Environmental Science Department, Second University of Naples, 81100, Caserta, Italy.
Centre for Bio-Archeology and Ecology, Ecole Pratique des Hautes Etudes (PALECO EPHE), Institut de Botanique, University of Montpellier 2, F-34090, Montpellier, France.
New Phytol. 2013 Jan;197(2):544-554. doi: 10.1111/nph.12044. Epub 2012 Dec 5.
Elevated CO₂ increases intrinsic water use efficiency (WUE(i) ) of forests, but the magnitude of this effect and its interaction with climate is still poorly understood. We combined tree ring analysis with isotope measurements at three Free Air CO₂ Enrichment (FACE, POP-EUROFACE, in Italy; Duke FACE in North Carolina and ORNL in Tennessee, USA) sites, to cover the entire life of the trees. We used δ¹³C to assess carbon isotope discrimination and changes in water-use efficiency, while direct CO₂ effects on stomatal conductance were explored using δ¹⁸O as a proxy. Across all the sites, elevated CO₂ increased ¹³C-derived water-use efficiency on average by 73% for Liquidambar styraciflua, 77% for Pinus taeda and 75% for Populus sp., but through different ecophysiological mechanisms. Our findings provide a robust means of predicting water-use efficiency responses from a variety of tree species exposed to variable environmental conditions over time, and species-specific relationships that can help modelling elevated CO₂ and climate impacts on forest productivity, carbon and water balances.
升高的 CO₂ 会提高森林的内在水分利用效率（WUE(i)），但这种效应的幅度及其与气候的相互作用仍不甚清楚。我们结合树轮分析和三个自由空气 CO₂ 富集（FACE、POP-EUROFACE，在意大利；北卡罗来纳州的杜克 FACE 和美国田纳西州的 ORNL）地点的同位素测量，涵盖了树木的整个生命周期。我们使用 δ¹³C 来评估碳同位素分馏和水分利用效率的变化，而 δ¹⁸O 则被用来作为一种替代物来探索 CO₂ 对气孔导度的直接影响。在所有地点，升高的 CO₂ 平均使 Liquidambar styraciflua 的 ¹³C 衍生水分利用效率提高了 73%，Pinus taeda 提高了 77%，Populus sp. 提高了 75%，但通过不同的生理生态机制。我们的研究结果为预测暴露在不同环境条件下的多种树种的水分利用效率响应提供了一种可靠的方法，以及有助于建模升高的 CO₂ 和气候对森林生产力、碳和水分平衡的影响的物种特异性关系。
