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Species variation in the hydrogen isotope composition of leaf cellulose is mostly driven by isotopic variation in leaf sucrose
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International audience. Experimental approaches to isolate drivers of variation in the carbon‐bound hydrogen isotope composition (δ2H) of plant cellulose are rare and current model sare limited in their application. This is in part due to a lack in understanding of how2H‐fractionations in carbohydrates differ between species. We analysed, for the first time, the δ2H of leaf sucrose along with theδ2H andδ18O of leaf cellulose and leaf and xylem water across seven herbaceous species and a starchless mutant of tobacco. Theδ2H of sucrose explained 66% of theδ2H variation in cellulose(R2= 0.66), which was associated with species differences in the2H enrichment of sucrose above leaf water (εsucrose:−126% to−192‰) rather than by variation in leafwaterδ2H itself .εsucrose was positively related to dark respiration (R2= 0.27), and isotopic exchange of hydrogen in sugars was positively related to the turnover timeof carbohydrates (R2= 0.38), but only when εsucrose was fixed to the literature accepted value of−171‰. No relation was found between isotopic exchange ofhydrogen and oxygen, suggesting large differences in the processes shaping post‐photosynthetic fractionation between elements. Our results strongly advocate thatfor robust applications of the leaf cellulose hydrogen isotope model, parameterization utilizingδ2H of sugars is needed.
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