Root exudation under maize/soybean intercropping system mediates the arbuscular mycorrhizal fungi diversity and improves the plant growth.

Introduction: Maize/soybean intercropping is a common cropping practice in Chinese agriculture, known to boost crop yield and enhance soil fertility. However, the role of below-ground interactions, particularly root exudates, in maintaining intercropping advantages in soybean/maize intercropping systems remains unclear. Methods: This study aimed to investigate the differences in root exudates between intercropping and monocropping systems through two pot experiments using metabolomics methods. Multiple omics analyses were conducted to explore correlations between differential metabolites and the community of Arbuscular Mycorrhizal Fungi (AMF), shedding light on the mechanisms underlying the dominance of intercropping from the perspective of root exudates-soil microorganism interactions. Results and discussion: The study revealed that intercropping significantly increased the types and contents of root exudates, lowered soil pH, increased the availability of nutrients like available nitrogen (AN) and available phosphorus (AP), and enhanced AMF colonization, resulting in improving the community composition of AMF. Besides, root exudates in intercropping systems differed significantly from those in monocropping, with 41 and 39 differential metabolites identified in the root exudates of soybean/maize, predominantly amino acids and organic acids. The total amount of amino acids in the root exudates of soybean intercropping was 3.61 times higher than in monocropping. Additionally, the addition of root exudates significantly improved the growth of soybean/maize and AMF colonization, with the mycorrhizal colonization rate in intercropping increased by 105.99% and 111.18% compared to monocropping, respectively. The identified metabolic pathways associated with root exudates were closely linked to plant growth, soil fertility improvement, and the formation of AMF. Correlation analysis revealed a significant relationship (P < 0.05) between certain metabolites such as tartaric acid, oxalic acid, malic acid, aspartic acid, alanine, and the AMF community. Notably, the photosynthetic carbon fixation pathway involving aspartic acid showed a strong association with the function of Glomus_f_Glomerace, the dominant genus of AMF. A combined analysis of metabolomics and high throughput sequencing revealed that the root exudates of soybean/maize intercropping have direct or indirect connections with AMF and soil nutrients. Conclusion: This suggests that the increased root exudates of the soybean/maize intercropping system mediate an improvement in AMF community composition, thereby influencing soil fertility and maintaining the advantage of intercropping.

Rhizosphere Bacteria Help to Compensate for Pesticide-Induced Stress in Plants.

Although exogenous chemicals frequently exhibit a biphasic response in regulating plant growth, characterized by low-dose stimulation and high-dose inhibition, the underlying mechanisms remain elusive. This study demonstrates, for the first time, the compensatory function of rhizosphere microbiota in assisting plants to withstand pesticide stress. It was observed that pak choi plants, in response to foliar-spraying imidacloprid at both low and high doses, could increase the total number of rhizosphere bacteria and enrich numerous beneficial bacteria. These bacteria have capabilities for promoting plant growth and degrading the pesticide, such as Nocardioides, Brevundimonas, and Sphingomonas. The beneficial bacterial communities were recruited by stressed plants through increasing the release of primary metabolites in root exudates, such as amino acids, fatty acids, and lysophosphatidylcholines. At low doses of pesticide application, the microbial compensatory effect overcame pesticide stress, leading to plant growth promotion. However, with high doses of pesticide application, the microbial compensatory effect was insufficient to counteract pesticide stress, resulting in plant growth inhibition. These findings pave the way for designing improved pesticide application strategies and contribute to a better understanding of how rhizosphere microbiota can be used as an eco-friendly approach to mitigate chemical-induced stress in crops.

Effects of nitrogen application on ammonium assimilation and microenvironment in the rhizosphere of drip-irrigated sunflower under plastic mulch.

