Recent advances in the use of Trichoderma-containing multicomponent microbial inoculants for pathogen control and plant growth promotion.

Chemical pesticides and fertilizers are used in agricultural production worldwide to prevent damage from plant pathogenic microorganisms, insects, and nematodes, to minimize crop losses and to preserve crop quality. However, the use of chemical pesticides and fertilizers can severely pollute soil, water, and air, posing risks to the environment and human health. Consequently, developing new, alternative, environment-friendly microbial soil treatment interventions for plant protection and crop yield increase has become indispensable. Members of the filamentous fungal genus Trichoderma (Ascomycota, Sordariomycetes, Hypocreales) have long been known as efficient antagonists of plant pathogenic microorganisms based on various beneficial traits and abilities of these fungi. This minireview aims to discuss the advances in the field of Trichoderma-containing multicomponent microbiological inoculants based on recent experimental updates. Trichoderma strains can be combined with each other, with other fungi and/or with beneficial bacteria. The development and field performance of such inoculants will be addressed, focusing on the complementarity, synergy, and compatibility of their microbial components.

Response of antioxidant activity, active constituent and rhizosphere microorganisms of Salvia miltiorrhiza to combined application of microbial inoculant, microalgae and biochar under Cu stress.

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.

Control of nitrogen and odor emissions during chicken manure composting with a carbon-based microbial inoculant and a biotrickling filter.

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.

Performance of microbial inoculation and tricalcium phosphate on nitrogen retention and conversion: Core microorganisms and enzyme activity during kitchen waste composting.

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.

Niche availability and competitive loss by facilitation control proliferation of bacterial strains intended for soil microbiome interventions.

Microbiome engineering - the targeted manipulation of microbial communities - is considered a promising strategy to restore ecosystems, but experimental support and mechanistic understanding are required. Here, we show that bacterial inoculants for soil microbiome engineering may fail to establish because they inadvertently facilitate growth of native resident microbiomes. By generating soil microcosms in presence or absence of standardized soil resident communities, we show how different nutrient availabilities limit outgrowth of focal bacterial inoculants (three Pseudomonads), and how this might be improved by adding an artificial, inoculant-selective nutrient niche. Through random paired interaction assays in agarose micro-beads, we demonstrate that, in addition to direct competition, inoculants lose competitiveness by facilitating growth of resident soil bacteria. Metatranscriptomics experiments with toluene as selective nutrient niche for the inoculant Pseudomonas veronii indicate that this facilitation is due to loss and uptake of excreted metabolites by resident taxa. Generation of selective nutrient niches for inoculants may help to favor their proliferation for the duration of their intended action while limiting their competitive loss.

Plant Biostimulant as an Environmentally Friendly Alternative to Modern Agriculture.

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.

Impact of bacterial and fungal inoculants on the resident rhizosphere microbiome and the volatilome of tomato plants under leaf herbivory stress.

Various studies have addressed the impact of microbial inoculants on the composition of the resident microbiome. How microbial inoculants impact plant metabolism and interact with the resident rhizobiota under herbivory stress remains elusive. Here, we investigated the impact of two bacterial and two fungal inoculants, inoculated as single species and as a synthetic community, on the rhizosphere microbiome and volatilome of tomato plants (Solanum lycopersicum) comparing nonstress conditions to exposed to leaf herbivory by Spodoptera exigua. Based on amplicon sequencing analysis, rhizobacterial community composition was significantly affected by all four inoculants and the magnitude of this effect was dependent on herbivory stress. Fungal community composition was altered by the microbial inoculants but independent of herbivory stress. The rhizosphere volatilome was impacted by the microbial inoculation and differences between treatments were evened under herbivory stress. Each microbial inoculant caused unique changes in the volatilome of stressed plants but also shared similar responses, in particular the enhanced production of dimethyl disulfide and benzothiazole. In conclusion, the introduction of microbial inoculants in the tomato rhizosphere caused unique as well as common changes in the rhizosphere microbiome and volatilome, but these changes were minor compared to the microbiome changes induced by herbivory stress.

Survival of a microbial inoculant in soil after recurrent inoculations.

