Rhizosphere Microenvironment Research Articles

Iron addition promotes mercury removal from soil by Robinia pseudoacacia-rhizobia symbiosis.

Iron plaques on the root surface can promote or inhibit the absorption and accumulation of heavy metals by plants. However, the mechanism by which iron regulates the response of Robinia pseudoacacia to mercury (Hg) have not been elucidated which hinders its application in divalent Hg (Hg2+) removal from Hg-contaminated soil. In this study, association analyses between transcriptome and metabolome were used to investigate effects of iron on the rhizosphere microenvironment and performance of R. pseudoacacia to assess its potential for Hg2+ removal. The results showed that the addition of 10 mg kg-1 iron significantly increased the development of iron plaques on root surface, and reduced the secretion of low-molecular-weight organic acids by roots, thereby changing rhizosphere soil characteristics and decreasing total Hg in roots. In addition, the secretion of choline supported signal transduction and enhanced the interaction between R. pseudoacacia and rhizobia, thereby inducing resistance to Hg2+. Anti-oxidative enzyme activities were increased and Hg2+ exposure of plants was reduced. Enhanced Hg2+ resistance was indicated by improved photosynthesis and growth despite promoted xylem loading and transport of Hg2+, resulting in its accumulation in aboveground tissues that is essential for Hg2+ removal. These results indicate that iron addition has a great potential to improve the growth of R. pseudoacacia in Hg-contaminated soil and promote the accumulation of Hg2+ in aboveground tissues for phytoremediation approaches.

Protective role of Mortierella alpina-derived lipids in resisting root rot in Panax ginseng

Root rot caused by Fusarium oxysporum is a major threat to the yield and quality of Panax ginseng. The use of antimicrobial compounds from antagonistic microorganisms is effective in controlling pathogens. Lipids from Mortierella can promote plant growth, but their role in disease resistance is unclear. In this study, we conducted a comprehensive analysis of the lipid components of Mortierella alpina and investigated the disease resistance properties and mechanisms of the total lipids and main component arachidonic acid (ARA). The results demonstrated that total lipids and arachidonic acid (ARA) directly inhibited the growth of F. oxysporum, F. solani, and Aspergillus sp., while promoting beneficial microorganisms such as Pseudomonas geniculate, Bacillus velezensis, and Trichoderma velutinum. These compounds also significantly induced the defense response of ginseng adventitious roots. Pot experiments revealed that total lipids and ARA significantly improved theresistance of ginseng to F. oxysporum root rot. Compared with F. oxysporum treatment alone, lipid addition increased the chlorophyll content, root length, fresh weight, and total saponin content. The increased expression of genes related to the jasmonic acid signaling pathway and relatively high nitrogen levels in the rhizosphere soil indicated increased defense mechanisms. Additionally, lipid addition increased the abundances of beneficial microorganisms such as Lysobacter, Gemmatimonas, Pedobacter, Pseudolabrys, and Mortierella, while decreasing Fusarium abundance. Overall, these findings demonstrate that Mortierella-derived lipids enhance ginseng resistance to root rot by directly inhibiting pathogens, modulating defense signaling pathways, and improving the rhizosphere microenvironment.

Regulation of the Rhizosphere Microenvironment by Arbuscular Mycorrhizal Fungi to Mitigate the Effects of Cadmium Contamination on Perennial Ryegrass (Lolium perenne L.).