This study investigated the effect of nitrogen application on the rhizosphere soil microenvironment of sunflower and clarified the relationship between ammonium assimilation and the microenvironment. In a field experiment high (HN, 190 kg/hm2), medium (MN, 120 kg/hm2) and low nitrogen (CK, 50 kg/hm2) treatments were made to replicate plots of sunflowers using drip irrigation. Metagenomic sequencing was used to analyze the community structure and functional genes involved in the ammonium assimilation pathway in rhizosphere soil. The findings indicated that glnA and gltB played a crucial role in the ammonium assimilation pathway in sunflower rhizosphere soil, with Actinobacteria and Proteobacteria being the primary contributors. Compared with CK treatment, the relative abundance of Actinobacteria increased by 15.57% under MN treatment, while the relative abundance decreased at flowering and maturation stages. Conversely, the relative abundance of Proteobacteria was 28.57 and 61.26% higher in the MN treatment during anthesis and maturation period, respectively, compared with the CK. Furthermore, during the bud stage and anthesis, the abundance of Actinobacteria, Proteobacteria, and their dominant species were influenced mainly by rhizosphere soil EC, ammonium nitrogen (NH4+-N), and nitrate nitrogen (NO3--N), whereas, at maturity, soil pH and NO3--N played a more significant role in shaping the community of ammonium-assimilating microorganisms. The MN treatment increased the root length density, surface area density, and root volume density of sunflower at the bud, flowering, and maturity stages compared to the CK. Moreover, root exudates such as oxalate and malate were positively correlated with the dominant species of Actinobacteria and Proteobacteria during anthesis and the maturation period. Under drip irrigation, applying 120 kg/hm2 of nitrogen to sunflowers effectively promoted the community structure of ammonium-assimilating microorganisms in rhizosphere soil and had a positive influence on the rhizosphere soil microenvironment and sunflower root growth.

Arbuscular mycorrhizal fungi by inducing watermelon roots secretion phthalates, altering soil enzyme activity and bacterial community composition to alleviate the watermelon wilt.

BACKGROUND: Long-term continuous cropping has resulted in the frequent occurrence of fusarium wilt of watermelon (Citrullus lanatus). AMF inoculation can alleviate the continuous cropping barrier and reduce the incidence of fusarium wilt of watermelon. Our previous study found that the root exudates of mycorrhizal watermelon can enhance watermelon resistance to this disorder. It is necessary to further isolate and identify the specific compounds in root exudates of mycorrhizal watermelon and explore their control effects on fusarium wilt of continuous cropping watermelon. RESULT: The results of this study showed that the root system of watermelon seedlings inoculated with AMF (Funneliformis mosseae or Glomus versiforme) secreted diisooctyl phthalate (A) and dibutyl phthalate (B). Compared with water treatment, treatment with 0.1 ml/L (A1, B1), 0.5 ml/L (A2, B2) and 1 ml/L (A3, B3) of A or B significantly increased soil enzyme activities, the numbers of bacteria and actinomycetes, and the bacteria/fungi ratio in the rhizosphere. Furthermore, the Disease indexes (DI) of A1 and B3 were 25% and 20%, respectively, while the prevention and control effects (PCE) were 68.8% and 75%, respectively. In addition, diisooctyl phthalate or dibutyl phthalate increased the proportions of Gemmatimonadetes, Chloroflexi, and Acidobacteria in the rhizosphere of continuous cropping watermelon, and decreased the proportions of Proteobacteria and Firmicutes, with Novosphingobium, Kaistobacter, Bacillus, and Acinetobacter as the predominant bacteria. Compared with the water treatment, the abundance of Neosphingosaceae, Kateybacterium and Bacillus in the A1 group was increased by 7.33, 2.14 and 2.18 times, respectively, while that in the B2 group was increased by 60.05%, 80.24% and 1 time, respectively. In addition, exogenous diisooctyl phthalate and dibutyl phthalate were shown to promote growth parameters (vine length, stem diameter, fresh weight and dry weight) and antioxidant enzyme system activities (SOD, POD and CAT) of continuous cropping watermelon. CONCLUSION: Lower watermelon fusarium wilt incidence in mycorrhizal watermelons was associated with phthalate secretion in watermelons after AMF inoculation. Exogenous diisooctyl phthalate and dibutyl phthalate could alleviate the continuous cropping disorder of watermelon, reduce the incidence of fusarium wilt, and promote the growth of watermelon by increasing the enzyme activities and the proportion of beneficial bacteria in rhizosphere soil. In addition, the low concentration of phthalate diisooctyl and high concentration of phthalic acid dibutyl works best. Therefore, a certain concentration of phthalates in the soil can help alleviate continuous cropping obstacles.

