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

The hydrogen isotopic composition (δ2H) of plant compounds is increasingly used as a hydro-climatic proxy, however, the interpretation of δ2H values is hampered by potential co-effecting biochemical and biophysical processes. Here, we studied δ2H 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 2H-enrichment in sugars and starch with a decreasing performance induced by increasing NO3-/NH4+ ratios and starch deficiency, and from leaves to roots. However, δ2H values of cellulose and n-alkanes were less affected. We show that relative concentrations of sugars and starch, interlinked with leaf gas-exchange, shape δ2H values of carbohydrates. We thus provide novel insights into drivers of hydrogen isotopic composition of plant compounds and the mechanistic modelling of plant cellulose δ2H values.

植物化合物的氢同位素组成（δ²H）正日益被用作水文气候代用指标，然而δ²H值的解译常受到潜在协同生化与生物物理过程的制约。本研究在两项独立的烟草（Nicotiana sylvestris）实验中，测定了叶片与根系中的水分、碳水化合物，以及叶片正构烷烃的δ²H值。实验设置包含两个核心变量：一是采用不同氮（N）素形态比例的土壤施肥方案，二是通过基因敲除诱导植株淀粉缺乏，二者均对植株生长表现与生物化学特征造成了显著影响。研究发现，随着NO₃⁻/NH₄⁺比例升高以及淀粉缺乏导致植株性能下降，糖类与淀粉中的氘发生显著富集，且该富集梯度从叶片延伸至根系。相较而言，纤维素与正构烷烃的δ²H值受上述因素的影响相对较小。本研究证实，与叶片气体交换过程相关联的糖类与淀粉相对浓度，是调控碳水化合物δ²H值的关键因素。据此，本研究为解析植物化合物氢同位素组成的驱动因子，以及构建植物纤维素δ²H值的机制模型提供了全新的认知。