Soil water content measurements deliver reliable estimates of water fluxes: a comparative study in a beech and a spruce stand in the Tharandt forest (Saxony, Germany).
Soil water content measurements deliver reliable estimates of water fluxes: a comparative study in a beech and a spruce stand in the Tharandt forest (Saxony, Germany).
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DOI：
10.1016/j.agrformet.2009.07.006
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发表时间：
2009-11
影响因子：
6.2
通讯作者：
K. Schwärzel;Alexander Menzer;Falko Clausnitzer;U. Spank;J. Häntzschel;T. Grünwald;B. Köstner;C. Bernhofer;K. Feger
中科院分区：
文献类型：
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作者：
K. Schwärzel;Alexander Menzer;Falko Clausnitzer;U. Spank;J. Häntzschel;T. Grünwald;B. Köstner;C. Bernhofer;K. Feger
以往的研究表明，土壤水分含量可以有很大的差异，在同质网站。在研究森林生态系统的水碳通量时，土壤水分的这种小尺度变异性往往被忽略。在本文中，土壤水分的小尺度变异性进行了分析，在两个对比的涡通量网站，挪威云杉林和欧洲山毛榉林。同时测量的降水，涡度协方差，和液流，从土壤含水量读数，被用来回答这个问题，如何代表土壤水分增益是在降雨和蒸散是在干旱时期。研究表明，云杉和山毛榉林下土壤水分的时空变异主要是由于土壤性质和根系强度的差异。这可以从树下土壤水分分布和流动路径在整个季节基本稳定的事实中得出结论。作为一种趋势，雨水优先积累的地区，主要特点是最大的土壤水分枯竭。因此，水分传感器的安装密度应与土壤性质的变化以及生根强度相对应。根据以前的研究和我们自己的结果，可以得出结论，10和30厘米之间的水平和垂直距离最适合含水量传感器检测优先流动路径，并提供可靠的土壤水分平衡估计。尽管优先流的发生，我们发现，土壤水分增加在暴雨期间和土壤水分亏缺在干旱期间可以相对较好地估计时，土壤性质的小尺度变异被认为是在实验装置。在一般情况下，蒸发估计涡度相关，树干液流，土壤水分平衡的基础上一致。然而，与云杉站点相比，在山毛榉站点，基于涡度相关的蒸散估计值与土壤水分平衡之间的差距往往相对较大。这些方法在空间范围上的差异只能在一定程度上解释这些差异。我们认为，这可能主要是由于缺乏水含量传感器在附近的山毛榉树干。因此，在我们的研究中，树干周围的茎流诱导的润湿和随后的干燥不能监测。这可能会导致低估的蒸发从土壤下山毛榉使用土壤水分平衡方法相比，涡度相关方法。最后，云杉下的土壤水分亏缺导致蒸腾作用显着减少时，实际有效植物土壤容量（AWC）是潜在AWC的40%。与云杉林相比，山毛榉的蒸腾作用没有因缺水而减少。
Previous studies have shown that soil water content can vary considerably within homogeneous sites. This small-scale variability of soil water is often neglected when studying water and carbon fluxes in forest ecosystems. In this paper, the small-scale variability of soil water was analyzed at two contrasting eddy-flux sites, a Norway spruce forest and a European beech forest. Simultaneous measurements of precipitation, eddy covariance, and sap flow, from soil water content readings, were used to answer the question of how representative soil water gain is during rainfall and evapotranspiration is during dry periods. Our study demonstrates that the spatial and temporal variability in soil water under spruce and beech was mainly due to the differences in soil properties and root intensity. This can be concluded from the fact that the pattern of soil moisture distribution and flow paths under the trees were generally stable throughout the season. As a tendency, areas with preferred accumulation of rainwater were mainly characterized by maximum soil water depletion. Therefore, the density of the installed water content sensors should correspond to the variability of soil properties as well as rooting intensity. Based on previous studies and our own results, it can be concluded that a horizontal and vertical distance between 10 and 30cm is best suited for water content sensors to detect preferential flow paths and deliver reliable estimates of soil water balance. Despite the occurrence of preferential flow, we found that the soil water increase during rainstorm periods and the soil water depletion during dry periods can be estimated relatively well when the small-scale variability of soil properties is considered in the experimental setup. In general, the evaporation estimates based on eddy covariance, sap flow, and soil water balance were consistent. However, compared to the spruce site, at the beech site the gap between the evapotranspiration estimates based on eddy covariance and soil water balance were often relatively large. Differences in the spatial extent of these methods can only explain these discrepancies to a certain extent. We suggest that this might be mainly due to the lack of water content sensors in the immediate vicinity of the beech tree trunk. Thus, stemflow-induced wetting and subsequent drying around the trunk could not be monitored in our study. This may result in an underestimation of evaporation from the soil under beech using the soil water balance method compared to the eddy covariance method. Finally, soil water depletion under spruce led to a significant reduction of transpiration when the actual available plant soil capacity (AWC) was <40% of the potential AWC. In contrast to the spruce stand, a reduction of transpiration of beech due to water shortage was not observed.