Over-application of chemical fertilizers and continuous cropping obstacles seriously restrict the sustainable development of tobacco production. Localized fertilization of beneficial microbes has potential advantages in achieving higher productivity, but the underlying biological mechanisms of interactions between rhizospheric microorganisms and the related metabolic cycle remain poorly characterized. Here, an integrative analysis of microbiomes with non-targeted metabolomics was performed on 30 soil samples of rhizosphere, root surrounding, and bulk soils from flue-cured tobacco under continuous and non-continuous monocropping systems. The analysis was conducted using UPLC-MS/MS platforms and high-throughput amplicon sequencing targeting the bacterial 16S rRNA gene and fungal ITS gene. The microbial inoculant consisted of Bacillus subtilis, B. velezensis, and B. licheniformis at the ratio of 1:1:1 in effective microbial counts, improved the cured leaf yield and disease resistance of tobacco, and enhanced nicotine and nitrogen contents of tobacco leaves. The bacterial taxa Rhizobium, Pseudomonas, Sphingomonadaceae, and Burkholderiaceae of the phylum Proteobacteria accumulated in high relative abundance and were identified as biomarkers following the application of the microbial inoculant. Under continuous monocropping, metabolomics demonstrated that the application of the microbial inoculant significantly affected the soil metabolite spectrum, and the differential metabolites were significantly enriched to the synthesis and degradation of nicotine (nicotinate and nicotinamide metabolism and biosynthesis of alkaloids derived from nicotinic acid). In addition, microbes were closely related to the accumulation of metabolites through correlation analysis. The interactions between plant roots and rhizospheric microorganisms provide valuable information for understanding how these beneficial microbes affect complex biological processes and the adaption capacity of plants to environments.IMPORTANCEThis study elaborated on how the microbial fertilizer significantly changed overall community structures and metabolite spectrum of rhizospheric microbes, which provide insights into the process of rhizosphere microbial remolding in response to continuous monocropping. we verified the hypothesis that the application of the microbial inoculant in continuous cropping would lead to the selection of distinct microbiota communities by establishing models to correlate biomarkers. Through correlation analysis of the microbiome and metabolome, we proved that rhizospheric microbes were closely related to the accumulation of metabolites, including the synthesis and degradation of nicotine. The interactions between plant roots and rhizospheric microorganisms provide valuable information for understanding how these beneficial microbes affect complex biological processes and the adaption capacity of plants to environments.

Microbial inoculation involves transplanting microorganisms from their natural habitat to new plants or soils to improve plant performance, and it is being increasingly used in agriculture and ecological restoration. However, microbial inoculants can invade and alter the composition of native microbial communities; thus, a comprehensive analysis is urgently needed to understand the overall impact of microbial inoculants on the biomass, diversity, structure and network complexity of native communities. Here we provide a meta-analysis of 335 studies revealing a positive effect of microbial inoculants on soil microbial biomass. This positive effect was weakened by environmental stress and enhanced by the use of fertilizers and native inoculants. Although microbial inoculants did not alter microbial diversity, they induced major changes in the structure and bacterial composition of soil microbial communities, reducing the complexity of bacterial networks and increasing network stability. Finally, higher initial levels of soil nutrients amplified the positive impact of microbial inoculants on fungal biomass, actinobacterial biomass, microbial biomass carbon and microbial biomass nitrogen. Together, our results highlight the positive effects of microbial inoculants on soil microbial biomass, emphasizing the benefits of native inoculants and the important regulatory roles of soil nutrient levels and environmental stress.

Although aerobic composting is usually utilized in livestock manure disposal, the emission of odorous gases from compost not only induces harm to the human body and the environment, but also causes loss of nitrogen, sulfur, and other essential elements, resulting in a decline in product quality. The impact of biotrickling filter (BTF) and insertion of carbon-based microbial agent (CBMA) on compost maturation, odor emissions, and microbial population during the chicken manure composting were assessed in the current experiment. Compared with the CK group, CBMA addition accelerated the increase in pile temperature (EG group reached maximum temperature 10 days earlier than CK group), increased compost maturation (GI showed the highest increase of 41.3% on day 14 in EG group), resulted in 36.59% and 14.60% increase in NO3--N content and the total nitrogen retention preservation rate after composting. The deodorization effect of biotrickling filter was stable, and the removal rates of NH3, H2S, and TVOCs reached more than 90%, 96%, and 56%, respectively. Furthermore, microbial sequencing showed that CBMA effectively changed the microbial community in compost, protected the ammonia-oxidizing microorganisms, and strengthened the nitrification of the compost. In addition, the nitrifying and denitrifying bacteria were more active in the cooling period than they were in the thermophilic period. Moreover, the abundance of denitrification genes containing nirS, nirK, and nosZ in EG group was lower than that in CK group. Thus, a large amount of nitrogen was retained under the combined drive of BTF and CBMA during composting. This study made significant contributions to our understanding of how to compost livestock manure while reducing releases of odors and raising compost quality.

