Plant hydraulic transport controls transpiration sensitivity to soil water stress
Plant hydraulic transport controls transpiration sensitivity to soil water stress
复制标题
DOI：
10.5194/hess-25-4259-2021
复制
发表时间：
2021
影响因子：
6.3
通讯作者：
Brandon P. Sloan;S. Thompson;Xue Feng
中科院分区：
文献类型：
--
作者：
Brandon P. Sloan;S. Thompson;Xue Feng
抽象的。土壤水分胁迫下植物蒸腾作用的下调是预测全球水、碳和能量循环的重要机制。目前，许多陆地生物圈模型（TBMs）用土壤湿度的经验校正函数（β）来表示这种机制-这是一种方便的方法，但会产生很大的预测不确定性。为了减少这种不确定性，隧道掘进机越来越多地采用基于物理的工厂水力模型（PHM）。然而，PHM引入了额外的参数不确定性和计算需求。因此，了解PHM和β预测为何以及何时出现分歧将有助于在TBM中进行模型选择。在这里，我们使用一个最低限度的PHM表明，耦合土壤水分胁迫和大气水分需求的影响，导致由土壤-植物水力运输（电导）控制的蒸腾反应谱。在这一传输限制谱中，β作为具有无限传导性的PHMs的端元情景出现，完全解耦了土壤水分胁迫和大气水分需求对蒸腾作用的影响。因此，PHM和β蒸腾预测分歧最小的土壤-植物系统，具有低水力传导率（运输限制），经历了高变化的大气水分需求，并有适度的土壤水分供应的植物。我们测试这些最低限度的模型结果，使用AmeriFlux网站的陆面模型。在这个传输受限的站点，PHM下调方案优于β方案，因为其对大气水分需求变化的敏感性。基于这一观察，我们开发了一种新的“动态β”，随着大气水分需求的变化-一种方法，克服了现有的偏差β方案，并有可能简化现有的PHM参数化和实施。
Abstract. Plant transpiration downregulation in the presence of soil water stress is a critical mechanism for predicting global water, carbon, and energy cycles. Currently, many terrestrial biosphere models (TBMs) represent this mechanism with an empirical correction function (β) of soil moisture – a convenient approach that can produce large prediction uncertainties. To reduce this uncertainty, TBMs have increasingly incorporated physically based plant hydraulic models (PHMs). However, PHMs introduce additional parameter uncertainty and computational demands. Therefore, understanding why and when PHM and β predictions diverge would usefully inform model selection within TBMs. Here, we use a minimalist PHM to demonstrate that coupling the effects of soil water stress and atmospheric moisture demand leads to a spectrum of transpiration responses controlled by soil–plant hydraulic transport (conductance). Within this transport-limitation spectrum, β emerges as an end-member scenario of PHMs with infinite conductance, completely decoupling the effects of soil water stress and atmospheric moisture demand on transpiration. As a result, PHM and β transpiration predictions diverge most for soil–plant systems with low hydraulic conductance (transport-limited) that experience high variation in atmospheric moisture demand and have moderate soil moisture supply for plants. We test these minimalist model results by using a land surface model at an AmeriFlux site. At this transport-limited site, a PHM downregulation scheme outperforms the β scheme due to its sensitivity to variations in atmospheric moisture demand. Based on this observation, we develop a new “dynamic β” that varies with atmospheric moisture demand – an approach that overcomes existing biases within β schemes and has potential to simplify existing PHM parameterization and implementation.