased in intercultivar grafts compared with intracultivar grafts, and showed positive relationships with Pseudomonas and Talaromyces. Conclusion: Scion cultivars modulated the assembly of rhizomicrobiome and the root exudation. Intercultivar grafting narrowed the differences between the rhizomicrobiomes of different cultivars, with a profound increase of Pseudomonas and Talaromyces, and root exudates, m-coumaric acid, methyl jasmonate, and sebacic acid. [ABSTRACT FROM AUTHOR]

Background and aims: Rhizosheath, a mixture of soil and mucilage that remains attached to the root system after being removed from the soil and shaken, plays a prominent role in the resistance of plants to drought stress. This study aims to investigate the effect of silicon (Si) on rhizosheath formation and mitigate the effects of drought stress in wheat. It was hypothesized that Si positively enhances root hair formation and rhizosheath formation under soil drying conditions, improving plant access to water under soil drying conditions. Methods: Wheat seeds were grown under different levels of Si (control, 150 and 300 mg kg−1 monosilicic acid, and 150 and 300 mg kg−1 nano-silicon) and irrigation (0.4 field capacity (FC) and 0.8 FC) under greenhouse conditions. Results: Under drought stress, the application of Si significantly increased root hair length, density, rhizosheath formation, and transpiration rate. Applying Si increased the length of root hairs by 45–107% and their density by 25–78%. Under drought stress, application of 150 and 300 mg kg−1 of monosilicic acid and nano-silicon increased rhizosheath formation by 40.3, 48.2, 16.8, and 17.5%, and transpiration rate by 17.8, 36.4, 11.4, and 29.1%, respectively. Si also increased superoxide dismutase and catalase activity, while decreasing malondialdehyde and hydrogen peroxide content. Conclusion: Silicon application in drought-stricken wheat improved water uptake, leading to improved plant water relations and other morpho-physiological and biochemical responses. This was achieved by modifying root system traits, particularly increasing root hair length and density, which facilitated the formation of rhizosheath. [ABSTRACT FROM AUTHOR]

Australian saltbush (Atriplex spp.) survive in exceptionally saline environments and are often used for pasture in semi-arid areas. To investigate the impact of salinity on saltbush root morphology and root exudates, three Australian native saltbush species (Atriplex nummularia , Atriplex amnicola , and Atriplex vesicaria) were grown in vitro in optimised sterile, semi-hydroponic systems in media supplemented with different concentrations of salt (NaCl). Histological stains and chromatographic techniques were used to characterise the root apical meristem (RAM) type and root exudate composition of the saltbush seedlings. We report that saltbush species have closed-type RAMs, which release border-like cells (BLCs). Monosaccharide content, including glucose and fructose, in the root mucilage of saltbush was found to be uniquely low, suggesting that saltbush may minimise carbon release in polysaccharides of root exudates. Root mucilage also contained notable levels of salt, plus increasing levels of unidentified compounds at peak salinity. Un-esterified homogalacturonan, xyloglucan, and arabinogalactan proteins between and on the surface of BLCs may aid intercellular adhesion. At the highest salinity levels, root cap morphology was altered but root:shoot ratio remained consistent. While questions remain about the identity of some components in saltbush root mucilage other than the key monosaccharides, this new information about root cap morphology and cell surface polysaccharides provides avenues for future research. Australian saltbush (Atriplex spp.), used for pasture in semi-arid areas, survive in exceptionally salty environments, but little is known about how salinity affects the root morphology and root exudates. We discovered that saltbush have closed-type root apical meristems and release limited sugars as root exudates, maintaining root:shoot ratio even at extreme salinity. These findings offer new insights into saltbush resilience and encourage further research into their unique root properties. [ABSTRACT FROM AUTHOR]

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

Drought and heat are recognized as the foremost abiotic stresses influencing plant growth and yield. In response to stressful conditions, plants undergo various physiological and biochemical modifications to enhance their resilience. Among these modifications, root exudates, comprising a diverse range of organic compounds, significantly impact plant resilience to drought and heat stresses. The soil microbiome plays a crucial role in mitigating drought and heat stress by enhancing plant resilience through various mechanisms, including nutrient acquisition, hormone production, and stress signal modulation. Its interaction with root exudates further amplifies these effects, as root exudates serve as key mediators in shaping microbial communities and promoting beneficial interactions. This review enunciates the crucial role of root exudates in conferring drought and heat stress tolerance, offering novel insights into the mechanisms, root structural changes, and physiological and biochemical adaptations. The role of microorganisms and their interaction with root exudates are explored to unveil the intricate network of interactions orchestrated by root exudates in stress adaptation, mitigation and resilience. In addition, this review examines the various physiological, abiotic, and biotic factors that impact the composition and dynamics of root exudates. Deciphering the complex interactions among these elements is essential to understanding the intricacies of plant stress responses. Furthermore, root exudate extraction techniques are briefed. Overall, this review aims to better understand and drive future research focused on integrating the role of root exudates, soil microbiome for improving adaptation, mitigation and resilience of crops to abiotic stresses such as drought and heat. [ABSTRACT FROM AUTHOR]

