Vegetation restoration is one of the most effective methods to control soil desertification. The change of the input and decomposition of soil organic matter (SOM) in the process of vegetation restoration not only affects the restoration of its own ecosystem, but also affects the biogeochemical cycle of soil carbon. In addition, the soil texture and the conversion and accumulation of organic carbon are also improved by vegetation restoration. Dissolved organic matter (DOM), an important component of SOM, can effectively evaluate the vegetation restoration status of desertification soil in arid area. However, the evolution and spectral characteristics of DOM in sandy soil with different restoration methods and vegetation types (such as grassland, shrub, coniferous forest. deciduous forest, etc.) are not well understood. Mu Us Sandy Land is located in the transition zone between desert steppe and forest steppe in the northwest of China, which is one of the four typical sand areas in China. In recent years, the restoration of Mu Us Sandy Land has achieved obvious results through engineering technologies such as sand-fixing plants, aerial seeding and soil recombination. In this study, the surface soil of three types of soils (sandy land, newly improved land and plant-covered land) was collected in Mu Us Sandy Land. In the present study, the source, content and composition of the DOM of soil under different land improvement measures and vegetation types (sandy land. SL; newly improved land, NL and plant-covered land, PL) in Mu Us Sandy Land were investigated using ultraviolet-visible spectral (UV-Vis) and fluorescence excitation-emission matrix spectrophotometry (EEM) with parallel factor analysis (PARAFAC), the correlation analysis and principal component analysis (PCA). Results showed that DOM content and DOC/SOC value were significantly under different types of land and vegetations cover. The proportion of dissolved organic carbon in shrub land and tree land showed an opposite trend to its content of dissolved organic carbon. Compared with bare sandy land, soil modification and vegetation cover significantly enhanced the content of DOC and the stability of SOC. Moreover, the stability of organic carbon in arbor covered land was slightly higher than that in grassland and shrub land. PARAFAC showed that the DOM of sandy land was mainly composed of tryptophan-like (C3), while the DOM of modified soil and vegetation covered land was mainly composed of humic acid-like (C1 and C2). Negative correlation between C1 and C3. C2 and C3 (*P < 0.01). Among different vegetation types, the total proportion of humic acids (C1 and C2) was in the order: Arbor>herb>shrub, and relative content of humic acid increased with the increased restoration years. DOM fluorescence index (FI value) decreased, biological index (BIX value) and humification index (HIX value) significantly increased in vegetation-covered soil, compared with SL and NL, which indicated obvious tenigenous characteristics, confirming the enhancement of organic carbon stability. The humification degree of soil in arbor area was higher than that in shrub land and grassland. Overall, compared with NL and SL. vegetation restoration process. especially the planting of arbor can contribute to the storage of soil organic carbon, increasing the content and the stability of DOM. This study provides a theoretical support and reference for the improvement of Mu Us Sandy Land management and it helps to provide a scientific basis for the accurate evaluation of soil improvement and ecological effects of vegetation restoration in sandy land. It will provide theoretical support for understanding the biogeochemical cycle of carbon in sandy land.