Microbial inoculants are attracting growing interest in agriculture, but their efficacy remains unreliable in relation to their poor survival, partly due to the competition with the soil resident community. We hypothesised that recurrent inoculation could gradually alleviate this competition and improve the survival of the inoculant while increasing its impact on the resident bacterial community. We tested the effectiveness of such strategy with four inoculation sequences of Pseudomonas fluorescens strain B177 in soil microcosms with increasing number and frequency of inoculation, compared to a non-inoculated control. Each sequence was carried out at two inoculation densities (106 and 108 cfu.g soil-1). The four-inoculation sequence induced a higher abundance of P. fluorescens, 2 weeks after the last inoculation. No impact of inoculation sequences was observed on the resident community diversity and composition. Differential abundance analysis identified only 28 out of 576 dominants OTUs affected by the high-density inoculum, whatever the inoculation sequence. Recurrent inoculations induced a strong accumulation of nitrate, not explained by the abundance of nitrifying or nitrate-reducing microorganisms. In summary, inoculant density rather than inoculation pattern matters for inoculation effect on the resident bacterial communities, while recurrent inoculation allowed to slightly enhance the survival of the inoculant and strongly increased soil nitrate content.

Use of ginger extract and bacterial inoculants for the suppression of Alternaria solani causing early blight disease in Tomato.

Early blight (EB), caused by Alternaria solani, is a serious problem in tomato production. Plant growth-promoting rhizobacteria promote plant growth and inhibit plant disease. The present study explored the bio-efficacy of synergistic effect of rhizobacterial isolates and ginger powder extract (GPE) against tomato EB disease, singly and in combination. Six fungal isolates from symptomatic tomato plants were identified as A. solani on the basis of morphological features i.e., horizontal septation (6.96 to 7.93 µm), vertical septation (1.50 to 2.22 µm), conidia length (174.2 to 187.6 µm), conidial width (14.09 to 16.52 µm), beak length (93.06 to 102.26 µm), and sporulation. Five of the twenty-three bacterial isolates recovered from tomato rhizosphere soil were nonpathogenic to tomato seedlings and were compatible with each other and with GPE. Out of five isolates tested individually, three isolates (St-149D, Hyd-13Z, and Gb-T23) showed maximum inhibition (56.3%, 48.3%, and 42.0% respectively) against mycelial growth of A. solani. Among combinations, St-149D + GPE had the highest mycelial growth inhibition (76.9%) over the untreated control. Bacterial strains molecularly characterized as Pseudomonas putida, Bacillus subtilis, and Bacillus cereus and were further tested in pot trials through seed bacterization for disease control. Seeds treated with bacterial consortia + GPE had the highest disease suppression percentage (78.1%), followed by St-149D + GPE (72.2%) and Hyd-13Z + GPE (67.5%). Maximum seed germination was obtained in the bacterial consortia + GPE (95.0 ± 2.04) followed by St-149D + GPE (92.5 ± 1.44) and Hyd-13Z + GPE (90.0 ± 2.04) over control (73.8 ± 2.39) and chemical control as standard treatment (90.0 ± 2). Ginger powder extracts also induce the activation of defence-related enzymes (TPC, PO, PPO, PAL, and CAT) activity in tomato plants. These were highly significant in the testing bacterial inoculants against A. solani infection in tomato crops.

Enhancing systematic tolerance in Bermuda grass (Cynodon dactylon L.) through amplified alkB gene expression and bacterial-driven hydrocarbon degradation.

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.

Adsorption mechanism of Cd2+ on microbial inoculant and its potential for remediation Cd-polluted farmland soils.

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.

Incorporating microbial inoculants to reduce nitrogen loss during sludge composting by suppressing denitrification and promoting ammonia assimilation.

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.

Identification of synthetic consortia from a set of plant-beneficial bacteria.

The use of microbial inoculants in agriculture as biofertilisers and/or biopesticides is an appealing alternative to replace or reduce the practice of agrochemicals. Plant microbiota studies are revealing the different bacterial groups which are populating plant microbiomes re-energising the plant probiotic bacteria (PPB) translational research sector. Some single-microbial strain bioinoculants have proven valid in agriculture (e.g., based on Trichoderma, mycorrhiza or rhizobia); however, it is now recommended to consider multistrain consortia since plant-beneficial effects are often a result of community-level interactions in plant microbiomes. A limiting step is the selection of a fitting combination of microbial strains in order to accomplish the best beneficial effect upon plant inoculation. In this study, we have used a subset of 23 previously identified and characterised rice-beneficial bacterial colonisers to design and test a series of associated experiments aimed to identify potential PPB consortia which are able to co-colonise and induce plant growth promotion. Bacterial strains were co-inoculated in vitro and in planta using several different methods and their co-colonisation and co-persistence monitored. Results include the identification of two 5-strain and one 2-strain consortia which displayed plant growth-promoting features. Future practical applications of microbiome research must include experiments aimed at identifying consortia of bacteria which can be most effective as crop amendments.

