Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise
Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise
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DOI：
10.1038/nature12291
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发表时间：
2013-07-18
期刊：
影响因子：
64.8
通讯作者：
Richardson, Andrew D.
中科院分区：
文献类型：
--
作者：
Keenan, Trevor F.;Hollinger, David Y.;Richardson, Andrew D.
陆地植物通过光合作用从大气中去除CO2，这一过程伴随着叶子中水蒸气的损失（1）。水损失与碳增益的比率，或水利用效率，是生态系统功能的关键特征，是全球水，能量和碳循环的核心。在这里，我们分析了整个生态系统碳和水交换的直接，长期测量（3）。我们发现在过去的二十年里，北方半球的温带和寒带森林的水利用效率大幅提高。我们系统地评估了各种相互竞争的假设来解释这一趋势，并发现所观察到的增加与强烈的CO2施肥效应最为一致。研究结果表明，气孔（1）-叶片表面调节气体交换的小孔-的部分关闭，即使在不断增加的大气CO2水平下，也能保持叶片内CO2浓度接近恒定。观察到的森林水利用效率的增加大于现有理论和13个陆地生物圈模型的预测。这种增加与生态系统水平光合作用和净碳吸收增加以及蒸散量减少的趋势有关。我们的研究结果表明，陆地植被的碳和水为基础的经济学的转变，这可能需要重新评估气孔控制在调节森林和气候变化之间的相互作用的作用，并重新评估耦合植被气候模型。
Terrestrial plants remove CO2 from the atmosphere through photosynthesis, a process that is accompanied by the loss of water vapour from leaves(1). The ratio of water loss to carbon gain, or water-use efficiency, is a key characteristic of ecosystem function that is central to the global cycles of water, energy and carbon(2). Here we analyse direct, long-term measurements of whole-ecosystem carbon and water exchange(3). We find a substantial increase in water-use efficiency in temperate and boreal forests of the Northern Hemisphere over the past two decades. We systematically assess various competing hypotheses to explain this trend, and find that the observed increase is most consistent with a strong CO2 fertilization effect. The results suggest a partial closure of stomata(1)-small pores on the leaf surface that regulate gas exchange-to maintain a near-constant concentration of CO2 inside the leaf even under continually increasing atmospheric CO2 levels. The observed increase in forest water-use efficiency is larger than that predicted by existing theory and 13 terrestrial biosphere models. The increase is associated with trends of increasing ecosystem-level photosynthesis and net carbon uptake, and decreasing evapotranspiration. Our findings suggest a shift in the carbon-and water-based economics of terrestrial vegetation, which may require a reassessment of the role of stomatal control in regulating interactions between forests and climate change, and a re-evaluation of coupled vegetation-climate models.