Many plants can thrive through drought and other stresses because of the fungi that grow alongside them. Science Moab spoke with Catherine Gehring, the Lucking Family professor at Northern Arizona University, who has been studying plant-associated fungi for more than 20 years. The Gehring Lab at NAU conducts research to understand the functioning of fungi and how they influence the natural world.
Science Moab: Can you explain a bit about the relationships between fungi and plants?
Gehring: There are many different kinds of fungi that associate with plants. We often think of the ones that cause disease, but there are many that live in association with plants. Some mycorrhizal fungi live in the soil and provide a link between plants, roots and the soil. They scavenge soil resources for plants in exchange for carbon and sometimes lipids. So that’s described mostly as a mutually beneficial relationship.
There are other relationships that plants have with fungi that are called endophytes. They are less well described, but they’re just fungi that live in plant tissues, but they don’t cause disease. They might be beneficial, they might be beneficial only in some circumstances, and they might turn on the plant and act like a disease in some circumstances. My lab group focuses mostly on mycorrhizal fungi. But we also have some work on root endophytes that we’re beginning to do because we see them all the time in our plant roots and we’re curious about how they function.
Science Moab: What sort of questions do you look at in your research?
Gehring: In my lab, we look at three main questions, and one is to figure out what happens to these fungi when there’s a fire, and how that influences if plants come back quickly. We also are interested in how plants and fungi interact with one another, including understanding whether the fungi are important in things like drought tolerance. The last big thing that we’re interested in is, if fungi are reduced in abundance in a place, is that affecting the ability of plants to reestablish? And if we bring back missing fungi, does that help us bring back the plants too?
Science Moab: Where do some of the fungi grow? Are they visible to the naked eye?
Gehring: We call them all mycorrhizal fungi, but there are actually different types. For example, if I were to dig up the roots of a pinyon pine, I could see with a naked eye if there were mycorrhizal fungi there or not, which are called ectomycorrhizal fungi. We call it colonizing the roots. So the seedling grew into the soil and a fungal spore germinated and they contacted each other and made an association. They have an area where they exchange materials, so the fungus gets sugar from the plant and provides nitrogen to the plant in return. They have this interface that is microscopic, but as the association develops, the fungi morphologically change the roots. Instead of being long and skinny with root hairs, they turn into these little clubby root tips with a coating of fungal material instead.
Science Moab: How are you analyzing the effect of fungi in drought scenarios?
Gehring: One thing that we’ve done is look at a group of pinyon pines over time, starting before we had our first 100-year drought when we were in a wet cycle. We sampled what fungi were on this group of trees when things were wetter, and now we’ve done it several times when conditions are drier. We can see that the amount of fungal diversity has changed dramatically with drought. We also have what we call a common garden where we compare different kinds of drought-tolerant and drought-intolerant pinyons. We plant them together in the same place, so they have access to sort of the same fungi, then give them different amounts of water and look at how they grow and which fungi they have.
We do greenhouse experiments, too, to see what it’s like without fungi at all, because we’re going to have some kinds of fungi in most places. We manipulate how much water plants get so we can simulate drought. In doing experiments like that, we figured out that the difference between a drought-tolerant and a drought-intolerant pinyon is really which mycorrhizal fungi they have. If you give them no mycorrhizal fungi at all, they respond similarly, but it’s the different fungi that you give them that make the difference for that drought tolerance.
Science Moab: What relationship do these fungi have with non-native species?
Gehring: We study tamarisk, which has taken over a lot of our riverside habitat from native cottonwoods and willows. And here in its non-native range, it doesn’t form mycorrhizal associations. After a long time of just having tamarisk, the fungi aren’t there anymore. We’ve been studying and trying to document that. Some of my graduate students are trying to see if taking fungi from a native cottonwood-willow forest and putting it in one of these tamarisk-affected areas affects cottonwood or willow restoration. If you bring the fungus back, is it easier to bring the trees back? And we’ve found that it is.
Science Moab: What do you do to use the fungi for restorations?
Gehring: Generally, what we do is to take a thin layer of soil from the tamarisk setting, and find some intact cottonwood forests that have mycorrhizae and good-looking cottonwoods near the place that we want to restore. We take a thin layer of that soil, mix it with sand and other kinds of sterile soil, and grow some cottonwoods in there. We grow some other plants that we know form mycorrhizal associations. Then, we bulk it up so that we have bins filled with cottonwoods that have lots of mycorrhizae. Then as we’re planting the cottonwoods for restoration, we just put a bit of that soil in when we’re planting.
Science Moab is a nonprofit dedicated to engaging community members and visitors with the science happening in Southeast Utah and the Colorado Plateau. To learn more and listen to the rest of this interview, visit www.sciencemoab.org/radio. This interview has been edited for clarity.