High biodegradability of dissolved organic carbon in the permafrost layer amplifies carbon emissions under warming

• Permafrost-layer DOC shows higher thermal mineralization potential than active-layer DOC. • Warming greatly increases CO 2 emissions from permafrost DOC due to its high biodegradability. • Aliphatic-rich, low-oxidation permafrost DOC fuels high CO 2 emissions under warming. • Highly biodegradable permafrost DOC may amplify carbon-climate feedback under warming. Permafrost thaw induced by climate warming may trigger rapid carbon release, yet the thermal response of soil dissolved organic carbon (DOC) in the active and permafrost layers remains poorly understood. In this study, we investigated the thermal mineralization potential of DOC in soils from the active and permafrost layers at six representative sites on the Tibetan Plateau. Through laboratory incubations at 5 °C and 15 °C, combined with DOC molecular characterization and microbial analyses, we found that warming significantly increased CO 2 emissions from permafrost-layer DOC far more than from active-layer DOC. This amplified response was largely attributed to the greater aliphaticity, lower oxidation state, and higher biodegradability of soil DOC in permafrost deposits. Our findings highlight that DOC in the permafrost-layer, which is often overlooked, constitutes a highly biodegradable and warming-sensitive carbon pool that could contribute disproportionately to CO 2 emissions, thereby intensifying carbon-climate feedbacks in alpine permafrost ecosystems.