Sugarcane is particularly exposed to water shortage because it has a long growth cycle, high biomass demand and substantial water and nutrient requirements. Prolonged deficit can suppress root development, photosynthesis, transpiration regulation, nitrogen uptake, stalk elongation and sucrose accumulation. The review cites yield reductions ranging from 30% to 60% under severe water deficit, with the magnitude varying by genotype and management. Drought also changes the rhizosphere itself: root architecture and exudation shift, nutrient diffusion slows, indigenous microbial communities reorganize and the carbon available to microbes changes. These dynamics determine whether introduced bacteria can establish and express their growth-promoting traits.

PGPR can act directly by producing phytohormones, mobilizing nutrients and altering root architecture. Candidate strains from genera including Bacillus, Azospirillum, Gluconacetobacter, Pseudomonas, Azotobacter, Rhizobium and Herbaspirillum have been associated with improved root biomass, chlorophyll content, water relations, nutrient uptake and antioxidant activity in sugarcane. Indole-3-acetic acid is among the mechanisms proposed to promote primary and lateral root development under water limitation, but the effective concentration range in sugarcane remains poorly defined. Excessive auxin can inhibit primary roots, while excessive abscisic acid can suppress growth and carbon assimilation. Evidence that bacterial hormone production directly causes drought tolerance in field-grown sugarcane is therefore limited.

Other direct mechanisms include phosphate, potassium, zinc, sulfur and silicon mobilization, as well as siderophore production and extracellular polymeric substances that may improve soil aggregation and water retention around roots. Under moderate water deficit, experiments have associated phosphate-solubilizing inoculation with increases of 8–18% in cane yield and improved sucrose content when microbes were combined with 75–100% of the recommended phosphorus fertilizer dose. These are condition-specific observations, not general effect estimates. Laboratory evidence also exists for zinc and silicate mobilization, yet direct demonstrations in drought-stressed sugarcane that these processes raise plant nutrient status, improve physiology and increase yield remain sparse.

Indirect mechanisms may also buffer drought stress. ACC deaminase cleaves 1-aminocyclopropane-1-carboxylate, the precursor of ethylene, and can reduce stress-induced ethylene that otherwise inhibits root elongation. Some sugarcane-associated Pseudomonas and Azospirillum strains have been linked with greater root growth, relative water content, chlorophyll retention and antioxidant-enzyme activity through this pathway, although activity is strain-specific and depends on microbial metabolism and colonization. Siderophores can improve iron acquisition and restrict pathogen growth by reducing iron availability. Biological nitrogen fixation by diazotrophs can contribute to nitrogen supply, but its contribution varies and commonly declines as drought intensifies. Field quantification of biological nitrogen fixation in drought-stressed sugarcane using isotopic techniques remains limited, and plant nitrogen status, yield and water-use efficiency have rarely been linked in the same experiments.

Pathogen suppression is a possible additional benefit, but it should be separated from direct drought tolerance. PGPR such as Bacillus, Pseudomonas and Streptomyces can inhibit important sugarcane pathogens, including Colletotrichum falcatum, Ceratocystis paradoxa and Sporisorium scitamineum, through antibiotics, siderophores, lytic enzymes, volatile compounds or induced systemic resistance. However, most studies of induced resistance come from other plants, and few experiments combine drought, pathogen challenge and inoculation in sugarcane. Biocontrol observed under adequate moisture cannot be assumed to persist when water shortage suppresses microbial metabolism, changes root exudation and alters plant–pathogen interactions. The review therefore treats disease suppression as a complementary, context-dependent possibility rather than a demonstrated cause of drought resilience.

Consortia are not automatically more effective than single strains. A consortium of two Bacillus megaterium strains, JTB1 and MT22, improved root development, biomass, antioxidant responses and photosynthetic gene expression in a pot experiment under differing water availability, but it did not consistently outperform the individual strains. This illustrates why a combination of potentially complementary traits cannot be assumed to be synergistic. The review distinguishes additive effects from true synergy, which requires the combined response to exceed the sum of individual effects. Factorial comparisons are needed to determine whether traits such as auxin production, ACC deaminase activity, nutrient mobilization and exopolysaccharide production interact beneficially or compete for limited microbial resources.

Translation from controlled environments to farms remains the central obstacle. The review reports that controlled experiments often show 20–60% improvements in plant-growth parameters after PGPR inoculation, whereas field trials commonly produce gains of 5–25% or inconsistent outcomes. These ranges summarize heterogeneous studies rather than a pooled meta-analysis. Sandy soils can change moisture rapidly and support weaker colonization than clay-rich soils, while pH, organic matter, mineralogy and indigenous communities alter nutrient availability and competitive pressure. Moderate drought may permit microbial establishment and nutrient mobilization; severe, prolonged drought can suppress root activity, exudation, microbial movement, nutrient diffusion and metabolite production. Inoculant persistence is rarely measured directly, making it difficult to distinguish biological failure from poor establishment.

Moving PGPR into reliable production will require standardized, multi-location and multi-season trials that follow plants from drought onset through peak stress and rewatering. Measurements should jointly track microbial survival and colonization, root exudation, soil moisture, pH, texture, organic matter, nutrient availability, plant physiology, water-use efficiency, cane yield and sucrose yield. Inoculation timing and severity thresholds should be tested across genotypes and soils, while neutral and negative results should be reported alongside benefits. Commercialization also depends on formulation stability, shelf life, compatibility with fertilizers and agrochemicals, industrial-scale quality control and cost–benefit analysis for a high-volume crop with often narrow margins. The review’s central conclusion is that PGPR are a promising component of integrated drought management, but not yet a universally reliable or independently validated route to resilient sugarcane production.

Subject of Research: Evaluation of plant growth-promoting rhizobacteria for drought resilience and nutrient acquisition in sugarcane

Article Title: Plant growth-promoting rhizobacteria as a soil-based strategy to improve nutrient acquisition and drought tolerance in sugarcane

Article References: Srivastava, A. K., Tiwari, R., Shukla, S. K., Srivastava, S., Srivastava, P., Srivastava, A., Jaiswal, V. P., & Tiwari, R. K. (2026). Plant growth-promoting rhizobacteria as a soil-based strategy to improve nutrient acquisition and drought tolerance in sugarcane. Discover Soil, 3(1), Article 173. https://doi.org/10.1007/s44378-026-00331-9

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00331-9

Keywords: sugarcane, drought stress, plant growth-promoting rhizobacteria, rhizosphere, nutrient acquisition, microbial inoculants, soil microbiology, field validation, drought management, Plant, growth-promoting, rhizobacteria

They collected rhizosphere soil from more than 20 individuals of each plant in each category, along with nearby non-rhizosphere soil. Three separate samples were collected for each soil type. High-throughput sequencing targeted bacterial 16S and fungal ITS regions, while 14 soil physicochemical and enzyme-activity indicators were measured.

The analysis detected 38,517 bacterial operational taxonomic units across 63 phyla and 518 genera, and 8,658 fungal OTUs across 15 phyla and 652 genera. Five alpha-diversity measures generally indicated greater richness and diversity under stronger waterlogging for both soil types associated with each plant. For R. acetosa, the reported rhizosphere Chao1 richness values were 3,433.82 ± 76.86 under weak stress and 3,676.56 ± 601.87 under strong stress.

Plant differences were clearer under weak stress than under strong stress. Rhizosphere bacterial Chao1 values under weak stress were 3,433.82 ± 76.86 for R. acetosa and 2,591.31 ± 882.75 for O. glauca. Under strong stress, the respective values were closer at 3,676.56 ± 601.87 and 3,549.41 ± 715.35.

Proteobacteria was the dominant bacterial phylum in samples associated with both plants, while Ascomycota led most fungal communities despite substantial variation among samples. In R. acetosa rhizosphere soil, Ascomycota represented 53.8% under strong stress, while Chytridiomycota, Glomeromycota and Rozellomycota together accounted for nearly 28%. In weak-stress O. glauca rhizosphere soil, Ascomycota represented about 60%, compared with 16.14% for Mortierellomycota and 17.00% for Chytridiomycota.

Linear discriminant analysis identified more fungal than bacterial biomarkers. R. acetosa had three fungal biomarkers in weak-stress rhizosphere soil, compared with 13 in strong-stress non-rhizosphere soil and 10 in strong-stress rhizosphere soil. O. glauca had three in strong-stress rhizosphere soil, five in weak-stress non-rhizosphere soil and 10 in strong-stress non-rhizosphere soil.

