Plant litter traits control the accumulation of mineral-associated organic carbon by influencing its molecular composition and diversity

Plant litter inputs represent an important approach for mineral-associated organic carbon (MAOC) accumulation critical for the long-term stability of soil organic carbon (SOC). However, a knowledge gap exists regarding how different contents of structural compounds in plant litters influence MAOC accumulation, as well as its molecular composition and diversity. In this study, wheat straw (Triticum aestivum L.), tree branch and leaves (Platanus×acerifolia) were employed as representative plant litters from forest and farmland ecosystems for an indoor experiment. We determined the dynamic changes of MAOC accumulation, as well as its organic functional groups, molecular composition and diversity through Fourier transform infrared spectroscopy (FTIR) and pyrolysis gas chromatography-mass spectrometry (py-GCMS). Compared with control (CK), the three plant litter types enhanced MAOC (0.90–2.09 times) accumulation, showing maximum increases in leaf litter and minimum in branch litter. FTIR indicated that MAOC was dominated by labile polysaccharide C-O functional groups, which explained the gradual decomposition of MAOC during incubation. Py-GCMS revealed that MAOC was formed via soil minerals selectively adsorbing organic molecules from plant litters i.e. ex vivo pathway. The molecular diversity of MAOC significantly increased after adding straw and leaves, which was beneficial to MAOC accumulation. This study provides a molecular perspective on the mechanisms for the formation of stable SOC pools.