The Role of Woodland Mycorrhizal Fungi

Hello everyone, my name is David Satori and I'm a mycologist specializing in mycorrhizal woodland ecology and in this video we'll be exploring the lives and ecological relationships of mycorrhizal fungi and the many ways that they support the health of our woodlands. Fungi could be found in almost every ecosystem on the planet, playing vital ecological roles which countless species of plants and animals depend upon and there's perhaps no better ecosystem to demonstrate the importance of fungal diversity than a woodland. In any given patch of woodland there could be dozens of species of fungi. Some are decomposers on leaf litter and deadwood, some are pathogenic to insects and others live inside living leaf tissue where they increase their host plants resistance to disease. But in this video I'd like to focus on one particular group of fungi which form intimate associations with plant roots and which have been shaping terrestrial ecosystems for the past 450 million years. So this mushroom is a species of rushula and it's a mycorrhizal fungus that lives in direct association with this birch tree behind me. So what we're seeing right now is just a visible fruiting structure of the fungus itself whereas the true body of the fungus lives below ground where it connects to the tree roots. The role of the fungus is to fan out and to forage for nutrients which it then exchanges with the trees for the benefit of both the tree and the fungus. About 85% of vascular plants form symbiotic relationships with mycorrhizal fungi. These fungi establish partnerships with plant roots where the fungus provides nutrients such as nitrates and phosphates in exchange for sugars that the plants photosynthesize. The mycelium that makes up the true body of the fungus is a network of fine threads called hyphae. These hyphae are a lot thinner than plant roots and they could extend and travel further than them squeezing into small soil pores that tap into nutrient and water reserves that the plant roots themselves can't access. This means that plants with mycorrhizal associations can often acquire more nutrients than plants without them. So we've just found a prolific patch of chanterelles right now which you can see dotted all around me over here which gives you a good idea of the extent of the mycelium that could be below ground. Now I would wager that all of these mushrooms come from the same fungal individual which could be connected to this birch tree or it could be connected to this scots pine or perhaps even both. So the growth of this mycorrhizal fungus is fueled by the sugars that it obtained from its host tree but as it's growing through the soil it detects molecules from other tree species which it then grows towards to form a new associations. That means one mycorrhizal fungus could be connected to multiple trees creating what's known as a common mycorrhizal network. Now this is a pretty clever strategy for the fungus because it means it's not dependent on one tree for its nutrition and being connected to different trees can increase its chances of survival. When we're out for a walk in the woods and we come across a mushroom patch like this we might think to ourselves that these are each individual fungi that we're seeing when really they could all be connected by one single network or you could think of it as a web as well that permeates the woodland soil. Mycorrhizal fungi can come in a variety of sizes some may be short-lived and only grow a few square meters whilst others might live for decades and grow 30 to 40 meters or more and a single tree can be colonized by dozens of species of mycorrhizal fungi each comprising multiple genetic individuals. So if we had a periscope into the underworld what we would see is a complex patchwork of many individual fungi each occupying their own space on the root systems of whatever trees that they can associate with. So far from being a uniform wood wide web that spans the entire forest a woodland is more like a busy and crowded metropolis with countless species of fungi each embedded within networks of cooperation and competition striving to acquire nutrition and to fulfill their life cycles. Mycorrhizal networks are more than just simple exchanges of nutrients between one tree and one fungus. They also allow the exchange of nutrients and information between trees as well. When a tree seed germinates it extends its new roots into a better fungal mycelium and it might form associations with mycorrhizal fungi that are also connected to its parent tree. Now in studies looking at nutrient transfers between trees researchers have found that nutrients can be redistributed between trees via mycorrhizal networks allowing parent trees to transfer nutrients to nearby seedlings which might be growing in much more shaded conditions where photosynthesis is a lot more difficult. To what extent this influences forest ecology on a broader scale is unknown but what we do know is that things aren't as altruistic as popular conceptions of mycorrhizal networks might suggest. Firstly mycorrhizal fungi don't always benefit their host trees and the direction of nutrient flows depends on many different factors such as soil fertility. In addition if mother trees unanimously improve the growth of their nearby seedlings you would expect the bigger seedlings to be the ones that are closest to the mother tree. But what we have in reality is usually the largest seedlings are the ones that are furthest away from the parent tree and the ones closest to it actually grow a lot smaller. So understanding the activity of mycorrhizal fungi is like trying to understand the behavior of animals. It's remarkably diverse and complex which makes it all the more fascinating. We might think of a woodland as an ecosystem composed of an assembly of trees but we know that these trees wouldn't survive if it wasn't for the ceaseless activity of mycorrhizal fungi making fungi just as important in these habitats as the trees themselves. The more we learn about mycorrhizal ecology the more the bigger picture opens itself up to us and we realize that woodlands are far more dynamic and interesting than we might have previously thought. Thanks for watching I hope you enjoyed this video and if you like what you've seen please subscribe to the Woodlands TV channel where you can find more content like this.