Arsenic stress triggers active exudation of arsenic-phytochelatin complexes from Lupinus albus roots.

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.

Exploring glycine root uptake dynamics in phosphorus and iron deficient tomato plants during the initial stages of plant development.

BACKGROUND: Phosphorus (P) and iron (Fe) deficiencies are relevant plants nutritional disorders, prompting responses such as increased root exudation to aid nutrient uptake, albeit at an energy cost. Reacquiring and reusing exudates could represent an efficient energy and nitrogen saving strategy. Hence, we investigated the impact of plant development, Fe and P deficiencies on this process. Tomato seedlings were grown hydroponically for 3 weeks in Control, -Fe, and -P conditions and sampled twice a week. We used Isotope Ratio Mass-Spectrometry to measure δ13C in roots and shoots after a 2-h exposure to 13C-labeled glycine (0, 50, or 500 µmol L-1). Plant physiology was assessed with an InfraRed Gas Analyzer and ionome with an Inductively Coupled Plasma Mass-Spectrometry. RESULTS: Glycine uptake varied with concentration, suggesting an involvement of root transporters with different substrate affinities. The uptake decreased over time, with -Fe and -P showing significantly higher values as compared to the Control. This highlights its importance during germination and in nutrient-deficient plants. Translocation to shoots declined over time in -P and Control but increased in -Fe plants, suggesting a role of Gly in the Fe xylem transport. CONCLUSIONS: Root exudates, i.e. glycine, acquisition and their subsequent shoot translocation depend on Fe and P deficiency. The present findings highlight the importance of this adaptation to nutrient deficiencies, that can potentially enhance plants fitness. A thorough comprehension of this trait holds potential significance for selecting cultivars that can better withstand abiotic stresses.

Understanding the dynamic interactions of root-knot nematodes and their host: role of plant growth promoting bacteria and abiotic factors.

Root-knot nematodes (Meloidogyne spp., RKN) are among the most destructive endoparasitic nematodes worldwide, often leading to a reduction of crop growth and yield. Insights into the dynamics of host-RKN interactions, especially in varied biotic and abiotic environments, could be pivotal in devising novel RKN mitigation measures. Plant growth-promoting bacteria (PGPB) involves different plant growth-enhancing activities such as biofertilization, pathogen suppression, and induction of systemic resistance. We summarized the up-to-date knowledge on the role of PGPB and abiotic factors such as soil pH, texture, structure, moisture, etc. in modulating RKN-host interactions. RKN are directly or indirectly affected by different PGPB, abiotic factors interplay in the interactions, and host responses to RKN infection. We highlighted the tripartite (host-RKN-PGPB) phenomenon with respect to (i) PGPB direct and indirect effect on RKN-host interactions; (ii) host influence in the selection and enrichment of PGPB in the rhizosphere; (iii) how soil microbes enhance RKN parasitism; (iv) influence of host in RKN-PGPB interactions, and (v) the role of abiotic factors in modulating the tripartite interactions. Furthermore, we discussed how different agricultural practices alter the interactions. Finally, we emphasized the importance of incorporating the knowledge of tripartite interactions in the integrated RKN management strategies.

Cadmium phytoremediation potential of Houttuynia cordata: Insights from growth, uptake, and rhizosphere mechanisms.

