Non-sterile Soil Research Articles

Efficacy of two different microbial consortia on salinity tolerance in chickpea: an in-planta evaluation on biochemical, histochemical, and genomic aspects.

This study aimed to identify and characterize actinobacteria and rhizobia with plant growth-promoting (PGP) traits from chickpea plants. Out of 275 isolated bacteria, 25 actinobacteria and 5 chickpea rhizobia showed 1-aminocyclopropane-1-carboxylate deaminase (ACCd) activity. Selected chickpea rhizobia were tested for their nodulating capacity under sterile and non-sterile soil conditions. Further screening on salinity and PGP traits identified three promising isolates: Nocardiopsis alba KG13, Sinorhizobium meliloti KGCR17, and Bacillus safensis KGCR11. These three isolates were analyzed for their compatibility and made into a consortium (Consortium 1). This along with another consortium made from our salinity-tolerant lab strains Chryseobacterium indologenes ICKM4 and Stenotrophomonas maltophilia ICKM15 (Consortium 2) was compared in planta studies. Trials revealed that Consortium 2 showed significant (p < 0.05) tolerance and on above-ground, below-ground traits and yield components than Consortium 1. Moreover, both consortia induced nodulation in saline-stressed plants, alleviated electrolyte leakage (2.3 vs. 0.4 in ICCV 2; 1.8 vs. 0.6 in JG 11), and increased chlorophyll content. Histochemical staining indicated reduced oxidative stress and lipid peroxidation in consortium-treated plants under salinity stress. Further, gene expression studies revealed mixed patterns, with up-regulation of antioxidant and transporter genes observed in consortium-treated plants, particularly in Consortium 2. Overall, Consortium 2 showed better gene expression levels for antioxidant and transporter genes, indicating its superior efficacy in mitigating salinity stress in chickpea plants. This study provides valuable insights into the potential use of these microbial isolates in improving chickpea productivity by enhancing salinity tolerance.

Do Streptomyces sp. Help Mycorrhization in Raspberry?

Actinobacteria may help the mycorrhizal symbiosis by producing various bioactive metabolites. Mycorrhizae, in turn, are very important since they increase the absorption of nutrients, promoting the growth of their host plant and making inoculation with arbuscular mycorrhizae fungi (AM) a common practice applied in agriculture and forestry. The cultivation of Rubus idaeus (raspberry) is widespread in Patagonia, Argentina; however, the potential benefits of using actinobacteria-mycorrhizal inoculums to enhance crop growth and yield remain unexplored. The objective of this work was to study the interaction between actinobacteria (Streptomyces, Actinomycetota) and AM in raspberry plants. We performed an experiment applying 4 treatments to raspberry plants growing in two substrates, sterile soil and natural (non-sterile) soil. The treatments consisted in a control (without inoculation) and three inoculations treatments (AM, Streptomyces SH9 strain, and AM + Streptomyces). After 3months of inoculation, mycorrhization parameters (%) and plant growth were recorded. When comparing both substrates, the mycorrhization parameters were higher in natural soil than in sterile soil. The co-inoculation with AM + Streptomyces SH9 showed the highest mycorrhization. Both factors (treatment x substrate) interacted showing that in sterile soil the treatments with the highest effect on mycorrhization parameters were AM and the co-inoculation, while in natural soil all inoculations improved mycorrhization parameters, being highest with the co-inoculation. These results show that Streptomyces SH9 strain helps the mycorrhizal symbiosis in raspberry, being the first report about the effect of a native rhizospheric actinobacterium on an economically important species, promising potential for environmentally friendly improvements in raspberry crops within the temperate Southern Patagonian region.

Degradation of non-phthalate plasticisers in soils by liquid chromatography coupled to high resolution mass accuracy spectrometry: A comparison with sterile soil

