Ecosystem services and assessment of the soil biological activity exemplified by the mountain chernozem soils of the Central Caucasus

Abstract

Different subtypes of mountain chernozem soils (total area 845 km2) of Kabardino-Balkar Republic formed at a height range of over 500 m a.s.l. within the elbrusskiy variant of vertical zones distribution of the Central Caucasus. These unique highly productive pedoenvironments are actively used in agriculture, that leads to a significant change of their biological properties. The purpose of the study is the comparative evaluation of biological indicators and general level of biological activity in the upper horizons (0-20cm) of natural and arable mountain chernozem soils of the Central Caucasus. The criterion for the evaluation of the overall biological activity is an integral index of the ecologic–biological soil state (IIEBSS, %), defined on the basis of the following soil parameters of biological activity: content and reserves of humus, content and reserves of microbial biomass carbon (Cmic), basal and substrate - induced respiration rate, enzymatic activity (urease, invertase, phosphatase, dehydrogenase, catalase). The results of the study indicate a different degree of stability of the controlled biological activity indicators to the long-term agricultural impact. In the arable horizons the urease activity is reduced by 63% - invertase by 57% - the basal respiration rate by 48% - the phosphatase by 44% - dehydrogenase by 42% - humus content and substrate - induced respiration rate by 29% - microbial biomass carbon content (Cmic) by 28% - Cmic reserves by 21% - humus reserves by 20% and catalase activity by 16%. These changes in all the indicators result in decrease of the overall level of biological activity of mountain agrochernozems. The decrease in the IIEBSS value by 35-42% is alarming, because according to the opinion of leading experts the loss of the bioenergy potential by more than 30% points to disturbance of threshold stability of soil systems and their abilities to restore its natural resource properties. However, it should be noted that the high natural fertility of the mountain chernozems allows them to maintain a stable state after long-term agricultural use. Arable horizons are characterized by favorable physical and chemical properties, quite high content of humus (5%) and microbial biomass carbon (more than 1050 mcg C/g). It should make every efforts to maintain and increase the productivity of these rare and fertile soils which are able to date to provide ecosystem services, functioning both in natural and agrogenic conditions. The conservation of the natural mountain chernozem soils is prerequisite for maintaining unique ecosystems in foothill steppes and meadows, which are currently on the brink of extinction.