Phylogenetic and biochemical drivers of plant species variation in organic compound hydrogen stable isotopes: novel mechanistic constraints

Summary Significant variation in plant organic compound hydrogen stable isotope (δ 2 H) values among species from a single location suggests species biochemistry diversity as a key driver. However, the biochemical mechanisms and the biological relevance behind this species‐specific δ 2 H variation remain unclear. We analyzed δ 2 H values of cellulose and n ‐alkanes across 179 eudicot species in a botanical garden sampled in 2019, and cellulose, n ‐alkanes, fatty acids and phytol δ 2 H values from 56 eudicot species sampled in 2020. We utilized the observed species variation in δ 2 H values to determine phylogenetic structure and mechanistic constraints for biochemical 2 H‐fractionation. A strong phylogenetic signal in lipid compound δ 2 H values implies that the drivers of species variation in lipid δ 2 H values are evolutionarily conserved. By contrast, species variation in cellulose δ 2 H values was not strongly linked to phylogeny. Generally low‐explanatory power of relationships between δ 2 H values of different compounds ( R 2 < 0.26) implies nonubiquitous drivers of species variation in plant organic compound δ 2 H values. Historically, variable biochemical 2 H‐fractionation was often attributed to δ 2 H values of H incorporated from NADPH. Instead, the results from this study suggest that species variation in biochemical 2 H‐fractionation largely occurs independently within biosynthetic pathways. For lipids, these mechanisms appear strongly linked to evolutionary history.