In recycled hydroponics, successive crop cultivation by maintaining electrical conductivity (EC) suffers lower growth performance due to accumulating autotoxic root exudates. In this study, the efficiency of alternate current electro degradation (AC-ED) was evaluated for degrading allelochemicals and recovering retarded lettuce yield cultivated in EC-adjusted repeatedly used nutrient solutions. From benzoic acid (BA)-added nutrient solution, BA was completely degraded after 24 h by applying AC-ED at 551 and 940 Hz frequency with 50 and 80% electrical duty. In lettuce bioassay, fresh mass was negatively affected without the AC-ED-treated solution. Finally, lettuce seedlings were hydroponically grown in a plant factory using a half-strength Enshi nutrient solution. Culture solutions were unchanged in non-renewed solutions. Nutrient elements were supplied based on the EC (1.42 dS m−1) of culture solutions. The fresh weight of lettuce was gradually decreased in subsequent cultures. Nutrient absorption rate was reduced in non-renewed solutions though enough of all nutrient elements were available in the solution. In the final culture, the highest shoot fresh weight (SFW) was recorded in the renewed (83.0 g plant−1) solution which was similar to the AC-ED-treated solution (81.0 g plant−1) and the lowest (58.0 g plant−1) was in the non-renewed solution. By applying AC-ED, 40% lettuce yield was recovered in the EC-adjusted solution without renewing. Therefore, it is recommended that the continuous application of AC-ED with the capacity of 551 Hz and 50% duty would be applied for recovering the retarded lettuce yield cultivated with repeatedly used culture solutions in recycled hydroponics. [ABSTRACT FROM AUTHOR]

Heterologous double-root grafting represents an effective strategy to mitigate challenges associated with continuous coffee cropping and reduce soil-borne diseases. However, its specific regulatory mechanism remains unclear. Therefore, a field experiment was conducted including six different grafting combinations for C. canephora cv. Robusta (Robusta) and Coffea Liberica (Liberica): Robusta scion with a homologous double root (R/RR), Liberica scion with a homologous double root (L/LL), Robusta scion with a heterologous double root (R/RL and L/RL), and Liberica scion with a heterologous double root (L/LR and R/LR); these combinations were conducted to clarify the effects of heterologous double-root grafting combinations on the root exudates and soil microbial diversity, structure, and function of Robusta and Liberica. The results demonstrated notable differences in root exudates, rhizosphere microbial structure, and function between Robusta and Liberica. Despite Liberica having lower diversity in its rhizosphere microbial communities and relatively higher levels of potential pathogenic bacteria, it showed stronger resistance to diseases. Roots of Robusta in heterologous double-root coffee seedlings significantly enhanced the secretion of resistance compounds, increased the relative abundance of potentially beneficial bacteria, and reduced the relative abundance of potential pathogenic fungi. This enhances the rhizosphere immunity of Robusta against soil-borne diseases. The results indicated that grafting onto Liberica roots can strengthen resistance mechanisms and enhance the rhizosphere immunity of Robusta, thereby mitigating challenges associated with continuous cropping. [ABSTRACT FROM AUTHOR]

Abstract Drought can seriously affect the yield and quality of tea. The interaction between rhizosphere microorganisms and tea plants could enhance the drought resistance of tea plants. However, there are few studies on the effects of abundant and rare microorganisms on tea plants. In this study, the contributions of abundant and rare bacteria in the rhizosphere microorganisms of ‘FudingDabaicha’ and ‘Baiye No.1’ to the resistance of tea plants to drought stress were studied using 16SrRNA sequencing, co-occurrence network analysis, and PLS-PM modeling analysis. By measuring the contents of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), malondialdehyde (MDA), proline, soluble sugar and soluble protein, it was found that the activity of antioxidant enzymes and the content of osmotic substances increased significantly after drought stress (p

Abstract Analyzing root exudates during drought poses a serious challenge; sampling root exudates in soil is destructive to roots and leads to biased molecular analysis, along with microbial decomposition and exudate sorption to soil components. Hydroponic approaches are useful to overcome these problems but lack the utility to induce drought. Nondestructive sampling techniques are thus needed to analyze root exudates from the same plants over time in combination with highly controlled variable water/nutrient stress. The proposed aeroponic approach demonstrated that cotton could be grown to maturity in the aeroponic system, then a progressive drought treatment applied while simultaneously collecting root exudates from the same plants over time. Treatments of varying irrigation rates consisted of well-watered cotton (control) that was compared to cotton given progressive water stress (drought) and subsequent drought recovery for two weeks. Plants were entering flowering as drought treatment was applied. Nondestructive morphological measurements of plant productivity were made. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was employed to analyze the molecular profile of exudates, whereas gas chromatography-mass spectroscopy (GC-MS) was used to quantify abscisic acid (ABA). Plant development was highly responsive to reduced irrigation intervals with decreased canopy height, number of green leaves, biomass, and water content. As revealed by FT-ICR MS, the complexity and connectivity of unique biochemical transformation networks in response to drought was greatest at 9 days after treatment, where severe visual symptoms were observed. Overall, the aeroponic approach is a promising technology to simulate drought while sampling root exudates nondestructively, advancing root system research and plant-stress response mechanisms.

Abstract Root exudates serve as a bridge connecting plant roots and rhizosphere microbes, playing a key role in influencing the assembly and function of the rhizobiome. Recent studies have fully elucidated the role of root exudates in recruiting rhizosphere microbes to enhance plant performance, particularly in terms of plant resistance to soil-borne pathogens; however, it should be noted that the composition and amount of root exudates are primarily quantitative traits regulated by a large number of genes in plants. As a result, there are knowledge gaps in understanding the contribution of the rhizobiome to soil-borne plant disease resistance and the ternary link of plant genes, root exudates, and disease resistance-associated microbes. Advancements in technologies such as quantitative trait loci (QTL) mapping and genome-wide association studies (GWAS) offer opportunities for the identification of genes associated with quantitative traits. In the present review, we summarize recent studies on the interactions of plant and rhizosphere microbes through root exudates to enhance soil-borne plant disease resistance and also highlight methods for quantifying the contribution of the rhizobiome to plant disease resistance and identifying the genes responsible for recruiting disease resistance-associated microbes through root exudates.

