San José José J, Montes Ruben A, Florentino Adriana
Centro de Ecología, Instituto Venezolano de Investigaciones Científicas, Apartado Postal 21827, 1020-A, Caracas, Venezuela.
Departamento de Estudios Ambientales, Universidad Simón Bolívar, Apartado Postal 89000, 1080-A, Caracas, Venezuela.
Oecologia. 1995 Feb;101(2):141-150. doi: 10.1007/BF00317277.
Water relations were analysed in a semi-deciduous forest grove occurring in the oxisols of the Orinoco savannas. This grove has a shallow unconsolidated ironstone cuirass, which is overlaid by a sandy loam layer (0.0-0.5 m) that contains more than 90% of the grove forest root phytomass. Evapotranspiration and through drainage were calculated by using data from the soil profile as related to physical characteristics of the site root zone, hydraulic conductivity, volumetric water content and potential hydraulic gradient. Mean annual evapotranspiration was 783 mm year and annual through drainage below the root zone was 14% (162 mm year) of the gross rainfall. This drainage recharged the 42% of the annual saturation deficit of the water table. Similar mean annual evapotranspiration (770 mm year) was also calculated by using the water balance components. The mean daily coupling omega factor (Ω) between the grove canopy and the surrounding atmosphere indicated that a high degree of coupling (Ω=0.14±0.16) occurs in the grove and evapotranspiration was mainly controlled by surface conductance. As the dry season proceeded, the soil saturation deficit (δθ) increased rapidly resulting in a threshold surface conductance (0.030-0.005 m s) for δθ ranging from 0.05 to 0.10. Hypotheses to explain the omnipresence of perennial species in the wide range of physical conditions in neotropical savannas are discussed.
对奥里诺科稀树草原氧化土中一片半落叶林进行了水分关系分析。这片树林有一层浅的未固结铁矿石覆盖层，上面覆盖着一层砂壤土（0.0 - 0.5米），该砂壤土含有超过90%的树林根系植物量。通过使用与场地根区物理特征、水力传导率、体积含水量和潜在水力梯度相关的土壤剖面数据，计算了蒸散量和深层排水。年平均蒸散量为783毫米/年，根区以下的年深层排水量为总降雨量的14%（162毫米/年）。这种排水补充了地下水位年饱和亏缺的42%。利用水平衡组分也计算出了相似的年平均蒸散量（770毫米/年）。树林冠层与周围大气之间的平均日耦合ω因子（Ω）表明，树林中存在高度耦合（Ω = 0.14 ± 0.16），蒸散主要受表面导度控制。随着旱季的推进，土壤饱和亏缺（δθ）迅速增加，导致δθ在0.05至0.10范围内的阈值表面导度为（0.030 - 0.005米/秒）。讨论了解释新热带稀树草原广泛物理条件下多年生物种普遍存在的假说。