Rhizosphere microorganisms are crucial for enhancing plant stress resistance. Current studies have shown that Arbuscular mycorrhizal fungi (AMF) can facilitate vegetation recovery in heavy metal-contaminated soils through interactions with rhizosphere microbiota. However, the mechanisms by which AMF influences rhizosphere microbiota and plant growth under cadmium (Cd) stress remain unclear. In this study, Lolium perenne L. was inoculated with AMF (Rhizophagus irregularis) and grown in soils supplemented with Cd (0 mg kg-1, Cd0; 100 mg kg-1, Cd100). Plant biomass, antioxidant enzyme activities, peroxide content, Cd uptake, and rhizosphere bacterial community composition were evaluated. AMF inoculation reduced Cd influx in aboveground tissues, enhanced nutrient availability in the rhizosphere, and mitigated Cd biotoxicity. Additionally, AMF inoculation improved the scavenging efficiency of reactive oxygen species and alleviated oxidative stress in L. perenne, thereby mitigating biomass reduction. Moreover, AMF treatment increased leaf and root biomass by 342.94% and 41.31%, respectively. Furthermore, under the same Cd concentration, AMF inoculation increased bacterial diversity (as measured by the Shannon index) and reduced bacterial enrichment (as indicated by the ACE index). AMF promoted the enrichment of certain bacterial genera (e.g., Proteobacteria and Actinobacteria) in the Cd100 group. These findings suggest that AMF regulated the composition of the rhizosphere bacterial community and promoted the growth of potentially beneficial microorganisms, thereby enhancing the resistance of L. perenne to Cd stress. Cd contamination in soil severely limits plant growth and threatens ecosystem stability, highlighting the need to understand how AMF and rhizosphere microbes can enhance Cd tolerance in L. perenne. Therefore, inoculating plants with AMF is a promising strategy for enhancing their adaptability to Cd-contaminated soils.

Effect of mixed planting on soil nutrient availability and microbial diversity in the rhizosphere of Parashorea chinensis plantations.

Parashorea chinensis Wang Hsie (Pc) is an endangered tree species endemic to tropical and subtropical China. However, the acidic red soil areas where it is distributed generally face nutrient limitation. The study of the effects of mixed planting on soil biogeochemical processes contributes to the sustainable management and conservation of Pc. We selected pure and mixed stands of Pc and collected its rhizosphere and bulk soil samples to clarify the effect of mixed planting on the soil microbial community and the nutrient status. The results showed that (1) All stands were strongly acidic phosphorus-deficient soils (pH < 4.0, available phosphorus <10.0 mg·kg-1). There was a significant rhizosphere aggregation effect for soil organic C, total and available N and K, microbial biomass, and inorganic P fraction. (2) The mixed planting significantly increased the soil water content, organic C, available nutrients, the activities of β-1,4-glucosidase and urease, and microbial biomass. The inorganic P fractions are more influenced by rhizosphere, while organic P fractions are more influenced by tree species composition. (3) Fungi and their ecological functions are more susceptible to tree species than bacteria are, and have higher community compositional complexity and α-diversity in mixed plantations. And mixed planting can improve network complexity among key microorganisms. (4) The correlation between soil microorganisms and environmental factors was significantly higher in mixed forests than in pure forests. Soil organic C, available N and P, microbial biomass C and N, β-1,4-glucosidase, and stable P fractions were the key environmental factors driving changes in fungal and bacterial communities. In conclusion, the mixed planting patterns are more advantageous than pure plantations in improving soil physicochemical properties, enhancing nutrient effectiveness, and promoting microbial activities and diversity, especially Pc mixed with Eucalyptus grandis × E. urophylla is more conducive to soil improvement and sustainable management, which provides practical references for relocation protection of endangered tree species and species selection and soil fertility management in mixed planting. In addition, the study highlighted the key role of rhizosphere microenvironment in soil nutrient cycling and microbial community structure, which provides new perspectives for a deeper understanding of soil-microbe-plant interaction mechanisms.

Intercropping of tobacco and maize at seedling stage promotes crop growth through manipulating rhizosphere microenvironment.

