Long-term fertilization regimes modulate dissolved organic matter molecular chemodiversity and greenhouse gas emissions in paddy soil

Dissolved organic matter (DOM) is a key factor in soil carbon sequestration and greenhouse gas emissions (GHGs). However, the molecular-level change of soil DOM and the implications of GHGs under different long-term fertilization regimes (LFRs) remain elusive. Therefore, we conducted a long-term field experiment with an unfertilized control (CK) and fertilization regimes (chemical fertilizer (F), straw (ST), and biochar (BC)), We employed the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to explore the molecular-level change of soil DOM. Our findings revealed that LFR, especially BC, increased the quantity, molecular weight, double bond equivalence, aromaticity index and molecular formula complexity of DOM. The F increased the molecular diversity and functional complexity of DOM and decreased the Gibbs free energy (ΔG Cox°), whereas BC and ST decreased the molecular diversity because of greater accumulation of lignin-like compounds and increased the ΔG Cox°. The specific molecular evolution and fractionation analysis indicated that LFR increased the aggregation of specific molecules: BC stimulated high O/C and molecularly stable lignin compounds accumulation, whereas ST promoted lignin and unsaturated hydrocarbon compound accumulation. Simultaneously, the F increased GHGs (CH 4 and N 2 O), whereas the BC significantly decreased the CH 4 emissions and the global warming potential. Furthermore, the correlation analysis revealed that the quantity and quality of DOM were closely correlated with GHGs, the quantity of DOM and unstable compounds increased the CH 4 and N 2 O emissions, and the relative abundance of persistent compounds decreased CH 4 emissions. These findings elucidate the potential mechanisms by which LFR, especially BC, regulates DOM characteristics and subsequently influences GHGs, which contributes to the development of more effective soil management strategies for mitigating GHGs while maintaining soil health and productivity. Graphical Abstract