Abstract Background Soybean seeds are rich in protein and oil. The selection of varieties that produce high-quality seeds has been one of the priorities of soybean breeding programs. However, the influence of improved seed quality on the rhizosphere microbiota and whether the microbiota is involved in determining seed quality are still unclear. Here, we analyzed the structures of the rhizospheric bacterial communities of 100 soybean varieties, including 53 landraces and 47 modern cultivars, and evaluated the interactions between seed quality traits and rhizospheric bacteria. Results We found that rhizospheric bacterial structures differed between landraces and cultivars and that this difference was directly related to their oil content. Seven bacterial families (Sphingomonadaceae, Gemmatimonadaceae, Nocardioidaceae, Xanthobacteraceae, Chitinophagaceae, Oxalobacteraceae, and Streptomycetaceae) were obviously enriched in the rhizospheres of the high-oil cultivars. Among them, Oxalobacteraceae (Massilia) was assembled specifically by the root exudates of high-oil cultivars and was associated with the phenolic acids and flavonoids in plant phenylpropanoid biosynthetic pathways. Furthermore, we showed that Massilia affected auxin signaling or interfered with active oxygen-related metabolism. In addition, Massilia activated glycolysis pathway, thereby promoting seed oil accumulation. Conclusions These results provide a solid theoretical basis for the breeding of revolutionary soybean cultivars with desired seed quality and optimal microbiomes and the development of new cultivation strategies for increasing the oil content of seeds. Video Abstract

In this study, we selected walnut shell-derived pristine HC (pHC) and two modified derivatives obtained by oxidative and alkali treatments (designated mHC-O and mHC-A, respectively) to investigate the passivation performance of Pb(II) in contaminated soil. The yields of mHC-A and mHC-O were 70.58% and 95.38%, respectively, after posttreatment. According to the XPS, FTIR, and acidity titration results, the amounts of the three major OCGs (i.e. C−O, C=O, and O−C=O) all increased after H2O2 oxidation. Moreover, chemical modification fundamentally changed the structural characteristics of pHC. DTPA extraction tests indicated that the extractable Pb content after 30 days of incubation decreased by 13.60%, 19.32% and 14.53% at 7% (w/w) doses of HC, mHC-O and mHC-A, respectively, compared to that of the control. Furthermore, mHC-O was superior to pHC and mHC-A in terms of Pb passivation efficiency, which was consistent with the results of BCR sequential extraction and leaching tests using three root exudates. For mHC-O at the 7% dose, the contents of bioavailable Pb in the contaminated soil were 19.85 and 8.83 mg/kg based on DTPA leaching and BCR analysis, respectively, while they were 0.616, 0.564 and 0.07 mg/kg in the root exudate leaching tests of Ophiopogon japonicus, radish and spinach, respectively, indicating that the root exudate leaching method lowered the bioavailable Pb content compared to the DTPA and BCR methods. Overall, Oxidation posttreatment with HC could improve the passivation of Pb in contaminated soils. [ABSTRACT FROM AUTHOR]

Abstract Background Sugarcane red rot is a soil-borne disease caused by Colletotrichum falcatum. It can reduce the yield of sugarcane and the purity of sugarcane juice, which seriously restricts the development of sucrose industry. Biocontrol bacteria can control diseases by regulating rhizosphere microecology. In this study, the effects of biocontrol bacteria on sugarcane rhizosphere microecology were studied by metagenomics and metabolomics, and the control effects of biocontrol bacteria and rhizosphere dominant bacteria on sugarcane red rot were further explored by pot experiment. Results The results of metagenomic sequencing showed that inoculation with B. velezensis YC89 and pathogens could significantly change the microbial diversity of the sugarcane rhizosphere. The relative abundance of beneficial strains such as Streptomyces, Burkholderia, Sphingomonas, and Rhizobium increased significantly in the rhizosphere of sugarcane in the YC treatment group. Pseudomonas was significantly enriched in the rhizosphere of sugarcane in the C treatment group. The results of metabolome sequencing showed that the content of amino acids in sugarcane root exudates increased after inoculation with B. velezensis YC89, and the contents of phenolic acids and flavonoids decreased. Spearman correlation analysis showed that there was a significant correlation between differential metabolites and rhizosphere microorganisms. The results of pot experiment showed that YC89 strain and three rhizosphere microorganisms could significantly reduce the disease index of red rot and promote the growth of sugarcane plants. In addition, these strains can also significantly increase the JA and SA content of sugarcane leaves and induce plant system resistance-related enzyme activities. Among them, the synthetic community treatment group had the best biocontrol effect on red rot, and its relative control effect was 67.50%. Conclusions Therefore, we conclude that B. velezensis YC89 could recruit beneficial rhizosphere microorganisms to enrich the rhizosphere and change the content of some phenolic acids and flavonoids in the root exudates. In addition, the isolated rhizosphere dominant bacteria and YC89 strain can resist red rot by inducing plant systemic resistance and promote the growth of sugarcane plants. This study provides a theoretical basis for the use of biocontrol bacteria to regulate rhizosphere bacteria to jointly control plant soil-borne diseases. Graphical Abstract

Abstract Background Elucidating the intricate structural organization and spatial gradients of biomolecular composition within the rhizosphere is critical to understanding important biogeochemical processes, which include the mechanisms of root-microbe interactions for maintaining sustainable plant ecosystem services. While various analytical methods have been developed to assess the spatial heterogeneity within the rhizosphere, a comprehensive view of the fine distribution of metabolites within the root-soil interface has remained a significant challenge. This is primarily due to the difficulty of maintaining the original spatial organization during sample preparation without compromising its molecular content. Results In this study, we present a novel approach, RhizoMAP, in which the rhizosphere molecules are imprinted on selected polymer membranes and then spatially profiled using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI). We enhanced the performance of RhizoMAP by combining the use of two thin (

