Mushrooms Can Make It Rain

A fly agaric (Amanita muscaria) fungus grows in the northwestern French city of Thorigne-Fouillard. With its red cap and white spots, the fly agaric is one of the most iconic and distinctive of fungi, renowned for its toxicity and hallucinogenic properties. Image credit: Damien Meyer/AFP/Getty Images

Welcome to the kingdom Fungi: the not-quite-plant, not-quite-animal organisms that have existed for somewhere between 760 million and 1 billion years and somehow have managed to remain full of mysteries. In one of their latest reveals, the fungi have presented us with yet another mysterious trait: They seem to be affecting the weather surrounding their habitats, scientists have found.

In other words, these mostly earth-dwelling organisms can stimulate rain in the atmosphere.

And they can do a lot more than that. Fungi come in all shapes and forms and affect humans and the planet in myriad ways. Whether you’re a mycophagist with exceptional taste for exotic mushrooms, a beer enthusiast, a sufferer of athlete’s foot, a farmer whose crops are assaulted by rust fungus, or even someone who has never given a single thought to the kingdom Fungi—you’ve crossed paths with them. Yet, scientists estimate they've discovered fewer than 10 percent of all fungal species, and researchers continue to learn new things about their origins, life spans, and relationship with plants and animals.

The finding that these organisms can affect the weather has raised questions about how they could be employed to help us control the weather and what impact they might have on the climate more broadly.

THE OTHER KIND OF MUSHROOM CLOUDS

It all started with sugar—mannitol, to be precise. This sugar alcohol is found in strawberries, pumpkins, candies, and cough drops, among other things. It’s common enough in food products, but scientists initially couldn’t figure out what it was doing in the atmosphere—especially above rainforests. Then they realized the sugar was clinging to spores that had been released in vast quantities above the forests; a single gilled mushroom can release as many as 30,000 spores every second. That, combined with prior research, got fungal biologist Nicholas Money of Miami University and his colleagues wondering about what else those spores did in the atmosphere. Was it possible the spores from mushrooms were actually seeding clouds?

Although “seeding” often describes human-engineered attempts to control the weather, clouds really do need condensation nuclei to form precipitation. Before moisture can form rain, snow, sleet or hail, it needs to form water droplets. In a process known as “super-cooling,” water stays liquid even at temperatures well below 0ºC and remains vapor until it comes in contact with a solid “seed.” This can be a speck of dust, a crystal of ice—or a mushroom spore.

But before Money could know whether spores could act as seeds for rain formation, he first needed to understand the mushrooms’ spore dispersal methods.

“Beautiful feats of evolutionary design can be observed in the fungi,” Money told mental_floss. “They’ve got ways of moving that nothing else in the world utilizes. They use squirt guns that squirt spores into the air. They have a snap-buckling device that launches a massive ball of spores that can travel a distance of many meters. Six meters. Astonishing for a microorganism. They have a mechanism based on the explosive formation of gas bubbles in their cells."

In the case of the gilled mushrooms Money was studying, the spores are propelled by the displacement of water droplets. As one droplet forms and slides down the spore to join a second droplet, the spore shoots into the air from the sudden shift in weight. Having seen water condense around the spore in the dispersal process, Money predicted new droplets would continue to condense even after the spore was airborne. Research in the lab showed that hypothesis to be true.

“Mushrooms are controlling the local weather patterns where there are really high numbers of mushroom spores—not only in rainforests, but also forests in the Northern Hemisphere,” Money said. “It’s not that mushrooms are the sole contributors to rainfall, but their spores may actually stimulate it.” In addition to helping the forest, producing rain is a nice trick for the fungi; they need humid conditions to flourish.

MICROBIAL CLIMATE CONTROL

Rainmaking fungus sounds like good news for the climate, but it’s not the full story of fungi’s effect on climate. Saprotrophic fungi—a group that decomposes a variety of carbon sources, including petroleum, leaf litter, wood, and food products—permeate these plants and materials to unlock nutrients. During the process, they convert carbon into carbon dioxide. This lignocellulose decomposition—meaning the breakdown of lignin and cellulose in the cell walls of plants—is the world’s largest source of carbon dioxide (CO2) emissions, surpassing CO2 emissions from the burning of fossil fuels by a factor of 10. This isn’t to say fungi are the drivers of climate change; in the past, the release of carbon dioxide was balanced by absorption of the gas by plants and photosynthetic microbes.

