This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: On the surface, the arid expanses of the Mojave Desert may seem inhospitable and largely removed from the global carbon cycle. But beneath the surface, its mineral-rich soils are running a carbon cycle of their own—one that could account for a surprisingly large share of the planet's annual carbon exchange.
In a new study published Sept. 23 in Science Advances, researchers in UC Berkeley's Department of Environmental Science, Policy, and Management (ESPM) detail a daily cycle of carbon dioxide (CO2) adsorption and desorption. At night, as temperatures drop, atmospheric carbon dioxide molecules latch onto minerals and other fine particles in Mojave soils through a process known as adsorption. When the sun rises and temperatures begin to climb, those same molecules detach from the soil and return to their gaseous state.
Lead author Anna Abramova, an ESPM doctoral candidate, said this newly documented cycle offers an alternative explanation for how soils exchange carbon with the air. Scientists primarily understand this exchange through soil respiration, which begins when plants and other vegetation convert CO2 into energy and organic carbon through photosynthesis. As plants grow, their roots and associated soil microbes return some of that carbon to the soil.
Microorganisms then feed on that organic carbon and convert it back to CO2 gas, which diffuses out of the soil and into the air. "It's always been assumed that this is entirely driven by a biological process," explained Ronald Amundson, a professor in ESPM and the study's senior author. He compares the process to how a "giant, living organism" might breathe.
In hot, dry climates like the Mojave, Amundson said, this process tends to slow because vegetation and plant life are sparser than in humid regions like the tropics. Since 2017, Amundson's team has monitored the Mojave using soil sensors that record real-time data. Their long-term monitoring revealed something unexpected.
"Instead of CO2 coming out of the soil and going back to the atmosphere, we found that carbon was flowing into the soil at night," said Amundson, who has studied soils across global ecosystems (including Chile's Atacama Desert, the driest nonpolar desert on Earth). "There's no biological explanation for this." Study co-author Jennifer Mills, Ph.D. '21 ESPM, previously found that at night, the CO2 concentration in soil 5 centimeters (2 inches) deep dropped below the concentration at the soil's surface, resulting in an influx of CO2. Amundson, who has used vacuum extraction lines in his Hilgard Hall lab to process gases for more than 30 years, knew CO2 can latch onto solid surfaces when cool.
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