The market for non-phthalate plasticisers (NPPs), such as adipates, citrates, phosphates, and carboxylates, has grown due to their low toxicity, but no studies have determined their metabolites during degradation processes in soil. This study evaluated the degradation of diethyl hexyl adipate (DEHA) and acetyl triethyl citrate (ATEC) in nonsterile soil, and the results were compared with those obtained from sterile soil, to determine whether microbial activity causes degradation in these NPPs. The analyses of these substances were performed using liquid chromatography coupled with quadrupole-Orbitrap high-resolution mass spectrometry (LC-Q-Orbitrap-HRMS). Plasticiser degradation followed a biphasic kinetic model, with a half-life time (DT50) of 9–12 days in non-sterile soil, but very slow in sterile soil (DT50 > 58 days). The degradation of target plasticisers in nonsterile soil resulted in the detection of eight metabolites of DEHA and ATEC, which were not detected in sterile soil. Among them, 4-[(2-ethylhexyl)oxy]-4-oxobutanoic acid (EHOBA), 4-((2-ethylhexyl)oxy)-4-oxo-1-carbonyl hexanoate (EHOCH), triethylcitrate (TEC) and N-acetyl glutamine (NAG) have been detected for the first time in this study. Most of these metabolites were detected after 14 days, increasing their concentration to 21 days, before completely degrading after 45 days. Nevertheless, mono–2-ethyl-5-hydroxyhexyl adipate (MEHHA), mono-2-ethyloxohexyl adipate (MEHOA), EHOCH, and diethyl citrate (DEC) were persistent in non-sterile soil (detected at 45 days) with an LD50 lower than their respective original molecules. Therefore, it is necessary to control the amount of these metabolites derived from the degradation of this type of plasticisers in the soil to avoid health risks, as they can end up in vegetables.

Small-size polyethylene and polylactic microplastic alterations on soil aggregate formation with soil sterilization

Soil microplastic contamination is emerging as a significant environmental concern affecting soil properties and biota, including soil aggregation. This study aimed to determine the influence of soil microplastics on soil aggregation, their impact through effects on soil microorganisms, and their effects on water and mechanical stability of soil aggregates. Soil incubation experiments were conducted using sterilized and non-sterilized soils with 15-μm polyethylene and polylactic microplastics over one month. Sterilized soils showed more water-stable aggregates, particularly in the 0.25–0.5 mm fraction (+49%), with both polyethylene and polylactic MPs significantly increasing this fraction (+34% and +35%, respectively). However, no significant effects of soil sterilization and MP addition were found on mechanical stability. The addition of MPs tended to decrease aggregate surface roughness but not significantly (−17～21%). The study provides insights into the complex interactions between microplastics and soil aggregation, suggesting that MP effects may not necessarily be related to their toxicity on soil microbes but could involve various physical interactions.

Piriformospora indica alleviates soda saline-alkaline stress in Glycine max by modulating plant metabolism.

Soil salinization is one of the major factors limiting agricultural production. Utilizing beneficial microorganisms like Piriformospora indica (P. indica) to enhance plant tolerance to abiotic stresses is a highly effective method, but the influence of P. indica on the growth of soybean in natural saline-alkaline soil remains unclear. Therefore, we investigated the effects of non-inoculation, P. indica inoculation, and fertilization on the growth, antioxidant defense, osmotic adjustment, and photosynthetic gas exchange parameters of soybean under two different levels of saline-alkaline stress in non-sterilized natural saline-alkaline soil. The study found that: 1) P. indica inoculation significantly promoted soybean growth, increasing plant height, root length, and biomass. Under mildly saline-alkaline stress, the increases were 11.5%, 16.0%, and 14.8%, respectively, compared to non-inoculated treatment. Under higher stress, P. indica inoculation achieved the same level of biomass increase as fertilization, while fertilization only significantly improved stem diameter. 2) Under saline-alkaline stress, P. indica inoculation significantly increased antioxidant enzyme activities and reduced malondialdehyde (MDA) content. Under mildly stress, MDA content was reduced by 47.1% and 43.3% compared to non-inoculated and fertilized treatments, respectively. Under moderate stress, the MDA content in the inoculated group was reduced by 29.9% and 36.6% compared to non-inoculated and fertilized treatments, respectively. Fertilization only had a positive effect on peroxidase (POD) activity. 3) P. indica inoculation induced plants to produce more osmotic adjustment substances. Under mildly stress, proline, soluble sugars, and soluble proteins were increased by 345.7%, 104.4%, and 6.9%, respectively, compared to non-inoculated treatment. Under higher stress, the increases were 75.4%, 179.7%, and 12.6%, respectively. Fertilization had no significant positive effect on proline content. 4) With increasing stress, soybean photosynthetic capacity in the P. indica-inoculated treatment was significantly higher than in the non-inoculated treatment, with net photosynthetic rate increased by 14.8% and 37.0% under different stress levels. These results indicate that P. indica can enhance soybean's adaptive ability to saline-alkaline stress by regulating ROS scavenging capacity, osmotic adjustment substance content, and photosynthetic capacity, thereby promoting plant growth. This suggests that P. indica has great potential in improving soybean productivity in natural saline-alkaline soils.

