Hydrogen isotope fractionation in carbohydrates of leaves and xylem tissues follows distinct phylogenetic patterns: a common garden experiment with 73 tree and shrub species.

Recent methodological advancements in determining the nonexchangeable hydrogen isotopic composition (δ 2 H ne ) of plant carbohydrates make it possible to disentangle the drivers of hydrogen isotope ( 2 H) fractionation processes in plants. Here, we investigated the influence of phylogeny on the δ 2 H ne of twig xylem cellulose and xylem water, as well as leaf sugars and leaf water, across 73 Northern Hemisphere tree and shrub species growing in a common garden. 2 H fractionation in plant carbohydrates followed distinct phylogenetic patterns, with phylogeny reflected more in the δ 2 H ne of leaf sugars than in that of twig xylem cellulose. Phylogeny had no detectable influence on the δ 2 H ne of twig or leaf water, showing that biochemistry, not isotopic differences in plant water, caused the observed phylogenetic pattern in carbohydrates. Angiosperms were more 2 H-enriched than gymnosperms, but substantial δ 2 H ne variations also occurred at the order, family, and species levels within both clades. Differences in the strength of the phylogenetic signals in δ 2 H ne of leaf sugars and twig xylem cellulose suggest that the original phylogenetic signal of autotrophic processes was altered by subsequent species-specific metabolism. Our results will help improve 2 H fractionation models for plant carbohydrates and have important consequences for dendrochronological and ecophysiological studies.