Changes in the rhizosphere microbiome and metabolites resulting from crop intercropping can significantly enhance crop growth. While there has been an increasing number of studies on various crop combinations, research on the intercropping of tobacco and maize at seedling stage remains limited. This study is the first to explore rhizosphere effects of intercropping between tobacco and maize seedling stages, we analyzed the nitrogen, phosphorus and potassium nutrients in the soil, and revealed the important effects on soil microbial community composition and metabolite profiles, thereby regulating crop growth and improving soil balance. Compared with mono-cropping, intercropping increased the biomass of the two crops and promoted the nutrient absorption of nitrogen, phosphorus and potassium. Under intercropping conditions, the activities of sucrase, catalase and nitrate reductase in tobacco rhizosphere soil and the content of available potassium, the activities of nitrate reductase and acid phosphatase in maize rhizosphere soil were significantly increasing. Rhizosphere soil bacterial and fungal communities such as Sphingomonas, Massilia, Humicola and Penicillium respond differently to crop planting patterns, and soil dominant microbial communities are regulated by environmental factors such as pH, Organic Matter, Available Potassium, Nitrate Reductase, and Urease Enzyme. Network analysis showed that soil microbial communities were more complex after intercropping, and the reciprocal relationship between bacteria and fungi was enhanced. The difference of metabolites in soil between intercropping and monocropping system was mainly concentrated in galactose metabolism, starch and sucrose metabolism pathway, and the content of carbohydrate metabolites was significantly higher than that of monocropping soil. Key metabolites such as D-Sucrose, D-Fructose-6-Phosphate, D-Glucose-1-Phosphatel significantly influence the composition of dominant microbial communities such as Sphingomonas and Penicillium. This study explained the effects of intercropping between flue-cured tobacco and maize on the content of soil metabolites and soil microbial composition in rhizosphere soil, and deepened the understanding that intercropping system can improve the growth of flue-cured crops seedlings through rhizosphere effects.

Effects of Modified Maifanite on the Growth and Rhizosphere Microenvironment of the Submerged Macrophyte Vallisneria natans (Lour.) Hara

Effects of Modified Maifanite on the Growth and Rhizosphere Microenvironment of the Submerged Macrophyte Vallisneria natans (Lour.) Hara

Macrogenome-based study on the mechanism of Bacillus velezensis SX13 in regulating rhizophere environment and cucumber growth under different cultivation environments

Microbial activities are the dynamic core of nutrient cycling in organic substrates, and the exploitation of plant growth-promoting rhizobacteria strains contributes to sustainable agricultural development. This study aimed to investigate the effect and mechanism of Bacillus velezensis SX13 in nutrient cycling and plant promotion under different substrate supply conditions. The effects of reduced substrate amount (sCK) and inoculation of SX13 strain under both substrate supply conditions (Bv and sBv) on rhizosphere microenvironment and plant growth were investigated using conventional substrate amount (CK) as a control. Results showed no significant difference in the α-diversity indexes (Chao1 and Shannon) of the rhizospheric microbial community among the four treatments. However, nonmetric multidimensional scaling analysis and principal coordinate analysis revealed that compared with CK treatment, the inoculation of SX13 strain and reduced substrate supply reshaped the β-diversity structure of microbial communities. Furthermore, inoculation with B. velezensis SX13 under both substrate supply conditions increased the abundance of Proteobacteria (1.64%–2.46 %), Acidobacteria (14.09%–43.07 %), and Firmicutes (179.29%–861.29 %). The results of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that the metabolic pathway with the highest abundance of enriched genes was also the pathway with the most enriched differential genes caused by reducing substrate supply or inoculation of B. velezensis SX13. The rhizosphere inoculation of B. velezensis SX13 significantly up-regulated the top genes related to carbohydrate esterases, carbohydrate binding modules, glycoside hydrolases, glycoside transferases, and polysaccharide lyases. As a result, the activities of carbon and nitrogen cycle-related enzymes such as cellobiohydrolase, β-glucosidase, urease, l-leucine amino peptidase, and β-1 4-N-acetylglucosaminidase were increased, which in turn accelerated nutrient cycling. B. velezensis SX13 and its mediated improvement of the rhizospheric microenvironment resulted in the up-regulation of root CsNRT family genes (such as CsNRT1.1, CsNRT1.4a, CsNRT1.4b, CsNRT1.5a, CsNRT1.5b, CsNRT1.5c, and CsNRT1.8), which accelerated nitrogen uptake, accumulation, and utilization efficiency and ultimately improved the yield and quality of cucumber. The effect of SX13 strain was more stable and efficient under conventional substrate supply conditions than under reduced substrate supply conditions.