Impact of soil sterilization on antagonistic efficiency against tobacco mosaic virus and the rhizosphere bacterial community in Nicotiana benthamiana

Soil microorganisms play a critical role in influencing plant growth and managing soil pathogens. Tobacco mosaic virus (TMV) induces significant economic losses in global agriculture and can impact the composition and function of soil microbial communities. Despite its importance, the interactions between viruses and soil microbial communities remain inadequately understood. In this study, we employed 16S rRNA gene sequencing coupled with bioinformatics analyses to thoroughly investigate the bacterial communities and physicochemical properties of the rhizosphere soils of healthy tobacco plants under both sterilized (WJ) and non-sterilized (YJ) conditions, as well as TMV-infected tobacco plants under both sterilized (WT) and non-sterilized (YT) conditions. Our findings demonstrated that TMV infection significantly modifies the physicochemical properties and bacterial community structure of rhizosphere soils, with these changes being more pronounced in non-sterilized soils. Moreover, the YT samples exhibited a more intricate network of bacterial interactions. They showed significant differences from WT samples in key bacterial genera that might be involved in the response to or antagonism of TMV. The genera Burkholderia-Caballeronia-Paraburkholderia and Dyella were highlighted. These results suggest that rhizosphere microorganisms actively respond to TMV infection, with a more pronounced response observed in non-sterilized soils. This study provides novel insights into the microbial dynamics associated with TMV infection and underscores the importance of soil microbial communities in plant health and disease resistance. Additionally, it offers an experimental framework for future research on soil-borne diseases, emphasizing the pivotal role of soil microbiota in disease ecology and soil impact.

Enhanced Growth and Contrasting Effects on Arsenic Phytoextraction in Pteris vittata through Rhizosphere Bacterial Inoculations.

This greenhouse study evaluated the effects of soil enrichment with Pteris vittata rhizosphere bacteria on the growth and accumulation of arsenic in P. vittata grown on a naturally As-rich soil. Inoculations were performed with a consortium of six bacteria resistant to 100 mM arsenate and effects were compared to those obtained on the sterilized soil. Selected bacteria from the consortium were also utilized individually: PVr_9 homologous to Agrobacterium radiobacter that produces IAA and siderophores and shows ACC deaminase activity, PVr_15 homologous to Acinetobacter schindleri that contains the arsenate reductase gene, and PVr_5 homologous to Paenarthrobacter ureafaciens that possesses all traits from both PVr_9 and PVr_15. Frond and root biomass significantly increased in ferns inoculated with the consortium only on non-sterilized soil. A greater increase was obtained with PVr_9 alone, while only an increased root length was found in those inoculated with either PVr_5 or PVr_15. Arsenic content significantly decreased only in ferns inoculated with PVr_9 while it increased in those inoculated with PVr_5 and PVr_15. In conclusion, inoculations with the consortium and PVr_9 alone increase plant biomass, but no increase in As phytoextraction occurs with the consortium and even a reduction is seen with PVr_9 alone. Conversely, inoculations with PVr_5 and PVr_15 have the capacity of increasing As phytoextraction.

Soil fungal communities associated with chili pepper respond to mineral and organic fertilization and application of the biocontrol fungus Trichoderma harzianum

