School of Applied Sciences, Auckland University of Technology Auckland, New Zealand ; Forest Ecology, ETH Zurich Zurich, Switzerland ; Institute of Botany, University of Basel Basel, Switzerland.
Front Plant Sci. 2012 Oct 16;3:229. doi: 10.3389/fpls.2012.00229. eCollection 2012.
Rising levels of atmospheric CO(2) have often been reported to reduce plant water use. Such behavior is also predicted by standard equations relating photosynthesis, stomatal conductance, and atmospheric CO(2) concentration, which form the core of dynamic global vegetation models (DGVMs). Here, we provide first results from a free air CO(2) enrichment (FACE) experiment with naturally growing, mature (35 m) Picea abies (L.) (Norway spruce) and compare them to simulations by the DGVM LPJ-GUESS. We monitored sap flow, stem water deficit, stomatal conductance, leaf water potential, and soil moisture in five 35-40 m tall CO(2)-treated (550 ppm) trees over two seasons. Using LPJ-GUESS, we simulated this experiment using climate data from a nearby weather station. While the model predicted a stable reduction of transpiration of between 9% and 18% (at concentrations of 550-700 ppm atmospheric CO(2)), the combined evidence from various methods characterizing water use in our experimental trees suggest no changes in response to future CO(2) concentrations. The discrepancy between the modeled and the experimental results may be a scaling issue: while dynamic vegetation models correctly predict leaf-level responses, they may not sufficiently account for the processes involved at the canopy and ecosystem scale, which could offset the first-order stomatal response.
大气中 CO(2)水平的升高通常被报道为减少植物水分利用。这种行为也被预测光合作用、气孔导度和大气 CO(2)浓度之间的标准方程所预测，这些方程构成了动态全球植被模型 (DGVM) 的核心。在这里，我们提供了一项自然生长的、成熟的（35 米）挪威云杉（Picea abies（L.））进行的自由空气 CO(2)富集 (FACE) 实验的初步结果，并将其与 DGVM LPJ-GUESS 的模拟结果进行了比较。我们在两个季节监测了 5 棵 35-40 米高的 CO(2)处理（550 ppm）树木的 sap 流、茎水亏缺、气孔导度、叶片水势和土壤水分。使用 LPJ-GUESS，我们使用附近气象站的气候数据模拟了这个实验。虽然模型预测蒸腾作用稳定减少 9%-18%（大气 CO(2)浓度为 550-700 ppm），但我们实验树木中各种用于描述水分利用方法的综合证据表明，对未来 CO(2)浓度没有变化。模型与实验结果之间的差异可能是一个比例问题：虽然动态植被模型正确预测了叶片水平的响应，但它们可能没有充分考虑到树冠和生态系统尺度上涉及的过程，这些过程可能会抵消第一级气孔响应。
