Changes in the Properties of Cryogenic Meadow–Chernozem Soils in the Central Part of the Sakha Republic under the Influence of Planted Spruce Stands

AbstractThis paper examines the effect of planted spruce (Picea obovata Ledeb.) stands on changes in the morphological characteristics, composition, and properties of cryogenic meadow–chernozem soils that formed in a cryoarid climate under meadow–steppe vegetation in the vicinity of the City of Yakutsk, the central part of the Sakha (Yakutia) Republic. It is shown that the initial morphological profile of the virgin soil (Wca–AUca–ABca–BCA–BCca–Cca) has been transformed over a 45-year exposure period into the profile of a forest humus–calcareous soil (O–OH–AJ–ABca–BCA–BC–Cca). The morphological structure of the virgin soil underwent the following changes: the forest litter (O) and litter–humus (OH) horizons formed; the thickness of the seasonally thawing layer decreased from 123 to 102 cm; and the 10% HCl effervescence depth, which indicates the presence of mobile carbonates (CaCO3 and MgCO3) in the soil, increased to 26 cm from the surface. In addition to the morphology, the composition and properties of the humus–calcareous soil have also changed significantly in comparison with the initial meadow–chernozem soil. The pH values of soil–water extracts from the AJ and ABca horizons of the humus–calcareous soil decreased by 1.0–0.7, respectively. The total amount of exchangeable bases (Ca+2 and Mg+2) increased in the 0-to 100-cm layer of the forest soil by 1.2 times in comparison with the meadow–steppe soil; the total salt content increased by 1.5 times; and the total N content and organic C content increased by 3.2 and 1.7 times, respectively. Concurrently, the amount of mobile carbonates in the secondary soil decreased by 2.9 times. The magnetic and salt profiles of the studied soils, as well as their salinization degrees and chemistry, have also changed, and the initial cryogenic–exudational water regime has been transformed into a permafrost, periodically-percolative regime due to the change in the vegetation growing on the studied soils.