Soils and Nitrogen Nutrition of Plants in Alpine Ecosystems of the Northwest Caucasus under Long-Term Increase in Availability of Biogenic Elements

An experiment with the enrichment of acid organic-rich mountain-meadow soils (Umbric Leptosols) of alpine ecosystems with mineral nutrients has demonstrated that the contents of organic carbon, total nitrogen, and labile organic compounds are stable and tolerant towards long-term (20 years) application of mineral fertilizers. Only the following direct effects are well pronounced: an increase in the content of inorganic nitrogen and phosphorus after the application of corresponding fertilizers, as well as a rise in pH as a result of liming. Plants are more sensitive indicators of changes in the conditions of nitrogen nutrition. They are characterized by active absorption of additional nitrogen, and the isotopic composition of nitrogen in them becomes heavier. The degree of these effects depends on the initial nitrogen availability. In addition to these direct effects, changes in the nitrogen status of plants also reflect changes in the transformation of nitrogen-containing compounds in soil and in the nitrogen nutrition of plants taking place due to an increased availability of phosphorus and lower acidity under the most phosphorus-depleted and most acid conditions, respectively. These impacts lead to the mobilization of soil organic nitrogen and are likely to reduce the role of mycorrhiza in plant nitrogen nutrition. As a result, a heavier isotopic composition of nitrogen is formed in some plant species.