Cadmium (Cd) pollutes 7.0 % of China's land area. This study examined the potential of Houttuynia cordata for Cd phytoremediation because of its ability to accumulate Cd in its growth matrix. H. cordata were planted in plastic pots filled with paddy field soils having low (LCd), medium (MCd), and high (HCd) Cd levels of 0.19, 0.69, and 2.91 mg/kg, respectively. After six months of growth, harvested plant parts were evaluated for Cd uptake and tolerance mechanisms. Metabolomics and metagenomics approaches were employed to investigate the soil rhizosphere mechanism. Results showed that the average plant biomass increased as soil Cd increased. The biomass Cd contents surpassed the allowable Cd limits for food (≤ 0.2 mg/kg) and medicinal uses (≤ 0.3 mg/kg). Cd contents were higher in H. cordata roots (30.59-86.27 mg/kg) than in other plant parts (0.63-2.90 mg/kg), with significantly increasing values as Cd soil level increased. Phenolic acids, lipids, amino acids and derivatives, organic acids, and alkaloids comprised the majority (69 in MCd vs HCd and 73 % in LCd vs HCd) of the shared upregulated metabolites. In addition, 13 metabolites specific to H. cordata root exudates were significantly increased. The top two principal metabolic pathways were arginine and proline metabolism, and beta-alanine metabolism. H. cordata increased the abundance of Firmicutes and Glomeromycota across all three Cd levels, and also stimulated the growth of Patescibacteria, Rozellomycota, and Claroideoglomus in HCd. Accordingly, H. cordata demonstrated potential for remediation of Cd-contaminated soils, and safety measures for its production and food use must be highly considered.

Driving Role of Zinc Oxide Nanoparticles with Different Sizes and Hydrophobicity in Metabolic Response and Eco-Corona Formation in Sprouts (Vigna radiata).

Zinc oxide nanoparticles (ZnO NPs) cause biotoxicity and pose a potential ecological threat; however, their effects on plant metabolism and eco-corona evolution between NPs and organisms remain unclear. This study clarified the molecular mechanisms underlying physiological and metabolic responses induced by three different ZnO NPs with different sizes and hydrophobicity in sprouts (Vigna radiata) and explored the critical regulation of eco-corona formation in root-nano systems. Results indicated that smaller-sized ZnO inhibited root elongation by up to 37.14% and triggered oxidative burst and apoptosis. Metabolomics confirmed that physiological maintenance after n-ZnO exposure was mainly attributed to the effective stabilization of nitrogen fixation and defense systems by biotransformation of the flavonoid pathway. Larger-sized or hydrophobic group-modified ZnO exhibited low toxicity in sprouts, with 0.89-fold upregulation of citrate in central carbon metabolism. This contributed to providing energy for resistance to NP stress through amino acid and carbon/nitrogen metabolism, accompanied by changes in membrane properties. Notably, smaller-sized and hydrophobic NPs intensely stimulated the release of root metabolites, forming corona complexes with exudates. The hydrogen-bonded wrapping mechanism in protein secondary structure and hydrophobic interactions of heterogeneous functional groups drove eco-corona formation, along with the corona evolution intensity of n-ZnO > s-ZnO > b-ZnO based on higher (α-helix + 3-turn helix)/ß-sheet ratios. This study provides crucial insight into metabolic and eco-corona evolution in bionano fates.

Root-secreted nucleosides: signaling chemoattractants of rhizosphere bacteria.

The rhizosphere is a complex ecosystem, consisting of a narrow soil zone influenced by plant roots and inhabited by soil-borne microorganisms. Plants actively shape the rhizosphere microbiome through root exudates. Some metabolites are signaling molecules specifically functioning as chemoattractants rather than nutrients. These elusive signaling molecules have been sought for several decades, and yet little progress has been made. Root-secreted nucleosides and deoxynucleosides were detected in exudates of various plants by targeted ultra-performance liquid chromatography-mass spectrometry/mass spectrometry. Rhizobacteria were isolated from the roots of Helianthemum sessiliflorum carrying the mycorrhizal desert truffle Terfezia boudieri. Chemotaxis was determined by a glass capillary assay or plate assays on semisolid agar and through a soil plate assay. Nucleosides were identified in root exudates of plants that inhabit diverse ecological niches. Nucleosides induced positive chemotaxis in plant beneficial bacteria Bacillus pumilus, Bacillus subtilis, Pseudomonas turukhanskensis spp., Serratia marcescens, and the pathogenic rhizobacterium Xanthomonas campestris and E coli. In a soil plate assay, nucleosides diffused to substantial distances and evoked chemotaxis under conditions as close as possible to natural environments. This study implies that root-secreted nucleosides are involved in the assembly of the rhizosphere bacterial community by inducing chemotaxis toward plant roots. In animals, nucleoside secretion known as "purinergic signaling" is involved in communication between cells, physiological processes, diseases, phagocytic cell migration, and bacterial activity. The coliform bacterium E. coli that inhabits the lower intestine of warm-blooded organisms also attracted to nucleosides, implying that nucleosides may serve as a common signal for bacterial species inhabiting distinct habitats. Taken together, all these may indicate that chemotaxis signaling by nucleosides is a conserved universal mechanism that encompasses living kingdoms and environments and should be given further attention in plant rhizosphere microbiome research.

