Specific Features of the Pool of Hydrolytic Enzymes in Soils of Agricultural Terraces in the Eastern Caucasus

A study of the influence of farming practices in the Middle Ages (X–XV AD) on the activities of 11 hydrolytic enzymes involved in the biogeochemical cycles of major elements in soils has been carried out. Agrostratozems of Medieval agricultural terraces in Dagestan mountains (Plaggic and Hortic Anthrosols) were chosen as objects of study. In all cases, the enzymatic activity of the studied soils decreased in all soil layers in the following sequence: alkaline phosphatase > phosphodiesterase > acid phosphatase > pyrophosphatase ≥ leucine aminopeptidase > arylsulfatase > chitinase > β-glucosidase > xylanase > α-glucosidase > cellobiohydrolase. The enzymatic activity of the studied soils was primarily determined by the amount of microbial biomass (C_mic). Thus, the activity of enzymes of various groups depended on C_mic by 61–94%. Agricultural practices associated with ploughing, manuring, and irrigation induce the convergence in the activity of nitrogen cycle enzymes in soils of the mountain zone, which is associated with similar features of the nitrogen cycle in agrogenic soils, regardless of bioclimatic conditions. The addition of organic materials has led to an increase in the physiological efficiency of microbial communities and the rate of enzyme production, and high levels of biological activity can persist in soil for about 1000 years. Ploughing with the application of organic fertilizers in the past led to an increase in enzymatic activity expressed per unit of microbial biomass (specific activity), therefore, this indicator can be used as an indicator of agrogenic transformation of soils in the past.