Abstract: Dissolved organic matter (DOM), the most active type of soil organic matter, plays a key role in soil biogeochemical cycling. Therefore, exploring the source, composition, environmental response, and accumulation mechanism of DOM during vegetation succession has great significance for predicting soil carbon cycling. In this study, DOM was extracted from topsoil and subsoil at plots after 12, 30, 40, 50, 80, and 120 years of primary succession along the Hailuogou Glacier retreat area. The concentrations and spectral characteristics of DOM were analyzed via a combination of elemental analysis, ultraviolet-visible spectroscopy, and three-dimensional fluorescence excitation-emission matrix spectroscopy. The results showed that concentrations of soil dissolved organic carbon and dissolved organic nitrogen of both topsoil and subsoil increased significantly during vegetation succession. Along the chronosequence, the protein-like components and optical indices were significantly enhanced, humic-like components and the optical indices decreased, the aromaticity degree of DOM increased first and then decreased. Soil pH and NH₄⁺-N content explained 62.2% of the total variation of surface soil DOM components, while soil moisture and pH explained 64.3% of that of subsurface soil DOM, indicating that environmental conditions were key factors affecting the concentrations and composition of soil DOM in the Hailuogou Glacier retreat area.

Key words: soil dissolved organic matter, primary succession, three-dimensional fluorescence excitation emission matrix spectra, ultraviolet-visible absorption spectra, glacial retreat