Assessment of biological activity in mountain chernozems and mountain-meadow chernozemic soils of natural biogeocenoses in the Central Caucasus, Russia

Indicators reflecting various aspects of biological properties (genetic, microbiological, biochemical) were estimated for the upper horizons (0-20 cm) of mountain chernozems (Mollic Chernozems, WRB, 2015) and mountain meadow chernozemic soils (Mollic Leptosols Eutric, WRB, 2015), that were formed in the conditions of natural biogeocenoses of the Central Caucasus (Elbrus variant of zonality within Kabardino-Balkaria). A comparative assessment was performed for the biological activity parameters (humic content and stock, microbial biomass carbon (Cmic) content and stock, the enzyme activity of hydrolases (invertase, phosphatase, urease) and oxidoreductases (catalase, dehydrogenase)) in combination with indicators of the soil density and acid-base properties of various subtypes of the studied soils (typical and leached). The obtained results showed that the studied types of mountain soils in the upper horizons are characterized by a porous loose composition (0.75-1.07 g/cm3), neutral (pHH2O = 7.0-7.4) and slightly alkaline (pHH2O = 7.9-8.0) by the reaction of the soil solution, high and very high content (9.5-19.1%) and stock of organic matter (173-276 t/ha). The maximal biological activity was noted in mountain-meadow chernozemic soils, which surpass mountain chernozems in humic content (by 42%) and stock (24%), Cmic content (38%) and stock (17%), relative total activity of hydrolases (36%), but inferior in activity of oxidoreductases (32%). Based on the data obtained, the integrative index of ecological and biological condition (IIEBC) was calculated, which reflects the general level of biological activity of the studied soils. Higher IIEBC values of mountain meadow chernozemic soils (80-100%) in comparison with mountain chernozems (70-74%) are due to the unique complex of soil-forming conditions in which these soils function. The established biological parameters of mountain soils of natural landscapes are necessary for use as reference in environmental studies of anthropogenically disturbed biogeocenoses.