The bigger they are, the harder they fall: CO₂ concentration and tree size affect drought tolerance.
The bigger they are, the harder they fall: CO₂ concentration and tree size affect drought tolerance.
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DOI：
10.1093/treephys/tpr009
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发表时间：
2011-02
期刊：
影响因子：
4
通讯作者：
D. Way
中科院分区：
文献类型：
--
作者：
D. Way
近年来的一个主要问题是，在世界许多地区，与干旱和热浪有关的树木普遍死亡（Hartmann 2011）。尽管气温上升和降水变化预计会导致更多的死亡事件，但大气中二氧化碳浓度的相关上升可能会提高树木的水分利用效率，从而减轻炎热和干旱对树木的影响。在这个问题上，Warren等人（2011年）报告了相反的情况-与环境CO2条件相比，CO2浓度升高促进了经历严重夏季干旱的温带树木（枫香，枫香）的衰老。林分暴露于CO2浓度升高有更大的根系生物量和较低的气孔导度（GS）比环境的立场，这应该增加吸水能力和土壤水分，分别提高耐旱性。然而，高CO2地块的树木受到干旱的打击更大：在干旱期间，它们比环境CO2中的树木脱落更多的叶子，并且具有较低的模拟净光合速率。该文件综合了广泛的数据在一些尺度，包括叶水平的气体交换，分支水力学，茎液流，细根动态和林分生物量估计，提供一个多方面的图片如何碳和水通量的影响，这一气候事件。结果也与最近的另一份报告一致，在CO2升高的情况下生长3年的美洲黑杨更容易受到水分胁迫的影响，并且在干旱期间比环境CO2的树木脱落更多的总叶面积（Bobich等人，2010）。二氧化碳浓度上升真的会增加森林对干旱的敏感性吗？二氧化碳浓度升高时gs降低是许多物种的共同反应，平均降低22%（Ainsworth和Rogers 2007），导致预期
A major concern in recent years has been the widespread tree mortality seen in many parts of the world associated with droughts and heat waves (Hartmann 2011). Although rising temperatures and shifting precipitation regimes are expected to cause more of these mortality events, the associated rise in atmospheric CO2 concentrations could improve tree water use efficiency, thus mitigating the effect of heat and drought on trees. In this issue, Warren et al. (2011) report the opposite— elevated CO2 concentrations promoted greater senescence in temperate trees (Liquidambar styraciflua, sweetgum) experiencing a severe summer drought when compared with ambient CO2 conditions. Stands exposed to elevated CO2 had greater root standing biomass and lower stomatal conductance (gs) than ambient stands, which should increase water uptake ability and soil moisture, respectively, thereby improving drought tolerance. However, trees in high-CO2 plots were hit harder by the drought: they shed more foliage and had lower modeled net photosynthetic rates during the drought than trees from ambient CO2. The paper synthesizes a wide range of data across a number of scales, including leaf-level gas exchange, branch hydraulics, stem sap flow, fine root dynamics and standlevel biomass estimates, to provide a multi-faceted picture of how carbon and water fluxes were affected by this climatic event. The results also concur with another recent report, where Populus deltoides grown at elevated CO2 for 3 years were more susceptible to water stress, and shed more total leaf area during a drought, than trees from ambient CO2 (Bobich et al. 2010). Could rising CO2 actually increase the susceptibility of forests to droughts? A reduction in gs at elevated CO2 is a common response across many species, with an average decrease of 22% (Ainsworth and Rogers 2007), leading to the expectation