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

Abstract

• 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.