Fungal necromass: The hidden key to soil health

The hidden architecture beneath our feet

Standing in a quiet woodland, one might notice the scent of damp earth and the rustle of leaves - but the most significant activity remains entirely invisible. Beneath the moss and leaf litter, a vast white webbing of fungal mycelium is engaged in a silent, planetary-scale negotiation. This network is not merely a passive inhabitant of the soil; it is one of the primary engines of carbon sequestration on Earth. Recent data confirms that fungal filaments represent the dominant pathway for plant-derived carbon entering the ground, often surpassing the contribution of roots and surface litter combined.

What we are only beginning to understand is that the health of our atmosphere cannot be separated from the vitality of these invisible webs.

The chemistry of carbon allocation

Plants operate as solar-powered pumps, pulling carbon dioxide from the atmosphere and converting it into sugars. In a striking display of biological cooperation, terrestrial plants channel a significant share of this fixed carbon directly to their mycorrhizal fungal partners - on average around 6% of assimilated carbon for arbuscular mycorrhizal (AM) symbioses and up to 13% for ectomycorrhizal (ECM) ones, with totals varying considerably by species and environment.

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According to a landmark study by Hawkins et al. (2023), this transfer accounts for 13.12 gigatons of carbon dioxide equivalents (CO₂e) annually. To put that into perspective, this volume is nearly 36% of the world's yearly fossil fuel emissions - a figure that fundamentally reframes how scientists and policymakers should think about soil biology.

This carbon does not simply vanish underground. Fungi use it to build cellular walls composed of chitin and glucans - chemically resilient materials that resist rapid decomposition. When living mycelium eventually dies, it becomes fungal necromass. Emerging research suggests this dead material may be even more vital to climate stability than the living network itself: in forest soils, microbial necromass accounts for approximately 35% of soil organic carbon (SOC), and of that microbial fraction, roughly two-thirds originates from fungi rather than bacteria.

The biological cement of soil stability

One of the most remarkable functions of mycelium is its ability to physically restructure the earth. Fungi produce a glycoprotein known as glomalin - described by scientists as biological cement. This substance coats fungal filaments and surrounding soil particles, binding them into stable macroaggregates.

These aggregates act as safe houses for carbon. By trapping organic matter within tight, mineralised clusters, the mycelium shields it from microbial decomposition and oxidation. Carbon sequestered within fungal-mediated aggregates can remain stable for decades, according to current field data.

This process is also climate-sensitive in ways scientists are only beginning to quantify. When precipitation increases, the formation of soil organic carbon is driven primarily through the mycorrhizal pathway rather than the root pathway. A 2025 study published in PNAS observed a 136% increase in mycelium-derived carbon under wetter conditions - reinforcing the role of fungi as dynamic climate buffers that actively respond to environmental change rather than merely passively storing what falls their way.

Frugal networks and the strategy of survival

Recent studies have revealed a fascinating distinction in how different fungal species manage their resources - and what that means for long-term carbon storage.

Some forest fungi exhibit what researchers call a frugal recycling strategy: instead of abandoning old, inactive mycelial networks, these species actively dismantle their aging structures and redeploy the nutrients locked inside them. Other groups are more wasteful, leaving behind large quantities of inactive biomass. This behavioural difference is not merely a biological curiosity - it directly changes how scientists must calculate long-term carbon budgets.

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Frugal species may sequester less carbon in the short term, while wasteful species leave a larger legacy of necromass that gradually integrates into stable soil carbon pools. Understanding which strategy dominates in a given ecosystem - and how climate stress might shift that balance - is now a critical frontier in mycorrhizal research.

Threats to mycorrhizal networks

Despite their planetary importance, mycorrhizal networks face serious and often underreported threats.

Tillage and soil disturbance are among the most damaging. Mechanical ploughing physically severs fungal filaments, breaking the continuity of networks that may have taken years to establish. Decades of deep tillage in industrial agriculture have dramatically reduced fungal biomass across vast areas of cultivated land.

Synthetic fertilisers, particularly high-nitrogen inputs, suppress mycorrhizal associations. When plants receive abundant nutrients from external sources, they have little incentive to invest carbon in fungal partners - effectively starving the network at its root. Fungicide use poses a more direct threat, killing the organisms on which this entire system depends.