Diphenyl ether herbicides are extensively utilized in agricultural systems, but their residues threaten the health of sensitive rotation crops. Functional microbial strains can degrade diphenyl ether herbicides in the rhizosphere of crops, facilitating the restoration of a healthy agricultural environment. However, the interplay between microorganisms and plants in diphenyl ether herbicides degradation remains unclear. Thus, the herbicide-degrading strain Bacillus sp. Za and the sensitive crop, maize, were employed to uncover the interaction mechanism. The degradation of diphenyl ether herbicides by strain Bacillus sp. Za was promoted by root exudates. The strain induced root exudate re-secretion in diphenyl ether herbicide-polluted maize. We further showed that root exudates enhanced the rhizosphere colonization and the biofilm biomass of strain Za, augmenting its capacity to degrade diphenyl ether herbicide. Root exudates regulated gene fliZ, which is pivotal in biofilm formation. Wild-type strain Za significantly reduced herbicide toxicity to maize compared to the ZaΔfliZ mutant. Moreover, root exudates promoted strain Za growth and chemotaxis, which was related to biofilm formation. This mutualistic relationship between the microorganisms and the plants demonstrates the significance of plant-microbe interactions in shaping diphenyl ether herbicide degradation in rhizosphere soils. [Graphic: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

Root exudates are known signaling agents that influence legume root nodulation, but the molecular mechanisms for nonflavonoid molecules remain largely unexplored. The number of soybean root nodules during the initial growth phase shows substantial discrepancies at distinct developmental junctures. Using a combination of metabolomics analyses on root exudates and nodulation experiments, we identify a pivotal role for certain root exudates during the rapid growth phase in promoting nodulation. Phenoxyacetic acid (POA) was found to activate the expression of GmGA2ox10 and thereby facilitate rhizobial infection and the formation of infection threads. Furthermore, POA exerts regulatory control on the miR172c-NNC1 module to foster nodule primordia development and consequently increase nodule numbers. These findings collectively highlight the important role of POA in enhancing nodulation during the accelerated growth phase of soybeans. [ABSTRACT FROM AUTHOR]

Gas exchange in the soil is determined by the size and connectivity of air‐filled pores. Root mucilage reduces air‐filled pore connectivity and thus gas diffusivity. It is unclear to what extent mucilage affects soil pore connectivity and tortuosity. The aim of this study was to gain a better understanding of gas diffusion processes in the rhizosphere by explaining the geometric alterations of the soil pore space induced by mucilage. We quantified the effect of a root mucilage analogue collected from chia seeds without intrinsic respiratory activity on oxygen diffusion at different water contents during drying–rewetting cycles in a diffusion chamber experiment. Quantification of oxygen diffusion showed that mucilage decreased the gas diffusion coefficient in dry soil without affecting air‐filled porosity. Without mucilage, a hysteresis in gas diffusion coefficient during a drying–rewetting cycle was observed. The effect depended on particle size and diminished with increasing mucilage content. X‐ray computed tomography imaging indicated a hysteresis in the connectivity of the gas phase during a drying–rewetting cycle for samples without mucilage. This effect was attenuated with increasing mucilage content. Furthermore, electron microscopy showed that mucilage structures formed in drying soil increase with mucilage content, thereby progressively reducing the connectivity of the gas phase. In conclusion, the effect of mucilage on soil gas diffusion highly depends on soil texture and mucilage content. The diminishing hysteresis with the addition of mucilage suggests that plant roots secrete mucilage to balance oxygen availability and water content, even under fluctuating moisture conditions. [ABSTRACT FROM AUTHOR]

The secretion of root exudates plays a crucial regulatory role in the process of soil carbon cycling. It is also significantly affected by global change factors (GCFs), yet the general patterns of these changes have not been fully explored, which greatly limits the accurate establishment of carbon cycling models under the background of global change.To address this, we conducted a meta‐analysis that included 1926 data pairs to examine the effects of global variability on root exudates. Furthermore, we performed multi‐model inference using Akaike's information criterion (AIC) to assess the relative importance of multiple factors such as annual average temperature (AAT), type of ecosystem, intensity of treatment, duration and more.The findings revealed that GCFs generally improved the production of root exudates. While the addition of nitrogen and its interaction with increased temperature significantly reduced the rate of root carbon secretion, all other factors significantly promoted it. Interestingly, as the intensity of warming increased, the rate of root carbon secretion caused by warming displayed a downward trend, with a threshold of 3.6°C. Furthermore, the influence of GCFs on root carbon secretion was found to be regulated by soil nitrogen, confirming the importance of nutrients from the rhizosphere in this process.These results underscore the importance of GCFs in root exudates and emphasize the crucial role of soil total nitrogen in the regulation of root carbon secretion. They also provide valuable scientific parameters for the development of more accurate models for the global‐change carbon cycle. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

The escalating risks of drought and salinization due to climate change and anthropogenic activities are a major global concern. Rhizobium–legume (herb or tree) symbiosis is proposed as an ideal solution for improving soil fertility and rehabilitating arid lands, representing a crucial direction for future research. Consequently, several studies have focused on enhancing legume tolerance to drought and salinity stresses using various techniques, including molecular-based approaches. These methods, however, are costly, time-consuming, and cause some environmental issues. The multiplicity of beneficial effects of soil microorganisms, particularly plant growth-promoting bacteria (PGPB) or plant-associated microbiomes, can play a crucial role in enhancing legume performance and productivity under harsh environmental conditions in arid zones. PGPB can act directly or indirectly through advanced mechanisms to increase plant water uptake, reduce ion toxicity, and induce plant resilience to osmotic and oxidative stress. For example, rhizobia in symbiosis with legumes can enhance legume growth not only by fixing nitrogen but also by solubilizing phosphates and producing phytohormones, among other mechanisms. This underscores the need to further strengthen research and its application in modern agriculture. In this review, we provide a comprehensive description of the challenges faced by nitrogen-fixing leguminous plants in arid and semi-arid environments, particularly drought and salinity. We highlight the potential benefits of legume–rhizobium symbiosis combined with other PGPB to establish more sustainable agricultural practices in these regions using legume–rhizobium–PGPB partnerships. [ABSTRACT FROM AUTHOR]

