Lake dissolved organic matters seasonal variations is a main driver of N2O emission: In molecular insights by using FT-ICR MS

• Dissolved organic matter seasonal variation in lakes driven the N 2 O emission • Phytoplankton released recalcitrant DOM in warm season led to low N 2 O emission • Microbe released high bioavailable DOM in cold season promoted N 2 O emission • DOM bioavailability regulated the denitrifier communities and functions Anthropogenic activities have introduced substantial quantities of carbon and nitrogen into aquatic system, which are hotspots for nitrous oxide emissions and play multiple roles in the global biogeochemical cycle. We characterized the seasonal variation of DOM by employing a comprehensive approach incorporating absorption spectroscopy, excitation-emission matrix fluorescence and Fourier transform ion cyclotron resonance mass spectrometry (FT–ICR MS). Results revealed that DOM seasonal variation could be the main factor driven lake N 2 O emission alteration. In warm seasons, lakes are predominant with recalcitrant aromatic compounds DOM released by phytoplankton, such as highly unsaturated and phenolic compounds, polyphenols., and lignin, accompanied by low N 2 O concentrations (0.03±0.02 μmol/L). In cold seasons, bioavailable components (Aliphatic, Sugar-like, Peptide-like) are dominated in lakes, the increased abundance of S-containing compounds and low aromaticity compounds largely influenced by anthropogenic emissions, leads to elevated N 2 O concentrations (1.91±0.06 μmol/L). The DOM with high bioavailable components promotes sediment N 2 O production ( nir / nosZ ( I+II) - type denitrifiers) (n=678). Recalcitrant DOM reduced sediment nirK and nirS- type denitrifiers, and increased nosZ (I+II) -type denitrifiers, enhance the N 2 O reduction and led to a lower N 2 O emission. This study advances the understanding of the microbial mechanisms that DOM regulates N 2 O emissions in lakes.