Accumulation of mineral-associated organic carbon under decade warming on the Tibetan Plateau

Soil carbon persistence under climate warming depends critically on how microbial processes regulate the transformation and stabilization of organic inputs. In cold alpine ecosystems, low temperatures constrain microbial metabolism, and warming has the potential to reshape microbial carbon processing with long-term consequences for soil organic carbon (SOC) storage. Using a 14-year in situ warming experiment in an alpine meadow on the Qinghai–Tibetan Plateau, we examined how sustained temperature increases alter microbially mediated SOC fractions across soil depths. Warming did not change particulate organic carbon (POC), but led to a pronounced accumulation of mineral-associated organic carbon (MAOC), increasing by 11% in surface soils and 6% in subsoils. This enrichment was driven by enhanced formation of iron- and aluminum-associated organic carbon in topsoil and calcium-associated organic carbon in deeper layers. Notably, MAOC stocks were tightly linked to fungal biomass and fungal-derived necromass carbon, indicating that warming preferentially stimulates fungal pathways that channel microbial residues into mineral-stabilized carbon pools. In contrast, the stability of POC under warming likely reflects counteracting effects of increased plant inputs and accelerated microbial breakdown. Together, these findings demonstrate that long-term warming reorganizes SOC through microbially driven mineral associations rather than bulk carbon inputs, highlighting microbial necromass formation and organo–mineral interactions as key mechanisms governing carbon stabilization in cold-region soils under climate change.