Long-term straw return promotes accumulation of stable soil dissolved organic matter by driving molecular-level activity and diversity

Abstract

Agricultural management practices play pivotal roles in affecting soil organic matter formation pathways, particularly through changes in soil dissolved organic matter (DOM). The potential effects of long-term straw return on the molecular-level activity and transformations of DOM were investigated in this study. Over 9 years, the soil DOM from straw return had high stability, unsaturation degree, oxidability, and strong aromaticity. The relative abundance of biologically refractory DOM components (i.e., lignin-, condensed aromatic-, and tannin-like formulas) increased by 4 %-33 %, whereas the relative abundance of biodegradable DOM components (i.e., lipids and protein/amino sugar-like formulas) decreased by 15 %-23 % under straw return. Furthermore, the positive effects of straw return on the intergroup transformations of biologically refractory compounds favored the persistence of recalcitrant organic matter in the soil. Importantly, intragroup transformations of recalcitrant-active molecules and biologically refractory compounds were critical pathways for stable DOM accumulation under straw return, and these were mainly driven by thermodynamically limited processes. Thus, our results indicated that long-term straw return promoted the persistence of stabilized soil DOM by driving molecular-level activity and diversity.