Soil fungi are diverse and common in crop systems with important ecological function such as saprotrophs, symbionts, and pathogens, all of which are key components for soil fertility and health. Agricultural practices including tillage, crop rotation, fertilization and pest management with pesticides and microbial biocontrol agents are known to affect the abundance and composition of soil fungi, but these factors are seldom integrated and studied in combination. The objective of this study was to examine the influence of mineral and organic (compost) fertilization, and soil inoculation with the biocontrol fungus Trichoderma harzianum individually and in combination on the resident soil fungal communities and plant performance in a greenhouse pot experiment with chili pepper grown in a disease-infested agricultural soil. Soil fungal communities were studied using Illumina MiSeq sequencing and taxonomic assignment using the UNITE database in terms of amplicon sequence variants (ASV). Main results showed that the combination of compost and T. harzianum inoculation completely controlled chili pepper wilt, which coincided with alterations in soil fungal diversity. The root pathogen Fusarium equiseti was the most abundant fungus (in relative terms) in all treatments and the ASV Trichoderma sp. was only found in the treatments in which T. harzianum had been applied. Soil application with T. harzianum at sowing also reduced chili pepper damping-off in non-sterile disease-infested soil, which coincided with a reduction of the relative abundance of F. equiseti. However, several other known Fusarium spp. pathogens were present in the natural disease infested agricultural soil and could also have been involved in the chili pepper wilt observed. In conclusion, our results show promising biocontrol traits of T. harzianum against chili pepper damping off and wilt most likely caused by Fusarium spp. The observed alterations in soil fungal diversity with T. harzianum and compost were probably involved in the reduction of chili pepper wilt but needs to be further studied.

Modeling and tracing of polycarbonate (PC) degradation in soil microcosm with a PC microplastics quantification method based on pyrolysis GC–MS

Understanding the migration and transformation of polycarbonate (PC) plastic wastes in the natural environment is crucial for assessing their environmental impact and bioremediation. In this study, PC plastic degradation was modeled and traced in soil microcosm by investigating physiochemical properties changes of PC, the formation of microplastics, and changes in soil microbial communities. Notably, PC microplastics quantification method was also successfully devised by pyrolysis gas chromatography mass spectrometry and also applied herein. Through gel permeation chromatography analysis, the molecular weight of the naturally aged PC film obviously reduced, whereas no change for unaged ones. After 12 months of soil burial, the surface corrosion and holes formation were emerged on the surfaces of both PC films in the non-sterilized soil harboring indigenous microorganisms by scanning electron microscope. The worsened thermal stability of both PC films in non-sterilized soil was demonstrated by thermogravimetric analysis. Meanwhile, the presence of increased hydroxyl group absorption and decreased carbonyl peak highlighted molecular chain breakage in both PC films by Fourier transform infrared spectroscopy. In particular, all the changes were more significant in aged PC than unaged ones. Furthermore, the increase of quantified PC microplastics on the surface of PC film in the non-sterilized soil accompanied the decreasing of microbial diversity and the enrichment of potential functional microorganisms. These findings revealed that the combination of natural aging and indigenous microbes exhibited a noticeable performance in PC plastics degradation in soil microcosm, providing new insights into the degradation mechanism of PC plastic wastes in the natural environment.

Synthetic community derived from grafted watermelon rhizosphere provides protection for ungrafted watermelon against Fusarium oxysporum via microbial synergistic effects

BackgroundPlant microbiota contributes to plant growth and health, including enhancing plant resistance to various diseases. Despite remarkable progress in understanding diseases resistance in plants, the precise role of rhizosphere microbiota in enhancing watermelon resistance against soil-borne diseases remains unclear. Here, we constructed a synthetic community (SynCom) of 16 core bacterial strains obtained from the rhizosphere of grafted watermelon plants. We further simplified SynCom and investigated the role of bacteria with synergistic interactions in promoting plant growth through a simple synthetic community.ResultsOur results demonstrated that the SynCom significantly enhanced the growth and disease resistance of ungrafted watermelon grown in non-sterile soil. Furthermore, analysis of the amplicon and metagenome data revealed the pivotal role of Pseudomonas in enhancing plant health, as evidenced by a significant increase in the relative abundance and biofilm-forming pathways of Pseudomonas post-SynCom inoculation. Based on in vitro co-culture experiments and bacterial metabolomic analysis, we selected Pseudomonas along with seven other members of the SynCom that exhibited synergistic effects with Pseudomonas. It enabled us to further refine the initially constructed SynCom into a simplified SynCom comprising the eight selected bacterial species. Notably, the plant-promoting effects of simplified SynCom were similar to those of the initial SynCom. Furthermore, the simplified SynCom protected plants through synergistic effects of bacteria.ConclusionsOur findings suggest that the SynCom proliferate in the rhizosphere and mitigate soil-borne diseases through microbial synergistic interactions, highlighting the potential of synergistic effects between microorganisms in enhancing plant health. This study provides a novel insight into using the functional SynCom as a promising solution for sustainable agriculture.6UoEKpA3MAKccxe2Gy9v1zVideo