Bacterial biomarkers were less widespread, but weak-stress R. acetosa rhizosphere soil contained Bacteroidetes, Gammaproteobacteria and Ramlibacter. PICRUSt2 produced predicted rather than directly measured metabolic profiles. Aerobic respiration I, pathway PWY-3781, represented about 1.5% of predicted bacterial pathways, and stronger waterlogging had little effect on the relative abundance of the 10 leading predicted bacterial pathways.

PWY-3781 and aerobic respiration II in yeast, PWY-7279, were leading predicted fungal pathways across the tested soils. Redundancy analysis associated R. acetosa bacterial and fungal community variation with electrical conductivity and pH. The first two bacterial ordination axes explained 34.25% and 16.58% of relative-abundance variance, respectively.

For O. glauca, bacterial structure was associated with nitrate nitrogen, total ammonium nitrogen and several enzyme activities, while fungal structure was associated with electrical conductivity, a nitrogen variable, total nitrogen and urease activity. The study was limited to one reservoir section, two plant species and a single March sampling campaign. Because waterlogging intensity was classified by elevation, the categories may also reflect spatial or environmental differences.

The findings therefore show associations rather than causation, and predicted metabolic potential does not establish that inferred pathways were active in the sampled soils.

Subject of Research: Association of waterlogging intensity with rhizosphere and non-rhizosphere microbial diversity in two dominant plants in the Three Gorges Reservoir

Article Title: Rhizosphere microbial community structure in the water-level-fluctuation zone under distinct waterlogging stresses

Article References: Zhou, L., Wu, S., Ma, M., Zou, H., Huang, J., & Yang, J. (2024). Rhizosphere microbial community structure in the water-level-fluctuation zone under distinct waterlogging stresses. One Ecosystem, 9, Article e133645. https://doi.org/10.3897/oneeco.9.e133645

Image Credits: AI Generated

DOI: 10.3897/oneeco.9.e133645

Keywords: Three Gorges Reservoir, waterlogging stress, rhizosphere microbiomes, microbial diversity, Rumex acetosa, Oxybasis glauca, bacterial communities, fungal communities, soil ecology, Rhizosphere, microbial, community

The experiment was conducted at the Training and Experimental Station of the Agricultural University of Plovdiv in southern Bulgaria. The site had a Mollic Fluvisol with an initial total organic carbon content of 1.14%, a slightly alkaline pH of 8.22, low available nitrogen, and comparatively high phosphorus and potassium. Thirty barley plots were arranged in a randomised complete block design, with three replicates per treatment.

In spring 2022, the researchers established two prior cropping systems: monocultured oats and an intercrop of oats and common vetch sown at a 3:1 vetch-to-oats ratio, for a total of 220 kg/ha. Oat monoculture biomass was harvested, while the oat–vetch biomass was ploughed into the soil as green manure to a depth of 30 cm. Winter barley was then planted in November 2022. Each cropping system received an unfertilised control, mineral NPK fertiliser at 100 kg/ha, vermicompost at 12 t/ha, half-rate mineral fertiliser plus vermicompost, or biochar at 10 t/ha.

Rhizosphere soil was collected from randomly selected barley plants at ripening in 2023. Samples were kept on ice during transport, sieved to 2 mm and stored at –80 °C before DNA extraction. The authors used 16S rRNA gene amplicon sequencing and bioinformatic analysis of ten samples. Reads underwent quality control, merging and chimera removal before inference of amplicon sequence variants and taxonomic assignment against SILVA v138. Sequencing quality was high: all samples exceeded 98% at Q20 and 95% at Q30, while Good’s coverage ranged from 0.998 to 1.000.

Proteobacteria, Actinobacteriota and Acidobacteriota dominated at the phylum level across the treatments. Vermicompost and combined mineral–vermicompost treatments had relatively elevated Actinobacteriota and Bacteroidota, while mineral-fertilised and unfertilised soils had relatively higher Acidobacteriota proportions. Biochar produced a comparatively distinct profile, including slightly higher Verrucomicrobiota and Chloroflexi. At genus level, Sphingomonas was consistently prominent, while green-manure and organic-amendment treatments showed enrichment of genera including Nocardioides, Agromyces, Rubrobacter, Solirubrobacter and Noviherspirillum.

Alpha-diversity measurements also varied among treatments. VC2, grown without green manure and treated with vermicompost, recorded the highest Chao1 richness at 2,868.429, narrowly ahead of VC1, which followed the oat–vetch green manure, at 2,864.731. VC2 also had the highest Shannon index at 10.572 and a Pielou evenness of 0.921. By comparison, the combined mineral–vermicompost treatments had lower richness values of 2,406.176 for MF1.VC1 and 2,379.850 for MF2.VC2, while Bch2 recorded 2,315.000. A treatment-comparison analysis identified 363 taxa shared across treatments. The largest numbers of treatment-specific taxa occurred in VC2, with 837, and VC1, with 779.

Community-composition analyses indicated that individual treatments occupied different positions in PCA and PCoA space. Bch1, VC2 and the MF2.VC2 treatment were relatively separated from several other groups, whereas Control1, MF1 and VC1 clustered more closely. Pairwise Bray–Curtis and UniFrac distances were also greatest for comparisons involving Bch2. These ordination and distance results show differences in the observed bacterial assemblages among treatments; the supplied results do not report the outcomes of the planned ANOSIM or PERMANOVA group comparisons.

The findings associate the preceding oat–vetch green manure with a legacy in the barley rhizosphere bacterial community. The study’s authors interpret the enrichment of degradative and nitrogen-cycling taxa under green manure and organic-input treatments as evidence that these practices may support broader microbial diversity and potential functional redundancy. They also report that mineral fertiliser alone was associated with comparatively lower diversity in some comparisons. These functional interpretations remain indirect because the analysis was based on bacterial community composition and inferred ecological roles rather than direct measurements of nutrient turnover, disease suppression or barley growth.

The experiment has several bounded limitations. It was conducted at one Bulgarian field site over a two-year rotation, with 16S data from ten samples representing the broader set of 30 plots, and it examined bacteria rather than fungi, protozoa or the complete soil food web. The study therefore shows treatment-associated shifts in the barley rhizosphere bacteriome, not demonstrated improvements in crop yield, soil fertility or farm performance. The authors note that broader metagenomic work incorporating fungal and protozoan contributions would be needed to assess the wider microbial community.

Subject of Research: A 2023 Bulgarian field study of how fertilisation and an oat–vetch green-manure legacy affected winter barley rhizosphere bacterial communities.

Article Title: Barley Rhizosphere Bacteriome Dynamics under Organic and Mineral Inputs: The importance of intercropping predecessor

Article References: Shilev, S., Petkova, M., Popova, V., Neykova, I., & Rangelov, I. (2025). Barley Rhizosphere Bacteriome Dynamics under Organic and Mineral Inputs: The importance of intercropping predecessor. Metabarcoding and Metagenomics, 9, Article e167231. https://doi.org/10.3897/mbmg.9.167231

Image Credits: AI Generated

DOI: 10.3897/mbmg.9.167231

Keywords: barley rhizosphere, bacterial communities, 16S rRNA sequencing, oat–vetch intercropping, green manure, vermicompost, biochar, mineral fertiliser, soil microbiome, field experiment, Barley, Rhizosphere

The investigators collected healthy L. aggregata individuals from wild populations in subtropical evergreen broad-leaved mountain forests in Huangshan City. Sampling took place in Shexian County at an elevation of 105 metres on 5 July 2023 and in Huangshan District at elevations of 290 metres on 8 August and 273 metres on 13 August 2023. Root samples and rhizosphere soil were processed separately. Rhizosphere microorganisms were isolated by serial dilution and cultivation on potato dextrose agar at 28 °C for two to seven days, while roots underwent surface sterilization before cultivation.

Colony characteristics were examined on potato dextrose agar, malt extract agar, cornmeal agar, oatmeal agar and water agar. Microscopic structures were measured and documented, and DNA was extracted from fresh mycelia. The phylogenetic study used six loci for Hawksworthiomyces—ITS, LSU, TEF1-α, RPB2, TUB2 and CAL—and six for Melnikomyces—ITS, LSU, SSU, TUB2, TEF1-α and ACT1. Alignments were analyzed using maximum-likelihood and Bayesian inference methods.

