Biochemical and biophysical drivers of the hydrogen isotopic composition of carbohydrates and acetogenic lipids | Science Advances

The hydrogen isotopic composition (δ ² H) of plant compounds is increasingly used as a hydroclimatic proxy; however, the interpretation of δ ² H values is hampered by potential coeffecting biochemical and biophysical processes. Here, we studied δ ² H values of water and carbohydrates in leaves and roots, and of leaf n -alkanes, in two distinct tobacco ( Nicotiana sylvestris ) experiments. Large differences in plant performance and biochemistry resulted from (a) soil fertilization with varying nitrogen (N) species ratios and (b) knockout-induced starch deficiency. We observed a strong ² H-enrichment in sugars and starch with a decreasing performance induced by increasing NO ₃ ⁻ /NH ₄ ⁺ ratios and starch deficiency, as well as from leaves to roots. However, δ ² H values of cellulose and n -alkanes were less affected. We show that relative concentrations of sugars and starch, interlinked with leaf gas exchange, shape δ ² H values of carbohydrates. We thus provide insights into drivers of hydrogen isotopic composition of plant compounds and into the mechanistic modeling of plant cellulose δ ² H values.