Deciphering the interaction of bacteria inoculants with the recipient endophytic community in grapevine micropropagated plants.

Engineering the plant microbiome with beneficial endophytic bacteria can improve the growth, health, and productivity of the holobiont. Here, we administered two beneficial bacterial strains, Kosakonia VR04 sp. and Rhizobium GR12 sp., to micropropagated grapevine cuttings obtained via somatic embryogenesis. While both strains colonized the plant endosphere, only Rhizobium GR12 sp. increased root biomass under nutritional-deficit conditions, as supported by the plant growth promotion traits detected in its genome. Phylogenetic and co-occurrence analyses revealed that the plant native bacterial community, originally dominated by Streptococcaceae and Micrococcaceae, dramatically changed depending on the inoculation treatments, as invading strains differently affected the relative abundance and the interactions of pre-existing taxa. After 30 days of plantlets' growth, Pantoea became a predominant taxon, and considering untreated plantlets as references, Rhizobium sp. GR12 showed a minor impact on the endophytic bacterial community. On the other hand, Kosakonia sp. VR04 caused a major change in community composition, suggesting an opportunistic colonization pattern. Overall, the results corroborate the importance of preserving the native endophytic community structure and functions during plant microbiome engineering.IMPORTANCEA better comprehension of bacterial colonization processes and outcomes could benefit the use of plant probiotics in the field. In this study, we applied two different beneficial bacteria to grapevine micropropagated plantlets and described how the inoculation of these strains impacts endophytic microbiota assembly. We showed that under nutritional deficit conditions, the response of the receiving endophytic bacterial communities to the invasion of the beneficial strains related to the manifestation of plant growth promotion effects by the inoculated invading strains. Rhizobium sp. GR12 was able to preserve the native microbiome structure despite its effective colonization, highlighting the importance of the plant-endophyte associations for the holobiont performance. Moreover, our approach showed that the use of micropropagated plantlets could be a valuable strategy to study the interplay among the plant, its native microbiota, and the invader on a wider portfolio of species besides model plants, facilitating the application of new knowledge in agriculture.

Variation Among Japanese Miso Breweries in Indoor Microbiomes is Mainly Ascribed to Variation in Type of Indoor Surface.

Miso is a microbially-fermented soybean food. The miso brewery indoor microbiome contributes to miso fermentation. Japanese breweries are not climate-controlled, so indoor spaces are strongly affected by the prevailing climate. Because climate influences microorganism distribution, our first hypothesis is that latitude, as a proxy for climate, is a major determinant of brewery indoor microbiome structure. Breweries vary in interior surface materials and in the way operations (steaming, processing, fermenting) are apportioned among rooms. Therefore, our second hypothesis is that more variability in indoor microbiomes exists among breweries than can be ascribed to a latitudinal gradient. Most miso produced today is inoculated with commercial microbial strains to standardize fermentation. If commercial strains outcompete indigenous microbes for membership in the indoor microbiome, this practice may homogenize indoor microbiomes among regions or breweries. Therefore, our third hypothesis is that inoculant fungal species dominate indoor fungal communities and make it impossible to distinguish communities among breweries or across their latitudinal gradient. We tested these hypotheses by sampling indoor surfaces in several breweries across a latitudinal gradient in Japan. We found that latitude had a significant but relatively small impact on indoor fungal and bacterial communities, that the effect of brewery was large relative to latitude, and that inoculant fungi made such small contributions to the indoor microbiome that distinctions among breweries and along the latitudinal gradient remained apparent. Recently, the Japanese Ministry of Agriculture, Forestry and Fisheries specified fungal inoculants to standardize miso production. However, this may not be possible so long as the indoor microbiome remains uncontrolled.

