In a new study published in Global Change Biology, Prof. ZHANG Yuanming's team from the Xinjiang Institute of Ecology and Geography of the Chinese Academy of Sciences have unveiled a previously underestimated factor in greenhouse gas emissions from arid environments: hydroxyl radicals, often dubbed "free radicals".

The researchers found that these highly reactive molecules are unexpectedly produced when desert soils get wet again after a dry period, which significantly influences the release of carbon dioxide (CO₂) and nitrous oxide (N₂O).

To investigate this phenomenon, the researchers collected surface soil samples from the expansive Gurbantunggut Desert. Back in the laboratory, they simulated the crucial process of soil rewetting to mirror real-world rainfall events. They measured changes in cumulative greenhouse gas emissions, enzyme activity, and the composition of organic matter alongside experiments specifically designed to control and neutralize hydroxyl radicals.

They aimed to pinpoint the exact sources of hydroxyl radical production and decipher the mechanisms by which these radicals directly impact the emission of CO₂ and N₂O through abiotic oxidation, especially during sporadic summer rainfall.

The researchers found that rapid microbial activation following soil rewetting is the primary pathway for hydroxyl radical production. During microbial metabolism, NADPH oxidase family enzymes catalyze oxygen molecules in the environment, leading to the generation of large quantities of hydroxyl radicals.

They further confirmed that hydroxyl radical oxidation synergizes with microbial enzymatic reactions during soil rewetting to promote CO₂ release and facilitates the transformation of NH₄^⁺ to NO₃⁻, thereby dominating N₂O emissions.

"While the direct impact of these radicals on CO₂ emissions was found to be moderate, their role in driving N₂O emissions proved to be far more pronounced and decisive," said GUO Xing, first author of the study.

This study highlights the critical role of hydroxyl radicals in biogeochemical cycles and their previously overlooked influence on major greenhouse gas emissions.