Isolation, characterization and identification of root nodule bacteria from Macrotyloma uniflorum (Lam.) Verdc

The present study was conducted to characterize the native plant growth promoting rhizobacteria (PGPRs) from the nodules of Macrotyloma uniflorum (Lam.) Verdc. The seeds of Macrotyloma uniflorum was grown in two different soils i.e., sterile and non-sterile soil and four bacterial isolates were isolated. The bacterial isolates were characterised on the basis of morphological and different biochemical analysis. Phylogenetic identification was done on the basis of 16S rRNA analysis. Four isolates obtained belongs to Bacillus velezensis and Enterobacter cloacae.

Efficacy of novel bacterial consortia in degrading fipronil and thiobencarb in paddy soil: a survey for community structure and metabolic pathways.

Fipronil (FIP) and thiobencarb (THIO) represent widely utilized pesticides in paddy fields, presenting environmental challenges that necessitate effective remediation approaches. Despite the recognized need, exploring bacterial consortia efficiently degrading FIP and THIO remains limited. This study isolated three unique bacterial consortia-FD, TD, and MD-demonstrating the capability to degrade FIP, THIO, and an FIP + THIO mixture within a 10-day timeframe. Furthermore, the bioaugmentation abilities of the selected consortia were evaluated in paddy soils under various conditions. Sequencing results shed light on the consortia's composition, revealing a diverse bacterial population prominently featuring Azospirillum, Ochrobactrum, Sphingobium, and Sphingomonas genera. All consortia efficiently degraded pesticides at 800 µg/mL concentrations, primarily through oxidative and hydrolytic processes. This metabolic activity yields more hydrophilic metabolites, including 4-(Trifluoromethyl)-phenol and 1,4-Benzenediol, 2-methyl-, for FIP, and carbamothioic acid, diethyl-, S-ethyl ester, and Benzenecarbothioic acid, S-methyl ester for THIO. Soil bioaugmentation tests highlight the consortia's effectiveness, showcasing accelerated degradation of FIP and THIO-individually or in a mixture-by 1.3 to 13-fold. These assessments encompass diverse soil moisture levels (20 and 100% v/v), pesticide concentrations (15 and 150 µg/g), and sterile conditions (sterile and non-sterile soils). This study offers an understanding of bacterial communities adept at degrading FIP and THIO, introducing FD, TD, and MD consortia as promising contenders for bioremediation endeavors.

Effects of organic contaminants on arbuscular mycorrhiza formation: A meta-analysis

Arbuscular mycorrhizal fungi (AMF) function mostly depends on their colonization to roots. However, it has not been systematically clear how arbuscular mycorrhiza (AM) formation is affected by organic contaminants. In this study, a meta-analysis was performed to estimate the effects of three groups of organic contaminants (polycyclic aromatic hydrocarbons (PAHs), crude oil, and pesticide) in soil on mycorrhizal colonization rates (MCRs) from various moderators, such as AMF (genus, species, and inoculation mode), contaminant (level, type, and source), and experimental conditions (plant type, duration, and soil sterilization). Our results showed that all MCRs (total, vesicular, arbuscular and hyphal) significantly decreased under the stresses of three contaminants. Generally, pesticide caused larger decrease in all MCRs than PAHs and crude soil except for vesicular MCRs. Mixed AMF showed larger decrease in the total and vesicular MCRs than single AM fungus, but contrary trends in the arbuscular and hyphal MCRs. Moreover, man-made contaminant seemed to produce larger negative effects on the total, vesicular, and arbuscular MCRs than industry contaminant. The inhibitive effects of three contaminants on the total and vesicular MCRs increased with increasing experimental duration, and were larger in the non-sterilized soil than in the sterilized soil. Hyphal and spore growth were also inhibited by three contaminants in most cases. Hyphal length and spore number of single AM fungus were lower than those of mixed AMF, and pesticide produced larger inhibition on the hyphal length and spore number than PAHs and crude oil. Similar trend was found in the non-sterilized soil relative to the sterilized soil. This study indicated that AM formation and AM structure were negatively affected by three organic contaminants, whereas the inhibitive degrees varied with AMF, organic contaminant and experimental conditions.

