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 (δ2H) 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 δ2H variation remain unclear. We analyzed δ2H 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 δ2H values from 56 eudicot species sampled in 2020. We utilized the observed species variation in δ2H values to determine phylogenetic structure and mechanistic constraints for biochemical 2H‐fractionation. A strong phylogenetic signal in lipid compound δ2H values implies that the drivers of species variation in lipid δ2H values are evolutionarily conserved. By contrast, species variation in cellulose δ2H values was not strongly linked to phylogeny. Generally low‐explanatory power of relationships between δ2H values of different compounds (R2 < 0.26) implies nonubiquitous drivers of species variation in plant organic compound δ2H values. Historically, variable biochemical 2H‐fractionation was often attributed to δ2H values of H incorporated from NADPH. Instead, the results from this study suggest that species variation in biochemical 2H‐fractionation largely occurs independently within biosynthetic pathways. For lipids, these mechanisms appear strongly linked to evolutionary history.