In the Hawksworthiomyces analysis, two isolates designated H. rhizosphaerae formed a distinct lineage with 100% maximum-likelihood bootstrap support and a Bayesian posterior probability of 1.00. This lineage was sister to a clade containing the ex-type strain of H. crousii and two strains of H. cylindroconidius. The new species differed from H. crousii in 3.13% of ITS sites and 4.68% of RPB2 sites, and from H. cylindroconidius in 1.78% of ITS sites.

Morphological observations supported recognition of H. rhizosphaerae as a new species. Its polyblastic conidiogenous cells measured 1.2–25.5 by 0.5–1.1 micrometres and bore short cylindrical denticles measuring 0.3–0.6 by 0.3–0.5 micrometres. Hyaline, guttulate, aseptate conidia measured 1.8–3.9 by 0.8–2.1 micrometres. Compared with H. crousii, the new species had narrower conidiogenous cells and smaller denticles, while its conidia were smaller and distinctly guttulate. Unlike H. cylindroconidius, which has monoblastic cells and longer unbranched conidiophores, H. rhizosphaerae has polyblastic cells with distinct denticles.

The second new species, M. linderae, was recovered from L. aggregata roots. Its six-locus phylogeny placed the two new isolates in a distinct clade sister to M. vietnamensis, supported by 93% maximum-likelihood bootstrap support and a Bayesian posterior probability of 0.97. The new species differed from M. vietnamensis in 4.55% of ITS sites and 1.06% of LSU sites.

M. linderae has narrow, pale-brown to brown conidiophores measuring 8.2–46.0 by 0.9–1.7 micrometres and polyblastic conidiogenous cells bearing cylindrical denticles. Its verrucose conidia measure 3.0–6.4 by 1.8–2.7 micrometres and are one-septate when mature, although some are two-septate; lateral, intercalary or terminal chlamydospores are also present. Its conidia and conidiophores are smaller and narrower than those of M. thailandicus and M. vietnamensis. The species epithet refers to the host genus Lindera.

Root material also yielded an isolate that grouped with the ex-holotype strain of H. taylorii with 100% maximum-likelihood bootstrap support and a Bayesian posterior probability of 1.00; its morphology was also consistent with that species. Earlier records included a Eucalyptus utility pole in South Africa, adult Hylurgus ligniperda beetles and the gut of the fungus-growing termite Macrotermes barneyi in China, and soil in China. The collection from L. aggregata roots therefore represents a new host record for H. taylorii.

This was a limited taxonomic investigation, not a functional or clinical study. Samples came from one plant species in one Chinese region, and the findings do not establish how the fungi affect plant growth, stress tolerance, nutrient acquisition or secondary metabolite production. The authors noted that the ecological significance of the root and rhizosphere associations remains unclear. They recommended broader sampling across hosts, substrates and regions, along with genome-scale analyses and further investigation of possible interactions with L. aggregata.

Subject of Research: Taxonomic discovery of novel root- and rhizosphere-associated fungi on Lindera aggregata in China

Article Title: Novel Hawksworthiomyces ( Ophiostomatales , Ophiostomataceae ) and Melnikomyces ( Venturiales , Sympoventuriaceae ) species and a new host record of Hawksworthiomyces on Lindera aggregata from China

Article References: Chen, M.-L., Mukjang, N., & Luo, X. (2026). Novel Hawksworthiomyces (Ophiostomatales, Ophiostomataceae) and Melnikomyces (Venturiales, Sympoventuriaceae) species and a new host record of Hawksworthiomyces on Lindera aggregata from China. MycoKeys, 139, 303-320. https://doi.org/10.3897/mycokeys.139.197994

Image Credits: AI Generated

DOI: 10.3897/mycokeys.139.197994

Keywords: taxonomy, fungal diversity, Hawksworthiomyces, Melnikomyces, Lindera aggregata, rhizosphere, plant-associated fungi, Anhui Province, new species, new host record, Novel, Ophiostomatales

The research team, led by Leonardo Zamora-Leiva of the Bionostra Chile Research Foundation together with colleagues at Universidad Andrés Bello and the University of Chile, sampled a trial established in 1998 at the Sugar Cane Research Institute in Santiago de Cuba. The experiment spans eleven fertilizer treatments varying nitrogen, phosphorus, and potassium, from plots receiving no nitrogen at all to those receiving very high doses of a single macronutrient. Because the fertilization regimes assigned to each plot have been maintained without interruption since the trial began, the soils sampled in 2022 carry the cumulative legacy of 24 years of continuous nutrient management, making the site an unusually clean natural laboratory for asking how sustained inputs shape the rhizosphere microbiome.

Using high-throughput sequencing of the bacterial 16S rRNA gene and the fungal internal transcribed spacer region, the researchers identified 421 bacterial and 471 fungal genera from 5,741 amplicon sequence variants across the treatments. The dominant bacterial phyla were Actinomycetota, Pseudomonadota, and Acidobacteriota, which together accounted for roughly 60 percent of relative abundance, while fungal communities were overwhelmingly dominated by Ascomycota, which exceeded 69 percent across all plots. These core lineages appeared in similar proportions regardless of whether a plot had been drenched in nitrogen for decades or left without it, and statistical tests for differences in alpha and beta diversity, along with differential abundance analyses using LEfSe and ANCOM-BC2, found no significant treatment effects on community composition.

The physicochemical data help explain why. Soil pH remained nearly constant across the site, ranging from 6.4 to 6.5 in potassium chloride and 7.7 to 7.9 in water, a stability the authors attribute to the massive buffering capacity conferred by consistently high reservoirs of exchangeable calcium and magnesium. Organic matter, available phosphorus, and potassium varied among plots, but those variations did not align with the theoretical fertilizer doses. The team argues that intense tropical rainfall and the leaching-prone clay matrix of sialitic soils, which are classified internationally as inceptisols or Cambisols, rapidly redistribute applied nutrients, homogenizing bulk soil chemistry and decoupling what farmers apply from what microbes actually experience.

Where the study becomes genuinely striking is in its network analysis. Rather than treating the bacterial and fungal datasets separately, the authors merged them into a single trans-domain co-occurrence network of 371 nodes and 747 edges, retaining only robust correlations with a Spearman coefficient above 0.6 and a false-discovery-rate-adjusted p-value below 0.01. The resulting architecture was highly modular, organized into 48 distinct structural modules, and overwhelmingly positive in sign: 99.8 percent of the correlations were cooperative or commensal rather than competitive. Fungal taxa, particularly Ascomycota and Basidiomycota, showed higher connectivity than bacteria, suggesting that fungi form the structural backbone of the rhizosphere interaction web in these soils.

Within that architecture, the vast majority of amplicon sequence variants, about 95 percent, behaved as peripheral nodes, while a small subset of highly connected connectors and module hubs, including taxa related to Pseudomonas, Steroidobacter, Gaiella, and Streptomyces, appeared to stabilize the whole system. A substantial fraction of the interacting taxa remained taxonomically unclassified, a reminder that tropical and Caribbean soil microorganisms are poorly represented in reference databases such as SILVA and UNITE. The authors suggest these unresolved lineages may include endemic or highly specialized microbes that contribute to the unique functioning of nutrient-leached tropical soils, and they call for expanding genomic reference databases to cover such environments.

The most ecologically revealing result came from an overlap analysis of which microbes appear under which fertilization regime. By intersecting presence-absence matrices across treatments, the team identified a universal core of 76 amplicon sequence variants shared across every nitrogen, phosphorus, and potassium gradient, a trans-domain alliance built on bacterial Bacillota and Pseudomonadota and fungal Ascomycota including genera such as Fusarium and Cladophialophora. This core appears to be the stable foundation of the sugarcane rhizosphere, resistant to profound nutritional fluctuations. Beyond it, each macronutrient recruited its own distinct satellite community: nitrogen variation recruited 18 exclusive specialists, predominantly fungal, while phosphorus addition recruited a much larger accessory cohort of 40 unique variants, heavily dominated by fungi including Talaromyces and various Basidiomycota. Potassium produced the most restricted response, with only six strict specialists.

This core-and-satellite assembly strategy has direct agronomic implications. Yield records from the trial show that fertilized plots consistently outperform unfertilized controls, but that yields plateau across a wide range of NPK doses, with the highest nitrogen treatments actually producing the lowest yields among fertilized plants. The new microbial data offer a possible explanation: once the universal core is in place, additional nutrients do not restructure the community but instead selectively recruit specialized accessory taxa to exploit available resources. Fertilization, in other words, may influence soil functioning by modulating specialized ecological niches rather than through broad taxonomic turnover, which is why diversity-based monitoring alone can miss the ecological consequences of management decisions.