Trichoderma virens and Pseudomonas chlororaphis Differentially Regulate Maize Resistance to Anthracnose Leaf Blight and Insect Herbivores When Grown in Sterile versus Non-Sterile Soils.

Soil-borne Trichoderma spp. have been extensively studied for their biocontrol activities against pathogens and growth promotion ability in plants. However, the beneficial effect of Trichoderma on inducing resistance against insect herbivores has been underexplored. Among diverse Trichoderma species, consistent with previous reports, we showed that root colonization by T. virens triggered induced systemic resistance (ISR) to the leaf-infecting hemibiotrophic fungal pathogens Colletotrichum graminicola. Whether T. virens induces ISR to insect pests has not been tested before. In this study, we investigated whether T. virens affects jasmonic acid (JA) biosynthesis and defense against fall armyworm (FAW) and western corn rootworm (WCR). Unexpectedly, the results showed that T. virens colonization of maize seedlings grown in autoclaved soil suppressed wound-induced production of JA, resulting in reduced resistance to FAW. Similarly, the bacterial endophyte Pseudomonas chlororaphis 30-84 was found to suppress systemic resistance to FAW due to reduced JA. Further comparative analyses of the systemic effects of these endophytes when applied in sterile or non-sterile field soil showed that both T. virens and P. chlororaphis 30-84 triggered ISR against C. graminicola in both soil conditions, but only suppressed JA production and resistance to FAW in sterile soil, while no significant impact was observed when applied in non-sterile soil. In contrast to the effect on FAW defense, T. virens colonization of maize roots suppressed WCR larvae survival and weight gain. This is the first report suggesting the potential role of T. virens as a biocontrol agent against WCR.

Orfamide production in Pseudomonas protegens CHA0T promotes rhizospheric colonization and influences assemblage of the bacterial community of wheat roots in soil.

Orfamides (Ofa) are a family of closely related cyclic lipopeptides (cLPs) produced by different soil-inhabiting and plant beneficial strains of the Pseudomonas protegens subgroup. Orfamides are required for swarming motility, they mediate toxicity on oomycetes, algae, and insects, and they can act as ISR elicitors. Ofa biosynthesis depends on a non-ribosomal peptide synthetase gene cluster whose expression is tightly controlled by the post-transcriptional regulatory cascade Gac-Rsm. Although the biological properties and physiological role of Ofa have been well characterized in vitro, the role of Ofa in the fitness of the producing bacterium in its niche has not been studied so far. Here, we used an Ofa biosynthesis-deficient mutant (ΔofaABC) derived from the biocontrol model strain P. protegens CHA0T to explore the relevance of this cLP in soil for the survival of strain CHA0T, its contribution to the bacterial competitiveness for colonization of wheat roots, and its impact on the corresponding rhizobacterial community structure. To facilitate CFU counts in non-sterile soil and root samples we used chromosomally tagged versions of CHA0T and its ΔofaABC mutant with mini-Tn7 constructs carrying antibiotic resistance markers. We confirmed that the tagged Ofa− mutant does not show drop-collapse activity neither it can swarm in semi-solid medium. We also confirmed that Ofa can be exploited in vitro as a social good by the Ofa− mutant to resume swarming in the presence of CHA0T cells. We found that Ofa production did not confer any advantage for bacterial survival along a period of 5 weeks after soil inoculation. However, we observed that Ofa production was associated with a higher competitiveness for colonization of the wheat rhizosphere. Expression of the ofa biosynthetic operon, by means of a transcriptional Pofa-gfp reporter fusion, was detected in the rhizoplane of colonized wheat roots, suggesting that Ofa is produced in situ on the surface of colonized wheat roots. Finally, we observed that seed inoculation with the wild type Ofa producer strain CHA0T resulted in a differential assemblage of the bacterial community of the wheat rhizosphere with respect to that of seeds bacterized with the Ofa deficient mutant. Overall, we provide evidence that Ofa is important for the competitiveness of P. protegens CHA0T cells to colonize the surface of wheat roots and that Ofa production in the rhizosphere can impact the structure of the assembled bacterial microbiome.

