Isotope composition of plant carbon and organic matter in burozems of the South of the Vitim plateau

Abstract

An analysis of the isotopic composition of vegetation and organic matter of permafrost burozems in the south of the Vitim Plateau was carried out. The soil profile is characterized by a pronounced uneven distribution of carbon. The main part of carbon reserves is concentrated in the humus-accumulative horizon, down the profile — much lower.

Vegetation on burozems belongs to the C-3 type of photosynthesis. In legumes, forbs, and semi-shrubs, the aboveground parts are somewhat depleted in the ¹³C isotope compared to the underground ones. In trees, the content of 13C in branches, needles, and leaves differs slightly.

The isotope composition of carbon in the upper horizons of soils depends on the type of phytocenosis and has close values to δ¹³C in dominant plants. With depth, carbon isotope fractionation shows a clear vertical differentiation along the soil profile.

The carbon of humic acids in soils from the humus-accumulative horizon and from cryogenic fissures slightly differs in isotope composition. The composition of stable carbon isotopes of humic acids in the soil profile remains approximately at the same level. These data indicate the similarity of the processes of humic acids formation in the upper soil layers and in humus pockets.