The review defines emerging contaminants as newly identified or increasingly detected pollutants that are not yet fully regulated. Agricultural chemicals, treated wastewater, sewage sludge, manure, industrial emissions, urban runoff and contaminated amendments are among their principal sources. Microplastics enter farmland through irrigation water, fertilizers, organic amendments and atmospheric deposition. Climate-related flooding can transport contaminants onto agricultural land, while drought can concentrate them in soils. Some less persistent compounds also degrade into transformation products that may have different or greater risks than their parents. Unlike heavily studied legacy pollutants, emerging contaminants create difficulties because their mixtures, pathways and ecological effects remain incompletely characterized.

Pharmaceutical residues illustrate how a small chemical can disturb major soil functions. Antibiotics entering soil through wastewater, biosolids and livestock manure can impose selective pressure on microorganisms, affecting processes such as nitrogen fixation, phosphorus solubilization and organic-matter decomposition. Tetracycline has suppressed the activity of nitrogen-fixing bacteria, potentially reducing nitrogen available to plants, while sulfamethoxazole and tetracycline have reduced activity of urease, an enzyme involved in organic-matter decomposition. Carbamazepine and oxytetracycline can persist in soil for extended periods. In experiments involving the earthworm Eisenia fetida, carbamazepine, diclofenac, fluoxetine and orlistat altered soil pH and the animals’ internal pH, indicating potential effects beyond microbial communities.

Plant uptake provides a possible route from contaminated soil to food. One study cited in the review detected five of six tested pharmaceuticals in radish and ryegrass tissues, with carbamazepine reaching 52 micrograms per gram in radish and 33 micrograms per gram in ryegrass; sulfamethazine remained below the study’s 0.01-microgram-per-gram detection limit. These measurements come from an individual experiment, not a systematic estimate of contamination across foods, and uptake varies with both compound properties and plant species. The review therefore treats crop accumulation as a food-safety concern requiring further assessment rather than evidence of a general contamination rate across agricultural markets.

Pesticides add another major pressure on soil–plant systems. A large European Union survey cited by the authors found at least one pesticide residue in 83% of topsoil samples, while 58% of samples contained mixtures of two or more pesticides. Glyphosate and its metabolite AMPA formed the most frequently detected mixture, appearing in 25% of samples. Organophosphate pesticides can kill decomposers such as earthworms, reducing organic-matter breakdown and soil aeration. Glyphosate can also interfere with root-exudate production, with research cited in the review associating this effect with reduced colonization by mycorrhizal fungi and rhizobacteria. Pesticide residues have been detected in bees, nectar and pollen, extending their effects beyond the root zone.

Industrial contaminants introduce persistent physical and chemical changes. A survey of United Kingdom farmland reported 320 to 12,560 microplastic particles per kilogram of soil and recorded 2022 levels 1.6 times those measured in 1966. Experimental studies reviewed by the authors found that increasing microplastic concentrations reduced bulk density and increased soil porosity by 7% to 15%, changes that can affect water retention and hydraulic conductivity. Results depended on moisture: toxicants leaching from microplastics reduced fungal richness in well-watered soil, whereas greater water retention under dry conditions benefited some organisms. Per- and polyfluoroalkyl substances, or PFAS, have likewise been detected in agricultural soils irrigated with contaminated effluent and have been linked experimentally to reduced seed germination, impaired root development and altered nutrient uptake.

At the microbial level, contamination can reorganize communities rather than merely suppress them. Exposure to antibiotics, fungicides, PFAS, textile dyes and plastics can shift microbial biomass, genetic composition, functional diversity and relative abundance. Direct toxicity may leave resistant organisms enriched, while altered pH, nutrient availability or habitat can favor other species. Microplastics may support specialized communities at the soil–plastic interface, known as the microplastisphere. Sewage sludge and manure can also enrich antibiotic-resistance genes, which may spread among microbes through horizontal gene transfer. In the rhizosphere, albendazole suppressed colonization by the mycorrhizal fungus Rhizophagus irregularis in Lotus japonicus and affected genes associated with arbuscule development and plant phosphorus uptake.

Plants and soil fauna respond in closely related ways. Contaminants have been associated with impaired seed germination, shortened roots, reduced shoot biomass, changes in root hairs and cell permeability, altered photosynthesis, leaf chlorosis and necrosis. Microplastics adhering to root surfaces may interfere with root-cell physiology in fava bean, rice and lettuce, while silver particles can impair ectomycorrhizal diversity, survival and nutrient transfer. Microplastics, organophosphates, dibenzofuran and polychlorinated dibenzodioxins have caused gastrointestinal injuries in earthworms. Antibiotics, nanoparticles and bisphenol A have also increased mortality or impaired reproduction in several groups of soil animals. Such changes can feed back into plant performance because these organisms contribute to decomposition, nutrient cycling, soil structure and microbial diversity.

Bio-based remedies seek to restore or replace impaired biological functions. Rhizosphere microbiome management uses plant-growth-promoting rhizobacteria, mycorrhizal fungi and other inoculants to improve nutrient access, suppress pathogens, increase stress tolerance or support contaminant degradation. One soybean experiment using Bradyrhizobium japonicum and Pseudomonas putida reported increases of 33% to 56% in yield, root length and shoot length under environmental stress. Another study found that co-inoculation with indigenous Pseudomonas and Bradyrhizobium increased soybean yield by more than 10%. Bioaugmentation can acclimatize contaminant-degrading microorganisms before inoculation; one reviewed method removed 99% of target ibuprofen in 21 days, although identifying effective organisms and establishing them in field soils remain difficult. Biofertilizers offer related functions through biological nitrogen fixation, nutrient solubilization, phytohormone modulation and biocontrol, but their shelf life, strain compatibility and variable survival in soils limit deployment.

Nano-fertilizers and hybrid nano-biofertilizers approach the problem through nutrient delivery. Their small particles provide a high surface-area-to-volume ratio and can encapsulate nutrients for foliar, seed or soil application. Trials reviewed in the article report improved nutrient concentrations and crop performance in rice, tomato, peas, soybean, barley and wheat. Hybrid products combine microbial inoculants with particles of silver, copper, iron, nickel, silicon, titanium or zinc, or with organic carriers such as chitosan, cellulose and starch. The authors describe this as an early-stage field with potential for lower nutrient losses and improved nutrient-use efficiency, but nanofertilizers can also reduce carbon mineralization, diminish microbial diversity and harm biota. The review’s conclusion is therefore promising rather than definitive: performance depends on crops, contaminants, climate, soils and farming systems, and the evidence does not yet show that combined interventions can reliably deliver higher yields or safer food at global scale. The authors call for realistic long-term studies, stronger monitoring and regulatory frameworks, farmer education, and coordinated research, policy and stakeholder action across different agricultural environments.

Subject of Research: Emerging contaminants and bio-based and nano-enhanced strategies for agricultural soil health

Article Title: Addressing emerging contaminants in agriculture affecting plant–soil interaction: a review on bio-based and nano-enhanced strategies for soil health and global food security (GFS)

Article References: Nwankwo, C. E. I., Okeke, E. S., Umeoguaju, F. U., Ejeromedoghene, O., Adedipe, D. T., & Ezeorba, T. P. C. (2025). Addressing emerging contaminants in agriculture affecting plant–soil interaction: a review on bio-based and nano-enhanced strategies for soil health and global food security (GFS). Discover Toxicology, 2(1), Article 4. https://doi.org/10.1007/s44339-025-00018-w

Image Credits: AI Generated

DOI: 10.1007/s44339-025-00018-w

Keywords: emerging contaminants, agricultural soils, plant–soil interactions, rhizosphere microbiome, biofertilizers, nano-fertilizers, nutrient cycling, pesticides, PFAS, food security, Addressing, emerging

The three compost matrices had broadly similar chemical properties. On a dry-weight basis, total organic carbon ranged from 26.88% to 28.88%, total nitrogen from 2.62% to 2.89%, and their carbon-to-nitrogen ratios from 9.66 to 10.66. All met the organic-carbon and nitrogen thresholds specified in EU Regulation 2019/1009. Their pH values were alkaline, ranging from 8.02 to 8.13, while electrical conductivity ranged from 4.05 to 4.72 decisiemens per meter. Thermogravimetric analysis also indicated mature, stable material. The ratio between the second and first exothermic events rose from 0.90 in the plastic-free compost to 0.99 in the compost with twice the average plastic content, suggesting a somewhat greater share of thermally stable organic compounds, but not a deterioration in compost quality. Regulated trace elements in all three composts remained below the regulatory limits, and increasing plastic content did not produce a consistent enrichment of potentially toxic elements.