Canola (Brassica napus L.) is a profitable grain crop for Australian growers. However, weeds remain a major constraint for its production. Chemical herbicides are used for weed control, but this tactic also leads to the evolution of herbicide resistance in different weed species. The suppression of weeds by crop interference (competition and allelopathic) mechanisms has been receiving significant attention. Here, the weed suppressive ability and associated functional traits and stability of four selected canola genotypes (PAK85388-502, AV-OPAL, AV-GARNET, and BAROSSA) were examined at different locations in NSW, Australia. The results showed that there were significant effects of canola genotypes and of genotypes by crop density interaction on weed growth. Among the tested genotypes, PAK85388-502 and AV-OPAL were the most weed suppressive and, at a plant density of 10 plants/m2, they reduced the weed biomass of wild radish, shepherd's purse, and annual ryegrass by more than 80%. No significant differences were found in the primary root lengths among canola varieties; however, plants of the most weed-suppressive genotype PAK8538-502 exhibited a 35% increase in lateral root number relative to plants of the less weed-suppressive genotype BAROSSA. The analysis of variance revealed a significant influence of genotypes with PAK85388-502 and AV-OPAL performing the best across all the research sites. Results showed that canola genotypes PAK85388-502 and AV-OPAL were more weed suppressive than AV-GARNET and BAROSSA and may release specific bioactive compounds in their surroundings to suppress neighboring weeds. This study provides valuable information that could be utilised in breeding programs to select weed-suppressive varieties of canola in Australia. Thus, lateral root number could be a potential target trait for weed-suppressive varieties. Additionally, other root architecture traits may contribute to the underground allelopathic interaction to provide a competitive advantage to the crop. [ABSTRACT FROM AUTHOR]

Plants resist the invasion of plant-parasitic nematodes (PPNs) by releasing root chemical substances, activating immune responses, and utilizing plant resistance (R) genes. A balance of interaction is formed between plants and PPNs, including multilayer communications and signal exchanges. The signal network involved in plant–nematode competition includes attraction and repellency of root exudates, perception of nematode-associated signals, activation of plant signals, interference of PPNs with plant defense, and interplay of plant systemic signals. Plant-parasitic nematodes (PPNs) are widely distributed and highly adaptable. To evade the invasion and infection of PPNs, plants initiate a series of defense responses. In turn, PPNs secrete effectors into the host tissues to suppress plant defense. In this ongoing battle between PPNs and plants, complex signal transduction processes are typically involved. This article aims to review the plant signaling network involved in host perception by the nematode, nematode perception, and downstream activation of plant defense signaling and how nematodes attempt to interfere with this network. Our goal is to establish a foundation for elucidating the signaling and regulatory mechanisms of plant–nematode interactions, and to provide insights and tools for developing PPN-resistant crops and technologies. [ABSTRACT FROM AUTHOR]

Hydroponic cultivation is an efficient, resource-saving technology that produces high yields of high-quality products per unit area without soil. While this technology can save water and fertilisers, water recirculation increases the accumulation of root exudates known to be toxic to the plant, causing growth inhibition. The usage of bioelectrochemical systems (BESs) is well-documented for wastewater treatment, desalination, contamination remediation, bioelectricity generation, etc. In this review we explore the issues associated with the usage of traditional approaches in detecting and removing the phytotoxic substances exudated from plant roots. Furthermore, we investigate the prospects of deploying BESs in hydroponic systems and highlight potential benefits and challenges. The application, feasibility and scalability of BES-hydroponic systems, as well as the possibility of integration with other technologies are all critically discussed. It is concluded that the use of BESs for hydroponic wastewater treatment and for real-time plant growth monitoring represents a novel and valuable strategy. This approach has the potential to overcome limitations of the existing treatment methods and contribute to the advancement of sustainable agriculture. [ABSTRACT FROM AUTHOR]

Investigating the quantity and spatiotemporal dynamics of metabolite release from plant roots is essential if we are to understand the ecological significance of root exudates in the rhizosphere; however, this is difficult to quantify. In the present study, we quantified in situ root exudation rates during three incubation periods (0-24, 24-48, and 48-72 h) and fine roots within four diameter ranges (<0.8, 0.8-1.0, 1.0-1.2, and 1.2-2.0 mm), and also measured nine morphological traits in the fine roots of Pinus massoniana. Higher root carbon (C) exudation rates were detected during the 0-24 h period. During the 0-24 h and 24-48 h periods, nitrogen (N) uptake rates were higher than N exudation rates, while during the 48-72 h period, N exudation rates exceeded uptake rates. As C exudation increased during 0-48h incubation period, the uptake of N tended to level out. We concluded that the 24-48 h incubation period was the most suitable for capturing root exudates from P. massoniana. The exudation of C from the roots was positively associated with root mass, length, surface area, volume, the number of root tips, and the root tissue density, when incubated for 0-24 h and 24-48 h. Furthermore, length-specific C exudation rates, along with N exudation and uptake rates, all increased as the diameter of the fine roots increased. The release of root exudates could be efficiently predicted by the fine root morphological traits, although the accuracy of prediction depended on the incubation period. Higher values for fine root morphological traits were generally indicative of higher nutrient requirements and tissue investment, as well as higher C exudation rates. [ABSTRACT FROM AUTHOR]

