Floating above your head, invisible to the eye, are billions of fungi spores drifting around on the wind. In fact, it’s estimated that at any one time, there are probably millions of tons of them wafting up into the atmosphere. But rather than being benign particles, they might actually be playing a critical role in maintaining a damp environment for both the fungi and the forests in which they live. The findings are published in PLoS One.
Researchers now think that the mushroom spores could be helping the clouds that form above the fungi to produce rain. This in turn forms a positive feedback loop, where the additional rain helps the mushrooms to propel more spores up into the atmosphere, and thus induce more rain. While the scientists don’t think that this is an intended consequence of the mushrooms' method of reproduction, they note that it probably does help to maintain the damp environments in which they thrive.
This is not the first time that small biological particles have been implicated in the formation of rain. Previously, it has been reported that bacteria can act as what are known as “aerosols,” which are small particles that act as a nucleus for the condensation of water, which grows until the droplet becomes so big it falls from the sky. Studies have also found evidence of microbes that induce rain and even snow in Antarctica, suggesting that the bacteria might be able to travel long distances in the clouds.
For those who study fungi, known as mycologists, the role that rain has in dispersing the spores formed by the fungi was already known. The spores are found typically in the gills or pores on the underside of mushrooms. As water condenses onto the spores, encouraged by a coating of sugars that cover them, the rapid displacement of fluid on the spore’s surface causes it to be projected away from the mushroom in the water droplet at up to 1.8 meters per second (6 feet per second). Impressively, an individual mushroom can release 30,000 spores every second.
As the water then evaporates and rises, it takes the spores with it, sending up to millions of tons of them into the air, which are then taken by air currents and updrafts into the clouds. As pollen, and previously mentioned bacteria, can be important in inducing rain formation, the scientists behind the current study were interested to see if the same could happen with the fungi spores. To test this idea, they collected spores from a variety of different fungi and placed them in a chamber in which they could control the humidity and observe how water droplets form on them using an Environmental Scanning Electron Microscope.
They found that when the relative humidity topped 100% as is typical in supersaturated clouds, the “water condensing on the spore forms large droplets,” which is enough to induce rain. However, if the humidity then falls below 100%, they found that the water evaporated off of the spore. This, suggests the authors, shows how the production of spores by fungi could have a significant impact on the formation of raindrops over forests where they typically live.
While this could be forming a positive feedback loop where there are lots of clouds, paradoxically, if environmental conditions shift, it could also have the opposite effect. If clouds fail to form, or rainfall is reduced in tropical ecosystems, stunting the growth of the damp living fungi, the subsequent reduction in the amount of spores being released into the atmosphere could exacerbate the frequency of droughts in an opposite feedback loop.