Mycorrhizal Fungi and Carbon Sequestration: Crucial Part of the Carbon Cycle
Introduction Mycorrhizal fungi, symbiotic partners of most terrestrial plants, play a crucial role in global carbon cycling. By forming intricate relationships with plant roots, these fungi facilitate the transfer and storage of carbon in soil ecosystems. This text explores the mechanisms by which mycorrhizal fungi contribute to carbon sequestration, their ecological importance, and the potential implications for climate change mitigation.
Carbon Fixation in Plants Carbon fixation is a critical process in photosynthesis, where plants convert atmospheric carbon dioxide (CO2) into organic compounds. This process is fundamental to the growth of plants and the sustenance of life on Earth. It primarily occurs in the chloroplasts of plant cells, utilising light energy to drive the conversion of CO2 and water into glucose and oxygen.
The most well-known pathway for carbon fixation is the Calvin Cycle, which takes place in the stroma of chloroplasts. The cycle begins when CO2 is attached to a five-carbon sugar, ribulose-1,5-bisphosphate (RuBP), by the enzyme RuBisCO. This reaction produces a six-carbon compound that immediately splits into two molecules of 3-phosphoglycerate (3-PGA). These molecules undergo a series of reactions using energy from ATP and NADPH, generated in the light-dependent reactions of photosynthesis, to form glyceraldehyde-3-phosphate (G3P). G3P is then used to synthesize glucose and other carbohydrates, which serve as energy sources and structural components for the plant.
Carbon fixation is not only vital for plant growth but also for the global carbon cycle. Through photosynthesis, plants act as carbon sinks, sequestering atmospheric CO2 and mitigating the effects of climate change. Additionally, the organic compounds produced via carbon fixation form the base of the food chain, supporting a wide range of organisms, from herbivores to apex predators.
In summary, carbon fixation in plants is an essential biochemical process that sustains life on Earth by converting CO2 into usable organic matter, thereby supporting plant growth and contributing to the global carbon balance.
Carbon Flow to Mycorrhizal Mycelia Mycorrhizal fungi receive a significant portion of carbon fixed by plants through photosynthesis. Estimates suggest that plants allocate between 5-20% of their total carbon uptake to these fungi. This carbon is used to build and maintain extensive mycelial networks, which can transport and store carbon in the soil. Plants allocate enough carbon to underground mycorrhizal fungi equivalent to roughly one-third of carbon emitted yearly by fossil fuels
(CELL PRESS)
Carbon particles flowing inside of hyphae of mycorrhizal mycelia
CREDIT: CARGILL & OYARTE-GALVEZ (AMOLF)
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Mechanisms of Carbon Storage Mycorrhizal fungi contribute to soil carbon storage through several mechanisms. First, they enhance the formation of soil aggregates by exuding compounds such as glomalin, which binds soil particles together, thereby stabilizing soil organic matter. Additionally, the mycelial networks themselves become part of the soil organic matter when they die and decompose, forming a stable carbon pool known as fungal necromass. Soil water stress (WS) affects the decomposition of soil organic carbon (SOC) and carbon (C) emissions. Glomalin, released by arbuscular mycorrhizal fungi into soil and defined as glomalin-related soil protein (GRSP), is an important pool of SOC with hydrophobic characteristics. Mycorrhizal fungi, such as Rhizophagus intraradices, have a positive effect on SOC pools under soil WS for C sequestration in GRSP secreted by extraradical mycorrhizal hyphae.
Ecological Importance Enhancing Soil Health Mycorrhizal fungi improve soil structure and fertility, which in turn enhances plant growth and resilience. The hyphal networks increase the surface area for nutrient exchange, allowing plants to access nutrients that are otherwise unavailable. This is particularly important in nutrient-poor soils, where mycorrhizal fungi can significantly boost plant productivity and health.
Biodiversity and Ecosystem Stability Mycorrhizal associations support plant diversity and ecosystem stability. By facilitating nutrient uptake, these fungi help a wide variety of plant species to thrive, thereby maintaining biodiversity. Furthermore, the carbon storage function of mycorrhizal fungi contributes to the overall stability and resilience of ecosystems, making them less susceptible to disturbances such as climate change.
Applications in Climate Change Mitigation Carbon Sequestration Potential The global contribution of mycorrhizal fungi to carbon sequestration is substantial. Studies estimate that these fungi are responsible for sequestering approximately 13 Gt of CO2e per year, which is equivalent to about 36% of annual CO2 emissions from fossil fuels. This highlights the potential of mycorrhizal fungi in mitigating climate change through enhanced carbon sequestration.
Sustainable Agriculture In agriculture, the use of mycorrhizal fungi can reduce the need for chemical fertilisers and pesticides, promoting more sustainable farming practices. By improving nutrient uptake and soil health, mycorrhizal fungi help to increase crop yields and quality, particularly in low-fertility soils. This can lead to a reduction in the environmental impact of agriculture and support global food security.
Conclusion Mycorrhizal fungi are vital components of terrestrial ecosystems, playing a key role in carbon sequestration and soil health. Their symbiotic relationships with plants have profound implications for global carbon cycling and climate change mitigation. By enhancing our understanding and application of these fungi, we can unlock their full potential to support sustainable agriculture and environmental restoration, contributing to a more sustainable future.
References:
Will fungi solve the carbon dilemma? (S. Emilia Hannula a,c, Elly Morri¨en a,b,* a Department of Terrestrial Ecology, Netherlands Institute of Ecology, PO Box 50, 6700 AB Wageningen, the Netherlands b Department of Ecosystem and Landscape Dynamics, Institute of Biodiversity and Ecosystem Dynamics (IBED-ELD), University of Amsterdam, P.O. Box 94240, 1090 GE Amsterdam, the Netherlands c Department of Environmental Biology, Institute of Environment)
Carbon allocation in mycelia of arbuscular mycorrhizal fungi during colonisation of plant seedlings (Aiko Nakano-Hylander, Pål Axel Olsson, Department of Ecology, Lund University, Ecology Building, SE-223 62 Lund, Sweden)
Wang, YJ., He, XH., Meng, LL. et al. Extraradical Mycorrhizal Hyphae Promote Soil Carbon Sequestration through Difficultly Extractable Glomalin-Related Soil Protein in Response to Soil Water Stress. Microb Ecol 86, 1023–1034 (2023). https://doi.org/10.1007/s00248-022-02153-y
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