For the soil incubation, each treatment was replicated three times in containers holding the equivalent of 500 grams of dry soil. An unamended control was compared with soils receiving the three composts at a nitrogen-equivalent rate of 100 kilograms per hectare. The soil was held at 23 degrees Celsius and 60% of its water-holding capacity for six weeks. Bulk carbon and nitrogen measures changed only slightly, with no significant treatment differences in total organic carbon or total nitrogen. Compost-amended soils had total organic carbon values about 2% to 5% above the control, while dissolved organic carbon tended to increase, reaching 24% above the control in the treatment containing the average plastic level. These small and partly nonsignificant changes contrasted with clearer responses in soil biological indicators, consistent with the short duration and moderate compost application rate.

Cumulative soil respiration was markedly higher in amended soils. By the end of the 42-day respiration measurement, the soil receiving the highest-plastic compost produced 81% more carbon dioxide than soil amended with plastic-free compost and 63% more than soil amended with compost at the national-average plastic content. The share of added carbon that was respired rose from 12% in the plastic-free treatment to 14% at the average plastic level and 22% at the highest level. The metabolic quotient, which expresses carbon dioxide production relative to microbial biomass carbon, was 97% higher in the highest-plastic treatment than in the unamended control. Because the composts were applied at the same nitrogen-based rate and contained comparable total carbon, the stronger response was associated with differences in compost characteristics rather than simply a larger carbon input. The elevated quotient indicates more respiration per unit of microbial biomass carbon and therefore lower apparent microbial metabolic efficiency, although the experiment cannot identify the precise mechanism responsible.

Microbial nitrogen and several enzyme activities also responded significantly to treatment. Microbial biomass nitrogen was 21% higher than in the unamended control after application of the highest-plastic compost and more than fivefold higher than in soil amended with plastic-free compost. By contrast, plastic-free compost produced the lowest microbial biomass nitrogen value, 74% below the control. Dehydrogenase activity increased by 86%, 92% and 109% over the control in the plastic-free, average-plastic and highest-plastic treatments, respectively. Laccase and tyrosinase activities, which participate in oxidative processes involving complex organic substrates, also responded. Laccase activity was about 7% to 8% above the control in the two plastic-containing treatments. Tyrosinase activity rose by approximately 212% at the average plastic level and 104% at the highest level, meaning the response was not proportional to plastic concentration. N-acetyl-beta-glucosaminidase activity, associated with the breakdown of chitin-derived and other amino-sugar compounds, increased by about 75% and 52% in the two plastic-containing treatments. Beta-glucosidase and phosphomonoesterase activities did not differ significantly.

The pot experiment used the same four treatments with four replicates each, placing three lettuce seedlings, Lactuca sativa cultivar Masaida, in each pot containing the equivalent of one kilogram of dry soil. Plants were maintained at 25 degrees Celsius for four weeks. After the crop was harvested, the amended soils contained 16% to 20% more total organic carbon, 26% to 31% more total nitrogen, 45% to 72% more dissolved organic carbon and 48% to 83% more total dissolved nitrogen than the control. Olsen phosphorus increased by 18% to 22% following lettuce growth, reversing the nonsignificant downward trend observed during the earlier incubation. The fact that phosphorus availability differed after cultivation but did not differ significantly among the three composts suggests that plant-soil processes were more important to this outcome than plastic concentration. Microbial biomass carbon and nitrogen did not differ significantly after lettuce growth, although the highest-plastic treatment had the highest mean values for both.

Lettuce shoot dry biomass increased in every amended treatment, with the greatest rise—26% above the unamended control—recorded in soil receiving the highest-plastic compost. Root biomass and the root-to-shoot ratio were not significantly affected, indicating that compost primarily increased aboveground production rather than changing the allocation of biomass between roots and shoots. Shoot nitrogen and phosphorus uptake did not differ significantly among treatments. Leaf potassium was notably higher in amended plants, increasing by 28% to 44% compared with the control. Leaf iron was lower by 41% to 57%, a pattern that could be associated with changes in soil iron availability, dilution by greater shoot biomass or altered rhizosphere interactions, but the study did not distinguish among these explanations. These findings show that the fertilizing effect of compost persisted despite the presence of certified plastic residues.

Element transfer to the crop did not show evidence of harmful accumulation. Although some DTPA-extractable metals differed after lettuce growth, the pattern was not consistently related to increasing plastic concentration. Chromium was highest in soil receiving the average-plastic compost, while copper fell in that treatment. Extractable iron decreased in the plastic-free and average-plastic treatments, and zinc increased in the plastic-free and highest-plastic treatments, with no single response tracking plastic dose. In lettuce leaves, lead was 26% to 32% lower in amended plants than in controls, zinc remained comparatively stable, and none of the other analyzed elements showed a significant treatment effect. The researchers therefore observed no accumulation of potentially toxic elements in lettuce leaves, even at twice the national-average plastic content. The finding applies to this compost, soil, crop and short experimental duration; it does not establish that repeated applications or exposure under other field conditions would produce the same outcome.

Overall, the study supports a distinction between certified compostable materials that have undergone industrial composting and persistent conventional plastics. At the tested concentrations, the residues did not compromise compost maturity, stability, nutrient quality or regulatory compliance. The composts continued to improve soil carbon, nutrient availability and lettuce shoot growth after application, and the realistic average plastic level generally produced soil responses comparable to plastic-free compost. The strongest signal was not reduced crop performance or toxic-element transfer but a change in microbial functioning, especially greater respiration and a higher metabolic quotient in soil amended with the highest-plastic compost. Because several enzyme responses peaked at the intermediate plastic level and the experiment used one soil, one crop and short controlled periods, the authors call for longer-term field research on repeated compost applications, cumulative exposure and the persistence or transformation of plastic-derived residues in agricultural soil.

Subject of Research: Effects of certified compostable plastic residues in municipal organic waste compost on soil biology, nutrient dynamics and lettuce growth

Article Title: Effects of compostable plastic residues in municipal organic waste compost on soil quality and lettuce growth

Article References: Paesano, A., Cupi, J., Cioffi, N., Gioacchini, P., Ciurli, A., Malena, P., Mazzon, M., & Marzadori, C. (2026). Effects of compostable plastic residues in municipal organic waste compost on soil quality and lettuce growth. Frontiers in Soil Science, 6, Article 1952297. https://doi.org/10.3389/fsoil.2026.1952297

Image Credits: AI Generated

DOI: 10.3389/fsoil.2026.1952297

Keywords: compostable plastics, municipal organic waste, compost quality, soil microbial activity, soil respiration, soil enzymes, nutrient availability, lettuce growth, plant-soil interactions, Effects, compostable, plastic

The review, conducted according to PRISMA guidelines using the Scopus database, identified studies that empirically examined how invasive goldenrods interact with abiotic and biotic elements of invaded ecosystems. The team coded each study across a standardized protocol covering taxonomy, geography, habitat, study design, temporal scope, ecological scale, data types, sampling methods, statistical approaches, and the role Solidago played in each analysis. The resulting dataset exposes a literature that has grown rapidly but unevenly, with only 7 percent of the analyzed studies published before 2012 and the vast majority appearing in the past decade across 115 different journals.

Perhaps the most consequential bias is taxonomic. Solidago canadensis dominated the field, appearing in 77 percent of the reviewed studies, while Solidago gigantea featured in 34 percent and Solidago altissima in just 11 percent. Other invasive members of the genus, including S. decurrens and the hybrid S. × niederederi, appeared in a mere 3 percent of publications, and S. nemoralis in fewer than 1 percent. Nearly three-quarters of the studies focused on a single species, which the authors warn is a genuine scientific hazard: conclusions drawn from S. canadensis cannot automatically be transferred to other goldenrods, whose invasion mechanisms and trait syndromes may differ substantially. Multi-species comparative work, they argue, is essential for building genus-wide predictive models and for avoiding management strategies calibrated to the wrong plant.

Geography tells a similarly lopsided story. Fifty-four percent of the studies were conducted in Europe and 42 percent in Asia, with Poland and Hungary anchoring the European effort and China, followed by Japan, Korea, and Georgia, dominating the Asian literature. North America, where these goldenrods are actually native, appeared almost exclusively in comparative studies. In Europe, gaps are especially evident in the Baltic and Balkan regions and across Northern and Southern Europe despite the continent-wide presence of the plants. Reports of S. canadensis in central, southern, and southwestern China, and of S. altissima and S. gigantea in Japan, have not been matched by proportionate ecological research. The authors also found that co-authorship networks cluster strongly along national lines, with large Chinese and Polish research groups producing most of the output, reinforcing regional concentrations of expertise and research questions.

