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

Abstract

Proportions of 13C/12C and 15N/14N 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 13C enrichment. The 13C/12C 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 15N (δ15N varies from –1.5 to –3.5‰) and δ13C (δ13C varies from –28.3 to –25.8‰). Meanwhile the sapwood (δ15N varies from –2.6 to 1‰ and δ13C varies from –27.5 to –27.1‰) and heartwood (δ15N varies from –2.5 to –3.5‰ and δ13C varies from –26 to –24.5‰) were more enriched in 15N and 13C. The significant difference between the values of 13C and 15N 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.