Overdieck D., Forstreuter M.
Technische Universität Berlin, Institut für Okologie, Okologie der Gehölze, Königin-Luise-Strasse 22, D-14195 Berlin, Germany.
Tree Physiol. 1994 Jul-Sep;14(7_9):997-1003. doi: 10.1093/treephys/14.7-8-9.997.
Beech trees (Fagus sylvatica L.) show reduced stomatal conductance and increased leaf area index in response to increased atmospheric CO(2) concentration. To determine whether the reduction in stomatal conductance results in lower stand evapotranspiration, we compared transpiration on a leaf-area basis and stand evapotranspiration on a ground-area basis in young European beech trees growing in greenhouses at ambient (360 +/- 34 micro mol mol(-1)) and elevated (698 +/- 10 micro mol mol(-1)) CO(2) concentrations. Trees were grown in homogenized natural soil at constant soil water supply for two growing seasons. At light saturation, leaf transpiration rates were, on average, 18% lower in the elevated CO(2) treatment than in the ambient CO(2) treatment. Mean transpiration coefficients (transpiration/net CO(2) uptake) of leaves were 179 and 110 in the ambient and elevated CO(2) treatments, respectively, indicating improved water use efficiency in trees in the elevated CO(2) treatment. Total leaf conductance was decreased by 32% at light saturation. The elevated CO(2) treatment resulted in a 14% reduction in stand evapotranspiration. In both CO(2) treatments, evapotranspiration increased linearly at a rate of 0.2 kg H(2)O m(-2) day(-1) for each 1 degrees C rise in air temperature between 14 and 25 degrees C. We conclude that, under Central European conditions, water losses from deciduous forest stands will be reduced by a doubling of tropospheric CO(2) concentration.
山毛榉树（欧洲山毛榉）在大气CO₂浓度升高时，气孔导度降低，叶面积指数增加。为了确定气孔导度降低是否会导致林分蒸散量降低，我们比较了在温室中生长的欧洲山毛榉幼树在环境CO₂浓度（360±34微摩尔/摩尔⁻¹）和升高的CO₂浓度（698±10微摩尔/摩尔⁻¹）下基于叶面积的蒸腾作用和基于地面面积的林分蒸散量。树木在均质的天然土壤中生长，在两个生长季节中土壤水分供应保持恒定。在光饱和条件下，CO₂浓度升高处理的叶片蒸腾速率平均比环境CO₂浓度处理低18%。在环境CO₂浓度和升高的CO₂浓度处理中，叶片的平均蒸腾系数（蒸腾作用/净CO₂吸收量）分别为179和110，这表明CO₂浓度升高处理的树木水分利用效率提高。在光饱和时，总叶导度降低了32%。CO₂浓度升高处理使林分蒸散量降低了14%。在两种CO₂处理中，在14至25℃之间，气温每升高1℃，蒸散量以0.2千克水·米⁻²·天⁻¹的速率线性增加。我们得出结论，在中欧条件下，对流层CO₂浓度加倍将减少落叶林分的水分损失。
