The literature indicates that the presence and activity of microbial biomass could be potential indicators of other changes in mineral soils, making it useful for monitoring and assessing the relationships between plants and soil and their effects on the health and quality of the soil. Therefore, the aim of the study was to determine whether if there were any changes in the C and N content or the basal respiration of microbial biomass in soils under black locust trees (Robinia pseudoacacia L.) between 2013 and 2014.