Abstract
Soil organic matter (SOM) was studied in different types of organo-mineral material (from surface horizons and partially isolated materials—cryoturbated or buried horizons) sampled from the surface horizons, the central parts of the Cryosol profiles, and the lower active layer. We found that the humic acids (HAs) of the cryoturbated and buried horizons showed an increased degree of oxidation and an increment of alkylaromatic and protonized aromatic fraction content. In contrast, the HAs of the surface horizons showed increased values of alkylic carbon components. The content of free radicals was essentially higher in the surface layers than in the cryoturbated and buried layers. While the bulk soil organic matter composition (total organic carbon, total nitrogen, and aromatic/aliphatic values) was not essentially different between surface, cryoturbated, and buried horizons, there were essential differences in elemental composition, carbon species, and free radical content. This indicates that the degree of humification in cryoturbated and buried organo-mineral material is higher than in surface horizons and that partial isolation results in relative stabilization of such material in soil profiles.
Highlights
In Cryosols, a complicated pattern of redistribution, migration, accumulation, and cryoconservation of soil organic matter (SOM) is implemented in the course of pedogenesis due to different processes of cryogenic mass exchange [1,2,3]
The surface organo-mineral horizon characteristic of the soils at the keysites is a combination of two genetically connected horizons (Figure 3a): the upper litter–peat horizon, which is nonuniform in botanical composition and friable, with weakly decomposed organic residues, acid, and a loss in ignition of 20–35%
This horizon is underlain by a thin raw-humus horizon, which is composed of organo-mineral material with partially decomposed organic residues, aggregated, weakly compacted, and weakly acidic, with a loss of ignition of 8–35%
Summary
In Cryosols, a complicated pattern of redistribution, migration, accumulation, and cryoconservation of soil organic matter (SOM) is implemented in the course of pedogenesis due to different processes of cryogenic mass exchange [1,2,3]. These processes disturb the paragenetic connection of soil horizons and can significantly and relatively quickly (regarding the time of soil formation) alter the structure of soil profiles. The migration and further long-term conservation of SOM occur in cryoturbated or buried fragments of the soil organic horizons in the middle parts of soil profile and lower active layer. The possible alteration of organic matter depends on the degree of its stabilization [9], and the last one can be assessed by various indexes of elemental composition, 13 C NMR (carbon-13 nuclear magnetic resonance), and ESR (electron spin resonance)
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