Posted by jlwile on December 1, 2011If you have been reading this blog for any length of time, you know that I am fascinated by symbiotic relationships that are common throughout creation. Some of these relationships are between two specific species, others are between three specific species, and others are between many, many different species. Of all the incredible symbiotic relationships out there, one of the most ubiquitous is the relationship between plants and fungi. It is estimated that 90% of all plant species form a relationship with one or more species of fungus.1 Because these relationships are so common, we give them a special name: mycorrhizae.
In this relationship, the fungus invades a plant’s roots and takes carbon-based nutrients from the plant. At first glance, you might think the fungus is a parasite that infects the plant and takes nutrients from it. If you look at the picture above, for example, you might be inclined to think that the root is infected with a fungal parasite. That’s not the case, however, because while the fungus does, indeed, take nutrients from the plant, it also supplies the plant with critical nitrogen- and phosphorus-based chemicals that the plant has a hard time extracting from the soil. Thus, this is a mutually-beneficial relationship, which is often called a mutualistic relationship.
Because mycorrhizae are common throughout creation, there are many species of plants and fungi that participate in them. Nevertheless, the details of how mycorrhizae work are poorly understood. A new study has started to unravel those details, and the results are truly fascinating.
In the study, the scientists gave a plant’s root two different fungi. Each fungus was introduced to a different portion of the root, and each portion of the root was given a separate compartment of soil. The researchers then varied the amount of phosphorus in the soil compartment, which varied how much phosphorus-based chemicals each fungus could give to the plant. They found that when each fungus could give the plant more phosphorus-based chemicals, the plant gave the fungus more nutrients. However, when each fungus could not give the plant many phosphorus-based chemicals, the plant did not give the fungus many nutrients, even if it had a plentiful supply that it could give.2
Interestingly enough, they also manipulated the root to control how many nutrients it gave to the fungus. They found that when the root gave each fungus a lot of nutrients, the fungus gave the plant a lot of phosphorus-based chemicals. However, when the plant gave each fungus only a few nutrients, the fungus gave the plant only a few phosphorus-based chemicals, regardless of how much phosphorus was available to the fungus.
In the end, then, in a mycorrhizae, there is a real relationship between the plant and the fungus. If the fungus “treats the plant nicely,” the plant will treat the fungus nicely in return. However, if the plant doesn’t think the fungus is “doing its fair share,” the plant will “punish” the fungus accordingly. Of course, this “give and take” happens both ways, because the fungus will also “punish” or “reward” the plant, depending on what the plant does.
In the end, the authors see this as an example of a nonhuman “market economy,” where fungi and plants try to do the best job that they can do in order to get the best reward. Here is how they put it:
…in the mycorrhizal mutualism, both sides interact with multiple partners, so that neither partner can be “enslaved.” Cooperation is only stable because both partners are able to preferentially reward the other. This provides a clear, nonhuman example of how cooperation can be stabilized in a form analogous to a market economy, where there are competitive partners on both sides of the interaction and higher quality services are remunerated in both directions.
Humans think we are so clever because we have a market economy that rewards industrious behavior and punishes sloth. Well, it looks like plants and fungi have a very similar system. We know that our market economy is the result of a lot of forethought and design. How did the plant/fungus market economy come into being? Most likely, it was also the result of a lot of forethought and design.
1. Gopi K. Podila and Ajit Varma, Basic Research and Applications of Mycorrhizae, I K International Publishing House, 2004, p. 87
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2. E. Toby Kiers, et. al., “Reciprocal Rewards Stabilize Cooperation in the Mycorrhizal Symbiosis,” Science 333:880-882, 2011
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