Substrate chemistry trumps mineral protection in governing temperature sensitivity of organic carbon mineralization in saline lake sediments

Abstract

Organic carbon sequestered in lake sediments represents a crucial but vulnerable reservoir within the global carbon cycle. However, the temperature sensitivity of organic carbon mineralization in saline and alkaline lake sediments, particularly under global warming, remains poorly understood. This study addresses this knowledge gap by employing microcosm incubation, coupled with absorption spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, to investigate the temperature-dependent mineralization dynamics of organic carbon in saline lake sediments sourced from the Qinghai-Tibet Plateau. The results revealed that, although lake sediments are rich in mineral−bound organic carbon, the stability of organic carbon under warming conditions is primarily governed by substrate concentration and molecular composition, rather than mineral protection. Specifically, increases in organic carbon concentration and the proportion of labile organic matter significantly enhance mineralization activity and its temperature sensitivity (Q₁₀), thereby accelerating the turnover of sedimentary organic carbon pools, and challenging the classical Carbon Quality-Temperature (CQT) hypothesis. Moreover, dissolved and insoluble organic carbon pools exhibited comparable temperature response patterns, together contributing to the accumulation of recalcitrant organic carbon at high temperature conditions. This study systematically disentangles the relative contributions of substrate properties and mineral protection to organic carbon stability and elucidates temperature-driven shifts in sediment carbon pools. These findings provide critical insights into the vulnerability and future trajectory of lake sediment organic carbon reservoirs under climate warming scenarios.