By: Alexis Billings
As humans, we understand stress as something we commonly experience, and other species on this planet also experience it, affecting us all physically. We humans also either own plants or have some knowledge of how they work; we know they react to a lack of basic needs in the way we would experience bodily symptoms. This has to do with stress interrupting homeostasis, the balance in organisms. In a similar way that humans have a gut microbiome that is essential to our health, plants have a relationship with mycorrhizal fungi that help keep them healthy.
Mycorrhizal fungi, or mycorrhizae, is a type of fungi found in the soil practically everywhere connecting plants by the roots. They help provide the plants with nutrients and, in return, benefit from the plants. There are two main types of mycorrhizal fungi: EMF, which is on the outside of the roots, and AMF, which is located inside the root cells. Despite their differences, they do tend to respond to stressors in similar ways. Stressful events and conditions affect the physiology of the organism, and because mycorrhizae live below ground they are always exposed to extreme environments. While some stressful conditions can lead to health issues and even death, stress is beneficial to fitness. Fitness in biological terms refers to the ability of an organism to survive well and long enough to pass on its genetic information to its offspring. Long-term stress, though not fun to deal with for probably any species, appears to increase mycorrhizal genetic diversity. This allows for the mycorrhizae to hold up better in those hostile environments, kind of like building up its immunity.
There is evidence of stressful situations and environments affecting mycorrhizae fruiting bodies, the mushrooms. And yes, if you didn’t know, the mushrooms we all see and love are just the small fruits of the extensive mycorrhizal organisms underground. But we also have evidence, specifically of AMF, supporting their host plants in times of drought by changing carbon groups in the DNA of the plant. There is also evidence of mycorrhizae sensing environment changes and then changing signaling pathways in the plants to build up a stress tolerance. So all while the mycorrhizae is having to handle its own stress, it also further supports the plant by directly affecting its stress responses. This, in turn, goes back to benefiting the mycorrhizae, creating a full circle of stress and fighting back.
The thing is, there is a lot more we don’t know about how mycorrhizae actually make these changes to itself and its host plant. The biological process of building stress tolerance and the genetics of stress tolerance in mycorrhizae need to be further researched to find out if the responses are similar to that of other mycorrhizal species with other host plants. More evidence is also needed on the mechanisms of this stress tolerance on a more molecular level. And what about plants that have no relationships with mycorrhizal fungi? Do they feel more stressed handling it on their own and how do they handle that stress without the help of fungi?
In all, we need to know more about the relationship between plants and mycorrhizae and the stress tolerance of both organisms. From the evidence that has been studied, it seems like stress is somewhat beneficial in the end. They experience that stress and change to combat that stressor. Stress is a common thing, though sometimes it feels like the opposite, but maybe this is a chance to realize we can make the stress beneficial if we want to. It’s comforting to know that humans are not the only ones to experience stress, so maybe we can learn something from how others handle stress.
Branco, S., Schauster, A., Liao, H.-L. and Ruytinx, J. (2022), Mechanisms of stress tolerance and their effects on the ecology and evolution of mycorrhizal fungi. New Phytol, 235: 2158-2175. https://doi.org/10.1111/nph.18308