Unraveling the mechanism of interaction: accelerated phenanthrene degradation and rhizosphere biofilm/iron plaque formation influenced by phenolic root exudates.

Phenolic root exudates (PREs) secreted by wetland plants facilitate the accumulation of iron in the rhizosphere, potentially providing the essential active iron required for the generation of enzymes that degrade polycyclic aromatic hydrocarbon, thereby enhancing their biodegradation. However, the underlying mechanisms involved are yet to be elucidated. This study focuses on phenanthrene (PHE), a typical polycyclic aromatic hydrocarbon pollutant, utilizing representative PREs from wetland plants, including p-hydroxybenzoic, p-coumaric, caffeic, and ferulic acids. Using hydroponic experiments, 16S rRNA sequencing, and multiple characterization techniques, we aimed to elucidate the interaction mechanism between the accelerated degradation of PHE and the formation of rhizosphere biofilm/iron plaque influenced by PREs. Although all four types of PREs altered the biofilm composition and promoted the formation of iron plaque on the root surface, only caffeic acid, possessing a similar structure to the intermediate metabolite of PHE (catechol), could accelerate the PHE degradation rate. Caffeic acid, notable for its catechol structure, plays a significant role in enhancing PHE degradation through two main mechanisms: (a) it directly boosts PHE co-metabolism by fostering the growth of PHE-degrading bacteria, specifically Burkholderiaceae, and by facilitating the production of the key metabolic enzyme catechol 1,2-dioxygenase (C12O) and (b) it indirectly supports PHE biodegradation by promoting iron plaque formation on root surfaces, thereby enriching free iron for efficient microbial synthesis of C12O, a crucial factor in PHE decomposition.

Common mycorrhizal network: the predominant socialist and capitalist responses of possible plant-plant and plant-microbe interactions for sustainable agriculture.

Plants engage in a variety of interactions, including sharing nutrients through common mycorrhizal networks (CMNs), which are facilitated by arbuscular mycorrhizal fungi (AMF). These networks can promote the establishment, growth, and distribution of limited nutrients that are important for plant growth, which in turn benefits the entire network of plants. Interactions between plants and microbes in the rhizosphere are complex and can either be socialist or capitalist in nature, and the knowledge of these interactions is equally important for the progress of sustainable agricultural practice. In the socialist network, resources are distributed more evenly, providing benefits for all connected plants, such as symbiosis. For example, direct or indirect transfer of nutrients to plants, direct stimulation of growth through phytohormones, antagonism toward pathogenic microorganisms, and mitigation of stresses. For the capitalist network, AMF would be privately controlled for the profit of certain groups of plants, hence increasing competition between connected plants. Such plant interactions invading by microbes act as saprophytic and cause necrotrophy in the colonizing plants. In the first case, an excess of the nutritional resources may be donated to the receiver plants by direct transfer. In the second case, an unequal distribution of resources occurs, which certainly favor individual groups and increases competition between interactions. This largely depends on which of these responses is predominant ("socialist" or "capitalist") at the moment plants are connected. Therefore, some plant species might benefit from CMNs more than others, depending on the fungal species and plant species involved in the association. Nevertheless, benefits and disadvantages from the interactions between the connected plants are hard to distinguish in nature once most of the plants are colonized simultaneously by multiple fungal species, each with its own cost-benefits. Classifying plant-microbe interactions based on their habitat specificity, such as their presence on leaf surfaces (phyllospheric), within plant tissues (endophytic), on root surfaces (rhizospheric), or as surface-dwelling organisms (epiphytic), helps to highlight the dense and intricate connections between plants and microbes that occur both above and below ground. In these complex relationships, microbes often engage in mutualistic interactions where both parties derive mutual benefits, exemplifying the socialistic or capitalistic nature of these interactions. This review discusses the ubiquity, functioning, and management interventions of different types of plant-plant and plant-microbe interactions in CMNs, and how they promote plant growth and address environmental challenges for sustainable agriculture.