The authors argue that trans-domain interaction networks provide crucial insights into how soils respond to long-term fertilization that are not evident from diversity or abundance data alone. In tropical sialitic soils, where leaching and rapid nutrient turnover render bulk chemistry erratic, physically protected rhizosphere microhabitats, formed by roots, fungal hyphae, and bacterial extracellular polymers, appear to act as ecological refuges that preserve microbial organization. Sustainable fertilization strategies, the study concludes, should aim to support these foundational microbial architectures while optimizing nutrient inputs, rather than assuming that more fertilizer simply means more of everything below ground. For sugarcane producers in Cuba and other tropical systems, the message is that the invisible network around the roots may matter as much as the nutrients themselves.

Subject of Research: Effects of long-term NPK fertilization regimes on sugarcane rhizosphere microbial diversity and bacterial-fungal co-occurrence networks in tropical sialitic soils

Article Title: Fertilizer regimes reshape microbial interaction networks without altering sugarcane rhizosphere diversity

Article References: Zamora-Leiva, L., Soto, J., Ramos-Tapia, I., & Paneque, M. (2026). Fertilizer regimes reshape microbial interaction networks without altering sugarcane rhizosphere diversity. SOIL, 12(2), 999-1019. https://doi.org/10.5194/soil-12-999-2026

Image Credits: AI Generated

DOI: 10.5194/soil-12-999-2026

Keywords: sugarcane, rhizosphere, soil microbiome, fertilization, co-occurrence networks, 16S rRNA, ITS sequencing, Ascomycota, nutrient leaching, inceptisols, tropical agriculture, soil ecology

The study, conducted by researchers at Liaocheng University in collaboration with the Tea Research Institute of the Shandong Academy of Agricultural Sciences, employed metagenomic sequencing to examine the rhizosphere soil of tea plants grown alongside white clover. Unlike traditional amplicon-based surveys, which typically target a single genetic marker and reveal only which organisms are present, metagenomic sequencing captures the collective genomes of entire microbial communities. This approach allowed the team to move beyond simple species inventories and probe what the soil microbes are actually capable of doing, identifying functional genes and enzymatic pathways that shift when clover is introduced into the tea plantation system.

The most striking compositional change involved two bacterial phyla with well-documented roles in soil health. Proteobacteria, one of the largest and most metabolically versatile bacterial groups, includes many genera known to associate closely with plant roots, where they can solubilize nutrients, produce plant growth-promoting compounds, and suppress soil-borne pathogens. Actinobacteria, meanwhile, are renowned for their ability to decompose complex organic matter and for producing a vast array of bioactive secondary metabolites, including many classical antibiotics. An increase in the relative abundance of both groups suggests that white clover intercropping favors microbes that are active participants in nutrient cycling and in the chemical ecology of the rhizosphere, the narrow zone of soil directly influenced by root secretions.

Legumes such as white clover host symbiotic nitrogen-fixing bacteria in specialized root structures, and this capacity is the primary reason they are used as companion plants. However, the new findings indicate that the influence of the legume extends well beyond simply adding nitrogen to the system. By releasing carbon-rich exudates from its roots and physically modifying the soil environment, the clover appears to reshape the entire microbial habitat, creating conditions that favor particular functional guilds. This is consistent with a growing body of research showing that plant species composition in intercropping systems acts as a powerful lever on below-ground biodiversity, with consequences that ripple through nutrient availability, disease suppression, and soil structure.

The functional analysis revealed that microbial genes in the intercropped plots were heavily enriched in carbohydrate and amino acid metabolism, according to annotation against the Kyoto Encyclopedia of Genes and Genomes pathway database. These two categories represent core metabolic activities of soil communities: carbohydrate metabolism reflects the breakdown of plant-derived sugars, cellulose, and other polysaccharides that fuel the soil food web, while amino acid metabolism is tied to the transformation of organic nitrogen compounds that ultimately determine how much nitrogen is available to the tea plants. A community tilted toward these pathways suggests heightened microbial processing of organic matter, which can accelerate nutrient turnover in the rhizosphere.

Perhaps the most intriguing result concerns the increased representation of genes involved in terpenoid and polyketide metabolism. Terpenoids are a chemically diverse class of compounds that include many plant volatiles and signaling molecules, and in tea they are directly relevant to flavor and aroma, contributing to the characteristic fragrance of tea leaves. Polyketides, on the other hand, are a family of secondary metabolites produced largely by bacteria and fungi, many of which display antimicrobial or signaling properties. An enrichment of microbial genes associated with the biosynthesis of these compounds hints that the intercropped rhizosphere may harbor a more chemically active microbial community, one potentially better equipped to compete with pathogens or to modulate plant physiology through small molecules. While the study does not establish a direct causal link between these genes and tea quality, the connection is a compelling avenue for future research, given that tea quality is famously sensitive to the growing environment.

The carbohydrate-active enzyme analysis added another layer of detail. Carbohydrate-active enzymes, often abbreviated CAZymes, are classified into families based on their catalytic mechanisms, and their profiles in soil can reveal what kinds of plant and microbial polymers the community is actively degrading. The significant enrichment of glycoside hydrolases, the enzyme class responsible for cleaving glycosidic bonds in complex carbohydrates, indicates intensified breakdown of polysaccharide substrates in the clover-intercropped soil. Among these, the families GH87, GH71, and GT53 showed the greatest increases. GH87 enzymes are known to target beta-1,3-glucans, components of fungal cell walls and certain plant tissues, which has led researchers to associate them with both fungal turnover and potential biocontrol activity. GH71 enzymes also act on glucan substrates, while GT53 belongs to a family of glycosyltransferases involved in building rather than breaking down carbohydrate structures, a distinction that may reflect shifts in microbial cell wall synthesis or extracellular polysaccharide production. The precise ecological meaning of these specific family-level shifts remains to be fully resolved, but their prominence suggests that clover intercropping restructures not just who lives in the soil but what biochemical work they perform.

It is worth placing these findings in the broader context of sustainable tea cultivation. Tea is typically grown as a monoculture over large areas, and decades of intensive management can deplete soil organic matter, disrupt microbial communities, and increase reliance on synthetic fertilizers. Cover crops and living mulches have been proposed as remedies, and white clover in particular is attractive because it tolerates shading, suppresses weeds through ground coverage, and fixes atmospheric nitrogen through its rhizobial symbiosis. Earlier agronomic studies have documented benefits of leguminous groundcovers in tea plantations, including improved soil moisture retention and reduced erosion, but the microbial dimension has often been inferred rather than directly measured. By generating a genome-resolved picture of the rhizosphere community, this study provides mechanistic grounding for observations that farmers and agronomists have made in the field.

The methodology deserves some attention as well. Metagenomic sequencing of rhizosphere soil generates enormous datasets, and the researchers relied on established annotation frameworks to assign functional meaning to the millions of gene fragments recovered. Pathway-level annotation through KEGG groups genes into broad functional categories, while differential abundance analysis identifies which genes or taxa increase or decrease significantly between treatments, in this case intercropped versus conventional plots. The CAZyme annotation follows a widely used classification system maintained by the carbohydrate-active enzyme database, which catalogs enzyme families across bacteria, archaea, fungi, and plants. Together, these complementary lenses allowed the team to triangulate the functional consequences of intercropping from multiple angles, strengthening confidence that the observed shifts are real rather than statistical noise.

Several caveats temper the interpretation. The study documents correlations between intercropping and microbial community change, and while the design supports an association, fully establishing causation would require additional experiments, such as transplanting soils or tracking communities over multiple seasons. Rhizosphere communities are also highly sensitive to seasonal variation, soil type, and local management history, so the magnitude of the effects observed here may differ across the diverse tea-growing regions of China and beyond. Furthermore, the enrichment of terpenoid and polyketide genes indicates potential for secondary metabolite production, but gene presence does not guarantee expression, and confirming that these pathways are actively deployed in the field would require transcriptomic or metabolomic follow-up.

Nevertheless, the work contributes to a shifting paradigm in agricultural microbiology. Rather than viewing soil microbes as passive recipients of whatever nutrients happen to be available, researchers increasingly recognize that farmers can deliberately shape microbial communities through cropping decisions. Intercropping, cover cropping, and crop rotation are emerging as tools for steering the rhizosphere toward configurations that support plant health. For tea, a crop whose economic value depends heavily on subtle chemical qualities, the possibility that a simple groundcover could enrich the soil microbiome in ways that influence flavor-relevant and defense-relevant metabolism is particularly noteworthy. The authors suggest that their findings provide theoretical insights into how soil microbial communities respond to white clover intercropping, and they position the work as a foundation for future studies aimed at harnessing rhizosphere microbiomes to support sustainable tea production. As interest in low-input agriculture grows worldwide, studies like this one, which connect a practical farming practice to molecular-level changes in the soil ecosystem, help bridge the gap between agronomic tradition and modern microbial science, offering growers evidence-based reasons to adopt practices that benefit both their crops and the living ground beneath them.