Climate coverage proved equally narrow. Using the Köppen–Geiger classification, the review found that 66 percent of field-based studies were conducted in humid continental climates with severe winters and warm summers, and 22 percent in humid subtropical climates. Marine west coast climates, which include western Germany, France, the United Kingdom, and Ireland where goldenrods are widespread, accounted for just 4 percent of the field research. Because invasion dynamics often hinge on climatic thresholds, the authors caution that this skew limits understanding of how goldenrods will behave as climate change shifts competitive balances and expands suitable habitat. Comparative cross-country studies were rare, appearing in only 4 percent of the corpus, while single-region studies made up nearly half.

Methodologically, the literature leans heavily on controlled environments. Ninety-seven percent of studies employed a single methodological approach, and ex situ experiments conducted in greenhouses and laboratories dominated at 42 percent. Field observations accounted for 40 percent, while in situ manipulative experiments such as removal or sowing trials made up only 14 percent. Just 3 percent of studies combined approaches. The review links this pattern to regional research traditions: Asian studies, particularly in China, favor ex situ experimentation, whereas European studies more often rely on field-based observation and in situ designs, a difference the authors connect to contrasting patterns of research and development investment on the two continents.

Time is the other glaring blind spot. Among field observation studies that reported temporal coverage, 68 percent lasted no longer than a single season, and long-term studies exceeding two years represented only 15 percent of the literature. Eighty-three percent of the analyzed articles captured only the current state of the invasion, with few incorporating retrospective analyses or future projections. The authors argue that this short-termism, likely driven by funding structures favoring rapid results, obscures delayed effects, feedback mechanisms, and successional processes that unfold over years. Chronosequence approaches and permanent plot monitoring, they suggest, are critical tools for revealing the legacy effects of invasion and the pace of ecosystem recovery after management interventions.

The review also examined how goldenrods figure conceptually in the research itself. Solidago served as an explanatory variable in 48 percent of studies, most commonly testing its effects on native vegetation, soil properties, insects and birds, and arbuscular mycorrhizal fungi, while it appeared as a response variable in 62 percent, tracking how biomass, spread, and traits respond to soil conditions, management practices such as mowing and herbicide application, habitat type, and climate. Statistically, the field remains conservative: analysis-of-variance methods were used in 61 percent of studies, correlation analyses in 36 percent, and general linear models in 27 percent, whereas structural equation modeling, machine learning, and simulation models appeared in fewer than 6 percent each. Only three studies used spatially explicit models, limiting the capacity to forecast spread under environmental change. Data collection centered overwhelmingly on plants, with soil properties the most frequent secondary focus, while insects, fungi, climate, and landscape structure received comparatively little attention.

Habitat selection reveals a further conservation-relevant gap. Nearly half of the field-based research focused on anthropogenic habitats, especially abandoned fields and fallow land, where goldenrods thrive on disturbance and where experimental access is easy and economic stakes are clear. Anthropogenic and semi-natural habitats were studied in roughly equal proportions, at 28 and 26 percent respectively, but semi-natural systems such as wetlands, riparian zones, and forests, where invasion impacts may be most damaging to biodiversity, remain underrepresented. Ecologically, 53 percent of studies examined individual plants and 44 percent plant communities, while ecosystem-level work appeared in 26 percent and landscape-level studies in only 19 percent, with most research confined to a single ecological level.

The authors outline a set of priorities to rebalance the field: expanding research into underrepresented regions and climate zones, conducting multi-species comparisons across the genus, prioritizing semi-natural and conservation-priority habitats, investing in long-term monitoring, integrating aboveground and belowground processes such as soil biota and mycorrhizal fungi, adopting landscape-level spatial analyses, and embracing advanced predictive tools including machine learning and structural equation modeling alongside socioeconomic and historical land-use data. The keyword analysis underlying the review does show the field evolving, with recent work increasingly addressing allelochemicals, drought responses, land-use change, and even tools such as Google Street View for mapping roadside invasions. But the broader message is sobering: goldenrod invasion science has grown fast, yet it remains, in the authors’ assessment, taxonomically narrow, geographically clustered, methodologically reductionist, and temporally shallow. Closing those gaps, the review concludes, is essential for ecological theory and for the practical business of protecting ecosystems from one of the world’s most successful plant invaders.

Subject of Research: Biases and knowledge gaps in global research on ecological interactions of invasive goldenrod (Solidago spp.)

Article Title: Assessing global trends, biases, and knowledge gaps in research on ecological interactions in goldenrod ( Solidago spp.) invasions

Article References: Regulska, E., Zarzycka, M. A., Obidziński, A., Kołaczkowska, E., Kowalska, A., Jabs-Sobocińska, Z., Wolski, J., Omeliańska, B., & Affek, A. N. (2026). Assessing global trends, biases, and knowledge gaps in research on ecological interactions in goldenrod (Solidago spp.) invasions. NeoBiota, 105, 153-175. https://doi.org/10.3897/neobiota.105.165501

Image Credits: AI Generated

DOI: 10.3897/neobiota.105.165501

Keywords: invasive species, Solidago, goldenrod, allelopathy, systematic review, invasion ecology, Solidago canadensis, biodiversity, ecological interactions, biogeography, plant–soil interactions, Assessing

Senecio inaequidens, a perennial subshrub in the daisy family, is one of Europe’s most successful plant invaders. Native to the highlands of Southern Africa, it hitchhiked into Europe in the late nineteenth century as a contaminant of wool shipments. Since then it has spread aggressively along roadsides, railways, quarries, vineyards, and dry grasslands, reaching heights of 40 to 100 centimeters. Its arsenal includes pyrrolizidine alkaloids, allelopathic chemicals that deter herbivores both above and below ground and can reshape soil microbial communities. Only tetraploid populations, carrying forty chromosomes, made it to Europe, while both diploid and tetraploid forms persist in its native range. This history made it an ideal test subject for disentangling how shared evolutionary history versus soil conditions shape competitive outcomes.

The research team, working under controlled growth chamber conditions, designed a fully factorial experiment. Individual ragwort plants occupied the center of each pot, surrounded by one of three competitive scenarios: a community of five species from the invader’s native South African range, a community of five species from the invaded range in Northern Italy, or no competitors at all. Half of the pots contained soil that had been autoclaved at 120 degrees Celsius for 45 minutes to suppress microbial life, while the other half retained the natural bacterial communities collected from the invaded quarry site at Collepedrino, in the Italian province of Bergamo. The South African suite included Aristida congesta, Hibiscus trionum, Salvia disermas, and two Wahlenbergia species, while the Italian suite comprised Bromopsis erecta, Hypericum perforatum, Onobrychis viciifolia, Poterium sanguisorba, and Trifolium repens.

The rationale behind this design draws on a century-old idea. Darwin’s naturalization hypothesis proposes that introduced species should struggle to establish in communities dominated by closely related natives, because related species tend to share traits, resource requirements, and enemies shaped by common evolutionary history. Phylogenetic distance therefore serves as a proxy for niche overlap and for the strength of competition an invader will face. At the same time, a parallel line of research suggests that soil microbes can tip the scales. Introduced plants may escape coevolved specialist pathogens from home, accumulate novel mutualists or antagonists abroad, or actively cultivate bacterial communities that favor their own growth. Which of these mechanisms dominates in practice has remained remarkably unclear.

After 84 days of growth at 29 degrees Celsius under a 14-hour day cycle mimicking ruderal Mediterranean habitats, the answer was unambiguous. Competitor community identity had the strongest effect on ragwort’s performance, with plants growing significantly shorter when surrounded by species from their native South African range compared with plants growing alone. Autoclaving the soil, by contrast, had no significant effect on plant height, and neither community identity nor soil treatment significantly influenced lateral spread. Statistical analysis using two-way ANOVA revealed a significant community effect on height, while soil effects fell well short of significance. In short, the evolutionary familiarity of the competitors, not the living soil, was the dominant force suppressing the invader.

Phylogenetic analysis sharpened the picture. The researchers calculated two complementary measures of relatedness: a community-weighted phylogenetic distance that integrated all competitor species according to their abundance, and the distance between ragwort and the single most abundant competitor in each pot. The community-wide metric showed no relationship with ragwort’s growth, but the distance to the dominant species mattered. The closer the dominant competitor was to ragwort on the angiosperm tree of life, the smaller the invader grew. The two Wahlenbergia species from South Africa were the most phylogenetically similar competitors in the experiment, and the South African communities produced the smallest ragwort individuals overall. This pattern supports Darwin’s naturalization hypothesis in its strongest form, but with a crucial refinement: it is the dominant, closely related species that deliver biotic resistance, not the community as a whole.