The substantial release of NH3 during composting leads to nitrogen (N) losses and poses environmental hazards. Additives can mitigate nitrogen loss by adsorbing NH3/NH4, adjusting pH, and enhancing nitrification, thereby improving compost quality. Herein, we assessed the effects of combining bacterial inoculants (BI) (1.5%) with tricalcium phosphate (CA) (2.5%) on N retention, organic N conversion, bacterial biomass, functional genes, network patterns, and enzyme activity during kitchen waste (KW) composting. Results revealed that adding of 1.5%/2.5% (BI + CA) significantly (p < 0.05) improved ecological parameters, including pH (7.82), electrical conductivity (3.49 mS/cm), and N retention during composting. The bacterial network properties of CA (265 node) and BI + CA (341 node) exhibited a substantial niche overlap compared to CK (210 node). Additionally, treatments increased organic N and total N (TN) content while reducing NH4+-N by 65.42% (CA) and 77.56% (BI + CA) compared to the control (33%). The treatments, particularly BI + CA, significantly (p < 0.05) increased amino acid N, hydrolyzable unknown N (HUN), and amide N, while amino sugar N decreased due to bacterial consumption. Network analysis revealed that the combination expanded the core bacterial nodes and edges involved in organic N transformation. Key genes facilitating nitrogen mediation included nitrate reductase (nasC and nirA), nitrogenase (nifK and nifD), and hydroxylamine oxidase (hao). The structural equation model suggested that combined application (CA) and microbial inoculants enhance enzyme activity and bacterial interactions during composting, thereby improving nitrogen conversion and increasing the nutrient content of compost products.

We analyzed the particle size distribution of soil aggregates in 0-20 and 20-40 cm soil layers of rice-wheat rotation field based on a field plot test with two treatments, conventional straw returning (CK) and straw returning with the addition of straw decomposition promoting microbial inoculants (IT). We evaluated the water stability indices of soil aggregates (the number of soil water stable large aggregates R0.25, the average weight diameter MWD, and the geometric average diameter GMD), and measured the contents of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in the soil aggregates of ＜0.053, 0.053-0.25, 0.25-1, ＞1 mm. The results showed that: 1) The number of aggregates ＜0.053, 0.053-0.25, ＞0.25 mm in the 0-20 and 20-40 cm soil layers under IT decreased by 10.0% and 6.8%, increased by 3.0% and 5.7%, and 17.9% and 26.1% compared with CK, respectively. IT effectively increased R0.25, MWD, and GMD by 26.4%, 20.0%, 18.2% and 18.2%, 10.5%, 10.0% in 0-20 and 20-40 cm soil, respectively. 2) Compared to CK, the TP content of 0.25-1 mm aggregates in 0-20 and 20-40 cm soil under IT was significantly increased by 40.3% and 37.5%, respectively, without difference in TN and SOC contents. There was no significant difference in nutrient contents of the other aggregates between the treatments. The contents of SOC and TN in large aggregates (>0.25 mm) were higher than those in silty aggregates (<0.053 mm). Compared to CK, the cumulative contribution rates of SOC, TN and TP of <0.053 mm aggregates under IT were decreased in two soil layers. There was no significant difference in the nutrient cumulative contribution rates of 0.053-0.25 mm aggregates between treatments. The cumulative contribution rates of SOC, TN, and TP of large aggregates (>0.25 mm) under IT were 32.1%, 19.6%, 52.8% and 22.8%, 11.8%, 42.9% higher than those under CK in 0-20 and 20-40 cm soils, respectively. 3) The number of <0.053 mm aggregates was significantly negatively correlated with SOC and TP contents, while that of 0.053-0.25 mm aggregates was negatively correlated with nutrient content. The number of large aggregates (>0.25 mm) were significantly positively correlated with SOC, TN, and TP contents. In conclusion, straw returning with microbial-inoculant addition could promote the formation of soil macroaggregates (>0.25 mm), and improve the water stability of soil aggregates, increasing nutrient contents in soil macroaggregates, with the nutrients transferring from silty aggregates to macroaggregates.
采用大田小区试验,分析了常规秸秆还田(CK)和秸秆还田配施促腐菌剂(IT)两种处理下稻田0～20和20～40 cm土壤团聚体粒径分布,评估了土壤团聚体水稳定性(土壤水稳性大团聚体数量R0.25、平均重量直径MWD、几何平均直径GMD),并测定了不同粒径(＜0.053、0.053～0.25、0.25～1、＞1 mm)土壤团聚体中有机碳(SOC)、全氮(TN)、全磷(TP)的含量。结果表明: 1)IT处理＜0.053、0.053～0.25及＞0.25 mm团聚体数量在0～20和20～40 cm土层分别较CK下降10.0%和6.8%、提高3.0%和5.7%及17.9%和26.1%;与CK相比,IT有效提高了R0.25、MWD、GMD,在0～20和20～40 cm土层中分别提高了26.4%、20.0%、18.2%和18.2%、10.5%、10.0%。2)与CK相比,IT处理0～20和20～40 cm土层中0.25～1 mm粒级团聚体的TP含量分别显著提高了40.3%和37.5%,TN和SOC含量无显著差异;其他粒径各养分在两处理间无显著差异,大团聚体(＞0.25 mm)的SOC和TN含量高于粉黏团聚体(<0.053 mm)。不同土层IT处理<0.053 mm粒级团聚体的SOC、TN和TP累计贡献率较CK有所降低;0.053～0.25 mm粒级团聚体的养分累计贡献率与CK差异不显著;大团聚体(＞0.25 mm)的SOC、TN和TP累积贡献率在0～20和20～40 cm土层中较CK分别提高了32.1%、19.6%、52.8%和22.8%、11.8%、42.9%。3)土壤<0.053 mm粒级团聚体数量与SOC和TP含量呈显著负相关,0.053～0.25 mm团聚体数量与养分含量呈负相关,大团聚体(＞0.25 mm)数量与SOC、TN和TP含量呈显著正相关。综上,秸秆还田配施促腐菌剂可以促进土壤大团聚体(＞0.25 mm)形成,提高了团聚体水稳定性,增加了土壤大团聚体中养分含量,促使养分从粉黏团聚体向大团聚体转移。.

