The research team, led by Mahlatse Ellias Moremi of the South African Sugarcane Research Institute alongside colleagues from the Agricultural Research Council, followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to sift through the literature. An initial database search across Scopus, Web of Science, PubMed and ScienceDirect yielded 536 records, which the authors narrowed down through independent screening to 42 eligible studies. From these, they catalogued a remarkable 146 bacterial genera and 95 fungal genera, classifying each according to three functional roles: nutrient solubilisation, pathogen suppression, and plant pathogenicity. This functional lens matters because the balance among these groups ultimately determines whether a soil supports crop growth or harbours disease.

The review arrives at a critical moment for a crop with enormous global significance. Sugarcane underpins more than 75 percent of world sugar production and roughly 40 percent of biofuel output, with Brazil, China and India dominating the supply. African nations contribute 5.6 percent of global production, led by South Africa, where the crop supports employment and food security while contributing to several United Nations Sustainable Development Goals, including Zero Hunger and Affordable and Clean Energy. Yet conventional practices such as pre-harvest burning, intensive tillage and long-term monocropping have been linked to soil degradation, nutrient imbalances and declining yields. The new synthesis provides the most comprehensive picture yet of how these pressures ripple through the microbial world.

Among the bacterial genera, a clear set of dominant players emerged. Sphingomonas, reported in 17 field studies, topped the list, followed by Bradyrhizobium with 14 reports, Bacillus with 13, and Gemmatimonas with 10. Streptomyces and Acidothermus each appeared in nine studies. These taxa are far from random arrivals: Sphingomonas, Bradyrhizobium and Bacillus are well documented for their roles in nitrogen fixation, nutrient cycling, disease suppression and plant growth promotion. On the fungal side, Talaromyces, Fusarium, Curvularia and Mortierella dominated the field-study records, while Fusarium, Trichoderma and Penicillium were the most frequently reported genera in greenhouse experiments. Notably, this roster spans the full functional spectrum, from beneficial solubilisers to notorious pathogens.

One of the most striking revelations concerns a mismatch between what lives in sugarcane soils and what the biotechnology industry sells. Commercial phosphorus-solubilising products are overwhelmingly built around Bacillus strains and the arbuscular mycorrhizal fungus Funnelformis. Yet the review shows that indigenous sugarcane soils are naturally dominated by a different suite of potent solubilisers, most notably Sphingomonas and Bradyrhizobium. The authors argue that this native phosphorus-mobilising potential represents a largely untapped resource, and that next-generation biofertilisers tailored to sugarcane systems might do better to harness these locally adapted taxa rather than relying on exotic inoculants that face fierce competition from established native communities.

The review also exposes how strongly experimental context shapes results. When the authors compared microbial responses across field and greenhouse settings, they found that Sphingomonas was the only genus consistently reported in both environments for intercropping studies—and even then, its response flipped, increasing in field conditions while decreasing in the greenhouse. The explanation likely lies in the stability of controlled environments, which favour microbial colonisation and metabolite production, versus the environmental variability of real fields, where moisture extremes, nutrient heterogeneity and resource competition constrain colonisation. The practical implication is sobering: greenhouse results cannot be straightforwardly extrapolated to the field, and robust conclusions demand integration across experimental scales.

Soil compartment added another layer of complexity. Under some treatments, such as nitrogen, phosphorus and potassium fertilisation combined with straw return, genera like Bryobacter, Bradyrhizobium and Sphingomonas showed consistent abundance patterns in both bulk soil and the rhizosphere, the narrow zone of root influence. Under other conditions, including sugarcane-wheat rotations and sugarcane-peanut intercropping, the same genera diverged sharply between compartments. Time mattered too: Fusarium abundance remained unaffected by organic amendments at 50 days but declined significantly after 100 days, indicating that some management effects only emerge after prolonged soil-microbe interactions. Any single snapshot, the authors caution, risks missing the true dynamics of these communities.

Crop genotype proved to be a decisive moderating factor throughout the synthesis. The widely grown variety ROC22 suppressed bacterial genera such as Acidothermus and Gemmatimonas while enriching fungal genera like Talaromyces and Mortierella, whereas the newer variety Z9 produced the opposite trend for Trichoderma. In one study, the effects of intercropping on Sphingomonas, Acidothermus and Gemmatimonas were completely reversed when comparing wild-type and genetically modified sugarcane. Arbuscular mycorrhizal fungal communities likewise shifted in a variety-specific manner under green cane harvesting. Because most genera responded to the interaction between variety and management rather than to either factor alone, the authors conclude that breeding strategies and microbiome research must be developed hand in hand.

