Department of Biology, West Virginia University, Morgantown, WV 26506
Department of Biology, West Virginia University, Morgantown, WV 26506.
Proc Natl Acad Sci U S A. 2021 Feb 16;118(7). doi: 10.1073/pnas.2014286118.
We conducted a meta-analysis of carbon and oxygen isotopes from tree ring chronologies representing 34 species across 10 biomes to better understand the environmental drivers and physiological mechanisms leading to historical changes in tree intrinsic water use efficiency (iWUE), or the ratio of net photosynthesis () to stomatal conductance (), over the last century. We show a ∼40% increase in tree iWUE globally since 1901, coinciding with a ∼34% increase in atmospheric CO (C), although mean iWUE, and the rates of increase, varied across biomes and leaf and wood functional types. While C was a dominant environmental driver of iWUE, the effects of increasing C were modulated either positively or negatively by climate, including vapor pressure deficit (VPD), temperature, and precipitation, and by leaf and wood functional types. A dual carbon-oxygen isotope approach revealed that increases in dominated the observed increased iWUE in ∼83% of examined cases, supporting recent reports of global increases in , whereas reductions in occurred in the remaining ∼17%. This meta-analysis provides a strong process-based framework for predicting changes in tree carbon gain and water loss across biomes and across wood and leaf functional types, and the interactions between C and other environmental factors have important implications for the coupled carbon-hydrologic cycles under future climate. Our results furthermore challenge the idea of widespread reductions in as the major driver of increasing tree iWUE and will better inform Earth system models regarding the role of trees in the global carbon and water cycles.
我们对来自 34 个物种的 10 个生物群落的树木年轮年代序列中的碳和氧同位素进行了荟萃分析，以便更好地了解导致过去一个世纪树木内在水分利用效率（iWUE）——即净光合速率（）与气孔导度（）的比值——发生历史变化的环境驱动因素和生理机制。我们发现，自 1901 年以来，全球树木 iWUE 增加了约 40%，同期大气 CO（C）增加了约 34%，尽管平均 iWUE 以及增加的速度在生物群落和叶片及木质功能类型之间存在差异。虽然 C 是 iWUE 的主要环境驱动因素，但 C 的影响受到气候（包括蒸气压亏缺（VPD）、温度和降水）以及叶片和木质功能类型的正向或负向调节。碳-氧双同位素方法表明，在约 83%的受检案例中，增加的主导了观测到的 iWUE 增加，这支持了最近关于全球增加的报告，而在其余约 17%的案例中，减少了。这项荟萃分析为预测 across biomes 和 across wood 和 leaf functional types 中树木碳增益和水分损失的变化提供了一个强有力的基于过程的框架，并且 C 和其他环境因素之间的相互作用对未来气候下的碳-水文耦合循环具有重要意义。我们的结果进一步挑战了广泛减少作为增加树木 iWUE 的主要驱动因素的观点，并将更好地为地球系统模型提供有关树木在全球碳和水循环中的作用的信息。