Salvia miltiorrhiza, a widely used medicinal herb renowned for its properties in promoting blood circulation, removing blood stasis and alleviating pain, is currently facing quality degradation due to excessive heavy metal levels, posing a threat to medication safety. In order to investigate the effects of microbial inoculant, microalgae and biochar on the growth of Salvia miltiorrhiza under copper (Cu) stress, as well as its Cu absorption, antioxidant activity, active component contents and rhizosphere microbial community, a pot experiment was conducted. Salvia miltiorrhiza plants were cultivated in the soil containing 400 mg/kg of Cu for six months and treated with microbial inoculant, microalgae and biochar, either individually or in combination. Almost all soil amendment treatments led to an increase in root biomass. Notably, co-application of microbial inoculant and microalgae had the optimal effect with a 63.07 % increase compared to the group treated solely with Cu. Moreover, when microbial inoculant was applied alone or in combination with microalgae, the Cu content in plant roots was reduced by 19.29 % and 25.37 %, respectively, whereas other treatments failed to show a decreasing trend. Intriguingly, Cu stress increased the active component contents in plant roots, and they could also be enhanced beyond non-stress levels when microbial inoculant and microalgae were applied together or in combination with biochar. Analyses of plant antioxidant activity, soil properties and rhizosphere microorganisms indicated that these amendments may alleviate Cu stress by enhancing peroxidase activity, facilitating plant nutrient absorption, and enriching beneficial microorganisms capable of promoting plant growth and mitigating heavy metal-induced damage. This study suggests that the combined application of microbial inoculant and microalgae can reduce Cu levels in Salvia miltiorrhiza while enhancing its quality under Cu stress.

Ensuring the safety of crop production presents a significant challenge to humanity. Pesticides and fertilizers are commonly used to eliminate external interference and provide nutrients, enabling crops to sustain growth and defense. However, the addition of chemical substances does not meet the environmental standards required for agricultural production. Recently, natural sources such as biostimulants have been found to help plants with growth and defense. The development of biostimulants provides new solutions for agricultural product safety and has become a widely utilized tool in agricultural. The review summarizes the classification of biostimulants, including humic-based biostimulant, protein-based biostimulant, oligosaccharide-based biostimulant, metabolites-based biostimulants, inorganic substance, and microbial inoculant. This review attempts to summarize suitable alternative technology that can address the problems and analyze the current state of biostimulants, summarizes the research mechanisms, and anticipates future technological developments and market trends, which provides comprehensive information for researchers to develop biostimulants.

