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Plants distribute enormous amounts of CO2 to mycorrhizal fungi

For over 450 million years, mycorrhizal fungi have been secret heroes, maintaining the balance of life on Earth. These fungi are critical to supplying plants with essential soil nutrients, ensuring their growth and survival. 

Recent scientific discoveries reveal that these tiny organisms not only form symbiotic relationships with almost all terrestrial plants but also act as vital channels, transporting carbon into soil ecosystems.

Mind-blowing amount of carbon exchanged by plants and fungi

According to a meta-analysis published in the journal Current Biology, these fungi could be managing an astronomical amount of carbon – 13.12 gigatons of carbon dioxide equivalents (CO2e) to be precise, which is approximately 36 percent of yearly global fossil fuel emissions. 

As nearly 70 to 90 percent of land plants engage in symbiotic relationships with mycorrhizal fungi, it’s been speculated for some time that a substantial amount of carbon is shuttled into the soil through the networks formed by these fungi.

Heidi Hawkins, research lead at Conservation South Africa, studies plant-soil-microbe interactions at the University of Cape Town. “We always suspected that we may have been overlooking a major carbon pool,” said Hawkins.

She goes on to emphasize that despite the focus on preserving and rehabilitating forests to counter climate change, there’s been a lack of attention given to the fate of the carbon dioxide drawn from the atmosphere during photosynthesis. This carbon dioxide is transmitted below ground to the mycorrhizal fungi by the plants themselves.

Symbiotic relationship between plants and mycorrhizal fungi 

In this symbiotic relationship, mycorrhizal fungi reciprocate the favor by transferring mineral nutrients to their plant partners. Such mutual exchanges are enabled through the interactions between fungal mycelium – the thread-like networks constituting most of the fungal biomass, and plant roots.

The underground transported carbon serves two functions for the fungi. Firstly, it’s used to grow a more extensive mycelium, thus allowing the fungi to further explore the soil. Secondly, the carbon gets bound in the soil due to the sticky substances released by the fungi and can remain underground as fungal necromass, providing a structural framework for soils.

Still much to be learned about this process

However, a crucial piece of the puzzle is still missing. “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,” said Hawkins. What remains uncertain is the duration for which the carbon stays within the fungi.

“We know that mycorrhizal fungi are vitally important ecosystem engineers, but they are invisible,” said Toby Kiers, a professor of evolutionary biology at Vrije University Amsterdam and co-founder of the Society for the Protection of Underground Networks (SPUN).

He emphasizes that our knowledge of these fundamental players at the base of Earth’s food webs is just beginning to take shape.

Time is of the essence

But the clock is ticking. The UN Food and Agriculture Organization has issued a stark warning: by 2050, 90 percent of soils could be degraded, and fungi are conspicuously absent from most conservation and environmental policies. This could severely hamper the productivity of both natural and crop plants.

Study co-author Katie Field is a professor of plant-soil processes at the University of Sheffield. “Mycorrhizal fungi represent a blind spot in carbon modeling, conservation, and restoration,” said Professor Field. 

She warns that the disruption of ancient life support systems in the soil undermines our efforts to curb global warming and compromises the health and resilience of ecosystems upon which we rely.

There’s a strong call to action from the research community. Merlin Sheldrake, co-author of the study, insists that humanity must not only limit destructive activities that harm underground ecosystems but also significantly accelerate research efforts. 

Developing open-source maps of the planet’s fungal networks

Sheldrake, who is part of organizations like SPUN, the Fungi Foundation, and GlobalFungi, shares that these bodies are driving a massive global sampling endeavor. The goal is to develop open-source maps of Earth’s fungal networks. 

These maps will help researchers identify properties of underground ecosystems, such as carbon sequestration hotspots, and document new fungal species capable of withstanding harsh conditions like drought and high temperatures.

However, it’s important to note that while these findings and data are based on the best available evidence, they are estimates and should be interpreted carefully. Sheldrake emphasizes the need for caution. 

“Although our numbers are only estimates, they are the best we are able to make with the data available. The limitations of our study make clear the urgent need for further empirical study of carbon and nutrient fluxes between plants and mycorrhizal fungi.”

Undoubtedly, mycorrhizal fungi play a significant role in our ecosystems and in the fight against climate change. The continuation and intensification of research in this area could unlock more secrets about these unsung heroes of the natural world. The question is whether we can learn enough in time to protect these vital, yet often overlooked, components of our planet’s health.

More about relationship between plants and fungi

The relationship between plants and mycorrhizal fungi is one of the most remarkable examples of symbiosis in nature. This mutualistic interaction has been critical for the survival and success of plants, especially in nutrient-poor soils, and has been in existence for millions of years.

Here’s how it works:

Nutrient Exchange

The primary benefit for plants in this symbiotic relationship is the enhanced access to nutrients. Fungi are particularly efficient at breaking down complex organic materials in the soil and absorbing nutrients such as phosphorus and nitrogen. The fungal hyphae, or thread-like structures, extend far beyond the reach of plant roots and are also much thinner, allowing them to access soil pores that roots cannot. These nutrients are then transferred to the plant.

Carbon Exchange

In return for these nutrients, plants provide the fungi with carbohydrates (sugars), which they produce during photosynthesis. This serves as the primary carbon and energy source for the fungi.

Improved Water Uptake

In addition to nutrient acquisition, the extensive network of fungal hyphae can also help plants with water uptake during times of drought.

Increased Resistance to Pathogens

Some types of mycorrhizal fungi can also provide increased resistance to plant diseases by serving as a physical barrier to pathogens, or by improving the plant’s own immune response.

Soil Structure

Lastly, mycorrhizal fungi contribute to soil aggregation, which is the binding of soil particles together into clusters. This process enhances soil structure, improves water holding capacity, and promotes root penetration.

Environmental Stress Resistance

The association with mycorrhizal fungi often provides plants with increased resistance to environmental stressors such as metal toxicity and salinity.

These various aspects of the plant-fungi symbiosis reveal the complex and fascinating web of interdependence that exists beneath our feet. It’s a classic example of mutualism in nature, where both organisms derive benefits from the relationship. It also underscores the importance of preserving these symbiotic relationships, which play a crucial role in the overall health of our ecosystems.

Video Credit: Cargill & Oyarte-Galvez (AMOLF)


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