Effect of shrub vegetation on soil organic matter fractionation and soil biochemical processes

Abstract

Abstract Aim Shrub layers are functional determinants of soil processes, yet their role in regulating soil organic matter (SOM) fractions, dissolved compounds, and enzymatic activity remains insufficiently quantified. This study evaluated the effects of three shrub species—European hazel ( Corylus avellana ), alder buckthorn ( Frangula alnus ), and rowan ( Sorbus aucuparia )—on soil biogeochemical functioning. Methods Soil chemical properties, SOM fractionation, dissolved organic matter, ionic composition, and enzymatic activity were analysed in Scots pine (Pinus sylvestris) stands on sandy Podzols in southern Poland. Soils under these shrubs were compared against pine monocultures. Labile SOM fractions and mineral-associated organic matter (MAOM) were quantified to distinguish between short-term nutrient cycling and long-term carbon stabilization using multivariate and regression analyses. Results Soils under shrubs exhibited significantly higher total carbon (C) and nitrogen (N), enhanced C and N accumulation in light SOM fractions, and increased concentrations of dissolved organic C and N compared to pine monocultures. Corylus avellana exerted the strongest influence by significantly enhancing labile soil organic matter fractions, enzymatic activity, and dissolved organic carbon and nutrient mobility, whereas rowan showed weaker and more selective effects mainly associated with longer-term stabilization processes. In contrast, buckthorn primarily stimulated dissolved organic carbon and ion leaching, indicating species-specific differences in the regulation of soil carbon turnover and nutrient cycling. Conclusions Since shrub species increase solute mobility and accelerate nutrient turnover, they have a basic impact on soil biogeochemistry. The findings indicate that, in pine-dominated forests, shrubs actively regulate soil processes rather than serving only as structural understory elements.