Autumn grass treated with a hydrolysable tannin extract versus lactic acid bacteria inoculant: Effects on silage fermentation characteristics and nutritional value and on performance of lactating dairy cows.

Hydrolysable tannins (HT) show potential as silage additive for autumn herbage silages, high in (rumen degradable) protein, as they may reduce proteolysis. Additionally, they have abilities to form pH-reversible tannin-protein complexes, non-degradable in the rumen but degradable in the abomasum and intestines of ruminants. Therefore they can improve milk N efficiency and shift N excretions from urine to faeces, possibly mitigating the environmental impact of ruminants. In this study, two small bunker silos were filled with autumn grass. One was treated with 20 g/kg DM HT extract (TAN) (TannoSan-L), the other with 8 mg/kg DM inoculant containing lactic acid bacteria (INO) (Bonsilage Fit G). Secondly, micro-silos (2.75 L) were filled with four treatments; (1) grass without additive (CON) (n = 5); (2) TAN (n = 5); (3) INO (n = 5); and (4) TAN + INO (n = 5). The bunker silos were used in a cross-over feeding experiment with periods of 4 weeks involving 22 lactating Holstein cows (average ± SD: 183 ± 36.3 days in milk, 665 ± 71.0 kg body weight, and 33.8 ± 3.91 kg/day milk yield). The HT dose was insufficient to reduce proteolysis or alter chemical composition and nutritional value in the micro- and bunker silages. Including grass silage added with TAN (3.2 g HT/kg DM) in the diet, did not affect feed intake nor fat and protein corrected milk yield in comparison to feeding the grass silage added with INO in a similar diet. The TAN-fed cows had an increased faecal N excretion and decreased apparent total-tract N and organic matter digestibility, but no improvement in the cows' N utilization could be confirmed in milk and blood urea levels. Overall, feeding an autumn grass silage treated with 20 g/kg chestnut HT extract did not affect the performance of dairy cows in comparison to feeding an autumn grass silage treated with a lactic acid bacteria inoculant.

Granular bacterial inoculant alters the rhizosphere microbiome and soil aggregate fractionation to affect phosphorus fractions and maize growth.

The constraint of phosphorus (P) fixation on crop production in alkaline calcareous soils can be alleviated by applying bioinoculants. However, the impact of bacterial inoculants on this process remains inadequately understood. Here, a field study was conducted to investigate the effect of a high-concentration, cost-effective, and slow-release granular bacterial inoculant (GBI) on maize (Zea mays L.) plant growth. Additionally, we explored the effects of GBI on rhizosphere soil aggregate physicochemical properties, rhizosphere soil P fraction, and microbial communities within aggregates. The outcomes showed a considerable improvement in plant growth and P uptake upon application of the GBI. The application of GBI significantly enhanced the AP, phoD gene abundance, alkaline phosphatase activity, inorganic P fractions, and organic P fractions in large macroaggregates. Furthermore, GBI impacted soil aggregate fractionation, leading to substantial alterations in the composition of fungal and bacterial communities. Notably, key microbial taxa involved in P-cycling, such as Saccharimonadales and Mortierella, exhibited enrichment in the rhizosphere soil of plants treated with GBI. Overall, our study provides valuable insight into the impact of GBI application on microbial distributions and P fractions within aggregates of alkaline calcareous soils, crucial for fostering healthy root development and optimal crop growth potential. Subsequent research endeavors should delve into exploring the effects of diverse GBIs and specific aggregate types on P fraction and community composition across various soil profiles.

Synthesis and application of a compound microbial inoculant for effective soil remediation.