Subject of Research: Effects of white clover intercropping on the rhizosphere microbiome of tea plantations

Article Title: White clover-tea intercropping modulates rhizosphere microbiome composition and structure

Article References: Zhao, M., Xu, Q., Gong, X., Xia, M., Cheng, T., Xie, H., Sun, L., Zhang, H., Ma, Q., & Ding, Z. (2026). White clover-tea intercropping modulates rhizosphere microbiome composition and structure. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09941-5

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09941-5

Keywords: white clover, tea plant, intercropping, rhizosphere, microbiome, metagenomics, soil microbiology, nitrogen fixation, terpenoids, carbohydrate-active enzymes, Proteobacteria, Actinobacteria

Published in Environmental Monitoring and Assessment, the research by Şahin Palta, Eren Baş, and Zekeriya Yavaşcı of Bartın University examined AMF spore density, community composition, and rhizosphere soil properties across five plant families in a natural rangeland. The findings challenge the assumption that soil chemistry alone dictates which mycorrhizal fungi thrive where. Instead, plant family identity emerges as a decisive driver, shaping fungal abundance and diversity in patterns that could reshape how we manage rangelands worldwide.

The numbers tell a dramatic story. AMF spore density peaked in soils beneath Asteraceae, the daisy family, at 609.8 spores per 50 grams of soil. At the opposite extreme, Urticaceae, the nettle family, hosted just 77.6 spores per 50 grams, a nearly eightfold difference. That gap is not a minor variation; it suggests that the plant above ground exerts a powerful influence on the reproductive output of fungi below, possibly through differences in root architecture, carbon allocation, or the chemical signals each family releases into the rhizosphere.

Correlation analysis added another layer of intrigue. AMF spore density showed a positive association with soil pH (r = 0.47), hinting that slightly alkaline conditions favor sporulation. But the fungi responded negatively to electrical conductivity (r = −0.49), available potassium (r = −0.44), and total nitrogen (r = −0.40). In other words, richer soils with more nitrogen and potassium actually hosted fewer spores. This counterintuitive pattern aligns with a growing body of evidence that mycorrhizal fungi invest less in reproduction when plants, flush with nutrients, depend less on fungal partners for mineral acquisition.

Five fungal species appeared in the rhizosphere soils of all five plant families: Acaulospora tuberculata, Claroideoglomus etunicatum, Funneliformis geosporum, Glomus sp., and Rhizophagus clarus. Their broad distribution across host groups suggests these are generalist symbionts, capable of partnering with a wide range of plants. Yet the study also found that community structure varied among plant families, indicating that host identity filters which species dominate even when the same core species are present everywhere.

Diversity metrics revealed further complexity. Species richness was highest in Urticaceae, despite that family hosting the fewest spores overall. Shannon diversity and evenness peaked in Lamiaceae, the mint family. Fabaceae and Asteraceae showed lower diversity values, and Jaccard similarity was highest between Fabaceae and Asteraceae, meaning their fungal communities overlapped more than any other pair. These patterns suggest that plant family identity shapes not just how many fungi are present, but which species coexist and how evenly they are distributed.

Soil organic carbon, total nitrogen, available potassium, and CaCO₃ content also varied among the sampled plant groups, reinforcing the idea that each plant family modifies its own rhizosphere environment. These modifications, in turn, feed back into fungal community dynamics. The result is a complex interplay between biotic and abiotic factors, where plant identity and soil chemistry jointly determine the belowground fungal landscape.

The implications extend far beyond Turkish rangelands. Mycorrhizal fungi are increasingly recognized as critical components of belowground biotic networks, influencing plant productivity, soil carbon sequestration, and ecosystem resilience. If plant family identity drives fungal community structure, then shifts in vegetation composition, whether from grazing, climate change, or land-use conversion, could cascade through soil food webs in unpredictable ways. Rangeland managers may need to consider not just which plants are present, but which families, to maintain healthy fungal communities.

The study also highlights the value of natural rangelands as living laboratories for understanding mycorrhizal ecology. Unlike agricultural systems, where fertilization and tillage disrupt soil structure, natural rangelands preserve the intricate relationships between plants and fungi that have evolved over millennia. By sampling across five plant families in a single rangeland, the researchers isolated the effect of host identity from broader environmental gradients, offering a cleaner test of how plant families shape their fungal partners.

As climate change and land degradation threaten rangelands globally, understanding the drivers of mycorrhizal fungal communities becomes ever more urgent. This study adds a crucial piece to the puzzle: the plant family above ground is not a passive backdrop but an active architect of the fungal world below. The next chapter in this research will likely explore the mechanisms behind these patterns, from root exudates to carbon allocation, unlocking new strategies for restoring degraded soils and sustaining the invisible partnerships that keep rangelands alive.

One reason spore counts offer such a revealing window into mycorrhizal ecology is that spores are not simply byproducts of fungal activity but the principal propagules through which many AMF species persist between growing seasons and disperse to new hosts. A spore is a thick-walled resting structure, often packed with lipid reserves, that can survive in soil for months or years until favorable conditions and a suitable host root coincide. When researchers count spores in a soil sample, they are therefore measuring not just fungal presence but the accumulated reproductive investment of the fungal community over time. The wet sieving and decanting approach traditionally used to extract these spores, first formalized in the 1960s, remains a standard technique because it separates spores from soil particles by density differences, allowing morphological identification under a microscope based on wall structure, color, and size.

It is worth noting that spore abundance does not always track the total amount of fungal activity inside roots. A plant family might support extensive hyphal colonization of its root system while producing relatively few spores, or conversely, a modest root infection might coincide with heavy sporulation. Different fungal genera follow different strategies in this respect. Some members of the Glomeraceae, for example, are known for rapid colonization of root tissue and abundant spore production, whereas species of Acaulospora tend to sporulate more slowly and may peak in abundance at different times of year. This means the patterns observed in the rangeland study reflect a snapshot of community structure that could shift with season, and repeated sampling across a full growing cycle would help establish whether the family-level differences are stable or transient.

The negative association between spore density and soil nitrogen deserves particular attention because it connects to a well-documented feedback in plant-fungal economics. When soil nitrogen and phosphorus are plentiful, plants can reduce the carbon they allocate to root exudates and to the fungal partners themselves, since the marginal benefit of the symbiosis declines. Fungi, receiving less carbon subsidy, may respond by reducing both vegetative growth inside roots and the production of spores. The rangeland soils beneath families associated with higher fertility may therefore have hosted fungi that were metabolically active but reproductively restrained, while the poorer soils beneath other families pushed fungi toward sporulation as a survival strategy. This trade-off between growth and reproduction helps explain why the most spore-rich soils were not necessarily the most nutrient-rich ones.

Electrical conductivity, which reflects the total concentration of dissolved salts in the soil solution, has long been recognized as a constraint on mycorrhizal communities. Studies from saline environments, including work in the salt-affected soils of Iran and semiarid Mediterranean regions, have shown that elevated salinity can suppress sporulation and shift community composition toward salt-tolerant fungal taxa. The negative correlation observed in the Turkish rangeland, though modest in magnitude, is consistent with this broader literature and suggests that even moderate variation in salinity within a single landscape can leave a measurable imprint on the fungal community.

The presence of the same five fungal species across all five plant families raises interesting questions about what ecologists call assembly rules. If host identity were the only filter operating, one might expect entirely distinct fungal suites beneath each family. Instead, the data suggest a two-tier structure: a cosmopolitan core of generalist symbionts present everywhere, overlaid by family-specific differences in the relative abundance of species and in the occurrence of rarer taxa. This layered pattern mirrors findings from other ecosystems, where a handful of dominant AMF species often account for most of the community while a long tail of infrequent species contributes to differences between habitats. The higher Jaccard similarity between Fabaceae and Asteraceae hints that these two families, despite their very different biology, may impose similar rhizosphere filters, perhaps through comparable root traits or exudate chemistry.