Mechanism of plant–soil feedback in a degraded alpine grassland on the Tibetan Plateau

Abstract Although biotic and abiotic factors have been confirmed to be critical factors that affect community dynamics, their interactive effects have yet to be fully considered in grassland degradation. Herein, we tested how soil nutrients and microbes regulated plant–soil feedback (PSF) in a degraded alpine grassland. Our results indicated that soil total carbon (STC; from 17.66 to 12.55 g/kg) and total nitrogen (STN; from 3.16 to 2.74 g/kg) exhibited significant (P &amp;lt; 0.05) decrease from non-degraded (ND) to severely degraded (SD). Despite higher nutrients in ND soil generating significantly (P &amp;lt; 0.05) positive PSF (0.52) on monocots growth when the soil was sterilized, a high proportion of pathogens (36%) in ND non-sterilized soil resulted in a strong negative PSF on monocots. In contrast, the higher phenotypic plasticity of dicots coupled with a higher abundance of mutualists and saprophytes (70%) strongly promoted their survival and growth in SD with infertile soil. Our findings identified a novel mechanism that there was a functional group shift from monocots with higher vulnerability to soil pathogens in the ND fertile soil to dicots with higher dependence on nutritional mutualists in the degraded infertile soil. The emerging irreversible eco-evolutionary in PSF after degradation might cause a predicament for the restoration of degraded grassland.

The potential of soil microbial communities to transform deoxynivalenol in agricultural soils—a soil microcosm study

Infestation of cereal fields with toxigenic Fusarium species is identified as an environmental source for the mycotoxin deoxynivalenol (DON). During rain events, DON may be washed off from infested plants and enter the soil, where microbial transformation may occur. Although some studies showed DON transformation potential of soil microbial communities in liquid soil extracts, these findings can not be transferred to environmental conditions. Accordingly, microbial transformation of DON in soil has to be investigated under realistic conditions, e.g., microcosms mimicking field situations. In this study, we investigated the potential of soil microbial communities to transform DON in six different agricultural soils at two levels (0.5 and 5 µg g–1). The dissipation and the formation of transformation products were investigated in a period of 35 days and compared to a sterilized control. In addition, we measured soil respiration and applied the phospholipid-derived fatty acid (PLFA) analysis to assess whether soil microbial community characteristics are related to the microbial transformation potential. Dissipation of DON in non-sterilized soils was fast (50% dissipation within 0.6–3.7 days) compared to the sterile control where almost no dissipation was observed. Thus, dissipation was mainly attributed to microbial transformation. We verified that small amounts of DON are transformed to 3-keto-deoxynivalenol (3-keto-DON) and 3-epi-deoxynivalenol (3-epi-DON), which were not detectable after 16-day incubation, indicating further transformation processes. There was a trend towards faster transformation in soils with active and large microbial communities and low fungi-to-bacteria ratio.

Exploration of the biodegradation pathway and enhanced removal of imazethapyr from soil by immobilized Bacillus marcorestinctum YN1

Excessive or inappropriate applications of imazethapyr cause severe ecological deteriorations and health risks in human. A novel bacterial strain, i.e., Bacillus marcorestinctum YN1, was isolated to efficiently degrade imazethapyr, with the degradation pathways and intermediates predicted. Protein mass spectrometry analysis identified enzymes in strain YN1 potentially involved in imazethapyr biodegradation, including methylenetetrahydrofolate dehydrogenase, carbon-nitrogen family hydrolase, heme degrading monooxygenase, and cytochrome P450. The strain YN1 was further immobilized with biochar (BC600) prepared from mushroom waste (i.e., spent mushroom substrate) by pyrolysis at 600 °C to evaluate its degrading characteristics of imazethapyr. Scanning electron microscope observation showed that strain YN1 was adsorbed in the rich pore structure of BC600 and the adsorption efficiency reached the maximum level of 88.02% in 6 h. Both energy dispersive X-ray and Fourier transform infrared spectroscopy analyses showed that BC600 contained many elements and functional groups. The results of liquid chromatography showed that biochar-immobilized strain YN1 (IBC-YN1) improved the degradation rate of imazethapyr from 79.2% to 87.4%. The degradation rate of imazethapyr by IBC-YN1 could still reach 81.0% in the third recycle, while the bacterial survival rate was 67.73% after 180 d storage at 4 °C. The treatment of IBC-YN1 significantly shortened the half-life of imazethapyr in non-sterilized soil from 35.51 to 11.36 d, and the vegetative growth of imazethapyr sensitive crop plant (i.e., Cucumis sativus L.) was significantly increased in soil remediated, showing that the inhibition rate of root length and fresh weight were decreased by 12.45% and 38.49% respectively. This study exhanced our understanding of microbial catabolism of imazethapyr, and provided a potential in situ remediation strategy for improving the soil environment polluted by imazethapyr.

