Water-use efficiency and transpiration across European forests during the Anthropocene
Water-use efficiency and transpiration across European forests during the Anthropocene
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DOI：
10.1038/nclimate2614
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发表时间：
2015-06-01
影响因子：
30.7
通讯作者：
Weigl, M.
中科院分区：
文献类型：
--
作者：
Frank, D. C.;Poulter, B.;Weigl, M.
地球的碳循环和水文循环通过植物气孔的气体交换紧密耦合(1-3)。然而，植物对自然环境中二氧化碳浓度升高的生理反应 (9,10) 的程度 (4-6) 和后果 (7,8) 的不确定性阻碍了陆地水循环和碳储存的建模 (11)。在这里，我们使用欧洲森林网络中每年解析的长期 Delta C-13 树轮测量来重建由大气 CO2 (Ca) 趋势引起的细胞间 CO2 (Ci) 的生理驱动响应。当从 Delta C-13 测量中去除气象信号时，我们发现欧洲各地的树木调节气体交换，因此大气中二氧化碳每增加 1 ppmv，C-i 就会增加约 0.76 ppmv，这与对恒定 C-i/C-a 比率的适度控制最为一致。这一响应对应于二十世纪阔叶林和针叶林地固有水分利用效率 (iWUE) 分别增加 14 +/- 10 和 22 +/- 6%。基于过程的全球植被模型集合显示了类似的二氧化碳对 iWUE 趋势的影响。然而，当在重新引入气候驱动因素的情况下运行这些模型时，尽管气孔开口减少，但计算出 20 世纪欧洲森林蒸腾量增加了 5%。这种违反直觉的结果是由于生长季节的延长、气候变暖时蒸发需求的增加以及叶面积的增加而产生的，这些因素共同对抗二氧化碳引起的气孔关闭的影响。我们的研究质疑水文循环的变化，例如蒸腾作用和空气湿度的减少，假设这是植物对人为排放的反应造成的。
The Earth's carbon and hydrologic cycles are intimately coupled by gas exchange through plant stomata(1-3). However, uncertainties in the magnitude(4-6) and consequences(7,8) of the physiological responses(9,10) of plants to elevated CO2 in natural environments hinders modelling of terrestrial water cycling and carbon storage(11). Here we use annually resolved long-term delta C-13 tree-ring measurements across a European forest network to reconstruct the physiologically driven response of intercellular CO2 (Ci) caused by atmospheric CO2 (Ca) trends. When removing meteorological signals from the delta C-13 measurements, we find that trees across Europe regulated gas exchange so that for one ppmv atmospheric CO2 increase, C-i increased by similar to 0.76 ppmv, most consistent with moderate control towards a constant C-i/C-a ratio. This response corresponds to twentiethcentury intrinsic water-use efficiency (iWUE) increases of 14 +/- 10 and 22 +/- 6% at broadleaf and coniferous sites, respectively. An ensemble of process-based global vegetation models shows similar CO2 effects on iWUE trends. Yet, when operating these models with climate drivers reintroduced, despite decreased stomatal opening, 5% increases in European forest transpiration are calculated over the twentieth century. This counterintuitive result arises from lengthened growing seasons, enhanced evaporative demand in a warming climate, and increased leaf area, which together oppose effects of CO2-induced stomatal closure. Our study questions changes to the hydrological cycle, such as reductions in transpiration and air humidity, hypothesized to result from plant responses to anthropogenic emissions.