Carbon and Nitrogen Isotope Composition of the Wood of Pinus sylvestris, Betula pendula and Populus tremula

Proportions of 13 C/ 12 C and 15 N/ 14 N isotopes were identified in different woody compartments of birch ( Betula pendula Roth), pine ( Pinus sylvestris L.) and aspen ( Populus tremula L.) trunks in preforest-steppe and pine-birch forests of the Middle Urals using mass spectrometry. The data were analyzed and interpreted from the perspective of the biochemical processes of carbon and nitrogen metabolism in leaves, cambial tissue, trunk wood, branches, roots, and soil. A lighter isotopic composition of carbon is characteristic of the leaves and trunk cambium. The trunk wood is characterized by a basal trend for 13 C enrichment. The 13 C/ 12 C ratio corresponds to the nitrogen content in the trunk wood tissues, indicating metabolic control of carbon fractionation in woody plants. The isotope composition of nitrogen in the trunk cambium was significantly depleted in 15 N (δ 15 N varies from –1.5 to –3.5‰) and δ 13 C (δ 13 C varies from –28.3 to –25.8‰). Meanwhile the sapwood (δ 15 N varies from –2.6 to 1‰ and δ 13 C varies from –27.5 to –27.1‰) and heartwood (δ 15 N varies from –2.5 to –3.5‰ and δ 13 C varies from –26 to –24.5‰) were more enriched in 15 N and 13 C. The significant difference between the values of 13 C and 15 N isotope discrimination consequently in the different woody compartments of trunk should be taken into account when interpreting data of wood organic matter in the context of paleoclimate.