The research team, led by Mailen Guerra Moreno and Roxana Paula Colombo of the University of Buenos Aires together with colleagues at the National University of Avellaneda and CONICET, sampled soils and plant roots at sites spanning the upper, middle, and lower sections of the basin. Their goal was to test whether three fungus-related variables, namely the richness of arbuscular mycorrhizal fungal species determined from spore morphology, the mycorrhizal status of the plants growing in each soil, and the concentration of glomalin-related soil proteins, could function as practical bioindicators of soil health. These biological measures were then compared against the chemical fingerprint of contamination at each site, particularly the burden of heavy metals and metalloids.

The Matanza-Riachuelo basin presents an unusually stark gradient of degradation. Tanneries, metalworking plants, chemical factories, and open dumps have discharged effluents into the river and its floodplain for more than a century, and millions of people live along its banks, many in informal settlements with direct exposure to contaminated soil and water. Previous studies have documented alarming concentrations of chromium, copper, lead, and other toxic elements in basin sediments and soils, along with groundwater quality problems that pose documented risks to human health. Yet, as the authors note, biological indicators of soil health have rarely been examined in urban basins of this kind, leaving a gap between chemical monitoring and the living condition of the soil itself.

The chemical results confirmed the severity of the problem and revealed a clear spatial pattern. The highest concentrations of heavy metal(loid)s were detected in the lower basin, the section closest to the Rio de la Plata, which receives a continuous influx of pollutants and endures intense anthropogenic pressure. The degree of contamination, expressed as a mean value across sampled sites, reached 44.55 in the lower basin, a figure that underscores how far this stretch of urban soil has drifted from any reference condition. By contrast, sites in the upper and middle basin, though still disturbed, carried lighter contaminant loads, allowing the researchers to evaluate how the fungal community responded along this gradient of toxicity.

What the fungi revealed was striking. Across all sampled sites, the family Glomeraceae dominated the arbuscular mycorrhizal community, accounting for 54.55 percent of the species recorded. Among the sixteen species of arbuscular mycorrhizal fungi described so far for the entire basin, eight appear here for the first time, making the survey a significant expansion of documented fungal diversity for the region. Only one species, Rhizoglomus intraradices, was detected at every sampled site, a finding that marks it as a remarkably tolerant generalist capable of persisting even in the most contaminated soils of the lower basin. The pattern echoes observations from other polluted environments worldwide, where a small set of hardy fungal generalists dominates while more sensitive species disappear.

The two candidate bioindicators behaved in opposite but complementary directions. Glomalin-related soil protein concentrations increased with soil toxicity, and the differences in protein levels were specifically associated with the lower basin and with elevated concentrations of copper and chromium. Glomalin is a glycoprotein produced on the walls of arbuscular mycorrhizal fungal hyphae, and it is known to bind metal ions and to help glue soil particles into stable aggregates. Its accumulation in the most toxic soils likely reflects both a stress response by the fungi and the sequestration of metals onto the protein itself, a mechanism documented in earlier laboratory and field studies of copper smelter sites, mangrove wetlands, and cadmium-contaminated fields.

Species richness, by contrast, moved in the opposite direction. The number of arbuscular mycorrhizal fungal species decreased as soil disturbance and contamination intensified, meaning that the most damaged sites hosted the simplest fungal communities. This loss of diversity matters because diverse mycorrhizal communities underpin resilient ecosystems, supporting plant nutrition, soil structure, and nutrient cycling. A community reduced to a handful of tolerant species may still function, but it represents a soil whose biological buffer capacity has been eroded. Together, the two measures form a paired signal: rising glomalin flags mounting metal stress, while shrinking species richness flags the loss of biological integrity.

The study also examined the mycorrhizal status of the plants themselves, asking which species growing across the basin were actually forming arbuscular mycorrhizal symbioses. This plant-level information complements the spore-based survey, since the presence of colonized roots confirms that the fungi found in the soil are actively engaged with the vegetation rather than merely persisting as dormant propagules. Riparian plants in the basin have been the focus of earlier restoration research, including work exploring lotus and other native species in symbiosis with mycorrhizal fungi as tools for rehabilitating degraded riverbanks, and the new findings give those efforts a diagnostic framework rooted in measurable soil biology.

