Simulated erosion of A horizon influences the dissolved organic matter chemodiversity and carbon sequestration of B horizon in Mollisols

Abstract

Erosion of the A horizon of Mollisols is expected to change the dissolved organic matter (DOM) chemodiversity in the underlying B horizon. Three simulated erosion treatments, which had an A horizon of 30, 20, and 10 cm depth, were established for 9 years under a corn-soybean rotation on Mollisols. Compared to the A horizon that was 30 cm deep, the 20 cm treatment had 24–63% more dissolved lignin-like compounds, a significant increase, in the 0–10, 10–20, and 20–30 cm layers of the B horizon. When the A horizon was 10 cm deep, 41% more lignin-like compounds accumulated in the 10–20 cm layer of the B horizon and 22% more lignin-like compounds were detected in the 20–30 cm layer of the B horizon. Relative to the A horizon of 30 cm depth, the 20 and 10 cm treatments reduced the lipid- and protein-like compounds by 69–87% in 10–20 and 20–30 cm layers of the B horizon layers. Labile compounds increased in the 0–10 cm layer of the B horizon but decreased in the 10–20 and 20–30 cm layers of the B horizon. The DOM degradation degree, expressed in terms of the degradation index and Gibbs free energy, were related to the lignin accumulation, indicating that lignin, a recalcitrant compound, was degraded. Notably, variations in DOM chemodiversity in eroded Mollisols were primarily controlled by soil physicochemical properties and not microbial traits. Therefore, eroded Mollisols have less carbon sequestration potential in the B horizon. To prevent soil deterioration in corn-soybean rotations, we recommend to incorporate a combination of organic and mineral fertiliser to a 20–30 cm soil depth in erosion-susceptible Mollisols.