McCarroll Danny, Whitney Matthew, Young Giles H F, Loader Neil J, Gagen Mary H
Department of Geography, Swansea University, Singleton Park, Swansea SA2 8PP,UK.
Tree Physiol. 2017 Aug 1;37(8):1021-1027. doi: 10.1093/treephys/tpx030.
Stable carbon isotope ratios from early-wood (EW) and late-wood (LW) are used to test competing models of carbon storage and allocation, providing a cost-effective alternative to measuring and dating non-structural carbohydrates in mature temperate broad-leaf forest trees growing under natural conditions. Annual samples of EW and LW from seven mature oaks (Quercus robur L.) from Scotland, covering AD 1924-2012, were pooled, treated to isolate alpha-cellulose and pyrolysed to measure the carbon isotope ratios. Late-wood values are strongly correlated with summer temperature of the year of growth and EW contains the same signal offset by 1 year. After a warm summer, isotopic ratios of EW are similar to those of the preceding LW, but following cold summers they are relatively enriched. The results conflict with established models of isotopic variation within oak tree rings but support 'two-pool' models for storage of non-structural carbohydrates, with EW formation, which occurs prior to budburst, preferentially using young reserves accumulated in the previous summer. Under poor growing conditions trees access older reserves. Slight average isotopic enrichment of EW may be explained by preferential accumulation of reserves during warmer summers rather than by isotopic enrichment during starch formation in non-photosynthetic tissue.
早材（EW）和晚材（LW）的稳定碳同位素比率被用于检验碳储存和分配的竞争模型，为测量和测定自然条件下生长的成熟温带阔叶林树木中的非结构性碳水化合物提供了一种经济高效的替代方法。采集了来自苏格兰的七棵成熟栎树（Quercus robur L.）在公元1924年至2012年期间的早材和晚材年度样本，将其合并，经过处理以分离出α-纤维素，然后进行热解以测量碳同位素比率。晚材值与生长年份的夏季温度密切相关，早材则包含相同的信号，但偏移了1年。在夏季温暖之后，早材的同位素比率与前一年晚材的相似，但在夏季寒冷之后，它们相对富集。这些结果与栎树年轮内既定的同位素变化模型相冲突，但支持非结构性碳水化合物储存的“双库”模型，早材在芽萌动之前形成，优先利用前一个夏天积累的新储备。在生长条件较差时，树木会利用更老的储备。早材轻微的平均同位素富集现象，可能是由于在较温暖的夏天储备优先积累，而非非光合组织中淀粉形成过程中的同位素富集所致。
