Development of physico-chemical and biological soil properties on the European ground squirrel mounds

Fossorial rodents through their burrowing activities are important disturbance agents in grassland ecosystems. The European ground squirrel (Spermophilus citellus) is a medium-sized ground squirrel occurring in central and south-eastern Europe. The aim of the study was to explore changes of physico-chemical and biological soil properties during mound development created by the European ground squirrel. The study was conducted at three study sites in the Western Carpathians. We sampled newly created mounds consisting of fresh excavated soil without vegetation, and old mounds with developed vegetation. We also collected control samples of undisturbed soil in the distance of 5 m to the north direction from each selected mound. We took soil samples for bulk density measurements, chemical and biological analyses from the depth of 0-0.1 m. The results showed that some soil properties were unchanged by mound formation and also across the mound development (e.g., Ca2+ concentration, richness and diversity of microbial communities). Several soil properties were altered by mound formation, but with no differences during the mound development (e.g., pH, sulphur concentration). On the other hand, some soil properties showed recovery patterns during the mound development towards an undisturbed soil (e.g., soil bulk density, carbon and nitrogen concentrations). Finally, a few properties showed enhanced values on the old mounds (e.g., phosphorus and potassium concentrations, N-mineralization and heterogeneity of microbial communities). These findings suggest that the European ground squirrel through physical disturbance and resources modulation creates soil patchiness and maintains heterogeneity of European grasslands influencing functions (e.g. soil fertility) and processes (e.g. soil aeration, decomposition and nutrient cycling) in grassland soils.