Currently, there is a noticeable scarcity of applications that harness composite microbial inoculants to stimulate straw decomposition, nitrogen fixation, and crop growth. This study addresses this gap by selecting and coculturing three bacterial strains to create a composite microbial inoculant named HY-1. This innovative inoculant exhibits multifunctional capabilities, including nitrogen fixation, straw decomposition, and crop growth promotion. Furthermore, we aimed to explore its impact on soil microbial communities. The results showed that the optimal preparation conditions for the compound microbial inoculant HY-1 were 28.5 ± 0.6 °C, pH = 7.34 ± 0.40, and bacteriophage ratio 1:2:1 (Microbacterium: Streptomyces fasciatus: Bacillus amyloliquefaciens). Compared to single strains, the combination exhibited higher levels of cellulose-degrading and nitrogen-fixing enzyme activity, increased the straw degradation rate by 37.91% within 180 days, and significantly promoted the growth of corn seedlings. Under the condition of straw return, the compound bio-fungicide HY-1 effectively improved the soil microbial diversity. At that time, the soil had the highest number of unique bacterial operational taxonomic units (166), and the abundance of Proteobacteria in the soil increased by 7.24%, while that of Acidobacteriota decreased by 2.27%. The biosynthetic function of the cell wall/membrane/periplasm and the metabolic function of transporting inorganic ions were significantly enhanced. In this study, we discovered that employing coculturing techniques to produce the composite microbial inoculant HY-1 and applying it in the field effectively compensates for the limitations of single-strain inoculants, which often exhibit fewer functions and less pronounced effects. This approach demonstrates significant potential for enhancing the quality of agricultural soils.

Combined application of microbial inoculant and kelp-soaking wastewater promotes wheat seedlings growth and improves structural diversity of rhizosphere microbial community.

Industrial processing of kelp generates large amounts of kelp-soaking wastewater (KSW), which contains a large amount of nutrient-containing substances. The plant growth-promoting effect might be further improved by combined application of growth-promoting bacteria and the nutrient-containing KSW. Here, a greenhouse experiment was conducted to determine the effect of the mixture of KSW and Bacillus methylotrophicus M4-1 (MS) vs. KSW alone (SE) on wheat seedlings, soil properties and the microbial community structure in wheat rhizosphere soil. The available potassium, available nitrogen, organic matter content and urease activity of MS soil as well as the available potassium of the SE soil were significantly different (p < 0.05) from those of the CK with water only added, increased by 39.51%, 36.25%, 41.61%, 80.56% and 32.99%, respectively. The dry and fresh weight of wheat seedlings from MS plants increased by 166.17% and 50.62%, respectively, while plant height increased by 16.99%, compared with CK. Moreover, the abundance and diversity of fungi in the wheat rhizosphere soil were significantly increased (p < 0.05), the relative abundance of Ascomycetes and Fusarium spp. decreased, while the relative abundance of Bacillus and Mortierella increased. Collectively, the combination of KSW and the plant growth-promoting strain M4-1 can promote wheat seedlings growth and improve the microecology of rhizosphere microorganisms, thereby solving the problems of resource waste and environmental pollution, ultimately turning waste into economic gain.

Microbial inoculants with higher capacity to colonize soils improved wheat drought tolerance.

Microbial inoculants have gained increasing attention worldwide as an eco-friendly solution for improving agriculture productivity. Several studies have demonstrated their potential benefits, such as enhanced resistance to drought, salinity, and pathogens. However, the beneficial impacts of inoculants remain inconsistent. This variability is attributed to limited knowledge of the mechanisms by which microbial inoculants affect crop growth and a lack of ecological characteristics of these inoculants that limit our ability to predict their beneficial effects. The first important step is believed to be the evaluation of the inoculant's ability to colonize new habitats (soils and plant roots), which could provide crops with beneficial functions and improve the consistency and efficiency of the inoculants. In this study, we aimed to investigate the impact of three microbial inoculants (two bacterial: P1 and P2, and one fungal: P3) on the growth and stress responses of three wheat varieties in two different soil types under drought conditions. Furthermore, we investigated the impact of microbial inoculants on soil microbial communities. Plant biomass and traits were measured, and high-throughput sequencing was used to characterize bulk and rhizosphere soil microbiomes after exposure to drought stress. Under drought conditions, plant shoot weight significantly increased (11.37%) under P1 treatments compared to uninoculated controls. In addition, total nitrogen enzyme activity increased significantly under P1 in sandy soil but not in clay soil. Importantly, network analyses revealed that P1, consisting of Bacillus paralicheniformis and Bacillus subtilis, emerged as the keystone taxa in sandy soil. Conversely, P2 and P3 failed to establish as keystone taxa, which may explain their insignificant impact on wheat performance under drought conditions. In conclusion, our study emphasizes the importance of effective colonization by microbial inoculants in promoting crop growth under drought conditions. Our findings support the development of microbial inoculants that robustly colonize plant roots for improved agricultural productivity.