CANOPY EVAPOTRANSPIRATION, LEAF TRANSPIRATION AND WATER USE EFFICIENCY OF AN ANDEAN PASTURE IN SE-ECUADOR – A CASE STUDY
CANOPY EVAPOTRANSPIRATION, LEAF TRANSPIRATION AND WATER USE EFFICIENCY OF AN ANDEAN PASTURE IN SE-ECUADOR – A CASE STUDY
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DOI：
10.3112/erdkunde.2016.01.02
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
B. Silva;Simone Strobl;E. Beck;J. Bendix
中科院分区：
文献类型：
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作者：
B. Silva;Simone Strobl;E. Beck;J. Bendix
使用激光闪烁计和气孔计相结合的方法，在五天内分析了同质热带山地牧场的冠层蒸散量 (ETSci) 和叶层蒸腾量 (Tleaf) 以及光合作用 (Pleaf) 之间的关系。研究期间天气状况从阴天到晴天。使用气孔计测量了主要牧草狗尾草叶子的气体交换（蒸腾作用与光合二氧化碳净吸收量），并在微气候变量（光合有效辐射（PAR）作为总光强、温度、空气水蒸气不足的代表）和土壤湿度数据的背景下进行生理解释。利用牧场的水分利用效率（WUE，光合二氧化碳净吸收量与叶片蒸腾失水量）来分析草地对研究区域环境变量的响应范围。 PAR 和空气水蒸气缺乏 (VPD) 似乎是 Tleaf 和 ETSci 的决定因素。狗尾草牧场的 WUE 范围为 1.9 至 5.8 μmol CO2 mmol-1 H20 day-1，在高 VPD 期间以及无云期间日照增强期间特别低。闪烁计收集的 ET 测量结果表明与使用 Penman-Monteith 方法 (TPM) 计算的水通量有很强的相关性 (r2 = 0.95)。此外，用气孔计测量的 Tleaf 与 ET 观测结果显示出合理的一致性 (r2 = 0.78)。 ETSci 的值范围为 2.26 至 4.96 mm day-1，Tleaf 的值范围为 0.83 至 2.41 mm day-1，但只有 ETSci 与可用能量（净辐射）表现出良好的对应性。与 ETSci 和 TPM 之间的相关性相比，Tleaf 和冠层 ETSci 之间的相关性较低，针对来自闪烁计路径的相邻提取区域的污染进行了测试，但没有发现任何影响。同样，也可以排除 Tleaf 土壤水分的限制。因此，ETSci 和 Tleaf 与传入能量和 VPD 的不同相关性可以追溯到 VPD 对 ET 的直接影响，而不是其对 Tleaf 的间接影响，而 Tleaf 还受到叶子气孔中生理过程的调节。
The relationship between canopy-level evapotranspiration (ETSci) and leaf-level transpiration (Tleaf) as well as photosynthesis (Pleaf) for a homogeneous tropical montane pasture was analyzed over five days using a combination of methods involving a laser scintillometer and a porometer. Weather conditions ranged from overcast to sunny during the period of study. The gas exchange of the leaves of the dominant pasture grass Setaria sphacelata (transpiration vs. photosynthetic CO2 net uptake ) was measured with a porometer and physiologically interpreted on the background of microclimate variables (photosynthetic active radiation (PAR) as proxy for total light intensity, temperature, water vapor deficit of the air) and soil moisture data. Water use efficiency (WUE, photosynthetic CO2 net uptake vs water loss by leaf transpiration) of the pasture was used to analyze the grass’ range of response to the environmental variables of the research area. PAR and water vapor deficit of the air (VPD) appeared to be the determinant factors for Tleaf and ETSci. WUE for the Setaria sphacelata pasture ranged from 1.9 to 5.8 μmol CO2 mmol-1 H20 day-1 and is particularly low during periods of high VPD combined with enhanced insolation during cloudless periods. ET measurements collected by the scintillometer demonstrated a strong correlation with water flux calculated using the Penman-Monteith approach (TPM) (r2 = 0.95). Also, Tleaf measured with the porometer showed reasonable coincidence with the ET observations (r2 = 0.78). Values of ETSci ranged from 2.26 to 4.96 mm day-1 and Tleaf ranged from 0.83 to 2.41 mm day-1, but only ETSci showed good correspondence with the available energy (net radiation). The lower correlation between Tleaf and canopy-level ETSci compared to that between ETSci and TPM was tested against contaminations from the adjacent fetch area of the scintillometer path, but no effects were found. Likewise, soil water limitations of Tleaf could be ruled out. Therefore, different correlations of ETSci and Tleaf with the incoming energy and VPD may be traced back to a direct effect of the VPD on ET in contrast to its indirect effect on Tleaf which is additionally regulated by physiological processes in the leaf stomata.