The carbon isotope composition of respired CO2 (δ13CR) and bulk organic matter (δ13CB) of various plant compartments informs about the isotopic fractionation and substrate of respiratory processes, which are crucial to advance the understanding of carbon allocation in plants. Nevertheless, the variation across organs, species and seasons remains poorly understood. Cavity Ring-Down Laser Spectroscopy was applied to measure δ13CR in leafy shoots and woody stems of maple (Acer platanoides L.), oak (Quercus robur L.) and cedar (Thuja occidentalis L.) trees during spring and late summer. Photosynthesis, respiration, growth and non-structural carbohydrates were measured in parallel to evaluate potential drivers for respiratory fractionation. The CO2 respired by maple and oak shoots was 13C-enriched relative to δ13CB during spring, but not late summer or in the stem. In cedar, δ13CR did not vary significantly throughout organs and seasons, with respired CO2 being 13C-depleted relative to δ13CB. Shoot δ13CR was positively related to leaf starch concentration in maple, while stem δ13CR was inversely related to stem growth. These relations were not significant for oak or cedar. The variability in δ13CR suggests (i) different contributions of respiratory pathways between organs and (ii) seasonality in the respiratory substrate and constitutive compounds for wood formation in deciduous species, less apparent in evergreen cedar, whose respiratory metabolism might be less variable.

中文翻译：

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生长季节中三种树种的木本茎和叶芽中呼吸二氧化碳的碳同位素组成：呼吸分馏的生理驱动因素。

不同植物区室的呼吸二氧化碳 (δ13CR) 和大量有机物 (δ13CB) 的碳同位素组成可了解呼吸过程的同位素分馏和底物，这对于增进对植物碳分配的理解至关重要。然而，人们对器官、物种和季节之间的差异仍然知之甚少。应用光腔衰荡激光光谱法测量春季和夏末枫树 (Acer platanoides L.)、橡树 (Quercus robur L.) 和雪松 (Thuja occidentalis L.) 的叶芽和木质茎中的 δ13CR。并行测量光合作用、呼吸、生长和非结构碳水化合物，以评估呼吸分解的潜在驱动因素。春季期间，枫树和橡树芽呼吸的 CO2 相对于 δ13CB 富含 13C，但夏末或茎中则不然。在雪松中，δ13CR 在整个器官和季节中没有显着变化，相对于 δ13CB，呼吸 CO2 的 13C 被耗尽。枫树中芽δ13CR与叶片淀粉浓度呈正相关，而茎δ13CR与茎生长呈负相关。这些关系对于橡木或雪松来说并不重要。δ13​​CR 的变异性表明（i）器官之间呼吸途径的不同贡献，以及（ii）落叶树种中呼吸基质和木材形成的组成化合物的季节性，在常绿雪松中不太明显，其呼吸代谢可能变化较小。