Decadal Application of Mineral Fertilizers Alters the Molecular Composition and Origins of Organic Matter in Particulate and Mineral-Associated Fractions

The extent to which long-term mineral fertilizers application regulates the quantity, quality and stabilization of soil organic matter (SOM) in soil matrix is still not fully resolved. By combining four biomarkers, i.e., free and bound lipids, lignin phenols and amino sugars, we quantified the molecular composition, decomposition and origins of SOM in response to 10-year fertilization (400 kg N ha−1 yr−1 , 120 kg P ha−1 yr−1 and 50 kg K ha−1 yr−1 ) in a cropland of North China. We focused on two contrasting fractions, namely, particulate organic matter (POM), and mineral-associated organic matter (MAOM). Fertilization increased soil organic carbon (SOC) by 23% in MAOM, and altered its compositions and origins, despite having a limited effect on bulk SOC levels. Fertilization increased plant-derived terpenoids by 46% in POM and long-chain lipids (≥C20 ) by 116% in MAOM, but decreased short-chain lipids (<C20 ) by 54% in the former fraction. Fertilization reduced suberin-derived lipids by 56% in POM and 30% in MAOM, but increased lignin phenols by 74% in POM and 31% in MAOM, implying crop residues were preferentially stabilized via the POM form. Fertilization decreased the contributions of microbial residues to SOC in both fractions. Overall, mineral fertilizers tended to reduce labile components within POM (e.g., short-chain lipids), leading to the accrual of recalcitrant molecules (i.e., long-chain lipids, cutin-derived lipids, and lignin phenols) in the MAOM fraction. Collectively, our study suggests that mineral fertilizers can increase SOM stability and persistence via modifying its molecular composition and preservation in the mineral-organic associations in a temperate agroecosystem.