Nature's cloud seeders are mushrooms, with spores that promote raindrops and may lead to downpours, new research finds.
The study, published in the journal PLOS ONE, documents a previously unknown feedback system whereby rain stimulates mushroom growth, and then the fully fruited mushrooms release spores that could result in later rain.
"We can watch big water droplets grow as vapor condenses on (the mushroom spore's) surface," said senior author Nicholas Money of Miami University's Biology Department. "Nothing else works like this in nature."
Raindrops do form to a lesser degree around many different types of particulate matter, such as pollen. In a similar process, people seed clouds with compounds like silver iodide and solid carbon dioxide (dry ice).
Lead author Maribeth Hassett, Money and co-author Mark Fischer determined that spores from certain mushrooms and other fungi are probably even more potent rainmakers -- and they're not pollutants.
Prior research conducted by Reginald Buller, whom Money refers to as the "Einstein of Mycology," found that mushroom spores are discharged from their gills by the rapid displacement of fluid on cell surfaces and stimulation from the mushroom's production of sugars, such as mannitol. A catapult mechanism shoots the moisture-laden spores into the air, where the liquid evaporates.
Droplets reform on the water-attracting spores in humid air, the scientists discovered after watching the process under electron microscopy. Over time, the droplets may evolve into large water drops that may produce rainclouds.
The effect is likely dramatic over rainforests that support very large populations of mushrooms and other fungi. It also could be significant during warmer months of the year above vast northern hemisphere boreal forests.
Any fungi that release their spores via a catapult mechanism can attract moisture, resulting in possible rainclouds, according to the scientists.
"Wild porcini, for example, has spores of this kind; oyster mushrooms too," Money said. "Sixteen thousand species of mushrooms can do the same trick, so the most abundant species of fungi are likely to have the greatest effect upon cloud formation."
Money, who is the author of the book "Mushroom," does not advise growing a bunch of mushrooms to relieve drought conditions.
"Nature works very well when we leave her alone," he said. "The problems start when we cut down too many trees, burn fossil fuels, and keep multiplying as if there are no limits to human population."
Fungi appear to be here for the long haul, though, having emerged on earth at least 500 million years ago. In addition to the new discovery about their rainmaking potential, they play a key role in ecosystems by decomposing plant tissues and dominating the recycling of nutrients in forests and grasslands.
"Without mushrooms, there would be no forests," Money said, "and without forests, humans would never have evolved."
Lynne Boddy of the Cardiff School of Biosciences told Discovery News that "it is intriguing to think about" the newly discovered positive feedback system, holding "that fungal spores may be responsible for causing rain to fall on forests, supplying the water that the fungi need to fruit."
Boddy said fungi "are absolutely crucial to the functioning of forests and other terrestrial ecosystems," and they often supply plants with mineral nutrients and water. Edible mushrooms supply such beneficial components to human diners also.