Mechanistic and future prospects in rhizospheric engineering for agricultural contaminants removal, soil health restoration, and management of climate change stress.

Climate change, food insecurity, and agricultural pollution are all serious challenges in the twenty-first century, impacting plant growth, soil quality, and food security. Innovative techniques are required to mitigate these negative outcomes. Toxic heavy metals (THMs), organic pollutants (OPs), and emerging contaminants (ECs), as well as other biotic and abiotic stressors, can all affect nutrient availability, plant metabolic pathways, agricultural productivity, and soil-fertility. Comprehending the interactions between root exudates, microorganisms, and modified biochar can aid in the fight against environmental problems such as the accumulation of pollutants and the stressful effects of climate change. Microbes can inhibit THMs uptake, degrade organic pollutants, releases biomolecules that regulate crop development under drought, salinity, pathogenic attack and other stresses. However, these microbial abilities are primarily demonstrated in research facilities rather than in contaminated or stressed habitats. Despite not being a perfect solution, biochar can remove THMs, OPs, and ECs from contaminated areas and reduce the impact of climate change on plants. We hypothesized that combining microorganisms with biochar to address the problems of contaminated soil and climate change stress would be effective in the field. Despite the fact that root exudates have the potential to attract selected microorganisms and biochar, there has been little attention paid to these areas, considering that this work addresses a critical knowledge gap of rhizospheric engineering mediated root exudates to foster microbial and biochar adaptation. Reducing the detrimental impacts of THMs, OPs, ECs, as well as abiotic and biotic stress, requires identifying the best root-associated microbes and biochar adaptation mechanisms.

Rhizosphere metabolic cross-talk from plant-soil-microbe tapping into agricultural sustainability: Current advance and perspectives.

Rhizosphere interactions from plant-soil-microbiome occur dynamically all the time in the "black microzone" underground, where we can't see intuitively. Rhizosphere metabolites including root exudates and microbial metabolites act as various chemical signalings involving in rhizosphere interactions, and play vital roles on plant growth, development, disease suppression and resistance to stress conditions as well as proper soil health. Although rhizosphere metabolites are a mixture from plant roots and soil microbes, they often are discussed alone. As a rapid appearance of various omics platforms and analytical methods, it offers possibilities and opportunities for exploring rhizosphere interactions in unprecedented breadth and depth. However, our comprehensive understanding about the fine-tuning mechanisms of rhizosphere interactions mediated by these chemical compounds still remain clear. Thus, this review summarizes recent advances systemically including the features of rhizosphere metabolites and their effects on rhizosphere ecosystem, and looks forward to the future research perspectives, which contributes to facilitating better understanding of biochemical communications belowground and helping identify novel rhizosphere metabolites. We also address challenges for promoting the understanding about the roles of rhizosphere metabolites in different environmental stresses.

Mechanism of tartaric acid mediated dissipation and biotransformation of tetrabromobisphenol A and its derivatives in soil.

