In a study published Tuesday in the journal Nature Communications, researchers explain the connection between the Asian dust and California’s iconic sequoias, which grow to an average height of about 164 to 279 feet despite a seeming lack of nutrients in the rocky soil of the Sierra.
The team found that Asian dust provides more phosphorus, one of the basic elements that plants need to survive, for sequoias in the Sierra than bedrock weathering – the breaking down of rock buried beneath soil. The mountain range is considered a phosphorus-limited ecosystem.
“In recent years it has been a mystery how all these big trees have been sustained in this ecosystem without a lot of phosphorus in the bedrock,” said Emma Aronson, an assistant professor of plant pathology and microbiology at the University of California, Riverside. “This work begins to unravel that mystery and show that dust may be shaping this iconic California ecosystem.”
Nutrients like nitrogen, carbon and phosphorus regulate life across the planet, which makes understanding their distribution critical to anticipating how ecosystems will react to various adjustments including those caused by global climate change.
Aronson, a co-author of the new paper, worked with fellow UC Riverside scientists to study the role of dust in mountainous forest ecosystems like the Sierra. As little is currently known about this relationship, analyzing the different sources for nutrients is critical.
The team quantified the importance of dust and bedrock in ecosystem nutrient supply across four sites in the Sierra at between 1,300 to 8,800 feet in elevation.
They then combined dust they collected with existing erosion data from the same locations. They captured the dust using homemade dust collectors – nonstick bundt pans filled with glass marbles to keep the dust from blowing out. The pans were attached to 6-foot poles to prevent dust kicked up by the team from interfering with their findings.
Isopotic signatures from several elements in the dust were used to determine their origin. Isotopes – two or more forms of the same element that contain different numbers of neutrons in their nuclei – act as a fingerprint for region of origin.
The percentage of dust from the Gobi Desert ranged from 20 percent on average at the lowest elevation to 45 percent on average at the highest elevation. The percentage of Asian dust increased at higher elevation sites because dust tends to travel high in the jet stream and not fall until it hits an object, such as a mountain, according to the researchers.
The team found that the amount of dust from sources in California’s Central Valley was greater at lower elevations, which they expected. However, the team also found more Central Valley dust found its way to higher elevations later in the dry season than just after spring rainfall.
“Considering we took our measurements in 2014, in the middle of the drought, this makes us think that the drought is a factor here,” Aronson said.
The researchers say their findings will hold true for other mountainous ecosystems and have implications for predicting forest responses to changes in climate and land use.
The study should help scientists predict the impacts of climate change, which will increase the volume of dust moving in the atmosphere and likely bring key nutrients to other far-flung mountain ecosystems.