Straw type and nitrogen-water management balance rice yield and methane emissions by regulating rhizosphere microenvironment

Context or problemStraw incorporation improves soil fertility but also poses environmental challenges due to increasing methane (CH4) emissions in paddy fields. Whether nitrogen (N) and water management can balance rice yield and CH4 emissions under different crop straw incorporation is still not well-documented. ObjectiveA three-year field experiment was conducted to probe the comprehensive effects of N application ratios and irrigation regimes on rice yield, rhizosphere soil properties, and CH4 emissions, along with the underlying mechanisms of CH4 emission variations among different straw types. MethodsA two-factor randomized block design was used with two Japonica rice cultivars as materials in 2020 and 2021. The straw incorporation treatment included no straw incorporation (NS), wheat straw incorporation (WS), and rape straw incorporation (RS). The N fertilizer application treatments included local farmers' fertilizer practice (LFP) and increasing basal fertilizer rate (IBF). Two irrigation practices, continuously-flooded irrigation (CF) and alternate wetting and drying irrigation (AWD), were designed under the WS and RS treatments in 2022. Results1) WS-IBF and RS-IBF enhanced yield by 6.70∼9.03 % and 8.13∼9.50 % compared to WS-LFP and RS-LFP, respectively. AWD further increased yield by 6.28∼7.76 % compared to CF. 2) WS-IBF and RS-IBF enhanced dissolved organic carbon (DOC) content, synchronously boosted the methanogens (mcrA) and methanotrophs (pmoA) abundances, but decreased the pmoA/mcrA ratio, which significantly promoted CH4 emission flux in early growth stage. This resulted in a 5.04∼8.01 % and 4.60∼7.88 % increase in CH4 emissions compared to WS-LFP and RS-LFP, respectively, but a decrease in yield-scaled CH4 emissions. AWD reduced DOC content, facilitated the conversion of ammonium N to nitrate N, increased dissolved oxygen content, and hence decreased CH4 emissions by 23.41∼24.38 % compared to CF. 3) RS significantly increased microbial biomass C, N, and related metabolites, leading to a 1.29∼2.73 % increase in yield compared to WS. Meanwhile, RS promoted Nitrospira abundance as well as pterin and flavonoid metabolites associated with mcrA inhibition, while decreasing Anaeromyxobacter abundance, ammonium N, and DOC content, resulting in an increase in the pmoA/mcrA ratio and a noticeable drop in CH4 emissions compared to WS. ConclusionsRS combined with IBF and AWD is a more sustainable integrated practice in light of the synergistic improvement in rice production and environmental benefits. ImplicationsThe results reveal that optimizing N and water management can synergize high-yield and low-carbon by regulating rhizosphere microenvironment in rice production under crop straw incorporation.

Earthworms improve the rhizosphere micro-environment to mitigate the toxicity of microplastics to tomato (Solanum lycopersicum)

Microplastics (MPs) are widespread in agricultural soil, potentially threatening soil environmental quality and plant growth. However, toxicological research on MPs has mainly been limited to individual components (such as plants, microbes, and animals), without considering their interactions. Here, we examined earthworm-mediated effects on tomato growth and the rhizosphere micro-environment under MPs contamination. Earthworms (Eisenia fetida) mitigated the growth-inhibiting effect of MPs on tomato plant. Particularly, when exposed to environmentally relevant concentrations (ERC, 0.02% w/w) of MPs, the addition of earthworms significantly (p < 0.05) increased shoot and root dry weight by 12–13% and 13–14%, respectively. MPs significantly reduced (p < 0.05) soil ammonium (NH4+-N) (0.55–0.69 mg/kg), nitrate nitrogen (NO3−-N) (7.02–8.65 mg/kg) contents, and N cycle related enzyme activities (33.47–42.39 μg/h/g) by 37.7–50.9%, 22.6–37.2%, and 34.2–48.0%, respectively, while earthworms significantly enhanced (p < 0.05) inorganic N mineralization and bioavailability. Furthermore, earthworms increased bacterial network complexity, thereby enhancing the robustness of the bacterial system to resist soil MPs stress. Meanwhile, partial least squares modelling showed that earthworms significantly influenced (p < 0.01) soil nutrients, which in turn significantly affected (p < 0.01) plant growth. Therefore, the comprehensive consideration of soil ecological composition is important for assessing MPs ecological risk.

