Differences in Dissolved Organic Matter Between Karstic Fissured/Non-fissured Soils

Abstract

Dissolved organic matter (DOM) is widespread in the environment and plays a role in various ecosystems. This study aimed to explore the differences between fissured/non-fissured soil DOM. Accordingly, the differences in DOM between fissured/non-fissured soils must be clarified to assess soil quality. This study used UV-Vis absorption spectroscopy and fluorescence excitation-emission matrix parallel factor analysis (EEMs-PARAFAC) to characterize soil samples with and without fissures. The fluorescence components of DOM were determined by comparison with OpenFluor. Significance, linear regression, and redundancy analyses were used to obtain the transformation relationship between DOM components and the effect of environmental factors on DOM. This study found that (1) the non-fissured soil DOM exhibited stronger aromaticity and hydrophobicity than the fissured soil DOM. This finding, along with the results of HIX, FI, and BIX tests, suggested that non-fissured DOM is influenced by both exogenous and microbial sources, while fissured DOM is influenced by microbial and autochthonous sources. (2) Protein-like components of non-fissured soils were more abundant (35%–51%) than those of fissured soils (17%–45%), and the transformation relationship between non-fissured components (A2→A3→A1) differed more than that between fissured components (A2→A1→A3), resulting in a greater loss of DOM protein-like components from non-fissured areas. (3) Fissure width (FW) and aperture (Ape): The width and aperture of fissures can significantly affect DOM loss and alter component characteristics under the influence of different environmental factors. Fissures with larger FW and Ape were found to result in higher soil quality (DOC/SOC) compared to non-fissures, with the highest DOC/SOC found in non-fissured coppices. Note that changes in vegetation type can also impact soil quality in fissures. The structure of the karst environment has a dichotomous effect on the component ratios and transformation direction of DOM in fissured/non-fissured soils. Non-fissured areas are more vulnerable to the loss of lighter fractions during rainfall and are also subject to anthropogenic activities. Therefore, the environment requires deeper and wider improvement.