Biotransformation is a major dissipation process of tetrabromobisphenol A and its derivatives (TBBPAs) in soil. The biotransformation and ultimate environmental fate of TBBPAs have been widely studied, yet the effect of root exudates (especially low-molecular weight organic acids (LMWOAs)) on the fate of TBBPAs is poorly documented. Herein, the biotransformation behavior and mechanism of TBBPAs in bacteriome driven by LMWOAs were comprehensively investigated. Tartaric acid (TTA) was found to be the main component of LMWOAs in root exudates of Helianthus annus in the presence of TBBPAs, and was identified to play a key role in driving shaping bacteriome. TTA promoted shift of the dominant genus in soil bacteriome from Saccharibacteria_genera_incertae_sedis to Gemmatimonas, with a noteworthy increase of 24.90-34.65% in relative abundance of Gemmatimonas. A total of 28 conversion products were successfully identified, and ß-scission was the principal biotransformation pathway for TBBPAs. TTA facilitated the emergence of novel conversion products, including 2,4-dibromophenol, 3,5-dibromo-4-hydroxyacetophenone, para-hydroxyacetophenone, and tribromobisphenol A. These products were formed via oxidative skeletal cleavage and debromination pathways. Additionally, bisphenol A was observed during the conversion of derivatives. This study provides a comprehensive understanding about biotransformation of TBBPAs driven by TTA in soil bacteriome, offering new insights into LMWOAs-driven biotransformation mechanisms.

Hydrolysis of riboflavins in root exudates under iron deficiency and alkaline stress.

Riboflavins are secreted under iron deficiency as a part of the iron acquisition Strategy I, mainly when the external pH is acidic. In plants growing under Fe-deficiency and alkaline conditions, riboflavins have been reported to accumulate inside the roots, with very low or negligible secretion. However, the fact that riboflavins may undergo hydrolysis under alkaline conditions has been so far disregarded. In this paper, we report the presence of riboflavin derivatives and products of their alkaline hydrolysis (lumichrome, lumiflavin and carboxymethylflavin) in nutrient solutions of Cucumis sativus plants grown under different iron regimes (soluble Fe-EDDHA in the nutrient solution, total absence of iron in the nutrient solution, or two different doses of FeSO4 supplied as a foliar spray), either cultivated in slightly acidic (pH 6) or alkaline (pH 8.8, 10 mM bicarbonate) nutrient solutions. The results show that root synthesis and exudation of riboflavins is controlled by shoot iron status, and that exuded riboflavins undergo hydrolysis, especially at alkaline pH, with lumichrome being the main product of hydrolysis.

Increased risk of heavy metal accumulation in mangrove seedlings in coastal wetland environments due to microplastic inflow.

The recovery phase of mangrove seedlings in coastal wetland ecosystems can be negatively affected by exposure to external pollutants. This study aimed to investigate the impact of microplastics (MPs) influx, specifically polystyrene (PS) and polymethyl methacrylate (PMMA), on the growth of Aegiceras corniculatum seedlings and their accumulation of heavy metals (HMs). PS and PMMA significantly increased HMs accumulation (up to 21.0-548%), particularly in the roots of seedlings, compared to the control treatment (CK). Additionally, elevated activities of malondialdehyde and catalase enzymes were observed in the leaves of seedlings, while peroxidase enzyme activity decreased. Topological analysis of the root sediment microbiota coexistence network revealed that the modularization data increased from 0.69 (CK treatment) to 1.07 (PS treatment) and 5.11 (PMMA treatment) under the combined stress of MPs and HMs. This suggests that the introduction of MPs intensifies microbial modularization. The primary cause of increased HMs accumulation in plants is the MPs input, which influences the secretion of organic acids by plants and facilitates the shift of HMs in sediment to bioavailable states. Furthermore, changes in microbial clustering may also contribute to the elevated HMs accumulation in plants. This study provides valuable insights into the effects of external pollutants on mangrove seedlings and offers new perspectives for the preservation and restoration of mangrove coastal wetlands.

Impacts of continuous cropping on the rhizospheric and endospheric microbial communities and root exudates of Astragalus mongholicus.

