δ 13C and δD compositions of n-alkanes from modern angiosperms and conifers:: An experimental set up in central Washington State, USA

This study investigates stable carbon and hydrogen isotope compositions of leaf wax n-alkanes from 3 angiosperm and 2 conifer species from a semi-desert natural environment. The delta C-13 and delta D n-C-27 alkane data show a clear distinction between Populus tremuloides/Syringa vulgaris (-31.9 to -32.7% and -168 to -186 parts per thousand respectively) and Pinus sylvestris/Picea pungens (-28.8 to -30.6 parts per thousand and -190 to -212 parts per thousand) throughout the 2005 growing season. Like the other angiosperm species, Betula pendula was D-enriched (-162 to -178 parts per thousand) relative to the conifer species. However, its delta C-13 values were more similar to those of Pinus sylvestris and Picea pungens in May, but had a similar to 4 parts per thousand positive shift later in the season. We suggest that the observed isotopic variations derive mainly from lower stomatal conductance for CO2 and H2O vapor in conifers relative to angiosperms. Betula pendula experienced severe environmental stress that affected its carbon metabolism for most of the season. Our results suggest that shifts in delta D and delta C-13 values of sedimentary leaf waxes may result not only from shifts in the paleoclimatic variables but also from temporal shifts in the distribution of angiosperms and conifers as well as from changes in the isotopic signatures of higher plants undergoing metabolic changes. (C) 2008 Elsevier Ltd. All rights reserved.