SGER: Modeling Transpiration and Water-Stress from Leaf-Level to Catchment-Scale: A Supplement for Graduate Study

这项研究的科学目的是开发和论证一种新的、基于过程的方法的适用性，以评估从单个树叶到整个流域的空间尺度，以及从几分钟到整个生长季的时间尺度。模型策略的核心是由两个先前存在的气孔导度的子模型构建的蒸腾公式。其中一种模式是“传统的”鲍尔等人。[1987]-Farquhar等人。[1980]气孔导度与二氧化碳同化耦合的生物物理模型(经Leuning[1995]修正)。第二种是由高等人提出的气孔导度的机理模型。[2002]这引发了土壤-植物-大气水连续体的动力学。通过耦合这两个气孔导度模型(第一个模型独立于土壤水分，第二个模型受土壤水分限制)，蒸腾作用可以根据对植物水分胁迫的定量和机械依赖性来评估。此外，植物水分胁迫本身成为根据模型要求的参数和其他自变量定义的变量；因此，它也代表了气候条件和植被状况。将这些过程扩展到景观和季节将提供对植物水分胁迫和蒸腾作用的时空异质性的洞察，并旨在帮助在分水岭尺度上实现水平衡闭合。研究地点是蒙大拿州的TenderFoot Creek实验森林，其子流域(Stringer Creek)目前是NSF资助的一项广泛的流域范围内二氧化碳-H2O关系研究的重点。实验流域被针叶林和草甸的镶嵌景观所覆盖，适合于检验模型对代表这些不同功能类型的植被的参数的敏感性。这项研究将描述2006年“水年”(2005年10月至2006年9月)期间Stringer Creek流域的蒸腾作用和植物水分胁迫，并特别强调2006年的生长季。将使用叶片水平的光合作用测量来估计森林和河岸草甸植被类型的子模型参数。2005年9月期间获得的激光雷达测量和其他IKONOS图像将被用来对整个Stringer Creek分水岭的蒸腾作用进行叶级估计。蒸腾量的估计将与Priestly-Taylor方法相结合，以估计土壤的蒸发量，从而产生流域尺度的蒸散量估计，该估计值可根据Stringer Creek的水收支和2005年安装在流域内的两个涡流协方差系统测量的蒸散量进行验证。这笔资金的更广泛影响将支持优秀的研究生，并提供一个极好的机会，以当前关于流域尺度水和碳循环耦合的研究为基础。其目标是对经过充分研究的分水岭的植物-水关系进行基于过程的建模，并改进进行分水岭尺度的陆地-大气水交换估计的方法和能力。

The scientific intent of this research is to develop and demonstrate the applicability of a new, process-based method for evaluating plant water-stress at spatial scales ranging from a single leaf to an entire watershed, and at temporal scales ranging from several minutes to an entire growing season. At the core of the modeling strategy is a formulation of transpiration constructed from two preexisting submodels of stomatal conductance. One model is the 'traditional' Ball et al. [1987] - Farquhar et al. [1980] biophysical model of stomatal conductance coupled to CO2 assimilation (as modified by Leuning [1995]). The second is a mechanistic model of stomatal conductance developed by Gao et al. [2002] that invokes the dynamics of a soil-plant-atmosphere continuum of water. By coupling these two models of stomatal conductance (the first independent of soil water and the second limited by soil water), transpiration may be evaluated in terms of a quantitative and mechanistic dependence upon plant water-stress. Moreover, plant water-stress itself becomes a variable defined in terms of the parameters and other independent variables required by the model; it is therefore also representative of climatic conditions and vegetation status. Scaling these processes across landscapes and seasons will provide insight into the spatial and temporal heterogeneity of plant water-stress and transpiration, and is intended to aid in water-balance closure at the watershed scale. The study site is the Tenderfoot Creek Experimental Forest in Montana, a subcatchment of which (Stringer Creek) is currently the focus of an extensive NSF-funded study of CO2 - H2O relations on a watershed-wide scale. The experimental watershed is covered by a mosaic landscape of conifer forests and meadows, appropriate for examining model sensitivities to parameters representing these diverse functional types of vegetation. The research would characterize transpiration and plant water-stress across the Stringer Creek watershed during the 2006 "water year" (October 2005 through September 2006) with particular emphasis on the 2006 growing season. Leaf-level photosynthesis measurements will be used to estimate submodel parameters for forest and riparian meadow vegetation types. LIDAR measurements obtained during September 2005 and additional IKONOS imagery will be used to scale leaf-level estimates of transpiration to the entire Stringer Creek watershed. Estimates of transpiration will be combined with a Priestly-Taylor approach for estimating evaporation from the soil, yielding a watershed-scale estimate of evapotranspiration that may be validated against both Stringer Creek's water budget and evapotranspiration measured by two eddy covariance systems installed within the watershed during 2005.The broader impacts of this funding will support an excellent graduate student and provide an outstanding opportunity to build on current research involving coupled water and carbon cycling at the watershed scale. The goal is to extrapolate process-based modeling of plant-water relations across a well-studied watershed, and improve methodologies and capabilities for making watershed-scale estimates of land-atmosphere water exchange.