Isotope composition of carbon and nitrogen in tissues and organs of Betula pendula

Ratios of 13 С/ 12 C and 15 N/ 14 N isotopes were identified in different parts and organs of drooping birch ( Betula pendula Roth) in preforest-steppe and pine-birch forests of the Middle Urals by mass spectrometry. The data were analyzed and interpreted from the perspective of biochemical processes of carbon and nitrogen metabolism in the leaf, cambial tissue, trunk wood, branches, roots, and in the soil. The lighter isotopic composition of carbon is characteristic for the leaves, trunk cambium as well as fine (<2 mm) roots. The trunk wood is characterized by the basal trend for 13 C enrichment. The heavier carbon isotopic composition inversely related to metabolic activity of organs and tissues, in addition, 13 С/ 12 C ratio corresponds to the nitrogen content in the organs and tissues, indicating the metabolic control of carbon fractionation in woody plants. The isotopic composition of nitrogen in the aboveground parts of the plant (leaves, trunk cambium, wood) and in the medium and fine roots was significantly depleted in 15 N (δ 15 N varies from 0 to–3‰), while main roots (δ 15 N = 0.6 ‰) and soil (δ 15 N = 2.4–6.7‰) were more enriched. The ratio of stable isotopes of carbon and nitrogen is an integrating index of carbon and nitrogen metabolism in plants.