Loustau D, Berbigier P, Roumagnac P, Arruda-Pacheco C, David J S, Ferreira M I, Pereira J S, Tavares R
Station de Recherches Forestières, INRA Centre de Bordeaux, BP45, F-33611, Gazinet, France.
Station de Bioclimatologie, INRA Centre de Bordeaux, BP 81, F-33883, Villenave d'Ornon, France.
Oecologia. 1996 Mar;107(1):33-42. doi: 10.1007/BF00582232.
The transpiration, sap flow, stomatal conductance and water relations ofPinus pinaster were determined during spring and summer in a 64-year-old stand in Ribatejo (Portugal). The transpiration of the pine canopy was determined from sap flow or eddy covariance techniques. Canopy conductance values (g ) were estimated from inversion methods using eddy covariance or sap flow data, respectively, and from scaling-up methods using stomatal conductance values measured in the field and leaf area index (LAI) values. The transpiration was closely controlled by the stomatal conductance of pines (Ω was 0.05-0.15). For wet soil conditions, the various estimates ofg showed reasonable agreement.g peaked in the morning at 0.01 m×s, exhibited a midday depression and showed a secondary peak in late afternoon. This behaviour could be predicted simply on the basis of the stomatal sensitivity to air vapour pressure deficit. On a seasonal basis, monthly average values ofg decreased from 4×10 m×s in spring to 1.7×10 m·s in late summer. Accordingly, the transpiration peaked at 3 mm×d on wet soil in May. It decreased progressively during the summer drought to 0.8 mm×d at the end of August. The minimal value of needle water potential was maintained at -1.9 MPa but predawn values decreased from -0.6 MPa in May to -0.9 MPa in July. It may have reached lower values in August. The amount of water stored in the trunk accounted for a 12% (10 kg×tree×day) of the daily transpiration in spring. The storage capacity of the canopy was within the same order of magnitude. The trunk storage increased to 25% (13 kg×tree×day) of the daily transpiration at the end of summer under drought conditions. The sap flow beneath the crown lagged accordingly behind transpiration with a time constant estimated between 26 min in spring and 40 min at the end of summer.
在葡萄牙里巴特茹一片64年树龄的林分中，于春季和夏季测定了海岸松的蒸腾作用、液流、气孔导度及水分关系。通过液流或涡度相关技术测定了松树冠层的蒸腾作用。冠层导度值（g）分别通过利用涡度相关或液流数据的反演方法，以及利用田间测定的气孔导度值和叶面积指数（LAI）值的尺度扩展方法进行估算。蒸腾作用受松树气孔导度的严格控制（Ω为0.05 - 0.15）。对于湿润的土壤条件，g的各种估算值显示出合理的一致性。g在早晨达到峰值，为0.01 m·s，中午出现下降，并在傍晚出现第二个峰值。这种行为仅根据气孔对空气蒸汽压亏缺的敏感性就能简单预测。从季节来看，g的月平均值从春季的4×10 m·s降至夏末的1.7×10 m·s。相应地，5月湿润土壤上的蒸腾作用峰值为3 mm·d。在夏季干旱期间逐渐下降，到8月底降至0.8 mm·d。针叶水势的最小值维持在 - 1.9 MPa，但黎明前的值从5月的 - 0.6 MPa降至7月的 - 0.9 MPa。8月可能更低。树干中储存的水量在春季占每日蒸腾量的12%（10 kg·树·天）。冠层的储存能力处于同一数量级。在干旱条件下，夏末树干储存量增加到每日蒸腾量的25%（13 kg·树·天）。树冠下的液流相应地滞后于蒸腾作用，时间常数估计在春季为26分钟，夏末为40分钟。
