Direct Salinity Effect on Absorbance and Flourescence of Chernozem Water-Extractable Organic Matter

Abstract

Abstract Soil-derived dissolved organic matter (DOM) has a significant impact on aquatic ecosystems. Identifying the fluorescence signatures of DOM from different soils in river and sea waters can provide valuable insights into its migration patterns. This makes crucial the assessment of pH, salinity, and other parameters contribution to the variability of DOM fluorescence. Present study investigates the changes of DOM of typical Chernozems under varying salinity using UV-visible absorbance and excitation–emission matrices of fluorescence spectroscopy coupled with parallel factor analysis (EEMs-PARAFAC). Water-extractable organic matter (WEOM) as a proxy for DOM was isolated from soils of two field experiment plots with contrasting land uses: long-term bare fallow (LTBF) and annually mowed steppe (Steppe). The extracts were incubated in the dark with varying NaCl concentrations and examined. Steppe WEOM exhibited high structural and aggregation resistance to salinity changes, while significant changes in optical parameters and loads of PARAFAC components were observed for LTBF WEOM. The remarkable stability of the Steppe WEOM can be attributed to its chemical diversity. Two distinct and sufficiently stable humic-like PARAFAC components have the potential to serve as markers of Chernozem DOM. The findings contribute to the limited existing knowledge on the direct influence of salinity on the transformation of specific soil types DOM.