The soil bacterial results added an unexpected twist. Sequencing the V5–V6 hypervariable regions of the bacterial 16S rRNA gene yielded nearly 690,000 valid sequences and 8,471 amplicon sequence variants across the samples. Pseudomonadota dominated the communities at 46.8 percent of sequences, followed by Actinomycetota and Bacteroidota. Both competitor identity and soil treatment significantly shaped bacterial community structure, together explaining nearly half of the variation. Most intriguingly, taller and wider ragwort plants were consistently associated with lower bacterial diversity in their pots, a statistically significant negative relationship for both species richness and the Shannon diversity index. Soils under South African communities, where ragwort performed worst, harbored the most diverse bacterial assemblages.

What could explain the link between vigorous invader growth and depauperate bacterial communities? The authors caution that their experiment cannot establish causality, but several mechanisms are plausible. Ragwort’s pyrrolizidine alkaloids may suppress susceptible microbial taxa, echoing earlier work showing that the species’ traits, particularly those linked to competitive ability and root allocation, correlate with rhizosphere bacterial diversity. Alternatively, the pattern may reflect the actions of co-introduced or generalist soil pathogens associated with native-range competitors, which could have compounded the aboveground suppression of ragwort in South African treatments. The authors also note an important methodological caveat: autoclaving can alter soil chemistry, nutrient availability, and physical structure, potentially confounding purely biotic interpretations, although residual DNA from cells killed some ninety days before sampling is likely negligible.

The findings also reconcile an apparent contradiction in the literature. An observational study in Northern Italy had found ragwort performing better in phylogenetically clustered communities, consistent with the pre-adaptation hypothesis, which holds that invaders succeed where they share environmental adaptations with natives. The new experimental results, showing the opposite pattern at fine spatial scales, fit an emerging synthesis in which both hypotheses operate simultaneously but at different scales. At broad geographic scales, environmental filtering favors aliens resembling native species; at the fine scale of individual interactions, where competition for limiting resources is intense, phylogenetic distance becomes an advantage and close relatedness becomes a liability. Context, scale, and resource levels determine which force prevails.

For land managers battling ragwort across Europe’s disturbed landscapes, the study’s implications are refreshingly concrete. Restoration efforts might do well to sow multi-species suites of native species that are phylogenetically close to the invader and competitively strong, deploying them at high abundance to maximize biotic resistance. The suggestion that diverse soil microbiota also constrain the invader opens a second avenue: testing soil amendments that boost microbial diversity and resilience in degraded sites. More broadly, the work demonstrates that the ecological naivety of recipient communities, their lack of evolutionary experience with a newcomer, can outweigh belowground feedbacks in determining invasion outcomes. As global trade continues to shuffle species across continents, understanding which natives are best equipped to resist them, and why, may prove one of the most valuable tools in restoration ecology’s growing arsenal.

Subject of Research: Eco-evolutionary experience and soil bacterial communities as drivers of the invasive success of Senecio inaequidens

Article Title: Eco-evolutionary experience outweighs soil effects in shaping Senecio inaequidens invasion success

Article References: Quaglini, L. A., Yannelli, F. A., Gandolfi, I., Franzetti, A., Caronni, S., Montagnani, C., Carbutt, C., Jeschke, J. M., Citterio, S., & Gentili, R. (2026). Eco-evolutionary experience outweighs soil effects in shaping Senecio inaequidens invasion success. NeoBiota, 106, 141-160. https://doi.org/10.3897/neobiota.106.182956

Image Credits: AI Generated

DOI: 10.3897/neobiota.106.182956

Keywords: invasive species, Senecio inaequidens, eco-evolutionary experience, Darwin's naturalization hypothesis, soil bacteria, plant competition, phylogenetic distance, biotic resistance, restoration ecology, allelopathy, soil microbiome, NeoBiota

The study, led by Jian-Guo Ma and Sheng-Hua Chang of Lanzhou University’s College of Pastoral Agriculture Science and Technology, together with colleagues including Fu-Jiang Hou and corresponding author Xiao-Bo Wang, set out to resolve a long-standing puzzle in plant ecology. Decades of research have established that grazing reshapes plant functional traits, the measurable characteristics such as leaf and root morphology that determine how a plant acquires resources and tolerates disturbance. A separate and rapidly growing body of work has shown that grazing also alters the profile of metabolites in the rhizosphere, the narrow zone of soil influenced by root secretions, which in turn shapes the microbial communities that live there. What remained unresolved was how these two fundamental axes of plant biology coordinate with each other when an ecosystem is subjected to multifactorial stressors year after year.

To answer that question, the team took advantage of a rare experimental asset: a grassland with a 22-year history of continuous grazing, arranged along a gradient of grazing intensities. Working with five co-occurring plant species, the researchers quantified two complementary measures. The first was the functional trait covariation strength, abbreviated FTCS, which captures how tightly a species’ functional traits move together as a coordinated suite. The second was the rhizosphere metabolite covariation strength, or RMCS, which measures the degree of coordination among the chemical compounds found in the soil surrounding each species’ roots. By tracking both metrics across four grazing intensities, the team could ask whether the two axes of plant biology respond to grazing in a coordinated, complementary fashion or according to some other logic.

The starting hypothesis was plausible enough. If grazing acts as an environmental filter, one might expect that plants whose traits respond strongly to changes in grazing-induced soil conditions would also show correspondingly strong shifts in their rhizosphere chemistry, with the two systems working in concert to help the plant cope with its surroundings. Under this view of complementary environmental coordination, the strength of trait covariation and the strength of metabolite covariation should both track the degree to which grazing has altered the soil, and the two response patterns should be correlated with each other across species and grazing treatments.

The data told a strikingly different story. The researchers found that functional trait covariation strength was indeed strongly coupled with how responsive a species’ traits were to grazing-induced changes in the soil. But rhizosphere metabolite covariation strength was completely decoupled from that same soil responsiveness, and the two soil-response metrics were themselves uncorrelated. That pattern effectively rejected the hypothesis of complementary environmental coordination. In other words, the chemical conversation happening in the rhizosphere is not simply mirroring the way a plant’s traits respond to altered soil conditions. The two systems appear to be operating under different rules, and the conventional expectation that they would reinforce each other does not hold in this ecosystem.

What the team found instead was a conserved negative correlation between functional trait covariation strength and rhizosphere metabolite covariation strength, a pattern that held consistently across all five species and all four grazing intensities. This inverse relationship is the signature of an intrinsic coordination trade-off. When a plant invests in tightening the internal coherence of its trait suite, it simultaneously loosens the coordination of its rhizosphere metabolite profile, and when its root chemistry becomes more tightly integrated, its traits become less covarying. Because the pattern was conserved across species and grazing treatments, the authors interpret it as an internal allocation constraint rather than a byproduct of external environmental filtering. It suggests that plants face a genuine budget: they cannot maximize coordination in both domains at once, and adaptation to chronic grazing involves navigating that budget rather than escaping it.

The trajectories of the two metrics along the grazing gradient added another layer of complexity. Both functional trait covariation strength and rhizosphere metabolite covariation strength followed non-monotonic, species-specific paths as grazing intensity increased, rising and falling in patterns that differed from one species to another. Yet when the researchers aggregated these individual trajectories across the five species, the combined response surfaces flattened across the grazing gradient. This flattening is what ecologists call emergent response diversity: although each species responds idiosyncratically to grazing pressure, the ensemble of responses averages out into a stable, buffered pattern at the level of the multi-species community. The concept echoes the portfolio effect familiar from fisheries science, where diversity among components stabilizes the aggregate, and it suggests that the very idiosyncrasy of individual species’ trade-off navigation is what keeps the community’s overall functional coordination steady.

The findings arrive at a moment when ecologists are increasingly recognizing that drylands, which cover a large fraction of the planet’s land surface, are being reshaped by livestock grazing on a global scale. Previous syntheses have documented both the costs of grazing, including negative effects on ecosystem structure and function in rangelands, and the nuanced ways in which grazing intensity modulates the delivery of ecosystem services in drylands. Other recent work has revealed unforeseen phenotypic diversity in dry and grazed worlds, indicating that plants possess far more adaptive flexibility than standard trait frameworks had anticipated. The new study adds a mechanistic piece to that picture by identifying where the flexibility resides: not in unlimited parallel adjustment of traits and chemistry, but in a structured trade-off between the two.

Why would such a trade-off exist in the first place? The authors’ framing points toward internal allocation. Building and maintaining a tightly coordinated trait suite requires physiological investment, and so does producing and regulating a coherent suite of rhizosphere metabolites, compounds that roots exude to recruit beneficial microbes, deter pathogens, and mobilize nutrients. Because both domains draw on the same finite pool of carbon, energy, and regulatory capacity, a plant that pushes hard on one front may necessarily relax on the other. The conserved negative correlation observed across species and grazing intensities is consistent with exactly that kind of shared-budget logic, and it reframes rhizosphere chemistry not as a passive consequence of trait expression but as an active, competing axis of the plant’s adaptive strategy.