Background: Sugarcane red rot is a soil-borne disease caused by Colletotrichum falcatum. It can reduce the yield of sugarcane and the purity of sugarcane juice, which seriously restricts the development of sucrose industry. Biocontrol bacteria can control diseases by regulating rhizosphere microecology. In this study, the effects of biocontrol bacteria on sugarcane rhizosphere microecology were studied by metagenomics and metabolomics, and the control effects of biocontrol bacteria and rhizosphere dominant bacteria on sugarcane red rot were further explored by pot experiment. Results: The results of metagenomic sequencing showed that inoculation with B. velezensis YC89 and pathogens could significantly change the microbial diversity of the sugarcane rhizosphere. The relative abundance of beneficial strains such as Streptomyces, Burkholderia, Sphingomonas, and Rhizobium increased significantly in the rhizosphere of sugarcane in the YC treatment group. Pseudomonas was significantly enriched in the rhizosphere of sugarcane in the C treatment group. The results of metabolome sequencing showed that the content of amino acids in sugarcane root exudates increased after inoculation with B. velezensis YC89, and the contents of phenolic acids and flavonoids decreased. Spearman correlation analysis showed that there was a significant correlation between differential metabolites and rhizosphere microorganisms. The results of pot experiment showed that YC89 strain and three rhizosphere microorganisms could significantly reduce the disease index of red rot and promote the growth of sugarcane plants. In addition, these strains can also significantly increase the JA and SA content of sugarcane leaves and induce plant system resistance-related enzyme activities. Among them, the synthetic community treatment group had the best biocontrol effect on red rot, and its relative control effect was 67.50%. Conclusions: Therefore, we conclude that B. velezensis YC89 could recruit beneficial rhizosphere microorganisms to enrich the rhizosphere and change the content of some phenolic acids and flavonoids in the root exudates. In addition, the isolated rhizosphere dominant bacteria and YC89 strain can resist red rot by inducing plant systemic resistance and promote the growth of sugarcane plants. This study provides a theoretical basis for the use of biocontrol bacteria to regulate rhizosphere bacteria to jointly control plant soil-borne diseases. [ABSTRACT FROM AUTHOR]

The functioning of living organisms in nature is possible only due to active interaction with microbiota. It is typical for phytobionts, the microbial cenosis of which is even more diverse. Plants contribute to the spread of microorganisms in the rhizosphere by releasing root exudates. The chemical composition of these exudates varies in different plant species and depends on the significant number of factors that affect their growth and development. The components of the plant root exudates stimulate expansion in the rhizosphere of microorganisms, useful for the plant growth. This microbiota improves the mineral life of plants considerably, stimulating their growth with biologically active compounds, increasing the availability of a number of microelements for them, protecting the growth of plants from phytopathogens and phytophages. It provides significant stimulation for the growth and development of phytobionts. It has been shown that microbial groups in the rhizosphere can induce some changes in the composition of plant root exudates. [ABSTRACT FROM AUTHOR]

Chemical signals are crucial in mediating ecological and evolutionary adaptation of plants to their environments. Indeed, invasive plants may produce greater amounts of chemical metabolites in their new ranges. Some of these chemicals can enhance their mutualistic interactions and improve invasive plant performance, but genetic mechanisms of such adaptations are unexplored.We used Triadica sebifera plants as a model to investigate evolutionary changes in chemical signals that enhance arbuscular mycorrhizal (AM) fungal associations. Previous studies found that T. sebifera plants from invasive populations had higher root exudate concentrations of the flavonoid quercetin and elevated AM fungal colonization compared with those from native populations. Here, we explored genetic variation in strigolactone concentrations in root exudates and their contribution to AM fungal colonization with strigolactone analogue GR24 additions. In addition, we studied how gene expression patterns related to flavonoid and strigolactone biosynthesis varied among invasive and native populations using comparative genomics, transcriptomics and fluorescent real‐time quantitative PCR.We found that plants from invasive populations had higher concentrations of the strigolactone 5‐deoxystrigol in root exudates that were correlated with higher AM fungal colonization rates, relative to those from native populations. Exogenous applications of GR24, a synthetic analogue of 5‐deoxystrigol, increased AM fungal colonization. We found higher expression of a single gene in flavonoid (FLS) and strigolactone (DAD1) biosynthesis pathways increased levels of quercetin and 5‐deoxystrigol in plants from invasive populations, respectively.Synthesis. Understanding the role of genetic evolution in enhancing mutualisms of invasive plants provides new insights into the underlying mechanisms of plant invasion. This study suggests that an invasive plant enhanced its mutualisms by upregulating the expression of key genes related to secondary metabolites in root exudates which stimulate symbiotic relationships with AM fungi. Thus, these findings provide insights into genetic mechanisms that underlie higher AM fungal colonization and enhanced invasive plant performance. [ABSTRACT FROM AUTHOR]

Earthworms benefit plant growth and play a vital role in shaping soil microbial communities. However, how earthworms modify the soil microorganisms and thus affect plant growth is still unclear. Although fertilizers alter the assembly of microbial communities, further investigations are required to test the effect of fertilizer type on the relationship between earthworms, soil microbial communities and plants.We evaluated the role of earthworms in soil microorganisms and maize plant growth characteristics under organic or chemical fertilizers in field and greenhouse experiments. We explored the relationships between earthworms, soil microbial community and plant growth under different fertilizer types.We found that the presence of earthworms promoted plant growth, increased the amount of plant root exudates, and enhanced the connections between rhizosphere bacterial, fungal and protist communities. Both earthworms and fertilizer application significantly changed the structure of soil bacterial, fungal and protist communities. The complexity of the soil microbial community network increased under organic, compared to chemical fertilizer application. The greenhouse experiment showed that the effect of earthworms on plant growth was weakened when maize plants were grown in sterilized soil under organic or chemical fertilizers.Synthesis and applications: Our study provides solid evidence that earthworms largely depend on soil microorganisms for their effects on plants under the application of different fertilizer conditions. This may provide new insights into reducing the amounts of fertilizer used by enhancing the role of earthworms and soil microorganisms. [ABSTRACT FROM AUTHOR]

