Short-term crop residue amendments altered the chemodiversity and thermodynamic stability of dissolvable organic matter in paddy soil

The chemodiversity and thermodynamic stability of dissolvable organic matter (DOM) in paddy soil under different crop residue managements remain unclear. Using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis, we explored the molecular composition of DOM in paddy soil 4 years following incorporation of maize residue in different forms (air-dried straw, manure and biochar). Compared to the control without amendments, manure increased the pool size of DOM but reduced its chemodiversity, while the straw and biochar amendments reduced the pool size but increased the chemodiversity of DOM by 0.22 and 0.05, respectively. Though approximately 60% of the compounds were shared among the treatments, those distinct among the treatments were shaped by residue-derived lignin-like compounds. Moreover, the nominal oxidation state of carbon (NOSC), which corresponds to the energy content in organic carbon, decreased with the maize residue amendments, regardless of the forms. Thus, crop residue amendments could lead to higher DOM persistence in the short-term, potentially slowing carbon turnover in paddy soil.