Global Impact: Studies Find Trees Communicate Via Fungi When Stressed

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Humans are a very social species. You get sad, you call your parents. You get sick, you call your partner or your best friend. We rely on each other for support and companionship. We take clues from people and connect them to the world around us in order to understand it and our needs. Plants aren’t so different from us in this way. New research has shed light on how we relate to our sessile, photosynthesizing counterparts.

Even trees know how to ask for help when they need it. When humans are stressed, we have a way of showing that to everyone around us, whether it’s yelling and screaming or asking someone else for help or advice. Trees can do this too. The environment is one large working system with various parts coming together to benefit themselves and one another. There’s a lot going on underground that we don’t see and it’s all about the fungi. I’m not talking about the mushroom caps you enjoy with dinner, I mean the underground body. The part that’s called mycelium. These are basically millions upon millions of little strands (each strand is called a hyphae) and they are what make up the body of fungi. The mushroom that we are all familiar with, is just the reproductive body part that sends off spores so that more fungi can grow elsewhere, much like pollen in a flower.

Mycelia can form large webs. Those ‘fairy rings’ as we called them when we were kids are really just one whole organism; the mycelia live underneath the ground and the fruiting bodies live above. A group of species named the honey fungus, measuring 2.4 miles (3.8 km) across in the Blue Mountains in Oregon, is said to be the largest living organism on Earth.

Now, these mycelia also have a symbiotic relationship with the tree roots underground which are called mycorrhizal associations. The word mycorrhizae is directly defined by the symbiotic relationship a fungus has with a plant; the fungi attaches to the plant’s roots. They supply the tree with water and mineral nutrients such as phosphorus and nitrogen that are scattered farther than the tree's roots can grow. The plant then provides the mycelia with about 30 percent of the sugars it produces from photosynthesis in the form of carbohydrates of which the fungi eat.

Here’s the important part. Since the mycelia can cover a lot more ground than the trees can, a single organism can have multiple mycorrhizal associations. This means that one fungus can form associations with many different tree roots. A study done by Suzanne Simard showed that Douglas fir and Paper Birch trees can transfer carbon between them via mycelia and other species have been studied to transfer nitrogen, phosphorus, etc. These two different tree species, inhabiting the same forest space, have been known to ‘help’ one another in this manner. Another example lies in smaller saplings. Research has shown that small seedlings in forest environments that were shaded out by larger trees, got more carbon from donor trees than larger trees that were performing well on their own. Without this assistance the seedling may have died, and this indirectly works as a way of maintaining diversity within a forest. This has been repeated with various tree species, obtaining the same results: Trees and other plants swap nutrients.

Plants can also send warning signals to others through this method. In 2010, Ren Sen Zeng of South China Agricultural University in Guangzhou did research with tomato plants that maintained mycorrhizal associations, and showed that when one plant was infected with a fungus that caused blight disease, others upped their defenses and were less likely to become infected themselves. Although controversy has stirred from this type of research. It may not be that the blight-infected tomato plant has warned the other plants in order to save them, as much as it would be just a plant increasing its defenses against sickness. For example, if you were in the office and one of your coworkers began to develop a cough. They aren’t coughing in order send you signals to stay away, to protect you. But you do stay away and take extra hygiene precautions to better your own health anyway.

Although this doesn’t discredit the shear strength of these mycorrhizal associations. Plants are also able to steal from each other when beneficial due to these networks. Orchids for example, do photosynthesize but also ‘steal’ carbon by rerouting it from other trees that are within the same mycorrhizal network. About 90% of all vascular land plants (plants with xylem and phloem, this includes all seed producing plants plus others) have mycorrhizal associations and they are utilized in these various ways over and over in different ecological systems.

These underground inner-workings function similarly to the internet in this regard. It’s endless stream connecting plants with information and resources across a wide area, providing them with various decisions to make with that information in mind. Therefore, if these connections are broken it can cause detrimental effects to the whole forest system. Selective removal of larger trees by loggers for example could destroy those connections making the network smaller and less resilient. Clear-cutting of trees would destroy all of those links, declining forest health in such a way that wouldn’t be recovered for years.

Next time you think of a tree or that small plant in the forest, see them as a whole system of life. Just like we need to ask for a little help sometimes when we’re in trouble, trees also know how to ask and receive help from others. They’re just a bit quieter than we are.