Nicholas School of the Environment and Earth Sciences, Duke University, Durham, North Carolina, 27708, USA.
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences (SLU), Umeå, SE-901 83, Sweden.
Ecol Appl. 2017 Jan;27(1):118-133. doi: 10.1002/eap.1423.
Canopy transpiration (E ) is a large fraction of evapotranspiration, integrating physical and biological processes within the energy, water, and carbon cycles of forests. Quantifying E is of both scientific and practical importance, providing information relevant to questions ranging from energy partitioning to ecosystem services, such as primary productivity and water yield. We estimated E of four pine stands differing in age and growing on sandy soils. The stands consisted of two wide-ranging conifer species: Pinus taeda and Pinus sylvestris, in temperate and boreal zones, respectively. Combining results from these and published studies on all soil types, we derived an approach to estimate daily E of pine forests, representing a wide range of conditions from 35° S to 64° N latitude. During the growing season and under moist soils, maximum daily E (E ) at day-length normalized vapor pressure deficit of 1 kPa (E ) increased by 0.55 ± 0.02 (mean ± SE) mm/d for each unit increase of leaf area index (L) up to L = ~5, showing no sign of saturation within this range of quickly rising mutual shading. The initial rise of E with atmospheric demand was linearly related to E . Both relations were unaffected by soil type. Consistent with theoretical prediction, daily E was sensitive to decreasing soil moisture at an earlier point of relative extractable water in loamy than sandy soils. Our finding facilitates the estimation of daily E of wide-ranging pine forests using remotely sensed L and meteorological data. We advocate an assembly of worldwide sap flux database for further evaluation of this approach.
林冠蒸腾（E）是蒸散作用的重要组成部分，它整合了森林能量、水分和碳循环中的物理和生物过程。量化 E 具有重要的科学和实际意义，为从能量分配到生态系统服务（如初级生产力和水产量）等各种问题提供了相关信息。我们估计了四个不同年龄和生长在沙质土壤上的松树林分的 E。这些林分由两种广泛分布的针叶树种组成：分别生长在温带和北方地区的湿地松（Pinus taeda）和欧洲赤松（Pinus sylvestris）。结合这些结果和所有土壤类型的已发表研究，我们得出了一种估计松树林分日蒸腾量的方法，该方法代表了从南纬 35°到北纬 64°的广泛条件。在生长季节和湿润土壤条件下，在日长归一化蒸气压亏缺为 1 kPa 时的最大日蒸腾量（E）随着叶面积指数（L）的每单位增加而增加 0.55 ± 0.02（平均值 ± 标准误差）mm/d，直到 L 达到~5，在这个快速增加相互遮荫的范围内，没有出现饱和的迹象。E 随大气需求的初始增加与 E呈线性关系。这两种关系不受土壤类型的影响。与理论预测一致，在壤土中相对可提取水分较早的点，E 与土壤水分的关系呈负相关，而在沙土中则没有。我们的发现有助于利用遥感 L 和气象数据来估算广泛分布的松树林的日蒸腾量。我们提倡建立一个全球 sap 通量数据库，以进一步评估这种方法。