The main management practices themselves produced a patchwork of outcomes. Excessive inorganic nitrogen generally suppressed overall microbial abundance, while moderate nitrogen and potassium applications promoted beneficial genera such as Acidothermus, Bradyrhizobium, Bacillus and Nitrospira. Organic inputs like vinasse enriched Burkholderia and Sphingomonas but depleted Bacillus, and combining molasses with urea and potassium chloride enhanced Bacillus while reducing Sphingomonas. Biofertiliser effects were exquisitely sensitive to strain composition, application rate and nitrogen context: a consortium containing Trichoderma asperellum and Bacillus subtilis enriched Bradyrhizobium and Trichoderma, while specialised consortia dominated by Methylobacterium depleted both Bacillus and Burkholderia. Intercropping outcomes depended heavily on the companion crop, with sugarcane-soybean systems enriching Bryobacter, Nitrospira, Penicillium and Trichoderma, and sugarcane-peanut systems promoting Acidothermus and Bradyrhizobium. Meanwhile, green cane harvesting promoted a broader range of beneficial taxa than straw return alone, and the deep-tillage technique known as Fenlong-ridging increased Bradyrhizobium and Talaromyces while reducing Sphingomonas, Penicillium and Curvularia.

Underlying these variable responses, the authors propose a mechanistic framework in which microbiome assembly is governed by chemical nutrient saturation, carbon complexity and spatial compartmentation. High inorganic nitrogen acts as a directional filter, acidifying soil and suppressing oligotrophic diazotrophs like Bradyrhizobium by reducing root carbon allocation, while versatile generalists such as Sphingomonas persist thanks to their protective sphingolipid cell walls. Easily degradable carbon sources trigger blooms of opportunistic copiotrophs, whereas lignocellulosic residues select for robust spore-forming decomposers. The review is candid about its limitations: the evidence base is heavily skewed toward China, which contributed 34 of the 42 studies, most research spans only a single growth cycle, soil classification was often poorly documented, and amplicon sequencing reveals composition rather than function. Still, the overarching message is clear. Soil microbial responses in sugarcane systems are profoundly context-dependent, emerging from interactions among management practices, environmental conditions and crop genotype. Sustainable production, the authors conclude, will require integrated, systems-based approaches that optimise these interactions rather than betting on any single intervention.

Subject of Research: Effects of sugarcane management practices on soil bacterial and fungal communities

Article Title: A scoping review of how various management practices influence bacterial and fungal genera within sugarcane production systems

Article References: Moremi, M. E., Mdlambuzi, T., Mashamaite, C. V., & Elephant, D. E. (2026). A scoping review of how various management practices influence bacterial and fungal genera within sugarcane production systems. Discover Soil, 3(1), Article 127. https://doi.org/10.1007/s44378-026-00283-0

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00283-0

Keywords: sugarcane, soil microbiome, bacteria, fungi, intercropping, fertilisation, straw return, biofertilisers, rhizosphere, pathogen suppression, nutrient solubilisation, sustainable agriculture

The study, conducted by researchers at Hochschule Osnabrück University of Applied Sciences in Germany and published in Discover Plants, assigned ninety-five young vanilla plants to five different nitrate-to-ammonium ratios, ranging from 100 percent nitrate to 100 percent ammonium, all at a constant total nitrogen concentration of 47 milligrams per litre. A tenth group of ten plants received no nitrogen at all as a control. The plants grew in perlite, an inert substrate that allowed the researchers to control the root environment with precision, over a 154-day period under carefully regulated temperature, humidity, carbon dioxide and light. Because perlite suppresses microbial nitrification, the ratio applied was largely the ratio the roots actually experienced, making the experiment an unusually clean test of nitrogen form.

The results were striking. Total dry mass declined linearly as the ammonium share increased, and relative growth rate proved the most sensitive indicator of all, with nitrogen form explaining roughly half of its variation. Compared with plants fed exclusively nitrate, those receiving exclusively ammonium accumulated 28 percent less total dry mass and grew 36 percent more slowly. The pure nitrate treatment produced the highest total dry mass of any nitrogen treatment, 1.73 grams per plant, and was the only nitrogen treatment to differ significantly from both the unfertilised control and the ammonium-only group. A 75:25 nitrate-to-ammonium ratio sustained growth rates statistically indistinguishable from pure nitrate, suggesting growers have a modest window of flexibility at the nitrate-rich end of the spectrum.

Beneath the surface, the chemistry of the root zone told much of the story. As the ammonium proportion rose, the substrate became progressively more acidic, with pH falling by about 1.2 units, from 5.93 under pure nitrate to 4.72 under pure ammonium. This acidification stems from the protons plants release when they take up ammonium, and in a weakly buffered substrate like perlite, watered only every two weeks to avoid waterlogging the vanilla’s sensitive roots, the effect accumulated unchecked. The researchers deliberately avoided corrective pH adjustment, since any neutralising agent would have introduced treatment-specific ions and muddied the comparison. From a practical standpoint, however, the coupled effect is exactly what a grower would encounter: choosing ammonium-rich fertilisers means accepting an increasingly sour root zone along with the nitrogen itself.

