School of Geography, University of Leeds, Leeds, Garstang North.
School of Geology, Geography and the Environment, Bennett Building, University Road, University of Leicester, Leicester, UK.
Tree Physiol. 2019 May 1;39(5):845-860. doi: 10.1093/treephys/tpz009.
Isotopes in tropical trees rings can improve our understanding of tree responses to climate. We assessed how climate and growing conditions affect tree-ring oxygen and carbon isotopes (δ18OTR and δ13CTR) in four Amazon trees. We analysed within-ring isotope variation for two terra firme (non-flooded) and two floodplain trees growing at sites with varying seasonality. We find distinct intra-annual patterns of δ18OTR and δ13CTR driven mostly by seasonal variation in weather and source water δ18O. Seasonal variation in isotopes was lowest for the tree growing under the wettest conditions. Tree ring cellulose isotope models based on existing theory reproduced well observed within-ring variation with possible contributions of both stomatal and mesophyll conductance to variation in δ13CTR. Climate analysis reveal that terra firme δ18OTR signals were related to basin-wide precipitation, indicating a source water δ18O influence, while floodplain trees recorded leaf enrichment effects related to local climate. Thus, intrinsically different processes (source water vs leaf enrichment) affect δ18OTR in the two different species analysed. These differences are likely a result of both species-specific traits and of the contrasting growing conditions in the floodplains and terra firme environments. Simultaneous analysis of δ13CTR and δ18OTR supports this interpretation as it shows strongly similar intra-annual patterns for both isotopes in the floodplain trees arising from a common control by leaf stomatal conductance, while terra firme trees showed less covariation between the two isotopes. Our results are interesting from a plant physiological perspective and have implications for climate reconstructions as trees record intrinsically different processes.
热带树木年轮中的同位素可以帮助我们更好地理解树木对气候的响应。我们评估了气候和生长条件如何影响四种亚马逊树木的年轮氧和碳同位素（δ18OTR 和 δ13CTR）。我们分析了两个非洪泛区（terra firme）和两个洪泛区树木的年轮内同位素变化，这些树木生长在季节变化不同的地点。我们发现 δ18OTR 和 δ13CTR 的年内变化存在明显的模式，主要由天气和源水 δ18O 的季节性变化驱动。在最湿润条件下生长的树木的同位素季节性变化最小。基于现有理论的树木年轮纤维素同位素模型很好地再现了观察到的年轮内变化，δ13CTR 的变化可能与气孔和质膜导度都有关。气候分析表明，terra firme δ18OTR 信号与盆地范围的降水有关，表明源水 δ18O 的影响，而洪泛区树木记录了与当地气候有关的叶片富集效应。因此，两种不同的过程（源水与叶片富集）内在地影响两种不同分析物种的 δ18OTR。这些差异可能是由于物种特有的特征以及洪泛区和 terra firme 环境中生长条件的对比造成的。δ13CTR 和 δ18OTR 的同时分析支持了这一解释，因为它表明洪泛区树木的两种同位素具有非常相似的年内变化模式，这是由叶片气孔导度的共同控制引起的，而 terra firme 树木的两种同位素之间的变化较小。我们的研究结果从植物生理学的角度来看很有趣，并且对气候重建具有启示意义，因为树木记录了内在不同的过程。