The contrast between richness and abundance in Urticaceae is especially instructive. Hosting the greatest number of species while producing the fewest spores suggests that many fungal taxa persisted there at low densities, possibly as opportunistic residents rather than dominant partners. Nettle family plants are often associated with nitrogen-rich soils, and the nutrient conditions they create may suppress the competitive dominance of a few aggressive sporulators, allowing more species to coexist at low levels. This decoupling of richness from abundance illustrates why diversity indices must be interpreted alongside raw counts, since a community can be diverse precisely because no single species thrives.

Future work building on these findings would benefit from molecular approaches, such as sequencing of fungal DNA directly from roots and soils, which can detect species that never sporulate during the sampling period and can quantify relative abundance more precisely than spore counts alone. Combining morphological spore identification with molecular community profiling, along with measurements of root colonization intensity and hyphal length in soil, would paint a fuller picture of how plant families shape not only fungal reproduction but the entire symbiotic economy of the rangeland belowground.

Subject of Research: Soil Microbiology

Article Title: Plant family identity drives arbuscular mycorrhizal fungal spore abundance and community structure in natural rangelands

Article References: Palta, Ş., Baş, E., & Yavaşcı, Z. (2026). Plant family identity drives arbuscular mycorrhizal fungal spore abundance and community structure in natural rangelands. Environmental Monitoring and Assessment, 198(11), Article 1214. https://doi.org/10.1007/s10661-026-16087-2

Image Credits: AI Generated

DOI: 10.1007/s10661-026-16087-2

Keywords: mycorrhizal fungi, rangelands, soil ecology, plant-fungal symbiosis, rhizosphere, biodiversity, Plant, family, identity, drives, arbuscular, mycorrhizal

The research focused on synthetic communities, or SynComs, which are deliberately constructed mixtures of microbial strains designed to perform specific functions in the plant root zone. Compatibility among the member strains has long been recognized as a critical variable for SynCom stability and functionality, yet the ecological and physiological consequences of compatibility for plant-microbe interactions have remained insufficiently understood. The team set out to close this gap by systematically comparing compatible and incompatible Bacillus-based SynComs and measuring their effects on tomato growth, rhizosphere microbiome assembly, and the organization of microbial interaction networks in the soil surrounding the roots.

The first line of evidence came from co-culture experiments on solid media. When compatible Bacillus strains were grown together, they displayed distinctive merged colony phenotypes: colonies grew into one another, biofilm formation was enhanced, and growth dynamics shifted in ways that suggested cooperative metabolism. Incompatible combinations, by contrast, formed sharp demarcation zones between colonies, a visible signature of antagonism in which each strain deploys antimicrobial compounds or competitive strategies against the other. These macroscopic phenotypes provided a rapid, screenable readout of the underlying social behavior of the strains, echoing a growing body of literature showing that competition, rather than cooperation, often dominates interactions among culturable microorganisms, and that positive interactions, while less frequent, can be reliably identified and harnessed when they occur.

Among the strain pairs tested, the compatible combination NMCN6 plus LNXM12 stood out. This pair showed higher attached biomass in co-culture and elevated relative production of indole-3-acetic acid, a plant hormone that Bacillus strains synthesize and release to stimulate root growth and development. Auxin production by plant growth-promoting rhizobacteria is one of the principal mechanisms by which these bacteria enhance plant performance, so the finding that a compatible pair produces more of this hormone than most incompatible combinations or single-strain inoculations points to a concrete physiological benefit of compatibility. The result suggests that when strains coexist peacefully, their combined metabolic output can exceed the sum of their individual contributions, a phenomenon consistent with emergent properties reported in mixed microbial consortia used in bioprocesses.

The team then moved from the petri dish to the greenhouse, where the consequences of compatibility became visible in plant architecture and physiology. Tomato plants inoculated with compatible SynComs grew significantly better than controls: plant height increased, root systems elongated, and measurements of photosynthesis and stomatal conductance rose, indicating that the plants were fixing carbon more efficiently and regulating gas exchange more actively. These gains align with the well-documented capacity of Bacillus species to promote plant growth through hormone production, nutrient mobilization, and induced systemic resistance against pathogens. Incompatible combinations produced a different pattern, with distinct soluble sugar responses in the plants rather than consistent evidence of stress, a nuance the authors interpret carefully, noting that soluble sugars participate in both stress signaling and normal carbon allocation, so their shifts cannot be read as a simple stress marker.

To understand how these above-ground and whole-plant effects related to the underground microbial world, the researchers turned to amplicon sequencing of the rhizosphere bacterial communities. The sequencing data revealed treatment-associated variation in community composition, meaning that the identity of the inoculated SynCom left a detectable fingerprint on the broader bacterial assemblage in the soil. Compatible SynComs were associated with the enrichment of specific bacterial taxa, suggesting that these communities selectively favored certain resident microbes, potentially those with beneficial or synergistic functions. Incompatible combinations produced distinct taxonomic profiles, indicating that antagonistic interactions among the inoculated strains reshaped the rhizosphere in a different direction.

Beyond taxonomy, the study examined the structure of microbial co-occurrence networks, which map statistical associations among bacterial taxa and serve as proxies for the underlying ecological interaction web. Compatible SynComs produced more interconnected and stable networks, whereas incompatible combinations yielded comparatively fragmented microbial associations. This distinction matters because network architecture is increasingly recognized as a determinant of microbiome stability: highly connected communities can be more resilient to perturbation, while fragmented networks may be more vulnerable to collapse or invasion. The results resonate with theoretical work on the ecology of the microbiome, which holds that networks, competition, and stability are tightly intertwined, and with empirical findings that host selection shapes crop microbiome assembly and network complexity.

Yet the authors are careful not to overstate the explanatory power of compatibility alone. Community composition differed significantly among individual treatments, but not among the broader compatibility categories when the analysis accounted for unequal within-group dispersion, a statistical subtlety that guards against attributing all observed variation to the compatibility label. The observed co-culture, plant, and microbiome responses, the team concludes, highlight differences among the selected Bacillus combinations that cannot be attributed to compatibility alone. This measured interpretation is a reminder that microbial social behavior is one thread in a complex web of strain-specific traits, environmental context, and plant genotype effects, and that rigorous experimental design must disentangle these factors before drawing broad conclusions.

The practical implications of the work are nonetheless substantial. The study provides a rational framework for selecting Bacillus strain combinations for further evaluation as plant inoculants, prioritizing pairs and consortia whose compatibility has been verified through simple co-culture screens before they are advanced to greenhouse and field trials. This approach addresses a persistent limitation of microbial inoculant technology, namely that multistrain products often fail in the field because member strains compete with one another or fail to establish in the rhizosphere. By screening for compatibility first, developers can assemble consortia whose members reinforce rather than undermine each other, improving the odds that the inoculant will persist, function, and deliver measurable agronomic benefits.

As agriculture confronts the dual challenges of feeding a growing population and reducing its reliance on hazardous chemical inputs, the ability to rationally design stable, compatible synthetic communities represents a meaningful step forward. The convergence of co-culture phenotyping, plant physiology, and microbiome sequencing in this study illustrates how multi-scale evidence can guide the engineering of the plant microbiome, transforming what was once a trial-and-error enterprise into a principled design discipline. If the framework holds up in broader strain collections and field conditions, the humble petri dish test of bacterial compatibility may become a standard first checkpoint on the road to more sustainable crop production.

Subject of Research: Bacillus synthetic communities, rhizosphere microbiome, plant-microbe interactions, microbial inoculants, tomato growth promotion

Article Title: Compatibility among Bacillus strains is linked to synthetic communities function, rhizosphere microbiome assembly and plant performance

Article References: Khan, A. R., Ali, Q., Khalid, S., Ayaz, M., Li, L., Jinbiao, M., Mundra, S., Kuptsov, V., Kolomiets, E., Gu, Q., Wu, H., & Gao, X. (2026). Compatibility among Bacillus strains is linked to synthetic communities function, rhizosphere microbiome assembly and plant performance. Plant Cell Reports, 45(11), Article 334. https://doi.org/10.1007/s00299-026-03998-0

Image Credits: AI Generated

DOI: 10.1007/s00299-026-03998-0

Keywords: Compatibility, Bacillus, strains, linked, synthetic, communities, function, rhizosphere, microbiome, assembly, plant, performance

The study site, Qianjin Farm in Shizuishan City, Ningxia Hui Autonomous Region, sits in a temperate continental climate where average annual precipitation is just 188.8 millimeters while evaporation reaches 2,512.6 millimeters. The plow-layer soil was moderately saline and notably infertile, with organic matter at 8.08 grams per kilogram, total nitrogen at 0.47 grams per kilogram, and available phosphorus at only 5.47 milligrams per kilogram. Groundwater sat 1.5 meters below the surface, a factor that typically drives salt upward into the root zone. Against this backdrop, researchers from Ningxia University and collaborating institutions designed five treatments: an untreated control, a microbial agent alone, an organic fertilizer alone, a silica powder alone, and the full combination of all three.

