Microbial activity and hydroxyl radical oxidation combine to induce CO₂ release from winter biocrusted soils

Soil CO₂ release under winter snow in arid regions significantly impacts the carbon balance. Enzymatic decomposition is believed to be the primary driver of CO₂ release, however, continuous snow cover promotes the formation of the hydroxyl radical (•OH). Under snow-covered conditions, whether •OH oxidation constitutes an alternative organic matter decomposition pathway to microbial activity, and how these processes interact, remains poorly understood. In this study, we investigated the differences in the CO₂ release rates at various depths in biological soil crusts under snow cover and examined the impacts of microbial activity and •OH oxidation on CO₂ release. The findings indicate that snow cover has an insulating effect on soil temperature, and that temperature fluctuations decrease with increasing depth. However, this insulating effect did not significantly alter the relative contribution of different soil layers to CO₂ release. The crust layer and the 0-5 cm soil layer are the primary zones of CO₂ release, while the 5-10 cm layer contributes less. In addition, prolonged infiltration of snowmelt promotes •OH generation, which may play a significant role in regulating CO₂ release during winter. Microbial activity primarily influences CO₂ production in the surface layer, whereas CO₂ emissions from deeper soil are mainly driven by •OH oxidation. This study highlights that under winter conditions when microbial activity is suppressed, both biotic and abiotic processes contribute to CO₂ release across different soil depths. Given that snow cover is widespread in terrestrial ecosystems, •OH-mediated CO₂ release from deeper soil may represent a previously overlooked carbon emission pathway.