Hydroxyl Radical-Driven Oxidation as a Key Pathway for Greenhouse Gas Production During Soil Drying-Rewetting

The drying-rewetting of soil can increase the release of greenhouse gases over a short time period and is one of the key pathways for greenhouse gas emissions in many terrestrial ecosystems, particularly in drylands. The mechanisms underlying this pulse of greenhouse gas emissions remain nearly unknown. Here, we conducted simulated soil rewetting experiments using typical cover of dryland soils (bareland, cyanobacteria/lichen-covered soil, and moss-covered soil). The ¹³C, ¹⁵N, and ¹⁸O labeling techniques allowed to explore the intrinsic mechanisms of rapid carbon (C) and nitrogen (N) release from the soils following rewetting. We found that the hydroxyl radical (˙OH) was produced after soil rewetting via the rapid activation of microorganisms. The carbon dioxide (CO₂) and nitrous oxide (N₂O) production strongly decreased after ˙OH removal, whereas the methane (CH₄) production was not affected. The synergistic action between ˙OH oxidation and microbial enzymatic reactions increased CO₂ production. The ˙OH also stimulated the oxidation of NH₄ ⁺ to NO₃ ^- and dominated the N₂O production. Our results confirm the role of ˙OH in the production of greenhouse gases and indicate that microbially mediated ˙OH oxidation mechanisms are an overlooked key pathway for the emission of greenhouse gases during the soil rewetting. In the context of climate change, the extreme weather-induced drying-rewetting cycles in soils are becoming more frequent, making greenhouse gas emissions via the ˙OH oxidation pathway increasingly important.