For the management and restoration of grazed grasslands, the implications are twofold. First, the decoupling of rhizosphere metabolite coordination from soil responsiveness means that monitoring plant traits alone, however informative, cannot capture the full adaptive response of vegetation to grazing; the underground chemical dimension follows its own dynamics and deserves independent attention. Second, the demonstration that response diversity among species buffers multi-species functional coordination underscores the ecological value of maintaining diverse plant communities in rangelands. If different species navigate the trait-metabolite trade-off in different ways, the community as a whole gains a form of insurance against escalating grazing pressure. As the authors conclude, internal allocation trade-offs appear to be a fundamental mechanism underlying plant adaptation, and coordination diversity among species may be one of the quiet engines that keeps chronically grazed ecosystems from coming apart.

Subject of Research: Coordination trade-offs between plant functional traits and rhizosphere metabolites under chronic grazing in arid grassland

Article Title: Intrinsic coordination trade-offs between functional traits and rhizosphere metabolites underpin plant adaptation to chronic grazing in an arid grassland

Article References: Ma, J.-G., Chang, S.-H., Yu, J.-F., Hou, F.-J., & Wang, X.-B. (2026). Intrinsic coordination trade-offs between functional traits and rhizosphere metabolites underpin plant adaptation to chronic grazing in an arid grassland. Plant and Soil. https://doi.org/10.1007/s11104-026-09100-7

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09100-7

Keywords: plant functional traits, rhizosphere metabolites, grazing, arid grassland, trade-offs, covariation strength, plant-soil interactions, root exudates, response diversity, ecosystem resilience, drylands, Lanzhou University

The research team, led by Yunyi Gu and Chengjin Chu of Sun Yat-Sen University together with colleagues from the Guangdong Academy of Forestry, Temple University, and the Guangdong Chebaling National Nature Reserve, worked in the Chebaling forest dynamic plot, a 20-hectare tract of protected mid-subtropical evergreen forest. Rather than sampling soil at a few scattered points, the researchers deployed high-resolution field sensing at 2,500 locations across the plot, capturing a detailed map of how sodium and other soil physicochemical properties vary from meter to meter. This dense spatial sampling was essential, because the team suspected that the fine-grained mosaic of soil conditions, not just their average values, might be what structures the forest above.

That suspicion proved well founded. The sodium data revealed pronounced spatial heterogeneity, with the variance in soil sodium peaking at a distance of roughly 200 meters, indicating that the forest floor is divided into broad patches of relatively sodium-rich and sodium-poor ground. When the researchers compared sodium against every other measured soil variable, sodium showed the strongest negative correlation with total tree species richness. In other words, the places in the forest where the soil carried the most sodium were the places hosting the fewest tree species, a pattern consistent with the osmotic and ionic stress that excess sodium imposes on plant cells.

The mechanism behind that stress is well understood at the physiological level. Sodium ions compete with potassium ions for uptake sites on root membranes, disrupting the enzyme function, stomatal regulation, and osmotic balance that potassium normally supports. At elevated concentrations, sodium accumulation in plant tissues causes ion toxicity, while the osmotic effect of salt in the soil solution makes it harder for roots to extract water. For most non-halophytic plants, sodium is at best a questionable nutrient and at worst a potent toxicant, which is why salinity is a major constraint on agriculture worldwide. What has been far less clear is whether these effects matter in humid, leached forest soils far from any coast, where salinity has traditionally been assumed to be a non-issue.

The subtropical forest data suggest that assumption deserves revision, but with a crucial twist: the impact of sodium depends on which fungal partners a tree relies on. The team classified every tree species in the plot by mycorrhizal type, separating arbuscular mycorrhizal (AM) species, whose roots are colonized by fungi that penetrate root cells, from ectomycorrhizal (EcM) species, whose fungal partners form a sheath around the roots, along with a residual category of other species. When the spatial correlations were computed separately for each group, a striking asymmetry emerged. Sodium was significantly and negatively correlated with richness for AM trees and for the other category, but the relationship vanished entirely for EcM trees.

This mycorrhizal split is more than a statistical curiosity. AM and EcM fungi represent two of the most ancient and widespread symbioses in terrestrial ecosystems, and they differ profoundly in how they acquire nutrients. Ectomycorrhizal fungi can enzymatically mine organic nitrogen and phosphorus directly from soil organic matter, effectively insulating their hosts from some forms of soil chemical stress, while arbuscular mycorrhizal fungi depend more heavily on the soil solution for nutrient uptake. That difference in foraging strategy could plausibly explain why EcM-associated trees appear buffered against sodium-driven filtering, whereas AM-associated species, which dominate the species pool of subtropical Chinese forests, bear the brunt of it. The result aligns with a growing body of work showing that mycorrhizal type shapes how trees respond to soil nutrient availability and can even influence soil carbon storage and global plant biogeography.

To move beyond simple correlations, the researchers turned to random forest regression, a machine-learning approach that quantifies the relative importance of many predictor variables simultaneously. The models delivered a verdict that few forest ecologists would have predicted a decade ago: soil sodium was the single most important predictor of total tree richness, of AM tree richness, and of richness in the other category, outranking soil temperature, pH, and the macronutrients that usually headline such analyses. For EcM species, by contrast, soil temperature and pH emerged as the primary correlates, reinforcing the picture of two functionally distinct tree guilds responding to different environmental filters within the same forest.

Tree size added a second layer of contingency. When the community was split by diameter at breast height, with small trees defined as stems under 10 centimeters and large trees at or above that threshold, sodium again dominated as the predictor for the small size class, while available phosphorus became the strongest correlate for large trees. This size-dependent pattern makes ecological sense. Young saplings and small stems have shallow, limited root systems and thin tissues, leaving them acutely vulnerable to osmotic stress and ion toxicity in sodium-enriched patches. Large, established trees, with deep roots and substantial nutrient reserves, are better equipped to tolerate sodium but remain constrained by phosphorus availability, a resource that is notoriously scarce and chemically locked away in the highly weathered soils of subtropical China. The study thus suggests that sodium acts as an early-life-stage filter, thinning the pool of recruits before trees ever reach the canopy.

The broader implications reach well beyond one forest plot. Ecologists have recently begun to argue that sodium deserves recognition as a ‘seventh macronutrient,’ one whose shortfall or excess ramifies through food webs, from ants and termites to decomposers and megaherbivores. At the same time, the anthropogenic salt cycle is accelerating: road de-icing, irrigation, mining, and land-use change are mobilizing salts into soils and waterways at rates that rival natural fluxes. If even humid subtropical forests, far from any obvious salinity source, show sodium-driven filtering of tree diversity, then rising salt loads elsewhere could quietly erode biodiversity in ecosystems currently considered safe. The Chebaling findings also suggest that conservation planning and restoration in species-rich forests may need to account for soil sodium maps, not just carbon and nutrient targets.

For the authors, the message is that the nutrient-centered framework governing plant-soil research needs expansion. Soil sodium, they conclude, is a critical yet underappreciated predictor of tree species richness, with effects strongly differentiated by mycorrhizal type and tree size. Integrating sodium into plant-soil studies, alongside the nitrogen and phosphorus paradigms of the past century, could sharpen predictions of how forest diversity will respond to environmental change. A forest’s hidden salt map, it turns out, may be quietly writing the rules of who lives where, one seedling at a time.

Subject of Research: Effects of soil sodium heterogeneity on tree species richness in a subtropical forest, mediated by mycorrhizal type and tree size class.

Article Title: Soil sodium differentially affects tree species richness depending on mycorrhizal type and size class in a subtropical forest

Article References: Gu, Y., Zhong, Y., Behm, J., Tan, H., Li, B., Liu, S., & Chu, C. (2026). Soil sodium differentially affects tree species richness depending on mycorrhizal type and size class in a subtropical forest. Plant and Soil. https://doi.org/10.1007/s11104-026-09074-6

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09074-6

Keywords: soil sodium, tree species richness, subtropical forest, mycorrhizal type, arbuscular mycorrhiza, ectomycorrhiza, spatial heterogeneity, soil salinity, nutrient limitation, forest ecology, plant-soil interactions, random forest

The concept of a core microbiome has become central to modern plant science. Just as humans carry consistent communities of gut bacteria that shape health, plants host recurring assemblages of microbes in the soil immediately surrounding their roots, on the root surface itself, and inside their tissues. These communities are not random collections; they are selected by the host and by environmental filters. Yet for many unusual plants, especially those thriving in chemically extreme environments, the identity of these constant microbial partners remains unknown. That gap is precisely what the team, led by Zihua Zhang and Linxi Yuan of Xi’an Jiaotong-Liverpool University together with colleagues at the Guangxi Academy of Agricultural Sciences and the University of Liverpool, set out to close.

