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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 carbohydrates. We thus provide insights into drivers of hydrogen isotopic composition of plant compounds and into the mechanistic modeling of plant cellulose δ 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.

Recent methodological advancements in determining the nonexchangeable hydrogen isotopic composition (δ 2 H ne ) of plant carbohydrates make it possible to disentangle the drivers of hydrogen isotope ( 2 H) fractionation processes in plants. Here, we investigated the influence of phylogeny on the δ 2 H ne of twig xylem cellulose and xylem water, as well as leaf sugars and leaf water, across 73 Northern Hemisphere tree and shrub species growing in a common garden. 2 H fractionation in plant carbohydrates followed distinct phylogenetic patterns, with phylogeny reflected more in the δ 2 H ne of leaf sugars than in that of twig xylem cellulose. Phylogeny had no detectable influence on the δ 2 H ne of twig or leaf water, showing that biochemistry, not isotopic differences in plant water, caused the observed phylogenetic pattern in carbohydrates. Angiosperms were more 2 H-enriched than gymnosperms, but substantial δ 2 H ne variations also occurred at the order, family, and species levels within both clades. Differences in the strength of the phylogenetic signals in δ 2 H ne of leaf sugars and twig xylem cellulose suggest that the original phylogenetic signal of autotrophic processes was altered by subsequent species-specific metabolism. Our results will help improve 2 H fractionation models for plant carbohydrates and have important consequences for dendrochronological and ecophysiological studies., (© 2023 The Authors New Phytologist © 2023 New Phytologist Foundation.)

Experimental approaches to isolate drivers of variation in the carbon-bound hydrogen isotope composition (δ 2 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 δ 2 H of leaf sucrose along with the δ 2 H and δ 18 O of leaf cellulose and leaf and xylem water across seven herbaceous species and a starchless mutant of tobacco. The δ 2 H of sucrose explained 66% of the δ 2 H variation in cellulose (R 2  = 0.66), which was associated with species differences in the 2 H enrichment of sucrose above leaf water ( ε sucrose : -126% to -192‰) rather than by variation in leaf water δ 2 H itself. ε sucrose was positively related to dark respiration (R 2  = 0.27), and isotopic exchange of hydrogen in sugars was positively related to the turnover time of carbohydrates (R 2  = 0.38), but only when ε sucrose was fixed to the literature accepted value of - 171 ‰. 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 δ 2 H of sugars is needed., (© 2022 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.)

Understanding δ18O and δ2H values of agricultural products like fruit is of particular scientific interest in plant physiology, ecology, and forensic studies. Applications of mechanistic stable isotope models to predict δ18O and δ2H values of water and organic compounds in fruit, however, are hindered by a lack of empirical parameterizations and validations. We addressed this lack of data by experimentally evaluating model parameter values required to model δ18O and δ2H values of water and organic compounds in berries and leaves from strawberry and raspberry plants grown at different relative humidities. Our study revealed substantial differences between leaf and berry isotope values, consistent across the different relative humidity treatments. We demonstrated that existing isotope models can reproduce water and organic δ18O and δ2H values for leaves and berries. Yet, these simulations require organ-specific model parameterization to accurately predict δ18O and δ2H values of leaf and berry tissue and water pools. We quantified these organ-specific model parameters for both species and relative humidity conditions. Depending on the required model accuracy, species- and environment-specific model parameters may be justified. The parameter values determined in this study thus facilitate applications of stable isotope models where understanding δ18O and δ2H values of fruit is of scientific interest., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The analysis of the non-exchangeable hydrogen isotope ratio (δ 2 H ne ) in carbohydrates is mostly limited to the structural component cellulose, while simple high-throughput methods for δ 2 H ne values of non-structural carbohydrates (NSC) such as sugar and starch do not yet exist. Here, we tested if the hot vapor equilibration method originally developed for cellulose is applicable for NSC, verified by comparison with the traditional nitration method. We set up a detailed analytical protocol and applied the method to plant extracts of leaves from species with different photosynthetic pathways (i.e., C 3 , C 4 and CAM). δ 2 H ne of commercial sugars and starch from different classes and sources, ranging from -157.8 to +6.4‰, were reproducibly analysed with precision between 0.2‰ and 7.7‰. Mean δ 2 H ne values of sugar are lowest in C 3 (-92.0‰), intermediate in C 4 (-32.5‰) and highest in CAM plants (6.0‰), with NSC being 2 H-depleted compared to cellulose and sugar being generally more 2 H-enriched than starch. Our results suggest that our method can be used in future studies to disentangle 2 H-fractionation processes, for improving mechanistic δ 2 H ne models for leaf and tree-ring cellulose and for further development of δ 2 H ne in plant carbohydrates as a potential proxy for climate, hydrology, plant metabolism and physiology., (© 2021 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.)