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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 δ¹³C and δD n-C₂₇ alkane data show a clear distinction between Populus tremuloides/Syringa vulgaris (−31.9 to −32.7‰ and −168 to −186‰, respectively) and Pinus sylvestris/Picea pungens (−28.8 to −30.6‰ and −190 to −212‰) throughout the 2005 growing season. Like the other angiosperm species, Betula pendula was D-enriched (−162 to −178‰) relative to the conifer species. However, its δ¹³C values were more similar to those of Pinus sylvestris and Picea pungens in May, but had a ∼4‰ 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 …