The practical implications extend well beyond Buenos Aires. Chemical analyses of heavy metals are expensive and tell only part of the story, since they reveal what is present but not how the living soil is responding. A biological indicator that can be measured from a soil sample, such as a glomalin protein assay or a spore-based diversity count, offers regulators and restoration practitioners a way to track whether remediation efforts are actually restoring ecological function. The authors suggest that the variables they studied could serve as reliable biological indicators of soil health in future studies, and the paired directionality they observed, with one measure increasing and the other decreasing along the contamination gradient, is precisely the kind of sensitivity that makes a bioindicator useful.

There are, of course, caveats. The study relied on spore morphology to identify fungal species, a classical method that can underestimate diversity compared with DNA sequencing, and glomalin-related soil protein measurements capture a pool of related compounds rather than a single molecule. Seasonal variation, plant community composition, and soil physical properties such as pH and electrical conductivity are also known to shape mycorrhizal communities and would need to be accounted for in any long-term monitoring program. Nevertheless, the work represents the first systematic attempt to link arbuscular mycorrhizal variables to the contamination gradient of the Matanza-Riachuelo basin, and it adds a new chapter to the growing recognition that the smallest inhabitants of urban soils may be its most honest witnesses. In a basin where the damage has been measured in tons of discharged metal for generations, the fungi offer something chemical tests cannot: a living record of how much the soil has suffered, and a benchmark for how far it still has to recover.

Subject of Research: Arbuscular mycorrhizal fungi as bioindicators of heavy metal contamination and soil health in an urban river basin

Article Title: Sensitivity variations on soil health indicators related to arbuscular mycorrhizae in a highly disturbed urban basin of Buenos Aires, Argentina

Article References: Guerra Moreno, M., Silvani, V. A., Godeas, A. M., & Colombo, R. P. (2026). Sensitivity variations on soil health indicators related to arbuscular mycorrhizae in a highly disturbed urban basin of Buenos Aires, Argentina. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38298-3

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38298-3

Keywords: arbuscular mycorrhizal fungi, soil health, heavy metals, glomalin, bioindicators, Matanza-Riachuelo basin, urban pollution, Glomeraceae, Rhizoglomus intraradices, soil microbiology, Buenos Aires, environmental monitoring

The stakes could hardly be higher. Mangroves buffer tropical and subtropical shores against storm surges, cyclones and erosion, sequester carbon at remarkable rates, and sustain coastal livelihoods across the tropics. Yet according to recent global assessments cited in the study, roughly half of the world’s mangrove ecosystems now face potential collapse. Without effective intervention, projections suggest that by 2050 around 7,065 square kilometres of mangroves could be lost outright, while another 23,672 square kilometres may become submerged as sea levels climb. Rising salinity is a central driver of this decline, impairing growth, photosynthesis and survival even in plants that evolved to live at the land-sea boundary.

The grey mangrove, Avicennia marina, is the most widely distributed mangrove species on Earth, stretching from the Arabian Gulf to the coasts of the Red Sea and across the Indo-Pacific. But even this hardy pioneer has its limits. Previous work has shown that elevated soil salinity reduces water potential, disrupts ionic balance and induces phosphorus deficiency, all of which stunt growth and diminish photosynthetic performance. The new study set out to test whether the right fungal partners could tip the balance back in the mangrove’s favour.

Arbuscular mycorrhizal fungi, or AMF, are among the most successful symbionts in nature, associating with more than 80 percent of terrestrial plant species. Their microscopic hyphae thread through the soil, extending the effective reach of plant roots and improving the uptake of water and nutrients, particularly phosphorus. Under saline conditions, these fungi are known to help plants maintain ionic homeostasis, activate antioxidant defences and preserve photosynthetic efficiency. What remained poorly understood was how they perform in mangrove ecosystems, where salinity is not an occasional stress but a permanent feature of the environment.