The consequences rippled through the plants’ nutrient status. Tissue nitrogen concentrations actually rose in every organ as ammonium increased, with shoot tissue showing the strongest response, but the researchers caution that this reflects lower nitrogen-use efficiency rather than superior nutrition. Because the ammonium-fed plants built less biomass, the nitrogen they absorbed was concentrated in a smaller body, a dilution effect that makes tissue appear nitrogen-rich even as the plant starves for structural growth. Descriptive, unreplicated leaf analyses also hinted at the well-known ammonium-cation antagonism: leaf calcium fell from 2.44 to 1.42 percent of dry mass and magnesium from 0.53 to 0.35 percent as ammonium rose, consistent with ammonium competing with these divalent cations at uptake sites while acidity displaces them from exchange surfaces.

Root architecture suffered too. Total root length peaked at 222.93 centimetres under pure nitrate and dropped to 143.53 centimetres under pure ammonium, echoing earlier findings that ammonium inhibits root elongation. Interestingly, nitrogen form did not change how plants partitioned biomass between roots and shoots; root mass fraction and root-to-shoot ratio were unaffected. Instead, ammonium stress showed up in organ morphology, with ammonium-fed plants producing leaves of unusually high specific leaf area, suggesting thinner or less densely built foliage. The researchers propose that luxury ammonium uptake without proportional structural investment, and possibly mild ammonium toxicity, may both be operating simultaneously under the high-ammonium regimes.

Perhaps the most intriguing finding emerged from splitting each vine into apical and basal sections. Because vanilla grows as a monopodial vine, producing each new node in strict sequence, the basal organs developed during the first half of the treatment while apical organs grew during the second, providing a within-plant proxy for time. Under pure nitrate, apical shoot dry mass exceeded basal by 48 percent, a normal developmental gradient for a vigorously growing vine. Under pure ammonium, that gradient was essentially abolished, indicating that ammonium-related constraints accumulated until they erased the inherent advantage of younger tissue. This treatment-by-position interaction was significant for all five positional parameters measured, providing the first evidence in an orchid that nitrogen-form effects intensify with prolonged exposure, a pattern previously documented in kale, where 75 percent ammonium caused no harm after four weeks but significant damage after eight.

Photosynthetic machinery, by contrast, remained largely intact. The maximum quantum efficiency of photosystem II, measured as Fv/Fm, stayed above 0.72 in all nitrogen-fertilised treatments and only dropped to 0.675 in nitrogen-starved controls, showing that none of the ammonium levels caused photoinhibition. Stomatal conductance did not differ among treatments, though the authors note that vanilla is an obligate crassulacean acid metabolism plant whose stomata close during daytime measurements, possibly masking real differences in gas exchange. Curiously, chlorophyll content in apical leaves followed a quadratic pattern, peaking at an intermediate ratio of roughly 45:55 nitrate to ammonium rather than under pure nitrate, hinting that a moderate ammonium share can optimise chlorophyll, a major nitrogen sink, even while whole-plant growth favours nitrate.

The authors are careful about interpretation. Because ammonium uptake and rhizosphere acidification are inseparable in practice, the growth decline cannot be attributed to nitrogen form alone; the observed response integrates both direct physiological effects and the secondary consequences of acidification and nutrient imbalance. The experiment was also confined to young vegetative plants under relatively low light of 77 micromoles per square metre per second, and the energetic costs of ammonium assimilation tend to intensify as light and growth demand rise, meaning the nitrate advantage could strengthen further under commercial greenhouse conditions. Whether the vegetative benefit carries over into flowering and pod production, which vanilla plants reach only after roughly three years of vegetative growth, remains to be tested.

Even with those caveats, the practical message is actionable. The researchers recommend a predominantly nitrate-based nitrogen supply, at least 75:25 nitrate to ammonium, for vegetative vanilla in soilless culture, a choice already standard in Phalaenopsis orchid production but never before evidence-based for vanilla. A small ammonium supplement of up to 25 percent may offer a workable compromise, supporting apical chlorophyll without triggering excessive acidification or the biomass losses seen at higher ammonium shares. For an industry squeezed between soaring demand, climate-vulnerable supply chains and reliance on synthetic vanillin substitutes, even incremental gains in how quickly young vines establish could matter enormously. This study transforms vanilla nitrogen management from folklore into data, and it suggests that the first evidence-based feeding recipe for the world’s favourite flavour begins with nitrate.

Subject of Research: Effect of the nitrate-to-ammonium ratio on vegetative growth, nutrient status, and physiology of Vanilla planifolia in soilless culture

Article Title: Nitrate-to-ammonium ratio shapes vegetative growth, nutrient status, and physiology of Vanilla planifolia in soilless culture

Article References: Vahl, M., Petersen, F., von Salzen, J., & Ulbrich, A. (2026). Nitrate-to-ammonium ratio shapes vegetative growth, nutrient status, and physiology of Vanilla planifolia in soilless culture. Discover Plants, 3(1), Article 394. https://doi.org/10.1007/s44372-026-00853-0

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00853-0

Keywords: Vanilla planifolia, nitrate, ammonium, nitrogen nutrition, soilless culture, hydroponics, rhizosphere pH, orchid, plant physiology, relative growth rate, ammonium toxicity, fertilisation