Their strategy was deliberately comprehensive. Rather than sampling a single site or a single growth stage, the researchers integrated three separate experiments: a field survey capturing the plant in its natural habitat and two pot experiments that allowed them to manipulate conditions, including the addition of selenium to the soil. Across all three, they characterized bacterial communities using amplicon sequencing of the 16S ribosomal RNA gene, the standard molecular fingerprinting method for bacteria, and then searched for taxa that appeared consistently across compartments, sites, and growth stages. The logic is straightforward: microbes that persist everywhere the plant grows, regardless of soil variation, are likely to matter functionally rather than being incidental passengers.

The search converged on two bacterial orders: Micrococcales and Rhizobiales. These two lineages formed the native core microbiome of C. hupingshanensis, present across the soil–plant continuum from bulk soil through the rhizosphere, the rhizoplane, and into internal plant tissues. The finding is notable because core microbiomes are often defined more narrowly, for example within roots alone or within a single site. Demonstrating a core that spans the whole continuum suggests a stable, co-evolved partnership between the hyperaccumulator and its bacterial entourage, one that survives transplantation into pots and the altered conditions of greenhouse cultivation.

Intriguingly, the two core orders showed distinct spatial preferences. Amplicon sequence variants belonging to Micrococcales became relatively more abundant in the rhizoplane, the thin layer of soil and microbial cells adhering directly to the root surface, where the plant and microbe are in the most intimate contact. Core variants from Rhizobiales, by contrast, peaked in the rhizosphere, the zone of soil influenced by root exudates. This compartmentalization hints at a division of labor: different microbial partners may occupy different niches along the root, potentially performing complementary functions related to nutrient transformation, stress alleviation, or the chemical processing of selenium before it crosses the root membrane.

Beyond taxonomy, the team examined the architecture of the microbial community as a network, identifying keystone taxa, the highly connected species whose removal would disproportionately destabilize the whole system. Within the subset of the native core microbiome, keystone roles were dominated by members of the phyla Proteobacteria and Firmicutes. The core taxa also made a noticeable contribution to microbial stability across different plant growth stages, meaning that as the plant matured and its root architecture and exudation patterns changed, the core community helped hold the broader ecosystem of root-associated microbes together. Stability of this kind is increasingly recognized as a hallmark of beneficial microbiomes, in both plants and animals.

The most provocative result, however, concerns selenium itself. The researchers found that core taxa in the rhizosphere were significantly associated with selenium concentrations in that soil compartment, suggesting a measurable relationship between the presence of these microbes and the chemistry that governs how much selenium is available for the plant to take up. Selenium in soils exists in multiple chemical forms, ranging from poorly soluble elemental particles to soluble selenate and selenite ions that plant roots can absorb via sulfur transporters. Microbes are known to interconvert these forms, oxidizing, reducing, or methylating selenium depending on the species involved. A rhizosphere community enriched in selenium-active bacteria could therefore shift the local speciation of the element in ways that favor hyperaccumulation.

Adding weight to this interpretation, the pot experiments showed that supplying soil with selenium significantly increased the diversity of the native core microbiome. In other words, the element that defines the plant’s ecological niche also appears to shape its microbial partnership, enriching the community precisely where selenium chemistry matters most. This feedback loop, in which the plant and its microbes jointly engineer a selenium-processing rhizosphere, offers a new mechanistic window into how hyperaccumulation might have evolved. Rather than being a purely plant-borne trait, selenium hyperconcentration in C. hupingshanensis may be a genuinely collaborative achievement, refined over evolutionary time in the seleniferous soils of Enshi and neighboring regions.

The implications extend well beyond one unusual mustard. Selenium is an essential micronutrient for humans, with an estimated one in seven people worldwide consuming less than adequate amounts, yet the margin between deficiency and toxicity is narrow. Understanding how hyperaccumulator plants and their core microbes mobilize, transform, and concentrate selenium could inform biofortification strategies, in which crops are engineered or managed to accumulate nutritional selenium in edible tissues. It could also aid phytoremediation, the use of plants to clean selenium-contaminated soils from mining and agricultural runoff, where microbial partners that enhance uptake or volatilize the element into harmless forms would be valuable allies. Previous work on other hyperaccumulators, including cadmium-accumulating Noccaea caerulescens and arsenic-tolerant Pteris vittata, has similarly revealed core endophytic communities with metal-processing capabilities, suggesting a general principle waiting to be exploited.

The study also carries a methodological message for microbiome science. By defining the core across three experiments, multiple compartments, and successive growth stages, the researchers filtered out the noise that plagues single-site surveys, where transient microbes often masquerade as important players. The identification of Proteobacteria and Firmicutes as keystone phyla, and of Micrococcales and Rhizobiales as the taxonomic backbone, provides concrete targets for the next phase of research: isolating these organisms, reconstructing synthetic communities, and testing directly whether they enhance selenium uptake under controlled conditions. If those experiments succeed, the invisible partners of a Chinese cliff-dwelling cress could become tools for building more nutritious crops and cleaner soils, a reminder that some of a plant’s most remarkable abilities are shared with the microscopic life it carries.

Subject of Research: The native core microbiome of the selenium hyperaccumulator Cardamine hupingshanensis across the soil–plant continuum

Article Title: A native core microbiome across the soil–plant continuum of the selenium hyperaccumulator Cardamine hupingshanensis

Article References: Zhang, Z., Yuan, L., Zhang, L., Liao, Q., Xing, Y., Pan, L., Liu, Y., & Paterson, S. (2026). A native core microbiome across the soil–plant continuum of the selenium hyperaccumulator Cardamine hupingshanensis. Plant and Soil. https://doi.org/10.1007/s11104-026-09174-3

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09174-3

Keywords: selenium hyperaccumulator, core microbiome, Cardamine hupingshanensis, rhizosphere, rhizoplane, Micrococcales, Rhizobiales, Proteobacteria, Firmicutes, keystone taxa, plant–soil interactions, phytoremediation

The experiment was carefully controlled. The team grew cotton in pots under four different nitrogen regimes: a conventional rate of 0.240 grams of nitrogen per kilogram of soil, a 15 percent reduction to 0.204 grams, a 30 percent reduction to 0.168 grams, and a treatment with no nitrogen at all. At the early flowering stage, a moment the researchers identified as a critical turning point in the plant’s life cycle, they collected the chemicals secreted by the roots, known as root exudates. They then measured a battery of indicators: soil nitrogen transformation rates, enzyme activities, microbial biomass, root architecture, total plant nitrogen accumulation, and ultimately the seed cotton yield that farmers actually harvest.

The headline numbers are striking. Compared with plants receiving the full conventional nitrogen dose, those receiving the moderate 15 percent cut produced 14.7 percent more seed cotton per plant. Nitrogen partial factor productivity, a measure of how much yield each unit of applied fertilizer delivers, jumped by 34.9 percent. Nitrogen agronomic efficiency, which captures the yield gain attributable to fertilizer relative to unfertilized controls, rose by 38.7 percent. In other words, less nitrogen did not merely maintain the crop; it actively improved both the harvest and the return on every kilogram of fertilizer invested. The deeper reductions and the zero-nitrogen treatment did not replicate these gains, pointing to a sweet spot rather than a simple rule that less is always more.

What happened below ground helps explain the paradox. Under the moderate reduction, cotton roots developed a compact, dense architecture with higher root tissue density. Rather than chasing nitrogen through long, thin exploratory roots, the plants appeared to reallocate carbon from rapid elongation toward structural reinforcement, building a sturdier, more concentrated root system. This shift reflects a classic economic trade-off in plant biology: when a resource is scarcer, plants invest their finite carbon budget more carefully, favoring traits that improve acquisition efficiency over sheer spatial reach. The result is a root system positioned to exploit the soil volume it occupies more thoroughly.

At the same time, the chemical conversation between root and soil changed. Root exudates, the suite of sugars, amino acids, nucleotides and other compounds that roots release into the rhizosphere, shifted in composition under the moderate nitrogen reduction. Metabolomic profiling revealed two compounds standing out as the dominant responsive metabolites: proline, an amino acid long known as a stress signal and osmoprotectant in plants, and hypoxanthine, a purine base derived from nucleotide metabolism. These are not random leakage products. Their emergence suggests that the plant deliberately reprograms its belowground chemistry when nitrogen supply tightens, broadcasting signals that reshape the microbial community living on its root surface.