Astragalus mongholicus is a medicinal plant that is known to decrease in quality in response to continuous cropping. However, the differences in the root-associated microbiome and root exudates in the rhizosphere soil that may lead to these decreases are barely under studies. We investigated the plant biomass production, root-associated microbiota, and root exudates of A. mongholicus grown in two different fields: virgin soil (Field I) and in a long-term continuous cropping field (Field II). Virgin soil is soil that has never been cultivated for A. mongholicus. Plant physiological measurements showed reduced fresh and dry weight of A. mongholicus under continuous cropping conditions (i.e. Field II). High-throughput sequencing of the fungal and bacterial communities revealed differences in fungal diversity between samples from the two fields, including enrichment of potentially pathogenic fungi in the roots of A. mongholicus grown in Field II. Metabolomic analysis yielded 20 compounds in A. mongholicus root exudates that differed in relative abundance between rhizosphere samples from the two fields. Four of these metabolites (2-aminophenol, quinic acid, tartaric acid, and maleamate) inhibited the growth of A. mongholicus, the soil-borne pathogen Fusarium oxysporum, or both. This comprehensive analysis enhances our understanding of the A. mongholicus microbiome, root exudates, and interactions between the two in response to continuous cropping. These results offer new information for future design of effective, economical approaches to achieving food security.

Chemically Mediated Plant-Plant Interactions: Allelopathy and Allelobiosis.

Plant-plant interactions are a central driver for plant coexistence and community assembly. Chemically mediated plant-plant interactions are represented by allelopathy and allelobiosis. Both allelopathy and allelobiosis are achieved through specialized metabolites (allelochemicals or signaling chemicals) produced and released from neighboring plants. Allelopathy exerts mostly negative effects on the establishment and growth of neighboring plants by allelochemicals, while allelobiosis provides plant neighbor detection and identity recognition mediated by signaling chemicals. Therefore, plants can chemically affect the performance of neighboring plants through the allelopathy and allelobiosis that frequently occur in plant-plant intra-specific and inter-specific interactions. Allelopathy and allelobiosis are two probably inseparable processes that occur together in plant-plant chemical interactions. Here, we comprehensively review allelopathy and allelobiosis in plant-plant interactions, including allelopathy and allelochemicals and their application for sustainable agriculture and forestry, allelobiosis and plant identity recognition, chemically mediated root-soil interactions and plant-soil feedback, and biosynthesis and the molecular mechanisms of allelochemicals and signaling chemicals. Altogether, these efforts provide the recent advancements in the wide field of allelopathy and allelobiosis, and new insights into the chemically mediated plant-plant interactions.

Synergistic effects of rhizosphere effect and combined organic and chemical fertilizers application on soil bacterial diversity and community structure in oilseed rape cultivation.

The combined application of chemical and organic fertilizers has been recognized to enhance soil fertility and foster the soil microbial ecosystem. However, the optimal ratio of chemical and organic fertilizers in oilseed rape cultivation is still uncertain, and the role of rhizosphere effect is still unclear. Thus, this study aimed to elucidate the impacts of varying ratios of chemical and organic fertilizers on the structure and potential functionalities of rhizosphere and non-rhizosphere soil microbial communities. The interplay of microbial communities with soil properties and oilseed rape root exudates was investigated in controlled pot cultivations receiving varying ratios of chemical and organic fertilizers. Results indicated clear segregation in the soil bacterial community, influenced by both fertilization treatments and rhizosphere effects. The bacterial community structure significantly correlated with nitrate nitrogen, organic acids, and dissolved organic carbon (DOC) content. Rhizosphere effects led to increased bacteria abundance, reduced diversity, and decreased network stability. Notably, F3 treatment receiving 25% chemical and 75% organic fertilizers showed a significantly higher abundance at 1.43 × 1011 copies g-1 dry soil, accompanied by increased species and genetic diversity, and ecological network complexity. This treatment also yielded the highest aboveground biomass of oilseed rape. However, the application of organic fertilizers also increased the risk of plant pathogenicity. This study reveals the impact of fertilizers and rhizosphere effects on soil microbial community structure and function, shedding light on the establishment of more effective fertilization schemes for oilseed rape agriculture.