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

Arbuscular mycorrhizal fungi are ancient symbionts that colonize the roots of most land plants, exchanging soil minerals such as phosphorus and nitrogen for plant carbon. For endangered plants clinging to survival in degraded and fragmented landscapes, these fungi can be the difference between thriving and failing, boosting nutrient uptake and stress tolerance when conditions turn harsh. Yet despite their conservation significance, the patterns and mechanisms governing AMF communities associated with rare plants in fragmented habitats have remained poorly understood, leaving a gap that conservation biologists have long wanted to fill.

To close that gap, a research team led by Yueling Li and Junmin Li of Taizhou University sampled roots and rhizosphere soils from five naturally fragmented populations of H. miconioides across eastern China. The team profiled the fungal communities using Illumina high-throughput sequencing of the 18S rRNA gene, a technique that reads the genetic barcodes of fungi present in each sample and allows researchers to identify which lineages dominate each microhabitat. By pairing these molecular data with measurements of soil chemistry and climate, the researchers could ask not only who lives where, but why.

The results revealed a striking compartmental split. The genus Glomus dominated both roots and rhizosphere soil, but it was significantly enriched inside the roots, suggesting that these fungi are particularly successful at establishing intimate colonization within the tree’s root tissue. In contrast, the genus Ambispora showed a clear preference for the rhizosphere, the narrow zone of soil directly influenced by root exudates. This root-versus-soil differentiation echoes a growing body of literature showing that the root endosphere and rhizosphere are not simply connected compartments but ecologically distinct habitats that filter fungal taxa in different ways.

Perhaps the most conceptually important finding concerns how these communities come together in the first place. Community assembly theory distinguishes deterministic processes, such as environmental selection that favors certain species under specific conditions, from stochastic processes, such as ecological drift and random dispersal, which shape communities by chance. Across most of the sampled regions and in both compartments, the AMF communities of H. miconioides were assembled largely by stochastic processes, with ecological drift prevailing. In other words, chance, more than environmental filtering, appears to govern which fungi colonize most of the tree’s fragmented populations.

But there was a telling exception. In the DPS region, deterministic forces took over, and specifically heterogeneous selection accounted for roughly 72 percent of rhizosphere community assembly. Heterogeneous selection occurs when environmental conditions vary strongly enough to push different communities in different directions, imposing distinct selective pressures across sites or microhabitats. The fact that this deterministic signal appeared only in one region and only in the rhizosphere underscores how strongly assembly mechanisms depend on geography and compartment, a regional contingency that the authors highlight as a key lesson for anyone attempting to generalize about mycorrhizal ecology in fragmented landscapes.

The study also used network analysis to examine how fungal taxa interact with one another. Here again, the two compartments told different stories. Rhizosphere-associated networks were more complex and more highly connected, consistent with the idea that soil communities experience a richer web of ecological interactions. Root-associated networks, by contrast, exhibited greater modularity, meaning the fungi inside roots cluster into more tightly linked, semi-independent subgroups. Modular structure in root communities may reflect functional specialization or the influence of the plant host in organizing its internal symbionts, and it suggests that the tree’s root environment imposes its own architectural logic on the fungal assemblage.

What drives these patterns environmentally? The researchers found that soil properties, including nitrate nitrogen, total phosphorus, and urease activity, together with climatic variables such as mean annual temperature and mean annual precipitation, exerted stronger regulatory effects on root AMF communities than on rhizosphere communities. These factors explained 15.27 percent of the variation in root communities but only 3.47 percent of the variation in rhizosphere communities. The asymmetry is intriguing: while the open soil community appears buffered and largely drift-assembled, the community inside the roots responds more sensitively to the chemical and climatic context, possibly because root colonization is metabolically costly and plants regulate symbiosis according to nutrient availability and stress.

For conservation practitioners, the implications are concrete. Because AMF communities differ between roots and soil, and because assembly rules shift from region to region, restoration efforts cannot assume that a single inoculum or soil treatment will work everywhere. The authors suggest that their findings provide fundamental references for the utilization of AMF in the conservation of H. miconioides, and the study builds on earlier work by the same group showing that these fungi can improve the species’ growth and drought stress tolerance. Matching fungal communities to local conditions, and understanding whether a given population’s symbionts are drift-assembled or selection-filtered, could improve the success of reintroduction and habitat restoration programs.

The broader significance extends well beyond one endangered tree. Habitat fragmentation is one of the dominant threats to global biodiversity, and its effects ripple underground, disrupting gene flow, altering microbial networks, and reshaping the symbioses on which plants depend. By documenting spatially explicit, compartment-specific patterns of AMF distribution and assembly in a naturally fragmented system, this study adds a crucial belowground dimension to fragmentation ecology. As sequencing costs fall and analytical frameworks for community assembly mature, the invisible fungal partners of rare plants are finally coming into focus, and with them, a new set of tools for keeping endangered species rooted in a fragmenting world.

Subject of Research: Arbuscular mycorrhizal fungal community assembly in the endangered plant Heptacodium miconioides under habitat fragmentation

Article Title: Root–rhizosphere differentiation and assembly mechanisms of arbuscular mycorrhizal fungi in the endangered species Heptacodium miconioides under habitat fragmentation

Article References: Li, Y., Luo, G., Ke, S., Lv, P., Jin, Z., & Li, J. (2026). Root–rhizosphere differentiation and assembly mechanisms of arbuscular mycorrhizal fungi in the endangered species Heptacodium miconioides under habitat fragmentation. Plant and Soil. https://doi.org/10.1007/s11104-026-09127-w

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09127-w

Keywords: arbuscular mycorrhizal fungi, Heptacodium miconioides, habitat fragmentation, rhizosphere, community assembly, ecological drift, Glomus, Ambispora, endangered plants, soil microbiology, conservation, high-throughput sequencing