Dirty transport brings pathogens from all over the world

Dust from all over the world lands in the Sierra Nevada Mountains carrying microbes that are toxic to plants and humans.

UC Riverside research shows that higher concentrations of dust land at lower elevations, where people are more likely to hike.

“Pathogenic dust is becoming more of a threat as the Earth gets drier and drier. Turns out you can’t climb a mountain to get away from it all,” said UCR microbial ecologist Mia Maltz, who led the study. “Some of these microbes can cause crop failure and human respiratory disease,” Maltz said.

At lower elevations, researchers found more powdery mildew and sooty mold, which can lead to the burning of forests and loss of crops. They also found fungi like Cryptococcus, a sticky yeast, and the plant pathogen Alternaria, both of which can be inhaled or cause infections in human lungs.

Researchers weren’t surprised to learn that the Sierra Nevada dust was a mixture of soil particles from as far away as the Gobi Desert in China and as close as the San Joaquin Valley in California. They were, however, surprised to learn of the mix of microbes in the dust and where they landed in the mountains.

They thought the evenly mixed Asian and local dust would contain the as a wide diversity of bacteria and fungi on board. Instead, they found that when the dust was more mixed, it had lower species richness.

Dust samples were collected at four sites in the Critical Zone Observatory Network in the Sierras, at elevations ranging from 400 to 2 700 meters. Researchers suspect that microbes regularly fall from the dust as they travel, which may explain why fewer types of bacteria and fungi have been found at the top than at the base of the mountains.

“I like to think that diversity is a good thing, like a safety net. You might lose a few while maintaining core community functions,” Maltz said. “In this case the loss of microbial diversity at higher altitudes does not appear to be a negative rather we are losing pathogens.”

Some dust traveling the globe and landing in the Sierra Nevada are natural and even beneficial for mountain ecosystems. Dust carries fungi and bacteria that help break down organic debris and enrich the soil.

There are also helpful microbes in dust that help plants grow. absorb nutrients like phosphorus that are needed for growth. The pines, in this ecosystem, get over % of what they need to produce their needles from dust.

“Without dust, trees wouldn’t have what they need to thrive and sequester carbon from the atmosphere at the levels they currently do,” said Emma Aronson, UCR environmental microbiologist and co -author of the study.

However, in a future climate, there will likely have more droughts, bringing more dust. If a greater proportion of the microbes landing in the Sierra Nevada are pathogenic, it could affect the species of plants and animals able to persist.

“With increased mortality of large conifers and other plants, there would be less carbon sequestered than there has been historically, and the atmosphere could get even hotter,” Aronson said.

Although the researchers did not set out to study climate change, the study offers insight into what could happen when there is less snowfall and longer dry seasons.

“Mountains are a good natural laboratory for climate change because they are cooler and wetter at the top, and warmer and drier at the base. They give us predictive power about how ecosystems will adapt to the changes we are already seeing,” Maltz said.

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