This study aimed to access the impact of soil polluted with petroleum (5, 10 g petroleum kg-1 soil) on Bermuda grass (Cynodon dactylon L.) with and without applied bacterial inoculants (Arthrobacter oxydans ITRH49 and Pseudomonas sp. MixRI75). Both soil and seed were given bacterial inoculation. The evaluated morphological parameters of Bermuda grass were fresh and dry weight. The results demonstrated that applied bacterial inoculants enhanced 5.4%, 20%, 28% and 6.4%, 21%, and 29% shoot and root fresh/dry weights in Bermuda grass under controlled environment. The biochemical analysis of shoot and root was affected deleteriously by the 10 g petroleum kg-1 soil pollution. Microbial inoculants enhanced the activities of enzymatic (catalase, peroxidase, glutathione reductase, ascorbate peroxidase, superoxide dismutase) and non-enzymatic (ɑ-tocopherols, proline, reduced glutathione, ascorbic acid) antioxidant to mitigate the toxic effects of ROS (H2O2) under hydrocarbon stressed condition. The maximum hydrocarbon degradation (75%) was recorded by Bermuda grass at 5 g petroleum kg-1 soil contamination. Moreover, bacterial persistence and alkane hydroxylase gene (alkB) abundance and expression were observed more in the root interior than in the rhizosphere and shoot interior of Bermuda grass. Subsequently, the microbe used a biological tool to propose that the application of plant growth-promoting bacteria would be the most favorable choice in petroleum hydrocarbon polluted soil to conquer the abiotic stress in plants and the effective removal of polyaromatic hydrocarbons in polluted soil.

The adsorption characteristics and mechanism of Cd2+ on microbial inoculant (MI) mainly composed of Bacillus subtilis, Bacillus thuringiensis and Bacillus amyloliquefaciens, and its potential for remediation Cd polluted soils through batch adsorption and soil incubation experiments. It was found that the Freundlich isotherm model and the pseudo-second-order kinetics were more in line with the adsorption processes of Cd2+. The maximum adsorption capacity predicted by Langmuir isotherm model suggested that of MI was 57.38 mg g-1. Scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) images exhibited the surface structure of MI was damaged to varying degrees after adsorption, and Cd element was distributed on the surface of MI through ion exchange. X-ray diffraction (XRD) results showed that CdCO3 was formed on the surface of MI. Moreover, the functional groups (-OH, C-H, and -NH) involved in the adsorption of Cd2+ through fourier transform infrared spectroscopy (FTIR). After applying MI to Cd-contaminated soil, it was found that soil pH, conductivity (EC) and soil organic matter (SOM) increased by 0.84 %-2.43 %, 31.6 %-241.48 %, and 8.11 %-24.1 %, respectively, when compared with the control treatments. The content of DTPA-Cd in the soils was significantly (P < 0.05) reduced by 15.48 %-29.68 % in contrast with CK, and the Cd speciation was transformed into a more stable residual fraction. The activities of urease, phosphatase and sucrose were increased by 3.5 %-45.18 %, 57.00 %-134.18 % and 52.51 %-70.52 %, respectively, compared with CK. Therefore, MI could be used as an ecofriendly and sustainable material for bioremediation of Cd-contaminated soils.

To address the challenge of increasing nitrogen retention in compost, this study investigated the effects of microbial communities on denitrification and ammonia assimilation during sludge composting by inoculating microbial inoculants. The results showed that the retention rates of total Kjeldahl nitrogen (TKN) and humic acid (HA) in MIs group (with microbial inoculants) were 4.94 % and 18.52 % higher than those in the control group (CK), respectively. Metagenomic analysis showed that Actinobacteria and Proteobacteria were identified as main microorganisms contributing to denitrification and ammonia assimilation. The addition of microbial agents altered the structure of the microbial community, which in turn stimulated the expression of functional genes. During cooling period, the ammonia assimilation genes glnA, gltB and gltD in MIs were 15.98 %, 24.84 % and 32.88 % higher than those in CK, respectively. Canonical correspondence analysis revealed a positive correlation between the dominant bacterial genera from the cooling stage to the maturity stage and the levels of NO3--N, NH4+-N, HA, and TKN contents. NH4+-N was positively correlated with HA, indicating NH4+-N might be incorporated into HA. Heat map and network analyses revealed NH4+-N as a key factor affecting functional genes of denitrification and ammonia assimilation, with Nitrospira identified as the core bacteria in the microbial network. Therefore, the addition of microbial agents could increase nitrogen retention and improve compost product quality.