increasing soil carbon can significantly mitigate carbon emissions and at the same time, adapt agricultural systems to climate change due to other numerous benefits. Soil carbon has positive effects on soil structure, water retention, and nutrient supply, and is crucial to sustain ecosystem services and agricultural productivity. What most people don’t realize is HOW this can happen. A key mechanism is through the keystone activities of arbuscular mycorrhizal fungi.


Key players


Arbuscular mycorrhizae are the dominant mycorrhizal association on planet Earth. Tey have been observed in the roots of more than 1,000 genera of plants representing some 200 families. It has been estimated that more than 80 to 90 percent of the estimated 400,000-plus species of vascular plants in the world form arbuscular mycorrhizae associations. Tese include most grains, vegetables, fruit and nut trees, vines and legumes. With regard to stabilizing our


increasingly unruly climate, mycorrhizal fungal biomass has been associated with the sticky carbon compound glomalin for hundreds of millions of years. Glomalin may be the most important soil component you have never heard of. Arbuscular mycorrhizal fungi play a key role in the carbon cycle by absorbing carbon that plant leaves fix in photosynthesis from the atmosphere. Carbon from the atmosphere is passed into the ground by the mycorrhizal fungi attached to the root system. Tese arbuscular mycorrhizal fungi are taxonomically included in the group Glomales, a major source of glomalin, and hence the name. Glomalin associated with endomycorrhizal fungal filaments is used to seal and gain enough rigidity to carry materials across the air spaces between soil particles. Bacteria associated with arbuscular mycorrhizal fungi are also a potential source of glomalin. Glomalin acts as a sticky organic glue that creates soil structure. Tink of it as the material that holds the soil architecture together, allowing air, water, and roots to easily move through it. Without good soil structure, soils are vulnerable to soil erosion (Rillig et al., 2002). In addition, glomalin creates stable soil aggregates that protect soil carbon. Glued together by glomalin, soil


aggregates shelter organic matter rich in carbon and nutrients. Te discovery is causing a reexamination of climate change modeling. Climate-change models are rapidly incorporating new data on mycorrhizal fungi, glomalin and soil carbon storage into predictions of global warming rates (Treseder et al., 2016). Mycorrhizal fungal activity has a key


role influencing the huge pool of carbon in our soils. As much as 30 to 40 percent of the glomalin molecule is carbon. Glomalin may account for as much as one-third of the world’s soil carbon and the soil contains more carbon than all plants and the atmosphere combined! While glomalin can last for decades and centuries in undisturbed soil, tillage and fallow can reduce it dramatically along with associated mycorrhizal fungi (Nichols and Millar, 2013). Other factors related to mycorrhizal


fungi drive soil carbon accumulation and have the potential to mitigate climate change (Orwin et al., 2011). Organic nutrient uptake has been shown to significantly increase carbon accumulation in mycorrhizal fungal biomass, roots, and plants. Arbuscular mycorrhizal fungal filaments absorb organic nutrients in the form of amino acids (Whiteside et al., 2009); their study revealed that mycorrhizal fungal filaments associated with Poa annua absorb carbon directly via the uptake of the amino acid glycine in the soil and was thereby transferred directly into plant leaves. Mycorrhizal fungi also can increase


carbon storage by improving the net primary productivity of cropping systems, especially systems limited by moisture or nutrients (Subramanian and Charest, 1999). For example, mycorrhizal inoculation had a significant effect in improving water relations and in retaining more green leaf area, leaf


water potential and stomatal resistance and transpiration rates in drought- stressed maize plants (Subramarian et al., 1995). Mycorrhizal fungi are key to crop growth and biomass production in stressful environments (Al-Karaki et al., 2004; Subramarian et al., 2006) (Fig. 5 shows mycorrhizal inoculated corn production on droughty site). Mycorrhizal fungi might also be key to maintaining plant productivity and successful species migrations on rigorous sites during periods of climate change. (Perry and Amaranthus, 1990).


Squashing the symbiosis Unfortunately, many conventional


agricultural practices reduce or eliminate mycorrhizal activity in the soil and release carbon dioxide into the atmosphere. Certain pesticides, chemical fertilizers, intensive cultivation, compaction, organic matter loss and erosion all adversely affect beneficial mycorrhizal fungi. An extensive body of laboratory and field-testing indicates that the majority of intensively managed agricultural lands lack adequate populations of mycorrhizal fungi (Douds et al., 1993). Without the binding power of


mycorrhizal filaments, soil structure deteriorates and a substantial amount of soil and carbon is eroded from surface soil (Amaranthus and Trappe, 1993). Nutrients can be leached from the soil into waterways, where they can damage water quality and aquatic life. By destroying large segments of the soil food web, a large quantity of carbon and nutrient capital is lost, and the farmer is forced to add more fertilizer. Intensive cultivation and erosion damage the soil and mycorrhizal fungi, thereby releasing carbon to the atmosphere. Where the mycorrhizal association has been suppressed, mycorrhizal


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