Including tree water storage dynamics in modeling of stomatal conductance

将树木储水动态纳入气孔导度建模

• 批准号: 1521238
• 负责人: Gil Bohrer
• 金额: $ 49.65万
• 依托单位: Ohio State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-06-15 至 2019-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1521238&HistoricalAwards=false
• 关键词: Including; tree; water; storage; dynamics

Water stored in trees has an important role in regulating how much water the trees lose through their leaves, a process called transpiration. As plants transpire, water is lost from branches and stems more quickly than it can be replenished by water uptake from the soil by the roots. In order to prevent excessive drying, plants respond to this "hydraulic stress" by reducing transpiration rates. However, current land-surface models do not represent these hydraulic processes and the level of water storage within trees, but predict the transpiration rates based directly on soil moisture. This can produce typical daily patterns of error in simulations of transpiration. This research proposes a model to represent these missing within-tree water dynamics. The FETCH2 model resolves water flow through the tree stem to simulate realistically reductions in transpiration due to hydraulic stresses. Data from a large scale ecological disturbance experiment will be used to validate this approach. FETCH2 will be developed so that it can be coupled with other ecosystem and land-surface models. We will test the effectivity of FETCH2 by comparing the results of several ecosystem models with and without FETCH2 simulations with observations of tree water status and transpiration made in the disturbance experiment site and in a nearby undisturbed control site. The research team has partnered with the Ohio Water Resources Center (OWRC) to develop a hands-on activity package to illustrate porous-media flow based on the curricular activities template drafted by Project 'WET' (Water Education for Teachers), which will use games and experiments to illustrate the scientific principles at the primary school level. Above-ground water storage in trees plays a key role in regulating transpiration in forest canopies. Plants transpire water from the stem storage. As transpiration rates are higher than the maximal recharge rate from the soil through the roots, stem, and branches, the above-ground storage becomes depleted and stomata close to restrict transpiration in response to the negative xylem water potential. These hydraulic limitations control transpiration in forest ecosystems under both wet and dry conditions. Current land-surface models do not represent the above-ground storage in trees. These models impose water resource limitations on transpiration by directly linking stomatal conductance to soil moisture. As the intra-daily dynamics of soil moisture are very different than the dynamics of water storage in the tree xylem, the current approach leads to deviations from the observed dynamics of transpiration. As a result, land surface models produce characteristic intra-daily patterns of errors in simulations of latent heat flux. This research will develop a framework to resolve such tree hydrodynamics that could be incorporated into hydrologic, land surface, and Earth System Models to replace the current empirical link between stomatal conductance and soil moisture. The FETCH2 model resolves the water flow and water potential in the tree stem and realistically links stomatal conductance to the water potential in the xylem, while water availability in the soil provides a bottom boundary condition for the hydrodynamic system. Data from a large scale ecological disturbance experiment at a forest in Michigan will be used to validate this approach. FETCH2 simulations will be compared to observations of sap flux and stem water storage in the forest plots and to land-surface model simulation results without the hydrodynamic module. Improvements to the simulation of stomatal conductance and transpiration in atmospheric, hydrologic, and Earth system models will propagate to connected variables such as soil moisture, the surface energy budget, and gross primary productivity. By incorporating the effects of forest canopy structure, tree water storage, and hydraulic strategy on stomatal conductance, this study may impact many types and classes of climate, hydrologic, and meteorological models.