To find out, the team grew even-aged Avicennia marina seedlings in a greenhouse in Kolkata under three salinity regimes: low at 9 deciSiemens per metre, moderate at 14 dS/m and high at 19 dS/m, levels that span the range these trees encounter in degrading coastal habitats. Seedlings were inoculated with either a consortium of Glomus species, including Glomus mosseae, G. multicaule and G. macrocarpum, a consortium of Gigaspora species, including Gigaspora margarita and G. gigantea, or a combined inoculum of both genera. Uninoculated salt-stressed seedlings and unstressed controls served as comparisons. After 180 days, the researchers measured everything from shoot and root length to photosynthetic pigments, antioxidant enzymes, osmolytes, oxidative damage markers and mycorrhizal soil proteins.

The results were striking. Seedlings receiving the combined Glomus and Gigaspora consortium grew tallest under every salinity level, reaching an average shoot length of 61.60 centimetres under high salinity, nearly three times the 21.20 centimetres recorded in the salt-stressed control. Root growth followed the same pattern, with consortium-treated seedlings producing roots almost 39 centimetres long under the harshest conditions, compared with barely 5 centimetres in unstressed controls. Intriguingly, the consortium also reduced the salt concentration of the surrounding soil, from 18.87 dS/m in uninoculated high-salinity pots down to 13.75 dS/m, suggesting the fungi actively modulate salt dynamics in the rhizosphere rather than merely helping plants tolerate it.

The biochemical story was equally compelling. Consortium-inoculated seedlings accumulated the most chlorophyll a and total chlorophyll under low and moderate salinity, indicating better-preserved photosynthetic machinery. Their roots showed the highest activities of catalase, acid phosphatase, alkaline phosphatase and dehydrogenase, enzymes that collectively dismantle reactive oxygen species and unlock soil phosphorus. Meanwhile, two classic markers of oxidative damage, malondialdehyde and hydrogen peroxide, plummeted in consortium-treated plants, falling to 1.09 and 1.44 nanomoles per gram respectively under high salinity, compared with values approaching 8.68 and 6.43 in stressed and unstressed controls. Lower MDA means less lipid peroxidation and better-protected cell membranes, a direct sign that the fungal partnership was shielding the seedlings at the cellular level.

The fungi also appeared to restructure the soil itself. Easily extractable glomalin-related soil protein, a glycoprotein produced by AMF hyphae that glues soil particles into stable aggregates, peaked at 11.60 micrograms per gram in consortium-treated pots under high salinity, far above the near-zero levels in controls. Glomalin improves soil structure, carbon sequestration and resilience in saline environments, and its accumulation may partly explain the reduced rhizosphere salinity observed in the study. Proline, an osmoprotective amino acid that helps cells retain water under salt stress, also climbed to its highest levels in consortium-inoculated seedlings, reinforcing the picture of a coordinated osmotic and defensive response orchestrated by the symbiosis.

Multivariate statistics sharpened the interpretation. Principal component analysis showed that the first two components captured more than 84 percent of the variation at each salinity level, and in every case the consortium treatment clustered with antioxidant enzymes, glomalin, proline and growth traits, while salt-only seedlings grouped with the oxidative damage markers. Hierarchical clustering and Pearson correlation analysis reinforced the same conclusion: growth, photosynthesis, osmotic adjustment and antioxidant defence rise and fall together, and the dual fungal inoculum sits at the centre of that coordinated network. Notably, Gigaspora alone excelled at promoting biomass, while Glomus alone drove anthocyanin accumulation under severe stress, hinting that the two genera supply complementary functions that only together deliver full protection.

The authors are careful to note that the molecular mechanisms behind these effects, the long-term persistence of the fungal benefits and the interactions with native microbial communities remain to be explored, and that field trials will be needed to validate the approach under natural coastal conditions. Even so, the study marks a significant step forward. As salinization accelerates across the Sundarbans and other vulnerable deltas, projections warn that a 50 percent rise in salinity by 2050 could cut mangrove ecosystem productivity by nearly 30 percent. A cheap, sustainable inoculum of native mycorrhizal fungi, applied to nursery-raised seedlings before outplanting, could give restoration projects a crucial head start. In the contest between rising seas and the forests that defend our coasts, the smallest players, threads of fungus thinner than a human hair, may prove to be the most decisive allies of all.

