Soils on the southern border of the cryolithozone of European part of Russia (the Subpolar Urals) and their soil organic matter fractions and rheological behavior

Soil organic matter (SOM) plays an important role in the functioning of mountain ecosystems. This article contains the results of a study on SOM of high-latitude soils of the Subpolar Urals and its influence on the deformation behavior of soils. The first approach of this study was to define the soils of the Subpolar region to identify the main soil types and their morphological and chemical properties. We investigated soil types of mountain-forest, subalpine and alpine tundra vegetation zones, as well as soil types with permafrost. We investigated SOM using the method of physical fractionation, which isolates three fractions of SOM: free particulate organic matter (fPOM (<) (1.6)), occluded particulate organic matter (oPOM (<) (1.6)) and heavy mineral-associated fraction (MaOM( > 1.6)). The deformation behavior of soils was studied using rheometry. Based on the results, SOM mainly consisted of heavy-fraction MaOM (< 1.6), accounting for 57-99%. The light fractions of free fPOM (< 1 . 6) and occluded oPOM (< 1.6) organic matter were considerably smaller (0.14-23.9%). However, the direct dependence of the organic carbon concentration on the content of light fractions fPOM (< 1.6) (0.89, p < 0.05) and oPOM (< 1.6) (0.84, p < 0.05) for the first mineral horizons was revealed. There also was a significant negative correlation between the carbon content and the heavy-fraction MaOM (> 1.6) ( 0.86, p < 0.05). Rheological studies showed that the stability, resilience and interparticle bonds in soils also depend on the contents of light fractions of SOM: fPOM (< 1.6) (0.52-0.85, p < 0.05) and oPOM (< 1.6) (0.46-0.60, p < 0.05).