Legume-inclusive crop rotational diversity systems shape molecular chemodiversity and biochemical transformation processes of latosol dissolved organic matter

Crop rotational diversity (CRD) represents a key sustainable strategy for mitigating environmental impacts while maintaining productivity. However, its influence on the content and chemodiversity of soil dissolved organic matter (DOM), particularly in legume-inclusive systems, remains unclear. To address this, a five-year field experiment was established to investigate how CRD regimes influence the quantity, chemodiversity, and biochemical transformations of DOM at the molecular level. Four CRD treatments were compared: continuous maize monoculture, chili pepper-maize rotation (two crop species, legume-free system), chili pepper-maize/green manure rotation (legume-inclusive system with one legume species), and chili pepper/maize-bean/green manure rotation (legume-inclusive system with two legume species). Results suggested that CRD significantly reduced the content of DOM in latosols by 38.49∼84.09% ( p < 0.05). Spectroscopic indices revealed a concurrent decrease in the aromaticity, humification degree, and molecular weight of DOM in CRD systems. Molecular analysis further indicated a decline in DOM chemodiversity with increasing crop diversity. Fungi exhibited more complex associations with DOM molecules than bacteria, with the key taxa Chloroflexi and Ascomycota playing central roles in DOM transformation processes. In legume-inclusive CRD systems, the higher frequencies of oxygen addition and dealkylation reactions facilitated the formation of more chemically stable and recalcitrant organic compounds, thereby promoting carbon sequestration. Our findings would not only furnish a novel perspective for elucidating the improvement of soil biological fertility driven by CRD regimes at a molecular level but also provide a theoretical foundation for the construction and optimization of soil agricultural planting patterns in tropical regions.