Soil Organic Matter and Its Fractions at Different Stages of Soil Salinization, as well as Their Resistance to Decomposition in Relation to Soil Bioactivity

The aim of the study was to conduct a comparative assessment of key biological activity indicators in soils with varying degrees of salinity. The research objectives included determining the decomposition rates of plant OM and cellulose, the intensity of soil respiration, and analyzing the total number of microorganisms and bacterial populations in the upper humus horizon of the saline soils. The stabilization process is closely linked to high soil moisture, elevated silt and clay content, and rising nitrogen levels. While rapid changes occur in the surface soil layers (0–10 cm), deeper layers respond much more slowly, retaining specific carbon structures. Ultimately, ecological restoration promotes effective soil carbon sequestration, although this effect is unevenly distributed and concentrated primarily in the surface layer. Based on the results obtained, it was established that the molecular structures of carbon are positively correlated with soil depth, and the dynamics of recovery change in the opposite direction. In both models developed, the processing of the topsoil is clearly separated from the processing of the deeper layers, indicating a noticeable vertical stratification: the topsoil responds more quickly to revegetation than the deeper soil