The Effect of Hydromorphism on Soils and Soil Organic Matter during the Primary Succession Processes of Forest Vegetation on Ancient Alluvial Sands of the European North-East of Russia

Abstract

The article considers the role of hydromorphism in the soil formation processes on ancient alluvial sandy deposits at the primary succession period. Soil organic matter was given special attention. The studies were carried out in the European north-east of Russia (the Komi Republic) in the middle taiga subzone in the territory of a building-sand quarry (61°57′35″ N, 50°36′22″ E) and background sites near the quarry. The authors analyzed the morphological structure of soil profiles, and the principal physical-chemical properties of mature and young soils forming under pine forests. Formation of forest litter and humus-accumulative horizons, as well as soil organic matter accumulation were thoroughly studied. Already in the fourth–fifth succession decades, the soils in a series of increasing hydromorphism actively demonstrated regularities that are normally characteristic of background soils, for example, increase in acidity, silt fraction, carbon and nitrogen reserves. Against moisture deficiency, the accumulation rate of organic carbon became slow and amounted to 0.07–0.11 t ha−1 year−1. The excessive soil moisture content increased the rate up to 0.38–0.58 t ha−1 year−1 due to the conservation of plant material in the form of peat. The upper 50-cm profile layer of young soil contains Corg stock 3–5 times less than that of background soils. The major soil-forming processes are litter formation and podzolization in drained conditions, litter formation in conditions of high moisture, and peat formation and gleization against excessive moisture.