And it turns out some fungi are helping those plants and microbes absorb and store even more CO2. When talking about climate change, most people immediately think of carbon in the atmosphere. But there’s actually much more carbon in the soil. Scientists estimate there are around 2500 billion tons of carbon in the soil, compared with only 800 billion tons in the atmosphere and 560 billion tons in plant and animal life.

One of the main ways carbon moves into and is stored in the soil is through mycorrhizal fungi, which has a symbiotic relationship with trees. The fungi, which fit broadly into three families, live on tree roots and take carbon from the tree while providing it with nitrogen, phosphorous, water, and micronutrients. A study that looked at the mycorrhizal relationship found that the less common fungi (ectomycorrhizas and ericoid mycorrhizas) help soil store up to 70 percent more carbon than soil filled with the more common mycorrhizal communities. They do this by absorbing more nitrogen, which in turn limits the activity of microorganisms that normally act as decomposers returning carbon to the atmosphere. What this means is that certain fungal types could potentially be harnessed to lock away more carbon—and keep it out of the atmosphere.

“There has been some work looking at bioengineering these fungi,” Greg Mueller, chief scientist and Negaunee Foundation vice president of science at the Chicago Botanic Garden, told mental_floss. He says the goal is to create "a sort of super-mycorrhizal fungi” that could help soil store more carbon than it would do without these specific fungi. But you might run the risk of losing the lesser-understood benefits of fungal biodiversity, Mueller added.

The other problem is mycologists just don’t know what all is out there in the soil. Based on prior sampling, scientists have found there’s more fungal life than anything else—but as for what the fungi do and how they function, there hasn’t been enough collected yet.

“It’s like there’s this big jar of jelly beans of different colors,” Mueller said. “We go in and grab a handful, but we haven’t gotten many colors yet. So far they’re distinct, but we might get repeat colors eventually.”

FUNGI OF THE FUTURE

Given how widespread fungi are, there are potentially numerous applications for bioengineering them to benefit the planet. In addition to harnessing fungi to store more carbon in the soil, scientists have suggested using mycorrhizal fungi to boost crop yields by providing the food plants with extra nutrients. This bio-fertilizer could reduce farmers’ need to use phosphorous fertilizers, which disrupt aquatic life and can cause deadly algal blooms.

The mycorrhizal fungi can also help scientists study climate change and monitor how shifting temperatures are affecting different types of forests. Using satellite imagery, a team at NASA’s Jet Propulsion Laboratory was able to detect the hidden network of fungi living among the trees. They discovered that the type of mycorrhizal fungi living with the trees impacts when the trees start growing leaves and when they reach peak greenness. By monitoring changes in these forests, scientists will be able to deduce how each type of fungi reacts to shifts in the climate.

But there’s also a chance that fungi will do as much harm as good. As temperatures warm, the rate at which certain fungal diseases kill plants and animals is rising. The fungal disease called white-nose syndrome has killed millions of bats, and the skin fungus Batrachochytrium dendrobatidis (Bd) attacks hundreds of species of amphibians around the world.

“Pathogens we’re seeing may become more of a problem because the trees that they attack are being stressed by climate change. What was once a nuisance might become a more important pathogen,” Mueller said.

Money takes an even bleaker view of the problem of climate change. “The biosphere is dependent on microorganisms,” he said. “But I don’t think mushrooms will save the planet, and I would say that most forcibly. The planet is changing, and the biggest philosophical challenge is how we respond to the fact that we damaged things and how we can restore things—if we can.”

Fungi are undoubtedly influential in ways most of us rarely consider. From seeding rain clouds to helping soil soak up carbon, these microbial life forms are having real and powerful impacts on the world—and human activity is having equally important impacts on them. The difficult task ahead of us is to better understand these interactions and whether they offer positive or negative effects on the planet. And while we wait for the scientists to do more research, we should all appreciate the invisible world beneath our feet—and above our heads.