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.

树木中储存的水在调节树木通过叶子流失的水分方面发挥着重要作用，这一过程称为蒸腾作用。当植物蒸腾时，水分从树枝和茎中流失的速度比根部从土壤中吸收水分的补充速度要快。为了防止过度干燥，植物通过降低蒸腾速率来应对这种“水压”。然而，当前的地表模型并不代表这些水力过程和树木内的储水水平，而是直接根据土壤湿度预测蒸腾速率。这可能会在模拟蒸腾作用时产生典型的日常错误模式。这项研究提出了一个模型来代表这些缺失的树内水动态。 FETCH2 模型解析流经树干的水流，以真实地模拟由于水力应力导致的蒸腾减少。来自大规模生态干扰实验的数据将用于验证该方法。 FETCH2 的开发将使其能够与其他生态系统和地表模型相结合。我们将通过比较使用和不使用 FETCH2 模拟的几个生态系统模型的结果以及在扰动实验地点和附近未受干扰的对照地点对树木水分状况和蒸腾作用的观察来测试 FETCH2 的有效性。 研究团队与俄亥俄州水资源中心（OWRC）合作，根据“WET”项目（教师水教育）起草的课程活动模板，开发了一个实践活动包来说明多孔介质流动，该活动包将使用游戏和实验来说明小学阶段的科学原理。树木的地上储水在调节森林冠层的蒸腾作用中起着关键作用。植物从茎储存中蒸发水分。由于蒸腾速率高于土壤通过根、茎和树枝的最大补给速率，地上储存量耗尽，气孔响应负木质部水势而接近限制蒸腾。这些水力限制在潮湿和干燥条件下控制森林生态系统的蒸腾作用。目前的地表模型并不代表树木的地上储存量。这些模型通过直接将气孔导度与土壤湿度联系起来，对蒸腾作用施加水资源限制。由于土壤湿度的日常动态与树木木质部储水的动态非常不同，当前的方法导致与观察到的蒸腾动态的偏差。因此，地表模型在潜热通量模拟中产生了典型的日内误差模式。这项研究将开发一个框架来解决此类树木流体动力学问题，该框架可以纳入水文、地表和地球系统模型中，以取代目前气孔导度和土壤湿度之间的经验联系。 FETCH2 模型解析了树干中的水流和水势，并将气孔导度与木质部中的水势实际联系起来，而土壤中的水可用性为水动力系统提供了底部边界条件。来自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 模拟将与森林地块中树液通量和茎水储存的观测结果以及没有水动力模块的地表模型模拟结果进行比较。大气、水文和地球系统模型中气孔导度和蒸腾模拟的改进将推广到土壤湿度、地表能量预算和总初级生产力等相关变量。通过综合森林冠层结构、树木蓄水和水力策略对气孔导度的影响，这项研究可能会影响许多类型和类别的气候、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.