Transformation of Nitrogen Compounds in Soils of Mountain Tundra Ecosystems in the Khibiny

Abstract

The content of nitrogen compounds and processes of nitrogen mineralization and nitrification were studied in the soils of four tundra ecosystems in the Khibiny Mountains. The results obtained demonstrate the differences between soils of heath and meadow ecosystems in the concentrations of extracted inorganic and organic nitrogen and in the activity of nitrogen transformation. The relationships between the activity of organic nitrogen mineralization and the C/N ratio in organic matter, as well as between the activity of mineralization and the amount of microbial biomass in the soils, differ among the soils. At the high C/N ratios, microorganisms assimilate more available nitrogen, which leads to a decrease in the intensity of organic N mineralization. In soils of meadow communities, as compared to the heath ones, the activity of N mineralization responds more rapidly to changes in the microbial biomass, the C/N ratio and proportion of microbial nitrogen in the labile nitrogen pool. The microbial community in the studied soils of the mountain tundra ecosystems substitutes the nitrogen mineralization for nitrogen immobilization at the C/N ratio in organic matter of about 20.5 and the carbon content in the microbial biomass of about 1000 mg/kg.