Lanthanides and actinides are emerging contaminants, but little is known about their uptake and distribution by plants and their interactions in the rhizosphere. To better understand the fate of these metals in plants, the bioassociation of 2, 20 and 200 µM Eu(III) by five hydroponically grown crops endemic to Europe was assessed. The metal's concentration and its speciation were monitored by inductively coupled plasma mass spectrometry and laser spectroscopy, whereas root exudation was investigated by chromatographic methods. It has been shown, that Eu(III) bioassociation is a two-stage process, involving rapid biosorption followed by accumulation in root tissue and distribution to the stem and leaves. Within 96 h of exposure time, the plant induces a change of Eu(III) speciation in the liquid medium, from a predominant Eu(III)aquo species, as calculated by thermodynamic modelling, to a species with longer luminescence lifetime. Root exudates such as citric, malic, and fumaric acid were identified in the cultivation medium and affect Eu(III) speciation in solution, as was shown by a change in the thermodynamic model. These results contribute to a comprehensive understanding of the fate of lanthanides in the biosphere and provide a basis for further investigations with the chemical analogues Cm(III) and Am(III). [ABSTRACT FROM AUTHOR]

Background: Elucidating the intricate structural organization and spatial gradients of biomolecular composition within the rhizosphere is critical to understanding important biogeochemical processes, which include the mechanisms of root-microbe interactions for maintaining sustainable plant ecosystem services. While various analytical methods have been developed to assess the spatial heterogeneity within the rhizosphere, a comprehensive view of the fine distribution of metabolites within the root-soil interface has remained a significant challenge. This is primarily due to the difficulty of maintaining the original spatial organization during sample preparation without compromising its molecular content. Results: In this study, we present a novel approach, RhizoMAP, in which the rhizosphere molecules are imprinted on selected polymer membranes and then spatially profiled using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI). We enhanced the performance of RhizoMAP by combining the use of two thin (< 20 μm) membranes (polyester and polycarbonate) with distinct MALDI sample preparations. This optimization allowed us to gain insight into the distribution of over 500 different molecules within the rhizosphere of poplar (Populus trichocarpa) grown in rhizoboxes filled with mycorrhizae soil. These two membranes, coupled with three different sample preparation conditions, enabled us to capture the distribution of a wide variety of molecules that included phytohormones, amino acids, sugars, sugar glycosides, polycarboxylic acids components of the Krebs cycle, fatty acids, short aldehydes and ketones, terpenes, volatile organic compounds, fertilizers from the soil, and others. Their spatial distribution varies greatly, with some following root traces, others showing diffusion from roots, some associated with soil particles, and many having distinct hot spots along the plant root or surrounding soil. Moreover, we showed how RhizoMAP can be used to localize the origin of the molecules and molecular transformation during root growth. Finally, we demonstrated the power of RhizoMAP to capture molecular distributions of key metabolites throughout a 20 cm deep rhizosphere. Conclusions: RhizoMAP is a method that provides nondestructive, untargeted, broad, and sensitive metabolite imaging of root-associated molecules, exudates, and soil organic matter throughout the rhizosphere, as demonstrated in a lab-controlled native soil environment. [ABSTRACT FROM AUTHOR]

Due to the widespread use of engineered nanomaterials (ENMs) for soil remediation and nano‐enabled sustainable agriculture, there is a growing concern regarding the behavior and fate of ENMs released into soil systems in the presence of natural root exudates (REs). Herein, we investigate the influence of REs on the fate and ecological effect of ENMs from a comprehensive perspective. We summarize the key roles reported in the literature for REs in physical changes (e.g., adsorption, dispersion/aggregation), chemical changes (e.g., oxidation/redox reactions, and dissolution), and biotransformation of ENMs, which will further determine the ecological risk of ENMs in natural soil systems. Moreover, this review highlights the potential adverse effects of ENMs on different soil organisms (e.g., bacteria, plants, and eisenia foetida) in the presence of REs. The remaining unclear mechanisms (e.g., oxidative stress and DNA damage) of ENMs toxicity at the cellular level influenced by REs are reviewed and presented. Finally, the review concludes by addressing the current knowledge gaps and challenges in this field. [ABSTRACT FROM AUTHOR]

The interactions between plants and rhizosphere microbes mediated by plant root exudates are increasingly being investigated. The root-derived metabolites of medicinal plants are relatively diverse and have unique characteristics. However, whether medicinal plants influence their rhizosphere microbial community remains unknown. How medicinal plant species drive rhizosphere microbial community changes should be clarified. In this study involving high-throughput sequencing of rhizosphere microbes and an analysis of root exudates using a gas chromatograph coupled with a time-of-flight mass spectrometer, we revealed that the root exudate metabolites and microorganisms differed among the rhizosphere soils of five medicinal plants. Moreover, the results of a correlation analysis indicated that bacterial and fungal profiles in the rhizosphere soils of the five medicinal plants were extremely significantly or significantly affected by 10 root-associated metabolites. Furthermore, among the 10 root exudate metabolites, two (carvone and zymosterol) had opposite effects on rhizosphere bacteria and fungi. Our study findings suggest that plant-derived exudates modulate changes to rhizosphere microbial communities. [ABSTRACT FROM AUTHOR]

