Solid phase molecular diversity enhances soil organic matter persistence

Molecular diversity has been proposed as a critical factor controlling soil organic matter (SOM) persistence. However, in contrast to dissolved organic matter, molecular diversity of solid phase organic matter remains largely unexplored. Here, we show the molecular diversity features of solid phase organic matter through a direct mass spectrometric scan of particulate and mineral associated organic matter. We found that the highest molecular diversity (Hill Number = 1603±124) existed in SOM that had the slowest carbon turnover rate, in which microbial decomposition and mineral interaction jointly controlled the diversity change of solid phase molecules. Molecular diversity became increasingly enriched from top to subsoil horizons (360% increase), consistent with a breaking down of large molecules into a range of low- to high-molecular-weight molecules. Together, these results suggest that molecular diversity may not operate as a limiting factor for carbon utilization by decomposers but as an ecosystem property that incorporates organo-mineral interactions.