Perhaps most consequentially, deforestation and land-use change eliminate the plant hosts that mycorrhizal fungi require to survive. Without trees and other symbiotic partners, the fungal networks collapse entirely - releasing stored carbon back into the atmosphere and leaving soils structurally weakened.

Recognising these threats is not merely academic. They directly inform what kinds of land management and agricultural policy will - or will not - protect one of Earth's most significant carbon sinks.

Integrating biochar and mycorrhizal pathways

Innovation in carbon management is increasingly looking toward the synergy between fungi and biochar - a stable form of carbon produced from organic waste through a process called pyrolysis. Biochar acts as a physical scaffolding for fungal growth, providing the porous microhabitats that mycelium uses as a base of operations.

Research indicates that arbuscular mycorrhizal fungi (AMF) facilitate the transfer of carbon into protected soil microsites and biochar-associated fractions. Data from recent trials show that biochar application can increase microbial necromass carbon by 13.9%, driving the formation of mineral-associated organic carbon (MAOC) - one of the most stable and long-lasting forms of carbon storage available in soils.

The biochar-fungi partnership is a compelling applied pathway: organic waste carbon is converted into a substrate that actively stimulates further carbon removal. By providing a structured home for fungal communities, biochar effectively multiplies the sequestration capacity of the mycelium already present in the soil.

Landscapes of the future

As researchers examine alpine ecosystems and managed plantations, the influence of elevation, climate, and nutrient availability becomes increasingly clear. In high-altitude environments, ectomycorrhizal fungi dominate and dictate the pace of carbon turnover. In Chinese fir plantations, even when nitrogen is added to the soil, mycelium remains the single largest contributor to carbon input - underscoring just how central these networks are to the carbon cycle across vastly different land types and management regimes.

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Significant questions remain. Scientists are still mapping how long carbon persists within specific fungal structures, and exactly what governs the decomposition of fungal necromass over decadal timescales. The migration of fungal molecules into larger soil carbon pools involves complex biochemical interactions that require far more quantitative field data to fully understand.

What this means for climate policy

The numbers here demand policy attention. If mycorrhizal pathways are responsible for sequestering carbon equivalent to more than a third of annual fossil fuel emissions, then land management practices that erode soil health are not just environmental concerns - they are active climate liabilities.

Regenerative agriculture, which prioritises soil biology, reduced tillage, and restored plant diversity, is not a niche farming philosophy. It is, in measurable terms, a climate intervention. Rewilding projects that reintroduce tree cover over degraded land are, in part, programmes for rebuilding mycorrhizal carbon infrastructure at scale.

Carbon accounting frameworks are only beginning to incorporate soil biology into their models. As measurement tools improve and longitudinal field data accumulates, the case for protecting - and actively restoring - mycorrhizal networks will only grow stronger. For now, the picture emerging from the science is one of profound interconnectedness: the vitality of the fungal webs threading through dark, cold earth beneath our feet is inseparable from the stability of the atmosphere above.

Frequently asked questions

What are mycorrhizal fungi? Mycorrhizal fungi are organisms that form symbiotic associations with the roots of most terrestrial plant species. They extend the effective reach of root systems through fine filaments called hyphae, helping plants access water and soil nutrients in exchange for carbon-rich sugars.

How do mycorrhizal fungi sequester carbon? Fungi receive carbon from their plant hosts and use it to build their own cellular structures, primarily composed of chitin and glucans. When this fungal tissue dies, it becomes necromass that integrates into stable soil organic carbon pools. Fungi also produce glomalin, a sticky glycoprotein that physically binds soil particles together and shields trapped organic matter from decomposition.

How much carbon do mycorrhizal networks store? Current estimates suggest that mycorrhizal fungi receive approximately 13.12 gigatons of CO₂e from plants each year - roughly 36% of global annual fossil fuel emissions. A significant portion of this eventually becomes long-term, stabilised soil carbon.

Can protecting fungi help address climate change? The evidence strongly suggests yes. Protecting soil health through reduced tillage, avoiding synthetic fertiliser overuse, and preserving forest cover all support the mycorrhizal networks responsible for moving and stabilising vast quantities of carbon underground. This is now an active area of climate policy research and agricultural reform.

What is glomalin and why does it matter? Glomalin is a glycoprotein secreted by mycorrhizal fungi that acts as a natural adhesive in soil. It binds mineral particles and organic matter together into stable aggregates, physically protecting trapped carbon from decomposition and helping maintain long-term soil structure.