The consequences of that chemical broadcast were measurable. The altered exudate profiles were associated with changes in rhizosphere enzyme activities, the catalytic workhorses that microbes use to break down organic matter and release plant-available nitrogen. They were also linked to enhanced retention of nitrogen in microbial biomass, meaning soil microorganisms under the moderate reduction treatment held onto nitrogen more effectively rather than letting it leach away or escape as gas. This matters because microbial nitrogen turnover is a key gateway in the soil nitrogen cycle: nitrogen locked in microbial cells is not lost, and it can be released back to the plant through the continuous cycle of microbial growth, death and decomposition, a process often described as the microbial nitrogen shuttle.

The researchers used structural equation-style path modeling to tie these threads together, and the picture that emerged is one of coupling. Early flowering root exudates appear to link yield formation directly to soil nitrogen transformation and plant nitrogen acquisition, potentially through microbial nitrogen turnover driven by rhizosphere carbon metabolism. In plain terms, the carbon the plant spends on exudates buys it a better-functioning nitrogen economy in the soil. This echoes a growing body of rhizosphere science showing that plants are not passive recipients of soil fertility but active engineers of it, investing photosynthate below ground to cultivate the microbial partners and processes that feed them.

Why early flowering? The timing is not incidental. Flowering marks a major developmental pivot, when the plant shifts resources from vegetative growth toward reproductive structures, and when demand for nitrogen surges to support boll formation in cotton. The study’s authors argue that this window represents a critical opportunity for rhizosphere intervention. If the exudate-mediated dialogue between root and microbe is most consequential at this stage, then management practices, whether fertilizer timing, biostimulants, or microbial inoculants, could be targeted precisely when the plant is most receptive, maximizing effect while minimizing inputs. Related work by the same group has implicated thiamine and L-lysine in cotton exudates under nitrogen reduction, and other studies have shown purine metabolites enriching beneficial root-associated bacteria, suggesting a broader vocabulary of root chemical signals waiting to be exploited.

The implications stretch well beyond cotton. High nitrogen inputs and low nitrogen use efficiency remain critical constraints in cotton production, as the authors note, but the same pattern plagues cereals, oilseeds and vegetables across global agriculture. Applied nitrogen that crops fail to take up does not simply vanish; it contributes to waterway eutrophication, greenhouse gas emissions as nitrous oxide, and the long-term degradation of soil health. A strategy that trims fertilizer by 15 percent while boosting yield and efficiency by double digits offers a template for reconciling productivity with sustainability. It also aligns with the broader scientific push, highlighted in recent reviews, to improve crop nitrogen use efficiency as a pillar of a sustainable green revolution.

Cautions remain. The study was conducted in pots, where root-soil interactions unfold differently than in open fields, and the authors note that data supporting the findings are available from the corresponding author upon reasonable request, inviting replication and field validation. The precise molecular mechanisms by which proline and hypoxanthine steer microbial nitrogen turnover remain to be fully resolved. Still, the core message is compelling and timely: the path to higher yields with lower inputs may not run through the plant’s leaves or even its genes alone, but through the chemical conversation it holds with the soil at the moments that matter most. Listening in on that conversation, and learning to speak it, could reshape how the world fertilizes its crops.

Subject of Research: Root exudate-mediated rhizosphere nitrogen cycling and nitrogen use efficiency in cotton under moderate nitrogen reduction

Article Title: Moderate nitrogen reduction enhances cotton yield and nitrogen use efficiency via early flowering root exudate–rhizosphere interactions

Article References: Shen, Z., Liu, M., He, Y., Liu, X., Wang, H., Yang, Y., Zhang, Q., Zhang, W., & Pu, X. (2026). Moderate nitrogen reduction enhances cotton yield and nitrogen use efficiency via early flowering root exudate–rhizosphere interactions. Plant and Soil. https://doi.org/10.1007/s11104-026-09169-0

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09169-0

Keywords: cotton, nitrogen use efficiency, root exudates, rhizosphere, proline, hypoxanthine, microbial nitrogen turnover, soil enzymes, early flowering, fertilizer reduction, plant-soil interactions, sustainable agriculture

The research team, led by Xinyue Yuan and Yuqing Zhang of Beijing Forestry University together with colleagues, set out to answer a question that has been nagging soil scientists for years. Root traits are increasingly recognized as key drivers of belowground processes, but it has remained unclear how different traits influence rhizosphere effects on carbon and nitrogen mineralization, and whether those influences travel through living pathways—such as stimulating microbial enzymes—or through non-living ones, such as disrupting the mineral particles that lock organic matter away. Disentangling these biotic and abiotic controls is essential if models of soil carbon storage and nutrient supply are to be improved, particularly in drylands, which cover roughly 40 percent of the land surface and are highly sensitive to climate and land-use change.

To do this, the team sampled rhizosphere and bulk soil from six dominant plant species in the temperate desert and quantified how much faster carbon dioxide was released and nitrogen was mineralized in the root-adjacent soil compared with root-free soil. They then measured a suite of root functional traits, including root exudation rates, root tissue density and specific root length, alongside indicators of the rhizosphere’s biotic and abiotic environment: the activity of key extracellular enzymes, the size of the dissolved organic nitrogen pool, and the abundance of amorphous iron and aluminum oxides—reactive minerals famous for binding organic molecules and shielding them from decomposition.

The results reveal a striking asymmetry between the two elements. For carbon, the decisive root traits were those associated with intense rhizosphere carbon release: species with high root exudation rates and low root tissue density produced the strongest positive rhizosphere effects on carbon mineralization. Mechanistically, the study links this to two parallel routes. High exudation stimulated the activity of β-1,4-glucosidase, the microbial enzyme that cleaves cellobiose during cellulose breakdown, effectively revving up the microbial machinery of decomposition. At the same time, exudation-driven chemistry decreased amorphous iron and aluminum oxides in the rhizosphere, weakening the mineral protection that otherwise keeps organic carbon out of microbial reach.

This second route is the more surprising of the two, and it connects the desert findings to a rapidly growing body of work on mineral-associated organic matter. Soils hold much of their carbon not as loose detritus but as organic molecules stuck to the surfaces of reactive minerals. Root exudates, particularly organic acids, can pry these molecules loose—a process sometimes described with the ‘unbutton’ model, in which organic acids displace organic matter from metal-stabilized complexes. By showing that the depletion of amorphous iron and aluminum oxides in the rhizosphere tracks the strength of the carbon mineralization effect across species, the new study provides field-based evidence that mineral destabilization is not a laboratory curiosity but a real, trait-dependent control on carbon cycling in desert soils.

Nitrogen told a different story. Here, the rhizosphere effect was driven by the same carbon-release traits—high exudation and low tissue density—but in combination with specific root length, a morphological trait reflecting fine-root construction. Intriguingly, the pathway did not run through β-1,4-N-acetylglucosaminidase, the chitin-degrading enzyme often assumed to govern nitrogen mineralization. Instead, species with these trait combinations enhanced the rhizosphere effect on nitrogen mineralization primarily by enlarging the pool of dissolved organic nitrogen in the root zone. In other words, the plants appeared to be flooding the rhizosphere with readily available organic nitrogen substrates rather than simply activating the enzymes that mine nitrogen from recalcitrant organic matter.

Why would nitrogen follow a substrate-driven route while carbon follows both enzymatic and mineral routes? The authors suggest that the relative contribution of biotic and abiotic processes simply differs between carbon and nitrogen turnover. Carbon mineralization is ultimately about giving microbes both energy and physical access to protected organic matter, so both enzyme activation and mineral unbuttoning matter. Nitrogen mineralization, by contrast, may be more immediately limited by the supply of small, soluble organic compounds; when roots and their exudates deliver those compounds directly, microbes need not invest heavily in extracellular enzymes to meet their nitrogen demands. This interpretation is consistent with earlier work showing that root exudates can increase nitrogen availability by stimulating microbial turnover of fast-cycling nitrogen pools, and with the broader recognition that competition between roots and microbes for nitrogen shapes rhizosphere chemistry.

The study also carries a conceptual message for the root economics framework, the idea that plant roots array themselves along a spectrum from fast, acquisitive tissues to slow, conservative ones. Traits such as low tissue density and high exudation mark the fast end of that spectrum, and the findings confirm that plants at this end do not merely acquire resources more aggressively—they actively restructure the biogeochemistry of the soil around them. Meanwhile, the independent contribution of specific root length to the nitrogen effect underscores that root traits are multidimensional: morphology, tissue construction and exudation behavior each leave distinct fingerprints on the soil, and no single axis captures them all.

For a temperate desert ecosystem, these mechanisms have outsized significance. Desert soils are typically poor in organic matter and strongly limited by nitrogen, so the plants that dominate them—shrubs and grasses with very different root architectures—effectively engineer their own nutrient supply. Species that exude heavily can unlock mineral-protected carbon and enlarge dissolved organic nitrogen pools, sustaining microbial activity through hot, dry periods when substrate scarcity would otherwise shut decomposition down. As climate change alters precipitation regimes and vegetation composition in drylands, shifts in the abundance of fast-trait versus slow-trait species could therefore feed back into regional carbon balances in ways that current earth system models, which rarely resolve rhizosphere processes at all, do not capture.