Subject of Research: Mycorrhizal fungi-mediated salinity stress tolerance in the grey mangrove Avicennia marina

Article Title: Arbuscular Mycorrhizal fungi alleviate salinity stress in Avicennia marina through morphophysiological and biochemical modulation

Article References: Paul, S., Parkash, V., Kaundal, R., Thapa, M., Dhara, B., & Mitra, A. K. (2026). Arbuscular Mycorrhizal fungi alleviate salinity stress in Avicennia marina through morphophysiological and biochemical modulation. Discover Plants, 3(1), Article 447. https://doi.org/10.1007/s44372-026-00916-2

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00916-2

Keywords: mangroves, Avicennia marina, arbuscular mycorrhizal fungi, salinity stress, Glomus, Gigaspora, glomalin, proline, antioxidant enzymes, coastal restoration, oxidative stress, plant physiology

Researchers led by Qiuyun Xu and Yajuan Shi of the Research Center for Eco-Environmental Sciences developed an alternative framework they call the soil health sensitivity distribution, or SHSD. Instead of asking how many species are harmed by a given concentration of lead, copper, or cadmium, the SHSD asks how many soil functions are impaired. Soil health, in this framing, is the sustained capacity of an ecosystem to function as a vital living system supporting plants, animals, and humans. The team built standardized soil microcosms containing wheat (Triticum aestivum), the compost earthworm Eisenia fetida, and the indigenous microbial community of Tianjin field soil, then exposed them to graded concentrations of the three metals for 30 days.

The choice of organisms was not arbitrary. The researchers compiled functional trait profiles for candidate plant and invertebrate species and used principal coordinate analysis together with Bray-Curtis and Gower dissimilarity metrics to identify the taxa closest to the centroid of each group’s trait space. Wheat and Eisenia fetida emerged as the most functionally representative choices, meaning their trait profiles best stand in for the broader community of soil plants and animals. Nine soil health indicators were then retained to represent complementary functional domains: microbial biomass, plant biomass, earthworm biomass change, nitrate content, the activities of four enzymes (FDA hydrolase, beta-glucosidase, urease, and neutral phosphatase), and glomalin content, a glycoprotein linked to soil structural stability.

The responses of these indicators to metal exposure were strikingly complex. Biomass measures generally declined with increasing metal concentrations, but the enzyme activities behaved in nonlinear, sometimes non-monotonic ways. Under cadmium stress, beta-glucosidase and neutral phosphatase showed U-shaped responses, while urease followed an inverted U. For copper, several enzymes rose at intermediate concentrations before falling at high doses. The team used principal component analysis to integrate these non-monotonic patterns, identifying concentration ranges at which combined carbon, nitrogen, and phosphorus cycling shifted adversely, and benchmark dose modeling to derive indicator-specific effect thresholds. For cadmium, the most sensitive indicator was glomalin content, with a threshold of just 0.89 milligrams per kilogram, whereas microbial biomass tolerated up to 53.44 milligrams per kilogram.

These indicator thresholds were then assembled into cumulative sensitivity distributions, from which hazardous concentrations were read. For lead, the model-averaged SHSD placed the concentration affecting 5 percent of soil health indicators at 113.89 milligrams per kilogram; for copper, the HC5 was 34.00 milligrams per kilogram; and for cadmium it was just 2.59 milligrams per kilogram. Coupling these distributions with spatially resolved exposure data from 86 topsoil samples collected across Tianjin in June 2022, the researchers produced probabilistic risk estimates for the entire municipality. Copper posed the highest regional ecological risk, with a mean estimate of 9.07 percent, followed by lead at 1.13 percent and cadmium at 0.52 percent. Spatially, copper risks peaked in the urban Core Area at 14.88 percent, while lead and cadmium risks were highest in Jinghai District.

When the same exposure data were run through conventional species sensitivity distributions, the risk estimates were dramatically higher: 22.42 percent for copper, 3.57 percent for lead, and 3.33 percent for cadmium. The SHSD-based risks were lower by 84.38 percent for cadmium, 61.90 percent for lead, and 59.55 percent for copper, a difference the authors report as statistically significant. The ranking of the three metals was broadly consistent between the two frameworks, and the spatial hotspots largely overlapped, suggesting that exposure patterns, shaped by historical industrial emissions, traffic-related deposition, and long-term fertilizer inputs, drive much of the geographic structure in both assessments.