Effects of sertraline hydrochloride with As(III) or Cd on rhizosphere micro-environment and root endophytes in rice

This study investigated the effects of the antidepressant sertraline hydrochloride (Ser-HCI) on rice physiology when combined with arsenic (III) or cadmium. Hydroponic experiments revealed that combined lower concentrations (0.2 and 0.6 mg L−1) of Ser-HCl and As (III) or Cd increased rice biomass and reduced pH and low molecular weight organic acids. The fluorescence intensity was enhanced with Ser-HCl and As-only treatments, with a significant difference (p < 0.05) in the dissolved organic matter index. There was a decrease in endophyte-specific operational taxonomic units, with proteobacteria dominating the rice root endophytes. The addition of Ser-HCl resulted in the Verrucomicrobiota increasing by 6.4 times, which was positively correlated with malic acid and negatively correlated with pH. Functional annotation highlighted alterations in carbohydrate metabolism pathways. This study provides insights into the interactive effects of Ser-HCl on rice when combined with As (III) or Cd, addressing gaps in our understanding of the impact of antidepressants on plant systems.

Intercropping improves maize yield and nitrogen uptake by regulating nitrogen transformation and functional microbial abundance in rhizosphere soil

Intercropping-driven changes in nitrogen (N)-acquiring microbial genomes and functional expression regulate soil N availability and plant N uptake. However, present data seem to be limited to a specific community, obscuring the viewpoint of entire N-acquiring microbiomes and functions. Taking maize intercropped with legumes (peanut and soybean) and non-legumes (gingelly and sweet potato) as models, we studied the effects of intercropping on N transformations and N-acquiring microbiomes in rhizosphere soil across four maize growth stages. Meanwhile, we compiled promising strategies such as random forest analysis and structural equation model for the exploitation of the associations between microbe-driven N dynamics and soil-plant N trade-offs and maize productivity. Compared with monoculture, maize intercropping significantly increased the denitrification rate of rhizosphere soils across four maize growth stages, net N mineralization in the elongation and flowering stages, and the nitrification rate in the seedling and mature stages. The abundance of most N-acquiring microbial populations was influenced significantly by intercropping patterns and maize growth stages. Soil available N components (NH4+-N, NO3−-N, and dissolved organic N content) showed a highly direct effect on plant N uptake, which mainly mediated by N transformations (denitrification rate) and N-acquiring populations (amoB, nirK3, and hzsB genes). Overall, the adaptation of N-acquiring microbiomes to changing rhizosphere micro-environments caused by intercropping patterns and maize development could promote soil N transformations and dynamics to meet demand of maize for N nutrient. This would offer another unique perspective to manage the benefits of the highly N-effective and production-effective intercropping ecosystems.

Hyperaccumulator extracts promoting the phytoremediation of rare earth elements (REEs) by Phytolacca americana: Role of active microbial community in rhizosphere hotspots

The increased usage of rare earth elements (REEs) leads to the extensive exploitation of rare earth mines, and the REEs pollution in soil caused by the legacy mine tailings has brought great harm to environment and human health. Although Phytolacca americana can remove REEs from contaminated soil to some extent, there is still an urgent problem to improve its efficiency. Hyperaccumulator extract is a new organic material with potential in metal phytoextraction, but its role in REEs phytoremediation and the related underlying processes remain unclear. In this study, hyperaccumulator extracts from P. americana root (PR), stem (PS), leaf (PL) and EDTA were used to improve the phytoremediation efficiency of REEs with P. americana. Soil zymography was applied to assess the enzyme hotspots’ spatial distribution in the rhizosphere, and the hotspots' microbial communities were also identified. The results indicated that the application of hyperaccumulator extracts improved the biomass and REEs uptake of P. americana, and the highest REEs content in plant was observed in the treatment of PS, which increased 299% compared to that of the control. Hotspots area of β-glucosidase, leucine aminopeptidase and acid phosphatase were concentrated in the pant rhizosphere along the roots and increased 2.2, 5.3 and 2.2 times after PS application compared to unamended soils. The PS application increased the relative abundance of Proteobacteria, Cyanobacteria, Bacteroidota and Firmicutes phyla in rhizosphere. Soil fungi have a higher contribution on promoting REEs activation than that of bacteria. Available P and extractable REEs were leading predictors for the plant biomass and REEs concentrations. The co-occurrence network showed that the application of PS creates a more efficient and stable microbial network compared to other treatments. In conclusion, stem-derived hyperaccumulator extract is excellent in stimulating REEs phytoremediation with P. americana by improving hotspots microbial activities and form a healthy rhizosphere microenvironment.