The unexpected effect of the compound microbial agent NP-M2 on microbial community dynamics in a nonylphenol-contaminated soil: the self-stability of soil ecosystem.

Nonylphenol (NP) is widely recognized as a crucial environmental endocrine-disrupting chemical and persistent toxic substance. The remediation of NP-contaminated sites primarily relies on biological degradation. Compound microbial products, as opposed to pure strains, possess a greater variety of metabolic pathways and can thrive in a wider range of environmental conditions. This characteristic is believed to facilitate the synergistic degradation of pollutants. Limited research has been conducted to thoroughly examine the potential compatibility of compound microbial agents with indigenous microflora, their ability to function effectively in practical environments, their capacity to enhance the dissipation of NP, and their potential to improve soil physicochemical and biological characteristics. In order to efficiently eliminate NP in contaminated soil in an eco-friendly manner, a simulation study was conducted to investigate the impact of bioaugmentation using the functional compound microbial agent NP-M2 at varying concentrations (50 and 200 mg/L) on the dynamics of the soil microbial community. The treatments were set as follows: sterilized soil with 50 mg/kg NP (CK50) or 200 mg/kg NP (CK200); non-sterilized soil with 50 mg/kg NP (TU50) or 200 mg/kg NP (TU200); non-sterilized soil with the compound microbial agent NP-M2 at 50 mg/kg NP (J50) or 200 mg/kg NP (J200). Full-length 16S rRNA analysis was performed using the PacBio Sequel II platform. Both the indigenous microbes (TU50 and TU200 treatments) and the application of NP-M2 (J50 and J200 treatments) exhibited rapid NP removal, with removal rates ranging from 93% to 99%. The application of NP-M2 further accelerated the degradation rate of NP for a subtle lag period. Although the different treatments had minimal impacts on the soil bacterial α-diversity, they significantly altered the β-diversity and composition of the bacterial community. The dominant phyla were Proteobacteria (35.54%-44.14%), Acidobacteria (13.55%-17.07%), Planctomycetes (10.78%-11.42%), Bacteroidetes (5.60%-10.74%), and Actinobacteria (6.44%-8.68%). The core species were Luteitalea_pratensis, Pyrinomonas_methylaliphatogenes, Fimbriiglobus_ruber, Longimicrobium_terrae, and Massilia_sp003590855. The bacterial community structure and taxon distribution in polluted soils were significantly influenced by the activities of soil catalase, sucrase, and polyphenol oxidase, which were identified as the major environmental factors. Notably, the concentration of NP and, to a lesser extent, the compound microbial agent NP-M2 were found to cause major shifts in the bacterial community. This study highlights the importance of conducting bioremediation experiments in conjunction with microbiome assessment to better understand the impact of bioaugmentation/biostimulation on the potential functions of complex microbial communities present in contaminated soils, which is essential for bioremediation success.

Prior Infection by Colletotrichum spinaciae Lowers the Susceptibility to Infection by Powdery Mildew in Common Vetch.

Anthracnose (Colletotrichum spinaciae) and powdery mildew (Erysiphe pisi) are important diseases of common vetch (Vicia sativa) and often co-occur in the same plant. Here, we evaluate how C. spinaciae infection affects susceptibility to E. pisi, using sterilized and non-sterilized field soil to test the effect of resident soil microorganisms on the plant's immune response. Plants infected with C. spinaciae (C+) exhibited a respective 41.77~44.16% and 72.37~75.27% lower incidence and severity of powdery mildew than uninfected (C-) plants. Moreover, the net photosynthetic rate, transpiration rate, and stomatal conductance were higher in the C- plants than in the C+ plants prior to infection with powdery mildew. These differences were not recorded following powdery mildew infection. Additionally, the activities of superoxide dismutase, polyphenol oxidase, and catalase were higher in the C+ plants than in the C- plants. The resident soil microbiota did not affect the plant responses to both pathogens. By uncovering the mechanistic basis of plant immune response, our study informs integrated disease management in a globally important forage crop.