Why the large gap? One obvious suspect is soil chemistry. SSD toxicity values are typically drawn from studies conducted in wildly different soils, where pH, organic matter, and cation exchange capacity strongly modulate metal bioavailability. When the researchers normalized the literature toxicity data to the physicochemical conditions of their microcosm soil using species-specific equations, part of the discrepancy vanished. For lead, normalization reduced the SSD-SHSD deviation by nearly 100 percent at low concentrations but the benefit shrank nonlinearly as concentrations rose, disappearing above roughly 3,223 milligrams per kilogram where direct toxicity dominates. For copper, normalization cut the deviation by 29.73 percent at the regional mean concentration. For cadmium, whose greater solubility and weaker binding to soil particles make it less sensitive to soil context, the effect was smaller and even reversed slightly at intermediate concentrations.

Normalization alone could not close the gap, however, and the residual difference points to something more intriguing: the integrated microcosm appears genuinely less sensitive than the sum of its parts. Using a partitioning framework originally proposed by Loreau and Hector, the team constructed expected SHSDs from additive combinations of microbial-only, earthworm-microbe, and plant-microbe assemblages. The observed SHSD from the full three-component system shifted consistently to the right, toward higher tolerated concentrations, for all three metals. The authors propose several candidate mechanisms. Earthworm bioturbation may promote stable metal-organic complexes and microbial colonization; plant root exudates may enrich carbon substrates and stimulate metal-immobilizing microbes; and microbial metabolism can mediate metal reduction, precipitation, and complexation. Functional redundancy adds another layer, as enhanced enzyme activities under moderate metal exposure suggest microbial consortia preserved nutrient cycling even when plant productivity declined. Feedback loops, such as glomalin-driven aggregate formation increasing the sorptive capacity of soil colloids, may further decouple organismal exposure from total contaminant load.

The authors are careful to frame these results as a demonstration rather than a replacement. The SHSD thresholds are microcosm-based functional tolerance values derived from a defined soil matrix, fixed exposure duration, and selected representative taxa; they are not yet universal regulatory criteria. Important determinants of bioavailability and ecosystem complexity, including pH, soil organic carbon, and microbial diversity, were not included as direct response indicators, and no field measurements of functional impairment were available to independently validate the thresholds. Sensitivity analyses also revealed that the choice of indicator weighting matters, particularly for cadmium: excluding glomalin content raised the cadmium HC5 from 2.59 to 6.81 milligrams per kilogram and collapsed the regional risk estimate to 0.01 percent, showing that a single highly sensitive structural endpoint can dominate the lower tail of the distribution.

Even with those caveats, the regulatory implications are considerable. The authors envision SHSD-derived thresholds combined with spatial exposure maps to support risk-based zoning and hotspot prioritization, joint probability estimates to rank remediation urgency among regions and contaminants, and monitoring programs built around indicators directly tied to ecosystem functioning, from microbial biomass to enzyme activities and nutrient-cycling metrics. Most compellingly, SHSD could slot into a tiered assessment strategy in which conventional SSDs provide screening-level species protection and SHSD supplies higher-tier information on how real soil systems respond under defined conditions. If validated across contrasting soils, pollution histories, and biological assemblages, the approach could shift soil risk assessment from a ledger of how many species die toward a measure of whether the living system itself keeps working, a question that matters far more for the farms, cities, and coastal wetlands sitting on contaminated ground.

Subject of Research: Soil health-based versus species-based sensitivity distributions for assessing ecological risks of metal contamination in soils

Article Title: Comparing soil-health- and species-based sensitivity distributions for metal risk assessment in Tianjin soils

Article References: Xu, Q., Shi, Y., Xiong, X., Qian, L., Fang, L., Zhou, X., & Shao, X. (2026). Comparing soil-health- and species-based sensitivity distributions for metal risk assessment in Tianjin soils. iScience, 29(10), Article 117644. https://doi.org/10.1016/j.isci.2026.117644

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117644

Keywords: soil health, ecological risk assessment, species sensitivity distribution, heavy metals, lead, copper, cadmium, soil microcosm, Tianjin, soil enzymes, glomalin, environmental toxicology