Role of Fungi

In nutrient cycling
ECM fungi enable plants to access organic nitrogen (N) bound in soil organic matter (SOM) and transfer this growth‐limiting nutrient to their plant host, has important implications for our understanding of plant–fungal interactions, and the cycling and storage of carbon (C) and N in terrestrial ecosystems.
​Zak et al. ​
Network structures of mycelia promote genetic adaptation to environmental change in the soil. They do this by providing continuous liquid films in which bacterial migration and contacts are favoured. These bacterial highways make it easier for Horizontal Gene Transfer to occur, whereby bacteria rapidly respond and adapt to environmental change by directly acquiring DNA sequences from other bacteria.
Mycelia is known to “translocate compounds from nutrient-rich to nutrient-poor regions… facilitate the access of bacteria to suitable microhabitats for growth, enable efficient contaminant biodegradation, and increase the functional stability in systems exposed to osmotic stress”
Plants that are involved in arbuscular mycorrhizal symbiosis comprise nearly 90% of all terrestrial plant species; these plants principally rely on arbuscular mycorrhizal fungi for enhancing nutrient uptake, particularly phosphorus. Other functions include:
  • Improving quality of soil eg structure and texture (Zou et al., 2016; Thirkell et al., 2017).
  • Expedite the decomposition process of soil organic matter (Paterson et al., 2016). mycorrhizal fungi
  • Affect atmospheric CO2 fixation by host plants, by increasing “sink effect” and movement of photo-assimilates from the aerial parts to the roots.
Arbuscular mycorrhizal fungi “account for less than 1% of the total modelled biomass … increased the biomass of macro-organisms in the Serengeti by 48%.” (With no fungi, plants would be only half as productive, resulting in less food for herbivores).
While plants differ in their relative dependence on fungi, warm season grasses derive as much as 90% of their phosphorus from mycorrhizal symbioses.
AMF isolated from soils with high Al saturation strongly reduced Al translocation to shoots (up to 5.8-fold in the higher Al level) and increased the Al exclusion in plants growing at high Al levels (over 70%), which may reflect the binding of Al in the rhizosphere by glomalin. By using a rhizobox compartmentation system, our results provide evidence that AMF alleviate Al phytotoxicity through a chemical barrier in which glomalin sequesters Al beyond the root surface, which seems to be an important trait of AMF and would be used for developing management strategies of acidic soils with high Al levels.
Mycorrhizal mycelial networks are the most dynamic and functionally diverse components of the symbiosis, and recent estimates suggest they are empowered by receiving as much as 10% or more of the net photosynthate of their host plants. They often constitute 20%–30% of total soil microbial biomass yet are undetected by standard measures of biomass used by soil scientists and agronomists. Mycorrhizal mycelia provide extensive pathways for carbon and nutrient fluxes through soil, often exceeding tens of metres per gram of soil. We consider the amounts of photosynthate “power” allocated to these mycelial networks and how this is used in fungal respiration, biomass, and growth and in influencing soil, plant, and ecosystem processes. The costs and functional “benefits” to plants linking to these networks are fungal specific and, because of variations in physiology and host specificity, are not shared equally; some plants even depend exclusively on these networks for carbon. We briefly assess the potential contribution of extra-radical mycorrhizal mycelium to sustainable agriculture
The contribution of ericoid mycorrhiza (ErM) and ectomycorrhiza (EcM) to nitrogen (N) supply of host plants is well known, whereas the role of arbuscular mycorrhiza (ArM) is insufficiently understood. Exoenzymes released into the soil from the ErM and EcM mycelium favor the hydrolysis of high-molecular-weight N-containing organic compounds of plant litter and soils to NH+4 or amino acids that are then transported toward plant roots and are absorbed by them. ArM-producing fungi have a limited capacity to release hydrolytic enzymes capable to decompose high-molecular-weight organic compounds into the soil (or do not have it at all). Therefore, they are specialized on the absorption of inorganic forms of N and amino acids appearing in the soil in the course of decomposition of high-molecular-weight N-containing compounds by saprotrophic microorganisms. The activity of hydrolytic exoenzymes and the role of mycorrhiza in the nitrogen nutrition of plants become more significant under conditions of the low supply with mineral N compounds and decrease upon the rise in availability of mineral N compounds. At the same time, mycorrhizal fungi and host plants may compete for the limited resource.
​Makarov (2019)​