The two oat varieties, Tianyan 60 and Musite 2, were chosen because prior work had established Musite 2 as salt-tolerant and Tianyan 60 as salt-sensitive. Both are widely grown in Ningxia’s salinized areas, giving the trial regional representativeness. Plots received identical base fertilization—90 kilograms per hectare of nitrogen, 177 kilograms per hectare of phosphorus pentoxide, and 60 kilograms per hectare of potassium oxide—so that any differences could be attributed to the modifiers rather than to nutrient inputs. The microbial agent, containing at least 200 million Bacillus cells per milliliter, was applied at 30 kilograms per hectare after dilution. The organic fertilizer, derived mainly from cow dung, was applied at 12 tons per hectare. The silica powder, at least 90 percent silicon dioxide, was applied at 105 kilograms per hectare.

The most striking result concerned available phosphorus. In the combined treatment, rhizosphere soil available phosphorus averaged 70.17 percent higher than with the microbial agent alone, 44.91 percent higher than with organic fertilizer alone, and 66.93 percent higher than with silica powder alone over the two years. Compared with the untreated control, the combined treatment raised available phosphorus by 137.65 to 158.28 percent, available potassium by 10.71 to 23.78 percent, soil organic matter by 11.05 to 251.3 percent, and soil water content by 16.27 to 50.58 percent. Simultaneously, soil pH dropped by 4.13 to 10.11 percent and nitrate nitrogen fell by 53.10 to 66.22 percent, indicating reduced salt stress and less nitrogen leaching.

Soil enzyme activity told a parallel story. Alkaline phosphatase and urease activities in the combined treatment were 26.05 to 44.70 percent and 23.46 to 25.87 percent higher than in the control, respectively. Catalase activity rose by 29.97 to 64.47 percent across modifier treatments, with the microbial agent and the full combination performing best. These enzymes are biocatalysts for phosphorus mineralization, urea hydrolysis, and hydrogen peroxide decomposition—processes that directly govern nutrient availability. Their elevation suggests that the modifiers did not merely add nutrients but accelerated the microbial machinery that releases them from organic and mineral reserves.

Shotgun metagenomic sequencing of rhizosphere DNA revealed how the microbial community responded. Dominant bacterial phyla included Pseudomonadota at 44.69 to 47.31 percent relative abundance, Bacteroidota at 13.03 to 15.94 percent, Actinomycetota at 10.11 to 11.63 percent, Acidobacteriota at 6.71 to 8.49 percent, and Gemmatimonadota at 3.47 to 5.66 percent, together accounting for more than 82 percent of bacterial sequences. The relative abundance of Bacteroidota peaked in the combined treatment, 111.92 percent higher than in the control. Among fungi, Ascomycota dominated at 46.40 to 62.21 percent, followed by Mucoromycota at 20.34 to 32.28 percent and Basidiomycota at 9.28 to 23.15 percent. Ascomycota abundance rose by 6.76 to 34.08 percent under modifier treatments, while Mucoromycota declined by 24.32 to 37.01 percent.

The researchers interpret these shifts through ecological strategies. Bacteroidota, an R-strategist with efficient nutrient absorption, thrives when labile organic matter and nitrogen temporarily increase—conditions created by the organic fertilizer and accelerated decomposition by the Bacillus agent. Ascomycota, a key fungal phylum indicating eutrophication, benefits from the same nutrient enrichment and possesses a powerful enzyme system suited to complex organic matter. Mucoromycota, which rapidly colonizes simple carbohydrates, briefly prospers early after amendment but is outcompeted as decomposition proceeds toward complex substrates. The combined treatment also raised bacterial Chao1 richness by 1.68 to 3.54 percent and fungal Chao1 and ACE indices by 22.74 to 35.31 percent and 9.78 to 10.99 percent, respectively, compared with the control.

Redundancy analysis showed that soil physicochemical properties explained 84.04 percent of variation in bacterial community structure and 79.58 percent in fungal structure. Dominant bacterial phyla correlated positively with enzyme activity and with soil water content, available phosphorus, available potassium, organic matter, and ammonium nitrogen, and negatively with pH and nitrate nitrogen. The Mantel test confirmed that bacterial community structure correlated with nitrate nitrogen, available potassium, organic matter, pH, water content, and catalase activity, while fungal structure correlated with all physicochemical properties except available phosphorus. Random forest analysis identified soil organic matter as the strongest predictor of oat yield, followed by the relative abundance of Chloroflexota and Ascomycota, available phosphorus, available potassium, and catalase activity.

Forage quality responded accordingly. Crude protein content peaked under the combined treatment for both varieties, reaching 9.28 percent in Tianyan 60 and 9.42 percent in Musite 2, representing two-year average increases of 12.78 to 27.44 percent and 22.02 to 35.08 percent over the control. The relative feeding value of Musite 2 under the combined treatment was 0.47 to 26.49 percent higher than under other treatments, and its acid detergent fiber content was significantly lower, indicating improved digestibility. Hay yield of Musite 2 under the combined treatment was 25.23 percent higher than the control on a two-year average, while organic fertilizer alone raised it by 21.51 percent. Musite 2 also showed higher ammonium nitrogen accumulation, lower nitrate nitrogen leaching, and significantly higher catalase activity than Tianyan 60, suggesting a more developed root system that efficiently captures nitrate from deeper layers and creates an oxidized rhizosphere favoring aerobic catalase-producing bacteria such as Pseudomonadota.

The mechanism, as the authors describe it, is a cascade. The microbial agent accelerates organic fertilizer decomposition and stimulates acid-producing microorganisms. Silica powder slowly hydrolyzes in soil to form silicic acid, which neutralizes alkali metal ions and lowers pH. Lower pH reduces phosphorus and potassium fixation, promotes mineral dissolution, and enhances ammonium adsorption onto soil colloids, curbing volatilization and leaching. Humic acid from the organic fertilizer and silicic acid from the powder combine through coordination bonds to form organic–inorganic composite colloids with porous structures, improving soil cohesion, humus content, porosity, and water-holding capacity. The enriched rhizosphere optimizes microbial habitats, driving community succession and diversity. Core functional microorganisms, notably Chloroflexota and Ascomycota, then secrete hydrolytic enzymes and oxidoreductases that speed nutrient conversion and release, supplying the available nutrients that support oat yield and quality formation.

The authors acknowledge limitations. The trial was conducted at a single site over two years, so transferability to other salinized lands requires additional validation. Three replicates per treatment limit statistical power for high-throughput metagenomic sequencing. The study did not include pairwise combinations of the three components, making it difficult to isolate binary interaction effects. Root morphological and physiological indicators—root length density, root surface area, root activity—were not measured, leaving the genotype-specific response mechanisms unresolved. Long-term continuous silica powder application carries potential environmental risks, including soil silicon accumulation and antagonistic interactions with trace elements such as iron and molybdenum, though no such imbalances appeared during the trial period.

Despite these caveats, the study provides a concrete reference for salinized land use, ecological health maintenance, and sustainable agricultural production in arid regions. It demonstrates that matching salt-tolerant oat varieties with a composite modifier can simultaneously alleviate salt stress, rebuild soil fertility, restructure rhizosphere microbial communities, and enhance forage yield and quality. The authors call for multi-site, multi-year trials with two-component combinations and root measurements to further reveal the regulatory mechanisms of the composite modifier in salinized soil–oat systems, supporting forage-based soil improvement practices across northwest China and beyond.