Introduction: The importance of plant rhizodeposition to sustain microbial growth and induce xenobiotic degradation in polluted environments is increasingly recognized. Methods: Here the "cry-for-help" hypothesis, consisting in root chemistry remodeling upon stress, was investigated in the presence of polychlorinated biphenyls (PCBs), highly recalcitrant and phytotoxic compounds, highlighting its role in reshaping the nutritional and signaling features of the root niche to accommodate PCB-degrading microorganisms. Results: Arabidopsis exposure to 70 µM PCB-18 triggered plant-detrimental effects, stress-related traits, and PCB-responsive gene expression, reproducing PCB phytotoxicity. The root exudates of plantlets exposed for 2 days to the pollutant were collected and characterized through untargeted metabolomics analysis by liquid chromatography-mass spectrometry. Principal component analysis disclosed a different root exudation fingerprint in PCB-18-exposed plants, potentially contributing to the "cry-for-help" event. To investigate this aspect, the five compounds identified in the exudate metabolomic analysis (i.e., scopoletin, N-hydroxyethyl-b-alanine, hypoxanthine, L-arginyl-L-valine, and Lseryl-L-phenylalanine) were assayed for their influence on the physiology and functionality of the PCB-degrading strains Pseudomonas alcaliphila JAB1, Paraburkholderia xenovorans LB400, and Acinetobacter calcoaceticus P320. Scopoletin, whose relative abundance decreased in PCB-18-stressed plant exudates, hampered the growth and proliferation of strains JAB1 and P320, presumably due to its antimicrobial activity, and reduced the beneficial effect of Acinetobacter P320, which showed a higher degree of growth promotion in the scopoletin-depleted mutant f6'h1 compared to Arabidopsis WT plants exposed to PCB. Nevertheless, scopoletin induced the expression of the bph catabolic operon in strains JAB1 and LB400. The primary metabolites hypoxanthine, Larginyl-L-valine, and L-seryl-L-phenylalanine, which increased in relative abundance upon PCB-18 stress, were preferentially used as nutrients and growth-stimulating factors by the three degrading strains and showed a variable ability to affect rhizocompetence traits like motility and biofilm formation. Discussion: These findings expand the knowledge on PCB-triggered "cry-forhelp" and its role in steering the PCB-degrading microbiome to boost the holobiont fitness in polluted environments. [ABSTRACT FROM AUTHOR]

Rhizodeposition fuels carbon (C) and nutrient cycling in soil. However, changes in the dynamics of microbial growth on rhizodeposits with increasing distance from the root is not well studied. This study investigates microbial growth on individual organic components of rhizodeposits and maize root‐derived exudates and mucilage from agricultural soil. By creating a gradient of substrate concentrations, we simulated reduced microbial access to rhizosphere C with increasing distance to the root surface. We identified distinct C‐thresholds for the activation of microbial growth, and these were significantly higher for rhizodeposits than singular, simple sugars. In addition, testing for stoichiometric constraints of microbial growth by supplementing nitrogen (N) and phosphorus (P) showed accelerated and increased microbial growth by activating a larger proportion of the microbial biomass. Early and late season exudates triggered significantly different microbial growth responses. The mineralization of early‐season exudates was induced at a high C‐threshold. In contrast, the mineralization of late‐season exudates showed 'sugar‐like' properties, with a low C‐threshold, high substrate affinity, and a reduced maximum respiration rate of microorganisms growing on the added substrate. Mucilage exhibited the highest C‐threshold for the activation of microbial growth, although with a short lag‐period and with an efficient mucilage degradation comparable to that of sugars. By determining kinetic parameters and turnover times for different root‐derived substrates, our data enable the upscaling of micro‐scale processes to the whole root system, allowing more accurate predictions of how rhizodeposition drives microbial C and nutrient dynamics in the soil. [ABSTRACT FROM AUTHOR]

The obstacle associated with continuous cropping is an important problem in the production of muskmelon (Cucumis melo L.). The allelochemicals from root exudates play an active role in root–microbe communication. The primary objective of this study was to delve into the impact of root exudates and the continuous cultivation of muskmelon on the growth and colonization patterns of Trichoderma viride T23. It was observed that the root exudates of muskmelon significantly promoted mycelial growth and the sporulation of Trichoderma viride T23 at concentrations of 0.05, 0.1 g·mL−1, while at a concentration of 0.05 g·mL−1, the enzyme activities of β-glucosidase, chitinase and cellulase were 12.34, 13.23, and 17.85 U·mL−1, respectively, which were higher than those of the control. With increasing concentrations of root exudates, the hyphal growth, spore germination, and the three enzyme activities of Trichoderma viride T23 were decreased. The findings from the pot experiments revealed that the total phenolic acid content in the soil of replanted muskmelon demonstrated a trend of escalating over the course of the first growth cycle of continuous cropping to the fourth growth cycle of continuous cropping. The population density in the rhizosphere soil of Trichoderma viride T23 in the first growth cycle and the second growth cycle of continuous cropping shows a significant difference compared with other treatments, which led to statistically significant increments of stem diameter, leaf area, fresh weight, dry weight and SPAD index. It is necessary to increase the dose of the beneficial microorganism or degrade the phenolics in the rhizosphere soil to promote effectiveness while increasing the growth cycles of continuous cropping. [ABSTRACT FROM AUTHOR]

Background and aims: Ensuring adequate and balanced nutrient supply is crucial for enhancing citrus fruit quality. Some plants could modulate nutrient bioavailability in soil through the enhancement of root exudation. The study aimed to reveal how citrus change its root exudates metabolism profile to adapt to the soil with secondary nutrients and micronutrients deficiency. Methods: Citrus sinensis Osbeck cv. Newhall ×Poncirus trifoliate (L.) Raf grown in Ganzhou citrus orchards was used to evaluate the effect of soil applied and foliar sprayed secondary nutrients and micronutrients (Ca, Mg, B, Fe, Zn, Se) on the mineral elements concentration, external and intrinsic quality of citrus. The hydroponic experiment was conducted with Poncirus trifoliate (L.) Raf grown either in full nutrient solutions or in specific nutrient shortage conditions (Ca, Mg, B) for 45 days to obtain root exudate and perform untargeted metabolomic analysis (UHPLC-MS/MS). Results: Adequate supplementation of secondary nutrients and micronutrients effectively enhanced the nutritional value and intrinsic quality (TSS/TA) of citrus. 791 features were identified in citrus root exudates. Some metabolites was identified as root exudates for the first time, such as hecogenin, bergaptol and limonin. In the absence of secondary nutrients and micronutrients, citrus roots will secrete more substances related to plant disease resistance, nutrient acquisition and plant-microbial interactions, such as resveratrol, cinnamaldehyde, scopoletin, and phloretin. Conclusion: These findings highlight the value of secondary nutrients and micronutrients in regulating fruit quality and root exudates metabolism profile of citrus. It reveal the strategies of citrus to mitigate the nutrient deficiency in soils. [ABSTRACT FROM AUTHOR]