Role of Plant-Growth-Promoting Rhizobacteria in Plant Machinery for Soil Heavy Metal Detoxification.

Heavy metals migrate easily and are difficult to degrade in the soil environment, which causes serious harm to the ecological environment and human health. Thus, soil heavy metal pollution has become one of the main environmental issues of global concern. Plant-growth-promoting rhizobacteria (PGPR) is a kind of microorganism that grows around the rhizosphere and can promote plant growth and increase crop yield. PGPR can change the bioavailability of heavy metals in the rhizosphere microenvironment, increase heavy metal uptake by phytoremediation plants, and enhance the phytoremediation efficiency of heavy-metal-contaminated soils. In recent years, the number of studies on the phytoremediation efficiency of heavy-metal-contaminated soil enhanced by PGPR has increased rapidly. This paper systematically reviews the mechanisms of PGPR that promote plant growth (including nitrogen fixation, phosphorus solubilization, potassium solubilization, iron solubilization, and plant hormone secretion) and the mechanisms of PGPR that enhance plant-heavy metal interactions (including chelation, the induction of systemic resistance, and the improvement of bioavailability). Future research on PGPR should address the challenges in heavy metal removal by PGPR-assisted phytoremediation.

Novel insights into the mechanism of laccase-driven rhizosphere humification for alleviating wheat 17β-estradiol contamination

Global-scale crop contamination with environmental estrogens has posed a huge risk to agri-food safety and human health. Laccase is regarded as an unexceptionable biocatalyst for regulating pollution and expediting humification, but the knowledge of estrogen bioremediation and C storage strengthened by laccase-driven rhizosphere humification (LDRH) remains largely unknown. Herein, a greenhouse microcosm was performed to explore the migration and fate of 17β-estradiol (E2) in water-wheat (Triticum aestivum L.) matrices by LDRH. Compared to the non-added laccase, the pseudo-first-order decay rate constants of E2 in the rhizosphere solution after 10 and 50 μM exposures by LDRH increased from 0.03 and 0.02 h−1 to 0.36 and 0.09 h−1, respectively. Furthermore, LDRH conferred higher yield, polymerizability, O-containing groups, and functional-C signals in the humified precipitates, because it accelerated the formation of highly complex precipitates by radical-controlled continuous polymerization. In particular, not only did LDRH mitigate the phytotoxicity of E2, but it also diminished the metabolic load of E2 in wheat tissues. This was attributed to the rapid attenuation of E2 in the rhizosphere solution during LDRH, which limited E2 uptake and accumulation in each subcellular fraction of the wheat roots and shoots. Although several typical intermediate products such as estrone, estriol, and E2 oligomers were detected in roots, only small-molecule species were found in shoots, evidencing that the polymeric products of E2 were unable to be translocated acropetally due to the vast hydrophobicity and biounavailability. For the first time, our study highlights a novel, eco-friendly, and sustainable candidate for increasing the low-C treatment of organics in rhizosphere microenvironments and alleviating the potential risks of estrogenic contaminants in agroenvironments.

Growth-promoting effects of self-selected microbial community on wheat seedlings in saline-alkali soil environments.

