Liu Che, Hölttä Teemu, Tian Xianglin, Berninger Frank, Mäkelä Annikki
Faculty of Agriculture and Forestry, University of Helsinki, Helsinki, Finland.
Institute for Atmospheric and Earth System Research (INAR), University of Helsinki, Helsinki, Finland.
Front Plant Sci. 2020 Nov 6;11:579319. doi: 10.3389/fpls.2020.579319. eCollection 2020.
Age-related effects on whole-tree hydraulics are one of the key challenges to better predicting the production and growth of old-growth forests. Previous models have described the optimal state of stomatal behaviour, and field studies have implied on age/size-induced trends in tree ecophysiology related to hydraulics. On these bases, we built a Bayesian hierarchical model to link sap flow density and drivers of transpiration directly. The model included parameters with physiological meanings and accounted for variations in leaf-sapwood area ratio and the time lag between sap flow and transpiration. The model well-simulated the daily pattern of sap flow density and the variation between tree age groups. The results of parameterization show that (1) the usually higher stomatal conductance in young than old trees during mid-summer was mainly because the sap flow of young trees were more activated at low to medium light intensity, and (2) leaf-sapwood area ratio linearly decreased while time lag linearly increased with increasing tree height. Uncertainty partitioning and cross-validation, respectively, indicated a reliable and fairly robust parameter estimation. The model performance may be further improved by higher data quality and more process-based expressions of the internal dynamics of trees.
年龄对整树水力的影响是更好地预测老龄林产量和生长的关键挑战之一。先前的模型描述了气孔行为的最佳状态，并且实地研究暗示了与水力相关的树木生理生态学中与年龄/大小相关的趋势。基于这些，我们构建了一个贝叶斯层次模型，将液流密度与蒸腾驱动因素直接联系起来。该模型包含具有生理意义的参数，并考虑了叶-边材面积比的变化以及液流与蒸腾之间的时间滞后。该模型很好地模拟了液流密度的日变化模式以及不同树龄组之间的差异。参数化结果表明：（1）仲夏期间幼树气孔导度通常高于老树，主要是因为幼树的液流在低至中等光照强度下更活跃；（2）叶-边材面积比随树高增加呈线性下降，而时间滞后随树高增加呈线性增加。不确定性划分和交叉验证分别表明参数估计可靠且相当稳健。通过提高数据质量和更多基于过程的树木内部动态表达，模型性能可能会进一步提高。
