Mineral, molecular composition and ecosystem type jointly determine the stability of soil organic carbon on the Qinghai-Tibetan Plateau

The magnitude of soil organic carbon (SOC) response to climate warming is contingent upon its stability. However, due to limited data, the spatial patterns and drivers of SOC stability remain unclear, particularly in alpine regions. Thermal analysis reveals the energy density of SOC, thus indirectly reflecting its stability. This study utilized the thermogravimetric index (TG-T50) to quantify the thermal stability of SOC and employed Nuclear Magnetic Resonance spectroscopy to characterize its molecular composition across the Qinghai-Tibetan Plateau (QTP). SOC thermal stability was found to decrease from the northwest to the southeast of the QTP. A strong positive correlation was observed between SOC thermal stability and molecular composition (r = 0.71, P < 0.001). Structural equation modeling results indicated that ecosystem type was the most important factor influencing SOC thermal stability, followed by mineral and climate variables. Changes in ecosystem type not only alter the quality of soil carbon inputs but also involve variations in climate and soil properties, thereby affecting SOC stability. Those findings highlight that SOC stability is an ecosystem-dependent property. The results show that SOC thermal stability is governed by its molecular composition, mineral protection, and ecosystem type in the QTP. These findings provide substantial evidence towards a more comprehensive understanding of SOC stability on the QTP and assist in predicting the dynamic changes of SOC in response to climate change.