Saline-alkali land is a type of soil environment that causes poor crop growth and low yields. Its management and utilization are, therefore of great significance for increasing arable land resources, ensuring food security, and enhancing agricultural production capacity. The application of plant growth-promoting rhizobacteria (PGPR) is an effective way to promote the establishment of symbiotic relationships between plants and the rhizosphere microenvironment, plant growth and development, and plant resistance to saline-alkali stress. In this study, multiple saline-alkali-resistant bacteria were screened from a saline-alkali land environment and some of them were found to have significantly promotive effects on the growth of wheat seedlings under saline-alkali stress. Using these PGPR, a compound microbial community was selectively obtained from the root-zone soil environment of wheat seedlings, and the metagenomic sequencing analysis of wheat root-zone soil microbiomes was performed. As a result, a compound microbial agent with a Kocuria dechangensis 5-33:Rossellomorea aquimaris S-3:Bacillus subtilis BJYX:Bacillus velezensis G51-1 ratio of 275:63:5:1 was obtained through the self-selection of wheat seedlings. The synthetic compound microbial agent significantly improved the growth of wheat seedlings in saline-alkali soil, as the physiological plant height, aboveground and underground fresh weights, and aboveground and underground dry weights of 21-day-old wheat seedlings were increased by 27.39% (p < 0.01), 147.33% (p < 0.01), 282.98% (p < 0.01), 194.86% (p < 0.01), and 218.60% (p < 0.01), respectively. The promoting effect of this compound microbial agent was also greater than that of each strain on the growth of wheat seedlings. This microbial agent could also regulate some enzyme activities of wheat seedlings and the saline-alkali soil, thereby, promoting the growth of these seedlings. In this study, we analyze an efficient microbial agent and the theoretical basis for promoting the growth of wheat seedlings under saline-alkali stress, thereby, suggesting an important solution for the management and utilization of saline-alkali land.

Relationship between fine root functional traits and rhizosphere microenvironment of &lt;i&gt;Machilus pauhoi&lt;/i&gt; at different sizes

Relationship between fine root functional traits and rhizosphere microenvironment of &lt;i&gt;Machilus pauhoi&lt;/i&gt; at different sizes

Intervention of rhamnolipid improves the rhizosphere microenvironment of cotton in desert saline lands

Rhamnolipids have been extensively studied for the remediation of soils contaminated with petroleum hydrocarbons. However, the literature on the effects of rhamnolipids on the soil microenvironment is scarce. In this study, we adopted a drip irrigation technique to apply a rhamnolipid solution to soil planted with cotton in a saline desert area. The results showed that the addition of rhamnolipids increased soil organic matter by 5.0–31.6 % and reduced soil electrical conductivity by 0.3–42.4 %. Additionally, it improved soil nutrient conditions, reshaped the composition and function of the microbial community in the rhizosphere soil, and ultimately promoted cotton growth by 3.3 – 9.0 %. Simultaneously, the addition of rhamnolipids enriched the diversity of the bacterial community. Although it reduced the diversity of fungal communities, it optimized the community structure of fungi. It is worth noting that higher concentrations of rhamnolipids may have toxic effects on soil fungi, the mechanism of which is unknown. These findings shed new light on understanding the effects of rhamnolipids on rhizosphere soil microorganisms and provide a new direction for sustainable agricultural production.

Unveiling the dual role of heterotrophic ammonia-oxidizing bacteria: enhancing plant regrowth through modulating cytokinin delivery.

This study aims to investigate the dual impacts of heterotrophic ammonia-oxidizing bacteria (HAOB) strains on the regrowth of Italian ryegrass by studying cytokinin delivery from roots to leaves. The dual impacts encompass both the "soil-inside-role" and "soil-outside-role," which refer to the HAOB operating inside and outside the rhizosphere soil within the rhizosphere microenvironment. The experimental design consisted of two sets of experiments, Exp-1 and Exp-2, involving different treatments. In Exp-1, various concentrations of NO3- were added to the roots to observe the soil-inside-role on cytokinin delivery from roots to leaves. In Exp-2, NO3- addition was combined with HAOB inoculation to observe the combined effects of the root-outside-role and root-inside-role on cytokinin synthesis and transport. The results indicated that NO3- concentrations ranging from 30 to 40 mmol L-1 had the most optimal effect on increasing leaf cytokinin content and delivery from roots to leaves, consequently promoting greater leaf regrowth biomass. When inoculated, the HAOB strain significantly increased rhizosphere soil nitrification rates under the soil-inside-role, leading to increased NO3- release from the soil and a subsequent boost in cytokinin delivery from roots to leaves. Additionally, the HAOB strain independently enhanced cytokinin delivery from roots to leaves outside the rhizosphere soil within the rhizosphere microenvironment, demonstrating its soil-outside-role. The combined effects of the soil-inside-role and soil-outside-role substantially increased leaf cytokinin content, playing a crucial role in promoting Italian ryegrass regrowth. The study's findings shed light on the mechanisms through which HAOB can enhance plant growth by performing dual roles in the rhizosphere, offering potential applications in agriculture. Understanding the interaction between HAOB, cytokinins, and plant growth could lead to more effective strategies for improving crop productivity and promoting sustainable agriculture.

