The decomposition of large woody trees is a long process that can take several decades. Even so, I am sometimes still surprised when I see fungus growing out of the trunk of a recently felled tree. I think to myself, “How did a spore pass the protective bark, germinate, spread and fruit so quickly?” Well, in 2010, researchers identified saprotrophic fungi within sapwood of several species of angiosperm trees. They found out that many saprotrophic fungi wait patiently inside the tree. When the tree dies, the latent fungi quickly form fruiting bodies to spread their spores to other living trees. This ecological understanding changes the way we all look at the mycological world, showing the importance of competition even for organisms that break down nutrient poor substrate such as wood.
Genetic technologies have come such a long way in the past two decades, that it is no surprise these findings were made possible by advancements in this discipline. Unraveling, sequencing and duplicating DNA is so much faster and cheaper than it used to be. Using a nested-PCR approach, David Parfitt and his team developed 11 PCR primers for 11 different wood decay species to determine their prevalence in several flowering tree species. Additionally, they compared their sequences to libraries of fungal ITS sequences in two tree species to see if these fungi have been identified as latently present before.
The diverse fungi within a single hazel tree using only 11 primers. Parfitt et al. 2010.
Saprotrophic fungal competition for wood is realer than I previously thought. Sometimes, when traversing numerous miles on a long hike, it seems like I pass countless trees. This is enough food to feed an army of saprotrophic fungi, right? That doesn’t stop species from competing. Competition for space and resources extends far before a tree dies. Trees not only act as a substrate for fungi to grow from, but also as a reservoir for fungi. Latently present fungi evolved this ecological dormancy so they could utilize this new resource faster. They slowly spread within the sapwood, and when proper conditions arise, they produce vast amounts of degradative enzymes and go to town.
The next time when you’re on your next hike, try finding a tree that recently died with an immense column of fungi fruiting from it. Depending on the size, this may not be the result of a single fungal entry point over one season. Large fungal columns represent latently present fungi. These fungi slowly spread throughout the sapwood while the tree is still alive. When the tree dies, the internal environment of the tree changes and promotes the fungi to grow. This research highlights the importance of competition, for these types of species interactions shape our ecological landscape. And remember, a fungus the competes, eats.
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