Species variation in the hydrogen isotope composition of leaf cellulose is mostly driven by isotopic variation in...

Experimental approaches to isolate drivers of variation in the carbon-bound hydrogen isotope composition (δ² H) of plant cellulose are rare and current models are limited in their application. This is in part due to a lack in understanding of how ² H-fractionations in carbohydrates differ between species. We analysed, for the first time, the δ² H of leaf sucrose along with the δ² H and δ¹⁸ O of leaf cellulose and leaf and xylem water across seven herbaceous species and a starchless mutant of tobacco. The δ² H of sucrose explained 66% of the δ² H variation in cellulose (R²  = 0.66), which was associated with species differences in the ² H enrichment of sucrose above leaf water ( $$ : -126% to -192‰) rather than by variation in leaf water δ² H itself. $$ was positively related to dark respiration (R²  = 0.27), and isotopic exchange of hydrogen in sugars was positively related to the turnover time of carbohydrates (R²  = 0.38), but only when $$ was fixed to the literature accepted value of $$ ‰. No relation was found between isotopic exchange of hydrogen and oxygen, suggesting large differences in the processes shaping post-photosynthetic fractionation between elements. Our results strongly advocate that for robust applications of the leaf cellulose hydrogen isotope model, parameterization utilizing δ² H of sugars is needed.