Subject of Research: The combination of microbial agent, organic fertilizer, and silica powder enhances oat yield and quality through regulating rhizosphere processes

Article Title: The combination of microbial agent, organic fertilizer, and silica powder enhances oat yield and quality through regulating rhizosphere processes

Article References: Chen, P., Luo, Y., Ma, L., He, M., Ma, H., Ma, W., & Sun, Q. (2026). The combination of microbial agent, organic fertilizer, and silica powder enhances oat yield and quality through regulating rhizosphere processes. Frontiers in Microbiology, 17, Article 1901736. https://doi.org/10.3389/fmicb.2026.1901736

Image Credits: AI Generated

DOI: 10.3389/fmicb.2026.1901736

Keywords: combination, microbial, agent, organic, fertilizer, silica, powder, enhances, yield, quality, regulating, rhizosphere

The rhizosphere is the narrow zone of soil where plant roots and microorganisms engage in an intense chemical dialogue. Root cells exude sugars, amino acids, organic acids, and secondary metabolites such as phenolics and flavonoids, and these compounds act simultaneously as chemoattractants, nutritional substrates, and signaling molecules that shape which microbes colonize the root surface. In rice, this microbial assembly performs critical biogeochemical work: nitrogen fixation, phosphorus solubilization, iron chelation via siderophores, and even methane cycling in the oxygen-starved paddy soil. The review emphasizes that recent advances in genomics, metabolomics, and high-throughput sequencing have transformed the soil microbiome from a fixed agricultural resource into an engineerable ecosystem, where specific taxa can be recruited or suppressed to meet defined objectives.

The historical foundation of this field rests on plant growth-promoting rhizobacteria, or PGPR. Early rice studies inoculated isolated strains of Rhizobium and Azospirillum to boost nitrogen availability and root development, with controlled-condition yield gains of roughly 8 to 22 percent compared with unfertilized controls. Cyanobacteria in the Azolla ecosystem contributed up to 40 kilograms of fixed nitrogen per hectare in 20 to 25 days. But the review documents a persistent problem: these benefits rarely transferred reliably to heterogeneous field conditions, where soil chemistry, native microbial competition, and climate variability conspired against single-strain inoculants. That inconsistency triggered the shift toward multispecies consortia that exploit functional complementarity between taxa.

The clearest evidence for the power of engineered consortia comes from phosphorus acquisition. A four-member SynCom isolated from rice-soybean intercropping systems, comprising Variovorax paradoxus, Novosphingobium subterraneum, Hydrogenophaga pseudoflava, and Acidovorax sp., increased rice biomass and phosphorus uptake in pot experiments by solubilizing soil phosphorus and upregulating four phosphate transporter genes in the rice genome, OsPht1;1, OsPht1;2, OsPht1;4, and OsPht1;6. Treated plants developed larger root surface areas and more root tips, morphological traits directly linked to phosphorus foraging efficiency. In parallel, single-strain studies with Herbaspirillum R3 raised available nitrate by 14.8 percent, ammonium by 27.8 percent, and available phosphorus by 22.7 percent in the rhizosphere, lifting theoretical yield by roughly 8.8 percent. Co-inoculation experiments pairing Rhodopseudomonas palustris with Bacillus subtilis pushed yield gains to 17.7 percent, exceeding either strain alone.

Beyond nutrient mobilization, microbial consortia appear to rewire plant stress physiology. Under salt stress, a multi-species PGPR consortium enriched metabolic pathways including nucleotide metabolism, purine metabolism, and ABC transporter functions, while shifting rhizosphere community structure toward beneficial phyla such as Proteobacteria and Acidobacteriota. Pre-treatment with microbial consortia elevated enzymatic antioxidants including superoxide dismutase, peroxidase, and catalase, along with the osmoprotectant proline, reducing oxidative damage in salt-stressed rice seedlings. Salinity-tolerant rice varieties in field surveys hosted distinct rhizosphere microbiomes enriched in nutrient-cycling and stress-adaptive taxa, and these compositional differences correlated with panicle number and grains per panicle, suggesting that microbiome structure may underpin real yield resilience in saline paddies.

The review also highlights quorum sensing as an emerging lever for community design. In Gram-negative bacteria, N-acyl homoserine lactones coordinate collective behavior in a cell-density-dependent manner, while Gram-positive systems use oligopeptide signals. AHL-producing bacteria including Acinetobacter lactucae, Aeromonas popoffi, Serratia oryzae, and Rhizobium wuzhouense are abundant in rice rhizospheres, and quorum sensing regulates biofilm formation that anchors beneficial consortia to root surfaces, protects them from abiotic stress, and creates nutrient exchange hubs that antagonize pathogens. Interfering with quorum signaling has been proposed both to suppress pathogens and to optimize beneficial community assembly, positioning quorum manipulation as a potential breakthrough in rhizosphere engineering.

Pathogen suppression through engineered communities represents another frontier. A cross-kingdom SynCom combining Trichoderma harzianum with multiple Bacillus strains reduced Fusarium crown rot severity in wheat by approximately 70 percent by remodeling the rhizosphere microbiome and metabolome, a proof of concept the review argues applies directly to rice diseases such as Magnaporthe oryzae blast, Xanthomonas oryzae bacterial blight, and Rhizoctonia solani sheath blight. In rice itself, a consortium of Pantoea ananatis and Pantoea dispersa strains suppressed leaf and panicle blast by inducing systemic defense responses and reactive oxygen species accumulation, even without strong direct antagonism in vitro. Metagenomic surveys of suppressive soils consistently enrich for biosynthetic gene clusters, particularly nonribosomal peptide synthetases and siderophore pathways, and recent work showed that Bacillus biofertilizer activated predatory protist taxa and elevated polyketide synthase gene abundance, correlating with suppression of Ralstonia solanacearum.

Translating these laboratory successes into commercial products demands industrial-scale bioprocessing and formulation innovation. Stirred-tank bioreactors must maintain cell concentrations above 10^8 cells per milliliter while balancing growth rates across consortium members, and emerging machine-learning control architectures dynamically regulate feed rates and environmental parameters to preserve target community composition. Encapsulation technologies offer a solution to the chronic shelf-life problem: conventional carrier-based products typically survive only 6 to 12 months, but Pseudomonas fluorescens encapsulated in 3 percent chitosan retained viability for roughly ten months, and trehalose-doped core-shell hydrogels extended Trichoderma harzianum viability from log 5.72 to log 7.30 CFU per gram after 180 days in 15 percent NPK fertilizer. Novel liquid double emulsions preserved both bacterial and fungal strains for up to 12 months at ambient temperatures, a critical advantage in hot, humid rice-growing regions.

Yet the review is candid about the field-scale gap. SynCom colonization efficiency frequently drops below 10 percent of greenhouse performance in non-sterile paddy soils, where native microbiota outcompete introduced strains and pH variation suppresses phosphorus-solubilizing gene expression. Environmental heterogeneity in temperature, moisture, and nutrient availability produces unreliable location-to-location comparisons, and some studies report limited or no yield improvement following microbial inoculation, particularly in nutrient-rich or highly competitive soils. Regulatory frameworks add further friction: the EU’s Fertilizing Products Regulation maintains strict positive lists that often exclude novel SynCom members, while Brazilian and Indian frameworks allow faster registration of multi-strain products provided they meet minimum viability standards of 10^8 CFU per gram. Ecological risks, including the potential for high-titer inoculants to outcompete rare native taxa and temporarily reduce local microbial diversity, demand long-term monitoring.

The review concludes that microbiome engineering will only deliver climate-resilient rice when integrated with host genetics and precision agriculture. Microbiome-shaping genes, host loci whose allelic variation influences rhizosphere community composition, could allow breeders to select rice varieties that heritably recruit nitrogen-fixing or phosphorus-solubilizing taxa, though direct experimental validation in rice remains limited. Precision farming platforms, including site-specific soil moisture and salinity sensors and algorithm-driven scheduling of inoculant applications timed to drought or salinity events, may synchronize microbial delivery with plant stress windows. Synthetic biology and iterative microbiome selection, in which communities are evolved under controlled stress imposition to enrich beneficial functions, point toward programmable holobionts, engineered plant-microbe systems that respond adaptively to environmental gradients. The authors argue that merging microbial design, host genetics, multi-omics tools, and rigorous multi-location field validation is the key to turning rhizosphere engineering from a laboratory promise into a trustworthy, climate-adaptive solution for the paddies that feed half the planet.

Subject of Research: Microbiology

Article Title: Microbial interventions in rice rhizosphere engineering: from soil microbiome manipulation to yield stability

Article References: Ullah, Q., Haider, W., & Usama, M. (2026). Microbial interventions in rice rhizosphere engineering: from soil microbiome manipulation to yield stability. Frontiers in Industrial Microbiology, 4, Article 1832866. https://doi.org/10.3389/finmi.2026.1832866

Image Credits: AI Generated

DOI: 10.3389/finmi.2026.1832866

Keywords: rice, rhizosphere, microbiome, SynComs, PGPR, biofertilizers, climate resilience, agriculture, phosphorus uptake, nitrogen fixation, Microbial, interventions