Modeling stomatal conductance in the earth system: linking leaf water-use efficiency and water transport along the soil-plant-atmosphere continuum
Modeling stomatal conductance in the earth system: linking leaf water-use efficiency and water transport along the soil-plant-atmosphere continuum
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DOI：
10.5194/gmd-7-2193-2014
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发表时间：
2014-01-01
影响因子：
5.1
通讯作者：
Oleson, K. W.
中科院分区：
文献类型：
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作者：
Bonan, G. B.;Williams, M.;Oleson, K. W.
地球系统模型中常采用Ball-Berry气孔导度模型来模拟蒸散的生物调节。然而，气孔导度(g(S))与水汽压差(D-S)和土壤水分的关系必须用经验参数表示。我们评估了社区土地模型4.5版(CLM4.5)中使用的Ball-Berry模型和一个替代的气孔导度模型，该模型将叶片气体交换、植物水力约束和土壤-植物-大气连续体(SPA)联系起来。SPA模型通过以下方式对气孔导度进行数值模拟：(1)优化单位失水的光合碳增益；(2)限制气孔开度，以防止叶片水势降至临界最小值以下。我们评估了两种优化算法：固有水分利用效率(Delta A(N)/Delta g(S)，气孔张开的边际碳增益)和水分利用效率(Delta A(N)/Delta E-L，蒸腾水分损失的边际碳增益)。我们在多层植物冠层模型中实现了气孔模型，以解决冠层内气体交换、叶水势和植物水力的剖面，并使用叶片分析、6个森林站点的涡动协方差通量和参数敏感性分析对模拟结果进行了评估。气孔模型之间的主要差异与土壤水分胁迫和水汽压亏缺反应有关。在没有土壤水分胁迫的情况下，SPA气孔模型在通量塔模拟中的性能与CLM BallBerry模型相当或略好，但在有土壤水分胁迫时显著优于CLM Ball-Berry模型。G(S)对土壤水分的函数依赖性来自于沿土壤-叶片途径的水分流动，而不是像在CLM Ball-Berry模型中那样是先验的。在Delta A(N)/Delta E-1优化中出现了类似的g(S)对D-S的函数依赖，但Delta A(N)/Delta g(S)优化没有出现类似的函数依赖。两个参数(气孔效率和根系导水率)使SPA气孔模型的误差最小。优化的临界气孔效率(L)给出的结果与叶片性状数据集中的最大A(N)和g(S)之间的关系是一致的，并与Ball-Berry模型的斜率(g(1))有关。根的导水率(R-r(*))与文献调查的估计值一致。SPA气孔模型中包含的两个核心概念，即植物在调节气孔导度方面既考虑到水分利用效率，又考虑到水力安全性，暗示了一种最优植物策略的概念，并提供了可检验的模型假设，而不是对植物行为的经验描述。
The Ball-Berry stomatal conductance model is commonly used in earth system models to simulate biotic regulation of evapotranspiration. However, the dependence of stomatal conductance (g(s)) on vapor pressure deficit (D-s) and soil moisture must be empirically parameterized. We evaluated the Ball-Berry model used in the Community Land Model version 4.5 (CLM4.5) and an alternative stomatal conductance model that links leaf gas exchange, plant hydraulic constraints, and the soil-plant-atmosphere continuum (SPA). The SPA model simulates stomatal conductance numerically by (1) optimizing photosynthetic carbon gain per unit water loss while (2) constraining stomatal opening to prevent leaf water potential from dropping below a critical minimum. We evaluated two optimization algorithms: intrinsic water-use efficiency (Delta A(n)/Delta g(s), the marginal carbon gain of stomatal opening) and water-use efficiency (Delta A(n)/Delta E-l, the marginal carbon gain of transpiration water loss). We implemented the stomatal models in a multi-layer plant canopy model to resolve profiles of gas exchange, leaf water potential, and plant hydraulics within the canopy, and evaluated the simulations using leaf analyses, eddy covariance fluxes at six forest sites, and parameter sensitivity analyses. The primary differences among stomatal models relate to soil moisture stress and vapor pressure deficit responses. Without soil moisture stress, the performance of the SPA stomatal model was comparable to or slightly better than the CLM BallBerry model in flux tower simulations, but was significantly better than the CLM Ball-Berry model when there was soil moisture stress. Functional dependence of g(s) on soil moisture emerged from water flow along the soil-to-leaf pathway rather than being imposed a priori, as in the CLM Ball-Berry model. Similar functional dependence of g(s) on D-s emerged from the Delta A(n)/Delta E-1 optimization, but not the Delta A(n)/Delta g(s) optimization. Two parameters (stomatal efficiency and root hydraulic conductivity) minimized errors with the SPA stomatal model. The critical stomatal efficiency for optimization (l) gave results consistent with relationships between maximum A(n) and g(s) seen in leaf trait data sets and is related to the slope (g(1)) of the Ball-Berry model. Root hydraulic conductivity (R-r(*)) was consistent with estimates from literature surveys. The two central concepts embodied in the SPA stomatal model, that plants account for both water-use efficiency and for hydraulic safety in regulating stomatal conductance, imply a notion of optimal plant strategies and provide testable model hypotheses, rather than empirical descriptions of plant behavior.