Linking hydraulic traits to tropical forest function in a size-structured and trait-driven model (TFS v.1-Hydro)
Linking hydraulic traits to tropical forest function in a size-structured and trait-driven model (TFS v.1-Hydro)
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DOI：
10.5194/gmd-9-4227-2016
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发表时间：
2016-11-24
影响因子：
5.1
通讯作者：
Meir, Patrick
中科院分区：
文献类型：
--
作者：
Christoffersen, Bradley O.;Gloor, Manuel;Meir, Patrick
基于启发式水分胁迫功能的森林生态系统模型很难预测热带森林对干旱的反应，部分原因是它们没有捕捉到在热带森林中观察到的水力特征的多样性（包括树木大小的变化）。我们开发了一种连续多孔介质方法来模拟植物水力学，其中本构方程的所有参数都是生物可解释和可测量的植物水力特性(例如，膨胀损失点pi(tlp)，体积弹性模量epsilon，水力电容C-ft，木质部水力电导率k(s,max)，木质部（P-50,P-x）和气孔（P-50,P-gs）在50%电导率损失时的水势，以及叶：边材面积比Lambda（l): Lambda(s)）。我们将该植物水力学模型嵌入到一个性状森林模拟器（TFS）中，该模拟器模拟了单个树木的光环境及其上边界条件（蒸腾），并提供了一种参数化个体间水力特性变化的方法。我们综合文献和现有数据库，将所有水力性状参数化为茎和叶性状的函数，包括木材密度（WD）、每面积叶质量（LMA）和光合能力（a (max)），并根据观测到的茎和叶水势以及林分尺度液通量的日变化和季节变化评估耦合模型（称为TFS v.1-Hydro）的预测结果。我们的水力性状综合揭示了叶片和木质部水力性状之间的协调关系，并且大多数水力性状与更容易测量的植物性状之间的关系具有统计学意义。TFS v.1-Hydro利用从这一综合中获得的最丰富的经验性状-性状关系，成功捕获了由于树木大小和光照环境的增加而导致的叶片和茎水势的个体变化，其中水力结构和植物性状的模型表示分别对模型预测的保真度施加了一级和二级控制。植物水力学模型对生态系统蒸腾总量的模拟有了实质性的改进。强调了植物水力学建模特征范式的不确定性和局限性。
Forest ecosystem models based on heuristic water stress functions poorly predict tropical forest response to drought partly because they do not capture the diversity of hydraulic traits (including variation in tree size) observed in tropical forests. We developed a continuous porous media approach to modeling plant hydraulics in which all parameters of the constitutive equations are biologically interpretable and measurable plant hydraulic traits (e.g., turgor loss point pi(tlp), bulk elastic modulus epsilon, hydraulic capacitance C-ft, xylem hydraulic conductivity k(s,max), water potential at 50% loss of conductivity for both xylem (P-50,P-x) and stomata (P-50,P-gs), and the leaf : sapwood area ratio Lambda(l) : Lambda(s)). We embedded this plant hydraulics model within a trait forest simulator (TFS) that models light environments of individual trees and their upper boundary conditions (transpiration), as well as providing a means for parameterizing variation in hydraulic traits among individuals. We synthesized literature and existing databases to parameterize all hydraulic traits as a function of stem and leaf traits, including wood density (WD), leaf mass per area (LMA), and photosynthetic capacity (A(max)), and evaluated the coupled model (called TFS v.1-Hydro) predictions, against observed diurnal and seasonal variability in stem and leaf water potential as well as stand-scaled sap flux.Our hydraulic trait synthesis revealed coordination among leaf and xylem hydraulic traits and statistically significant relationships of most hydraulic traits with more easily measured plant traits. Using the most informative empirical trait-trait relationships derived from this synthesis, TFS v.1-Hydro successfully captured individual variation in leaf and stem water potential due to increasing tree size and light environment, with model representation of hydraulic architecture and plant traits exerting primary and secondary controls, respectively, on the fidelity of model predictions. The plant hydraulics model made substantial improvements to simulations of total ecosystem transpiration. Remaining uncertainties and limitations of the trait paradigm for plant hydraulics modeling are highlighted.