Centre for Systems Biology (ZBSA), University of Freiburg, Habsburgerstr. 49, D-79104 Freiburg, Germany.
Tree Physiol. 2011 Oct;31(10):1088-102. doi: 10.1093/treephys/tpr093. Epub 2011 Sep 27.
The carbon (δ(13)C) and oxygen (δ(18)O) stable isotope composition is widely used to obtain information on the linkages between environmental drivers and tree physiology over various time scales. The tree-ring archive can especially be exploited to reconstruct inter- and intra-annual variation of both climate and physiology. There is, however, a lack of information on the processes potentially affecting δ(13)C and δ(18)O on their way from assimilation in the leaf to the tree ring. As a consequence, the aim of this study was to trace the isotope signals in European beech (Fagus sylvatica L.) from leaf water (δ(18)O) and leaf assimilates (δ(13)C and δ(18)O) to tree-ring wood via phloem-transported compounds over a whole growing season. Phloem and leaf samples for δ(13)C and δ(18)O analyses as well as soil water, xylem water, leaf water and atmospheric water vapour samples for δ(18)O analysis were taken approximately every 2 weeks during the growing season of 2007. The δ(13)C and δ(18)O samples from the tree rings were dated intra-annually by monitoring the tree growth with dendrometers. δ(18)O in the phloem organic matter and tree-ring whole wood was not positively related to leaf water evaporative enrichment and δ(18)O of canopy organic matter pools. This finding implies a partial uncoupling of the tree-ring oxygen isotopic signal from canopy physiology. At the same time, internal carbon storage and remobilization physiology most likely prevented δ(13)C in tree-ring whole wood from being closely related to intra-annual variation in environmental drivers. Taking into account the post-photosynthetic isotope fractionation processes resulting in alterations of δ(13)C and δ(18)O not only in the tree ring but also in phloem carbohydrates, as well as the intra-annual timing of changes in the tree internal physiology, might help to better understand the meaning of the tree-ring isotope signal not only intra- but also inter-annually.
碳（δ(13)C）和氧（δ(18)O）稳定同位素组成广泛用于获取环境驱动因素与树木生理学之间各种时间尺度上联系的信息。树木年轮档案尤其可用于重建气候和生理学的年际和年内变化。然而，对于从叶片同化到树木年轮的过程中，影响 δ(13)C 和 δ(18)O 的潜在过程，我们知之甚少。因此，本研究的目的是在整个生长季节内，通过韧皮部运输的化合物，追踪欧洲山毛榉（Fagus sylvatica L.）叶片水（δ(18)O）和叶片同化物（δ(13)C 和 δ(18)O）中的同位素信号到树木年轮木质部。在 2007 年的生长季节中，大约每两周采集一次用于 δ(13)C 和 δ(18)O 分析的韧皮部和叶片样本，以及用于 δ(18)O 分析的土壤水、木质部水、叶片水和大气水蒸汽样本。通过监测树木生长用树木生长计对树木年轮中的 δ(13)C 和 δ(18)O 样本进行年际定年。韧皮部有机物质和树木年轮全木质部中的 δ(18)O 与叶片水蒸发浓缩和冠层有机物质库的 δ(18)O 没有正相关关系。这一发现意味着树木年轮氧同位素信号与冠层生理学部分解耦。与此同时，内部碳储存和再利用生理学很可能阻止树木年轮全木质部中的 δ(13)C 与环境驱动因素的年际变化密切相关。考虑到光合作用后同位素分馏过程导致 δ(13)C 和 δ(18)O 不仅在树木年轮中，而且在韧皮部碳水化合物中发生变化，以及树木内部生理学的年内变化时间，这可能有助于不仅在年内，而且在年际上更好地理解树木年轮同位素信号的含义。