存储在树木中的水在调节树叶中损失了多少水，这是一种称为蒸腾的过程。随着植物的流逝，水从树枝上流失，茎的速度要比根部从土壤中吸收的水补充得多。为了防止过度干燥，植物通过降低蒸腾速率来应对这种“液压应激”。但是，当前的土地表面模型并不代表树木内的这些液压过程和储水水平，而是直接基于土壤水分的蒸腾速率。这可以在蒸腾模拟中产生典型的每日误差模式。这项研究提出了一个模型来表示这些缺失的树内水动力学。 Fetch2模型分解了水流的水流，以模拟由于液压应力而导致的蒸腾作用中的实际减少。大规模生态障碍实验的数据将用于验证这种方法。 Fetch2将开发，以便它可以与其他生态系统和土地表面模型结合使用。我们将通过比较有和没有Fetch2模拟的几个生态系统模型的结果，并在干扰实验部位和附近未受干扰的控制位点进行观察，以测试Fetch2的有效性。 研究小组已与俄亥俄州水资源中心（OWRC）合作开发了一个动手活动计划，以根据课程活动模板（由Project``湿）'（为教师提供水教育）来说明多孔媒体流量，该模板将使用游戏和实验来说明小学一级的科学原理。树木中的地上储水在调节森林檐篷的蒸腾方面起着关键作用。植物从茎存储中散发出水。由于蒸腾速率高于从土壤中通过根，茎和分支从土壤中的最大充值速率，因此，地上存储会耗尽，气孔接近限制性蒸腾作用，以响应负木质部水的潜力。这些液压局限性控制着潮湿和干燥条件下森林生态系统的蒸腾作用。当前的土地表面模型不代表树木中的地上存储。这些模型通过将气孔电导与土壤水分直接连接起来，对蒸腾作用施加了水资源限制。由于土壤水分的每日内部动力学与树木质部中的储水动力学大不相同，因此当前的方法导致偏离观察到的蒸腾动力学。结果，陆地表面模型在潜在热通量模拟中产生了每日误差的特征。这项研究将开发一个框架，以解决可以将其纳入水文，陆地和地球系统模型中的这种树木流体动力学，以取代气孔电导和土壤水分之间的当前经验联系。 Fetch2模型可以解决树茎中的水流和水电位，并实际将气孔电导与木质部的水潜力联系起来，而土壤中的水的供应为流体动力学系统提供了底部边界条件。密歇根州森林的大规模生态干扰实验的数据将用于验证这种方法。 Fetch2模拟将与森林图中的SAP通量和茎储存的观察结果以及没有流体动力模块的土地表面模型模拟结果进行比较。改善大气，水文和地球系统模型中气孔电导和蒸腾的模拟将传播到连接的变量，例如土壤水分，表面能预算和总生产力。通过纳入森林冠层结构，树木储存和液压策略对气孔电导的影响，这项研究可能会影响许多类型和类型的气候，水文和气象模型。

项目成果

Observations of stem water storage in trees of opposing hydraulic strategies

• DOI: 10.1890/es15-00170.1
• 发表时间: 2015-09-01
• 期刊: ECOSPHERE
• 影响因子: 2.7
• 作者: Matheny, Ashley M.;Bohrer, Gil;Vogel, Christoph S.
• 通讯作者: Vogel, Christoph S.

Contrasting strategies of hydraulic control in two codominant temperate tree species

• DOI: 10.1002/eco.1815
• 发表时间: 2017-04
• 期刊: Ecohydrology
• 影响因子: 2.6
• 作者: A. Matheny;R. Fiorella;G. Bohrer;C. Poulsen;T. Morin;A. Wunderlich;C. Vogel;P. Curtis

Tree level hydrodynamic approach for resolving aboveground water storage and stomatal conductance and modeling the effects of tree hydraulic strategy: Stomatal Conductance Parameterization

用于解决地上水储存和气孔导度并对树木水力策略的影响进行建模的树级水动力方法：气孔导度参数化

• DOI: 10.1002/2016jg003467
• 发表时间: 2016
• 期刊: Journal of Geophysical Research: Biogeosciences
• 作者: Mirfenderesgi, Golnazalsadat;Bohrer, Gil;Matheny, Ashley M.;Fatichi, Simone;de Moraes Frasson, Renato Prata;Schäfer, Karina V.
• 通讯作者: Schäfer, Karina V.