Characteristics of Microbial Abundance in Rhizosphere and Non-Rhizosphere Soils of Permafrost Peatland, Northeast China

The rhizosphere microenvironment is crucial to plant–soil physiological processes. The differences among microbial communities in the rhizosphere and non-rhizosphere peatland topsoil (0–15 cm) and subsoil (15–30 cm) in five plant communities dominated by Carex schmidtii, Chamaedaphne calyculata, Ledum palustre, Betula fruticosa, and Vaccinium uliginosum, as well as non-rhizosphere soil in discontinuous and continuous permafrost regions, were studied. We found that the bacteria and nifH gene abundances in the C. calyculata rhizosphere soil in the discontinuous permafrost region were higher than those in continuous permafrost region, while the nirK and nifH gene abundances in the non-rhizosphere soil of the discontinuous permafrost region were lower than those in the continuous permafrost region. The ratio of bacteria to fungi decreased and that of nirK to nirS increased significantly from the discontinuous to the continuous permafrost region, indicating that permafrost degradation can change soil microbial community composition. Fungal abundance was higher in the rhizosphere than the non-rhizosphere soils, suggesting that plant roots provide a more suitable environment for fungi. Moreover, the abundances of the topsoil bacteria; the fungi; and the nirK, nirS, and nifH genes were higher than those in the subsoil because of the organic matter from plant litter as a source of nutrients. The microbial abundance in the subsoil was also more affected by nutrient availability. To sum up, the microbial abundance varied among the different types of rhizosphere and non-rhizosphere soils, and the carbon and nitrogen cycling processes mediated by soil microorganisms may be greatly altered due to permafrost degradation under climate warming.

Rhizosphere interface microbiome reassembly by arbuscular mycorrhizal fungi weakens cadmium migration dynamics.

The prevalence of cadmium (Cd)-polluted agricultural soils is increasing globally, and arbuscular mycorrhizal fungi (AMF) can reduce the absorption of heavy metals by plants and improve mineral nutrition. However, the immobilization of the rhizosphere on cadmium is often overlooked. In this study, Glomus mosseae and Medicago sativa were established as symbiotes, and Cd migration and environmental properties in the rhizosphere were analyzed. AMF reduced Cd migration, and Cd2+ changed to an organic-bound state. AMF symbiosis treatment and Cd exposure resulted in microbial community variation, exhibiting a distinct deterministic process (|βNTI| > 2), which ultimately resulted in a core microbiome function of heavy metal resistance and nutrient cycling. AMF increased available N and P, extracellular enzyme activity(LaC, LiP, and CAT), organic matter content (TOC, EOC, and GRSP), and Eh of the rhizosphere soil, significantly correlating with decreased Cd migration (p < 0.05). Furthermore, AMF significantly affected root metabolism by upregulating 739 metabolites, with flavonoids being the main factor causing microbiome variation. The structural equation modeland variance partial analysisrevealed that the superposition of the root metabolites, microbial, and soil exhibited the maximum explanation rate for Cd migration reduction (42.4%), and the microbial model had the highest single explanation rate (15.5%). Thus, the AMF in the rhizosphere microenvironment can regulate metabolite-soil-microbial interactions, reducing Cd migration. In summary, the study provides a new scientific explanation for how AMF improves plant Cd tolerance and offers a sustainable solution that could benefit both the environment and human health.