The relationship between trees and fungi is fraught with tension.
On the one hand, many fungi pose a serious – often fatal – threat to trees. Fungi are some of the primary agents of decay. They help recycle the nutrients in dead trees, freeing them to be used by other organisms; and they feast on the tissues of living trees, often causing significant damage in the process.
But other fungi pose no danger to trees. Some are valuable, nearly necessary, to trees. Botanists call some of these fungi mycorrhizae or mycorrhizal fungi.
But before we examine mycorrhizal fungi’s relationship with trees, we’ll need to step back and talk a little bit about fungi in general.
Fungi are nearly everywhere. They populate the soil, grow on our bodies and colonize bathroom tiles. They even show up in our kitchens. This includes both inedible (mold) and edible types (mushrooms).
In fact, most people think of fungi as mushrooms, but this isn’t entirely accurate. Mushrooms are the fruiting bodies (reproductive structures) of a much larger fungal organism. Most of the organism occurs as threadlike hyphae, which typically snake through the soil, dead wood or whatever they are using as a food source. The hyphae absorb nutrition directly from their surroundings, as well as water and other resources.
When these hyphae invade wood, they cause decay through their feeding processes. As they digest the structural compounds in the wood (most commonly lignin or cellulose), the tree becomes weakened, leading to branch failure or large, open cankers. When the network of hyphae grows large enough, mushrooms are produced as a way to release spores.
However, not all fungi produce these types of predatory hyphae. Some – including mycorrhizal species – produce hyphae that surround or penetrate the finest roots of trees and plants. And when they do so, both the tree and the fungus benefit.
Mutualistic Relationships: Win-Win
Scientists usually consider the relationship between plants or trees and mycorrhizal fungi to be mutualistic, because both organisms benefit from the association (rarely, mycorrhizal fungi can cause problems for a plant or tree). This distinguishes these fungi from parasites and other types of symbiotic species, which harm the organism with which they interact.
The fungi involved in these relationships generally feed upon carbohydrates that are produced in the tree’s leaves and stored in the roots. In return, the roots leverage the superior absorbing capacity of the hyphae to draw more water and minerals from the ground than they would be able to do without the fungus’ help.
But mycorrhizae also provide several other benefits to plants and trees, although the reasons they do so often remain poorly understood. For example, trees whose roots are colonized by robust mycorrhizal populations are generally more resistant to insect attacks, survive better in contaminated soils and weather the effects of drought better.
Sometimes, soils become inhospitable to mycorrhizal fungi, which reduces the local population. This means that trees in the area will not be operating at maximum efficiency and become more susceptible to environmental stresses. This can cause the trees to decline or simply fail to live up to their potential. They may also become more susceptible to pests and pathogens.
Fortunately, this problem can often be remedied. First, the soil will need to be altered to address the underlying problem (such as compaction or the lack of sufficient organic material). Then, the area can be “seeded” with the spores of mycorrhizal fungi. Given a bit of time and luck, the fungi will flourish, thereby helping to restore the trees’ health and vigor.
If you are concerned that your trees may not be thriving because of poor soil conditions, contact your friends at Trav’s Tree Service. We’ll send one of our experienced arborists to investigate the matter and provide you with a proper plan of action. But don’t delay: The sooner you restore the soil to its proper condition, the sooner your trees will be able to get back on track.