Soil Glue

Characteristic mycorrhizal exudates including amino acids, organic acids, sugars and polysaccharides have been identified and can be quickly assimilated by the soil microbial biomass. Additionally, other fungal-specific exudates, such as glomalin (a fungal glycoprotein), are produced by AMF. Glomalin is highly persistent in soil (residence time of four to 62 years) and acts as soil ‘glue’, which can improve soil structure by enhanced soil aggregation. Qualitative and quantitative differences in mycorrhizal exudates might also contribute to soil chemical, physical and biological heterogeneity, creating hotspots of microbial activity and promoting soil activity. However, incorporation of recently fixed carbon into the soil microbial biomass represents only one route for the total diverted carbon, with a substantial carbon diversion to other fungal structures, particularly investment in the external mycelial network. Carbon turnover from fine AMF hyphae can be rapid (five to six days) with thicker hyphae taking up to 30 days, thus representing an important pathway by which plant-assimilated carbon enters the soil environment. This is in contrast to root turnover, which can take several years depending on the root diameter and plant species. Difficulties arise in attempting to apply these turnover times to all fungal tissues, however, especially if considering the carbon investment associated with the extraradical mycelial network or characteristic fungal structures. Intraradical vesicles, reproductive spores, arbuscules (in AMF), intraand extraradical hyphae collectively consume a large fraction of carbon allocated to the fungus. This carbon pool is likely to have a much longer mean residence time in soil than five to six days; an observation which is supported by data suggesting that the residence time of carbon in ECMF communities is four to five years. Collectively, these data suggest that mycorrhizas contribute to short and long-term soil organic carbon pools

https://www.sciencedirect.com/science/article/pii/S136013850900199X