The authors argue that their findings provide a mechanistic basis for predicting rhizosphere effects on soil carbon and nitrogen dynamics by integrating root functional traits with the biotic and abiotic processes they set in motion. In practical terms, that means a modeler could, in principle, estimate how much a given plant community accelerates decomposition from a handful of measurable root characteristics—exudation rate, tissue density, specific root length—plus the soil mineralogy that determines how much organic matter is mineral-protected in the first place. It is a compact recipe, but one built on a genuinely two-track understanding of the rhizosphere: microbes on one track, minerals on the other, and plant roots pulling the levers of both. For the barren-looking ground of the Mu Us Desert, the message is that the most important chemistry in the ecosystem happens in a few millimeters of soil, precisely where the roots decide it should.

Subject of Research: Rhizosphere effects of root traits on soil carbon and nitrogen mineralization in a temperate desert

Article Title: Root traits drive distinct biotic and abiotic controls of the rhizosphere effects on soil carbon and nitrogen mineralization in a temperate desert

Article References: Yuan, X., Guo, Y., She, W., Qin, S., & Zhang, Y. (2026). Root traits drive distinct biotic and abiotic controls of the rhizosphere effects on soil carbon and nitrogen mineralization in a temperate desert. Plant and Soil. https://doi.org/10.1007/s11104-026-09130-1

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09130-1

Keywords: rhizosphere, root traits, soil carbon mineralization, nitrogen mineralization, root exudation, mineral protection, enzyme activity, temperate desert, soil organic matter, plant-soil interactions, dissolved organic nitrogen, Mu Us Desert

The research team, led by Marceli Pacan and Agnieszka Kuźniar of The John Paul II Catholic University of Lublin, set out to address a persistent puzzle in agricultural biotechnology: why microbial biostimulants often deliver inconsistent results in the field. Wheat is the world’s third most significant crop and accounts for roughly half of all cereal cultivation in the European Union, so even modest improvements in how beneficial microbes perform could have enormous consequences. The scientists compared two modern winter wheat cultivars, ‘Hondia’ and ‘Tytanika’, with ‘Rokosz’, an ancient spelt wheat valued for its higher protein and mineral content and its adaptation to low-input farming. Their central hypothesis was that the metabolic response to endophyte colonization would depend on the host genotype—a proposition the data dramatically confirmed.

The experimental design was meticulous. In laboratory tests, the researchers first optimized the bacterial cell density and temperature for inoculation, finding that 6.67 × 10⁴ cells per milliliter at 15 to 20 degrees Celsius produced the best seedling vigor. They also screened six biochar carriers made from pine or ash wood at different pyrolysis temperatures, ultimately selecting an ash-wood biochar designated J500, which supported normal seedling growth across all cultivars and proved compatible with commercial fungicide seed dressings. This compatibility matters because real-world farmers apply fungicides alongside seed treatments, and a biopreparation that fails under those conditions would be useless in practice.

The heart of the study was a 40-day greenhouse pot experiment in which inoculated and control seeds of all three cultivars were grown in non-sterilized soil, deliberately preserving the natural soil microbiota. Every five days, the researchers measured the activities of two key defense enzymes: peroxidase (POX), which drives cell wall cross-linking and reactive oxygen scavenging, and phenylalanine ammonia-lyase (PAL), the gateway enzyme of the phenylpropanoid pathway that produces phenolic acids, flavonoids, and lignin precursors. The patterns that emerged were anything but uniform. In ‘Hondia’, POX activity stayed suppressed for most of the experiment and then surged fifteen-fold within just five days at day 40, while PAL activity collapsed to an eleven-fold reduction below control levels. In ‘Rokosz’, the opposite occurred: PAL activity climbed to 11.81 IU per gram fresh weight at day 20—the highest value recorded across all treatments—and remained elevated through the end of the experiment, while POX stayed quietly low.

Untargeted metabolomics using liquid chromatography coupled to quadrupole time-of-flight mass spectrometry revealed the chemistry behind these enzymatic divergences. At day zero, just four days after inoculation, both cultivars shared a common set of exclusively induced metabolites pointing to rapid defense priming: oxidized glutathione, L-tryptophan, allantoin, the coumarin scopoletin, and 12-oxo-phytodienoic acid, a jasmonic acid precursor that functions as a stress-signaling molecule. This early signature demonstrates that the endophytes trigger metabolic activation almost immediately, before any visible growth differences appear. Yet even at this earliest stage, the genotypes differed in character. Spelt ‘Rokosz’ showed a balanced distribution of up- and down-regulated molecular features, whereas ‘Hondia’ displayed a pronounced wave of induction in its non-polar, lipid-rich fraction, with 980 differential features compared to 419 in ‘Rokosz’.

By day 40, the two crops had committed to fundamentally different strategies. Modern ‘Hondia’ accumulated wax esters at extraordinary levels—palmityl palmitate increased nearly forty-fold, and several other long-chain wax esters appeared exclusively in treated plants—suggesting reinforcement of the cuticle, the plant’s outer physical barrier. Alongside this, the cultivar showed extensive remodeling of membrane lipids, including galactolipids and sterol esters, broad accumulation of free amino acids such as tryptophan and N-γ-glutamyl-phenylalanine, and shifts in indole-related metabolism consistent with altered hormonal regulation. Meanwhile, several phenylpropanoid-derived flavonoids were strongly down-regulated, indicating that ‘Hondia’ had shifted away from chemical defense toward enzymatic oxidative management and structural reinforcement.

Ancient spelt ‘Rokosz’ told a different story. Treated plants showed significant enrichment of the phenylpropanoid pathway: p-coumaric acid rose 5.3-fold, trans-cinnamaldehyde 4.6-fold, and compounds such as chlorogenic acid, esculetin, and the flavonoid rutin appeared exclusively in biopreparation-treated samples. HPLC profiling confirmed that vanillic acid and total phenolic acid concentrations increased significantly in ‘Rokosz’ but not in ‘Hondia’. Remarkably, ‘Rokosz’ also accumulated ferulic acid in its leaves at levels comparable to its roots—an unusual pattern for cereals, where phenolics typically concentrate in roots and cell walls—potentially enhancing ultraviolet screening and photoprotection in photosynthetic tissue. The picture is of an ancient grain that channels the microbial partnership into building a dense chemical shield.

Perhaps the most striking statistical finding was convergence: biopreparation treatment reduced the metabolic differences between the two cultivars from 760 differential traits under control conditions to 423 after treatment, a 44.3 percent reduction. In other words, the same microbial inoculant pulled both genotypes toward a shared, microbially induced metabolic state, even as each retained its characteristic strategy. The researchers interpret this as evidence that subspecies-level genetic architecture determines whether endophyte colonization triggers metabolic enhancement, as in spelt, or metabolic moderation, as in modern bread wheat—a distinction consistent with prior work showing that endophytes from wild wheat ancestors can make drought-stressed plants metabolically resemble well-watered controls.

For agriculture, the implications are direct and potentially transformative. Microbial inoculants are increasingly promoted as environmentally friendly alternatives to synthetic fertilizers and pesticides, but their field performance is notoriously variable. This study suggests that much of that variability may stem from genotype-treatment interactions rather than product quality: the identical formulation can produce profoundly different metabolic outcomes depending on the crop’s genetic background. The authors argue for precision agrobiotechnology, in which microbial consortia are matched to individual cultivars and metabolic markers—phenylpropanoids, wax esters, and oxylipin signals such as 12-OPDA—are incorporated into breeding programs to select genotypes with enhanced microbial responsiveness. As climate pressures intensify and the need to reduce chemical inputs grows, understanding these hidden metabolic dialogues between crops and their endophytic partners may prove essential to feeding the world sustainably.

Subject of Research: Genotype-specific metabolic and enzymatic responses of wheat and spelt to an endophytic bacterial biopreparation

Article Title: Endophyte-induced metabolic divergence in wheat genotypes: implications for plant–soil interactions

Article References: Pacan, M., Romanyuk, N., Fornal, E., Sumara, A., Nikolaichuk, H., Kruczyńska, A., Goraj, W., & Kuźniar, A. (2026). Endophyte-induced metabolic divergence in wheat genotypes: implications for plant–soil interactions. Plant and Soil. https://doi.org/10.1007/s11104-026-09133-y

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09133-y

Keywords: wheat, spelt, endophytes, metabolomics, plant–soil interactions, biostimulants, phenylpropanoid pathway, PAL, POX, biochar, Bacillus, sustainable agriculture