It is widely believed that mycorrhizal fungi could store carbon, as the fungi forms symbiotic relationships with almost all land plants and transports carbon, converted into sugars and fats by the plant, into soil, but until now the true extent of just how much carbon the fungi were storing wasn't known.
The discovery by a team of scientists, including researchers from the University of Sheffield, that fungi is storing over a third of the carbon created from fossil fuel emissions each year indicates that it could be crucial as nations seek to tackle climate change and reach net zero. Work is now being undertaken to see whether we could increase how much carbon the soil underneath us can store.
Mycorrhizal fungi have been supporting life on land for at least 450 million years and make up vast underground networks all around us - even forming beneath roads, gardens, and houses, on every continent on Earth.
The international team of scientists, including experts from the University of Sheffield's School of Biosciences, conducted a meta-analysis of hundreds of studies looking at plant-soil processes to understand how much carbon is being stored by the fungi on a global scale.
Their findings, published in Current Biology, revealed that an estimated 13.12 gigatons of CO2 is transferred from plants to the fungi annually, transforming the soil beneath our feet to a massive carbon pool and the most effective carbon capture storage unit in the world.
The amount of carbon stored equates to roughly 36 per cent of yearly global fossil fuel emissions - more than China emits each year.
Researchers are now calling for fungi to be considered in biodiversity and conservation policies, given its crucial role in cutting carbon emissions. At the current rate, the UN warns that 90 per cent of soils could be degraded by 2050, which could be catastrophic for not only curbing climate change and rising temperatures, but for the productivity of crops and plants too.
Professor Katie Field, Professor of Plant-Soil Processes at the University of Sheffield and co-author of the study, said: "Mycorrhizal fungi represent a blind spot in carbon modelling, conservation, and restoration - the numbers we've uncovered are jaw-dropping, and when we're thinking about solutions for climate we should also be thinking about what we can harness that exists already.
"Soil ecosystems are being destroyed at an alarming rate through agriculture, development and other industry, but the wider impacts of disruption of soil communities are poorly understood. When we disrupt the ancient life support systems in the soil, we sabotage our efforts to limit global heating and undermine the ecosystems on which we depend.
"More needs to be done to protect these underground networks - we already knew that they were essential for biodiversity, and now we have even more evidence that they are crucial to the health of our planet."
The researchers are now investigating how long the carbon is stored by the fungi in the soil, and are seeking to further explore the role that fungi plays in Earth's ecosystems.
Dr Heidi Hawkins, lead author of the study from the University of Cape Town, said: "We always suspected that we may have been overlooking a major carbon pool. Understandably, much focus has been placed on protecting and restoring forests as a natural way to mitigate climate change, but little attention has been paid to the fate of the vast amounts of carbon dioxide that are moved from the atmosphere during photosynthesis by those plants and sent belowground to mycorrhizal fungi.
"A major gap in our knowledge is the permanence of carbon within mycorrhizal structures. We do know that it is a flux, with some being retained in mycorrhizal structures while the fungus lives, and even after it dies. Some will be decomposed into small carbon molecules and from there either bind to particles in the soil, or even be reused by plants. And certainly, some carbon will be lost as carbon dioxide gas during respiration by other microbes or the fungus itself."
Professor Toby Kiers, senior author from Vrije University Amsterdam and co-founder of the Society for the Protection of Underground Networks, said: "The paper is part of a global push to understand the role that fungi play in Earth's ecosystems. We know that mycorrhizal fungi are vitally important ecosystem engineers, but they are invisible to most people.
"Mycorrhizal fungi lie at the base of the food webs that support much of life on Earth, but we are just starting to understand how they actually work. There's still so much to learn."
One of the projects which is now investigating the role of mycorrhizal fungi in soil carbon and other nutrient cycles in more detail is being led by the University of Sheffield's School of Biosciences. Using simulated future climates in specialised outdoor field experiments, the NERC-funded study aims to improve our understanding of the critical role of soil fungi, alongside other microbes, in moving carbon belowground and how this will be impacted by future climate change.
Research Report:Mycorrhizal mycelium as a global carbon pool
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