National Field Science Observation and Research Station of Yulong Mountain Cryosphere and Sustainable Development, State Key Laboratory of Cryospheric Sciences, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China.
Laboratory of Tree-Ring Research, University of Arizona, Tucson 85721, USA.
Tree Physiol. 2022 Nov 8;42(11):2203-2223. doi: 10.1093/treephys/tpac076.
Tree-ring intra-annual stable isotopes (δ13C and δ18O) are powerful tools for revealing plant ecophysiological responses to climatic extremes. We analyzed interannual and fine-scale intra-annual variability of tree-ring δ13C and δ18O in Chinese red pine (Pinus massoniana) from southeastern China to explore environmental drivers and potential trade-offs between the main physiological controls. We show that wet season relative humidity (May-October RH) drove interannual variability of δ18O and intra-annual variability of tree-ring δ18O. It also drove intra-annual variability of tree-ring δ13C, whereas interannual variability was mainly controlled by February-May temperature and September-October RH. Furthermore, intra-annual tree-ring δ18O variability was larger during wet years compared with dry years, whereas δ13C variability was lower during wet years compared with dry years. As a result of these differences in intra-annual variability amplitude, process-based models (we used the Roden model for δ18O and the Farquhar model for δ13C) captured the intra-annual δ18O pattern better in wet years compared with dry years, whereas intra-annual δ13C pattern was better simulated in dry years compared with wet years. This result suggests a potential asymmetric bias in process-based models in capturing the interplay of the different mechanistic processes (i.e., isotopic source and leaf-level enrichment) operating in dry versus wet years. We therefore propose an intra-annual conceptual model considering a dynamic trade-off between the isotopic source and leaf-level enrichment in different tree-ring parts to understand how climate and ecophysiological processes drive intra-annual tree-ring stable isotopic variability under humid climate conditions.
树木年轮内的年际稳定同位素（δ13C 和 δ18O）是揭示植物生态生理对气候极端变化响应的有力工具。我们分析了来自中国东南部马尾松的年轮δ13C 和 δ18O 的年际和细时间尺度的年内变化，以探讨环境驱动因素和主要生理控制之间的潜在权衡。结果表明，湿季相对湿度（5 月至 10 月 RH）驱动了 δ18O 的年际变化和年轮 δ18O 的年内变化。它还驱动了年轮 δ13C 的年内变化，而年际变化主要受 2 月至 5 月温度和 9 月至 10 月 RH 控制。此外，与干旱年份相比，湿润年份年轮 δ18O 的年内变化幅度较大，而 δ13C 的年内变化幅度较小。由于年内变化幅度的差异，基于过程的模型（我们使用 Roden 模型模拟 δ18O，使用 Farquhar 模型模拟 δ13C）在湿润年份比在干旱年份更好地捕捉到年轮 δ18O 的年内变化模式，而在干旱年份比在湿润年份更好地模拟了年轮 δ13C 的年内变化模式。这一结果表明，基于过程的模型在捕捉不同机制过程（即同位素源和叶片级富集）在干旱和湿润年份的相互作用方面存在潜在的不对称偏差。因此，我们提出了一个基于年内的概念模型，考虑了不同年轮部分同位素源和叶片级富集之间的动态权衡，以了解在湿润气候条件下，气候和生态生理过程如何驱动年轮稳定同位素的年内变化。
