The Pinus tabulaeformis plantation on the Loess Plateau was selected as the research site to study the changes of soil water-soluble carbon and nitrogen content and components of soil dissolved organic matter (SDOM) under different management measures (litter removal, young Pinus tabulaeformis forest, shrubs, grassland). The uncleared Pinus tabulaeformis plantation was used as the control. Results show that the soil water-soluble organic carbon content of shrubs and young Pinus tabulaeformis forests was significantly higher than that in other management measures. The content of soil water-soluble organic carbon decreased with an increase in soil depth, whereas soil water-soluble organic carbon/soil organic carbon (WSOC/SOC) increased. The change of soil water-soluble nitrogen content corresponded to that of water-soluble carbon. The content of soil water-soluble nitrogen content in the young Pinus tabulaeformis forest was higher than that of other management measures, and generally decreased with an increase in depth. Different management measures have significant effects on SDOM components. Based on three-dimensional fluorescence spectroscopy combined with parallel factor (EEM-PARAFAC) analysis, four components of SDOM are identified, which are mainly divided into categories, humus, protein-like, and soluble microbial metabolites in three major categories, among which the main component of the SDOM is the rich acid humus, and the highest content in the soil of the young forest of Pinus tabulaeformis is rich acid. The results suggested that management measures had certain effects on soil water-soluble carbon and nitrogen content as well as SDOM components, especially in young Pinus tabulaeformis forests and shrubs. The young Pinus tabulaeformis forest and shrubs increased the content of soil water-soluble organic carbon and water-soluble nitrogen, enhanced their ability to migrate and transform in the soil, and changed the structural composition of soil organic matter, hence enhancing the degree of humification and further improving soil quality.
Keywords: Chinese pine forest; management measures; parallel factor analysis; soil water-soluble carbon and nitrogen; three-dimensional fluorescence.