Are you passionate about social networks? If the answer is yes, you may be interested to know that under our feet, just a few centimeters from the surface, is the largest and oldest social network on Earth: the one established by mycorrhizal fungi with the roots of most plants.

All mycorrhizal fungi live in the soil and only a few ( ectomycorrhizae) are seen, from time to time, in the form of what we colloquially know as mushrooms or fungi. It is no coincidence that they are collected in forests, since the finest roots of trees are attached, surrounded and slightly penetrated by the filaments (hyphae) of ectomycorrhizal fungi. However, most plants establish associations with another subject of mycorrhizal fungi: endomycorrhizae, also called arbuscular mycorrhizae. These are much more discreet than ectomycorrhizae, since they never appear on the surface and cannot be distinguished with the naked eye when the roots are dug up.

You may ask yourself: what class relationship can two beings, plant and mycorrhizal fungus, so different from each other, establish? What is really amazing and interesting is that they manage to establish a symbiotic relationship from which both benefit greatly. The plant is able to form sugars in the leaves during the process of photosynthesis and, part of them, transports them to the roots to nourish the mycorrhizal fungus associated with them and allow their growth and proper functioning. In turn, some of the filaments or hyphae of mycorrhizal fungi protrude from the root as hair-like extensions that can reach distances unreachable for the bare root and can penetrate soil pores too small for the size of the root. In other words, thanks to these hyphae, the roots explore a larger volume of soil and, therefore, take more and better advantage of the resources it offers: water and mineral nutrients.

And there is still more. The same mycorrhizal fungus can be simultaneously associated with the roots of two or more plants, even if they belong to different families. This allows a transfer of water and mineral nutrients between plants that share a friendship with the same fungus. And not only of substances taken from the soil: a plant can, through this common link of hyphae, share its own substances (hormones, for example) that can influence the functioning of its neighbors. In other words: a real social network in the plant world.

Another question that may arise is:how does a plant distinguish whether the fungus that contacts its root is beneficial or, on the contrary, may cause a disease that will deplete its own development and put its offspring at risk? Actually, it does not know at first, so the plant acts with due caution and reinforces its defenses, including chemical subject defenses. Some of these chemical defenses are enzymes or substances with an important antioxidant capacity that remain in the plant organism even after the plant has recognized as 'friendly' that first contact. In this way, plants are, in a certain sense, vaccinated, but with an analogy to the animal kingdom.

All these benefits provided by mycorrhizal fungi to plants raise the hope that these inconspicuous and silent creatures may prove crucial in favoring plant resilience to climate change conditions. More efficient uptake of water and minerals from the soil may increase plant resilience under conditions of water scarcity, for example. On the other hand, the accumulation of defense compounds may help plants to slow down the attack of pathogens that may colonize new geographical areas as a consequence of global warming and that are still too cold today for their survival and development.

The study of the effects of mycorrhizal fungi on the growth and functioning of plants and on the quality of plant products included in the human per diem expenses is one of the lines of research of the group of Stress Physiology in Plants of the Biodiversity and Environment Institute of the University of Navarra. The most recent research has focused on a context of climate change and has grapevine as the main protagonist. Recently, this group of research has received funding from the Ministry of Science and Innovation of the Government of Spain to develop the project graduate "Contribution of beneficial edaphic microorganisms to the adaptation of commercial grapevine varieties to climate change" (Ref. PID2020-118337RB-I00) in which the role that beneficial soil microorganisms (especially mycorrhizal fungi) can play in the adaptation of several commercial grapevine cultivars (red varieties) to future environmental conditions will be evaluated, paying special attention to the increase in temperature and CO2 levels in the air, as well as to drought. The results derived from this study could provide valuable information for the advice of grape growers.

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Nieves Goicoechea
Researcher at Biodiversity and Environment Institute of the University of Navarra.