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Direct response of tree growth to soil water and its implications for terrestrial carbon cycle modelling
Global Change Biology ( IF 10.8 ) Pub Date : 2020-10-16 , DOI: 10.1111/gcb.15397 Annemarie H. Eckes‐Shephard 1 , Egor Tiavlovsky 2 , Yizhao Chen 1 , Patrick Fonti 3 , Andrew D. Friend 1
Global Change Biology ( IF 10.8 ) Pub Date : 2020-10-16 , DOI: 10.1111/gcb.15397 Annemarie H. Eckes‐Shephard 1 , Egor Tiavlovsky 2 , Yizhao Chen 1 , Patrick Fonti 3 , Andrew D. Friend 1
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Wood growth constitutes the main process for long‐term atmospheric carbon sequestration in vegetation. However, our understanding of the process of wood growth and its response to environmental drivers is limited. Current dynamic global vegetation models (DGVMs) are mainly photosynthesis‐driven and thus do not explicitly include a direct environmental effect on tree growth. However, physiological evidence suggests that, to realistically model vegetation carbon allocation under increased climatic stressors, it is crucial to treat growth responses independently from photosynthesis. A plausible growth response function suitable for global simulations in DGVMs has been lacking. Here, we present the first soil water‐growth response function and parameter range for deciduous and evergreen conifers. The response curve was calibrated against European larch and Norway spruce in a dry temperate forest in the Swiss Alps. We present a new data‐driven approach based on a combination of tree ring width (TRW) records, growing season length and simulated subdaily soil hydrology to parameterize ring width increment simulations. We found that a simple linear response function, with an intercept at zero moisture stress, used in growth simulations reproduced 62.3% and 59.4% of observed TRW variability for larch and spruce respectively and, importantly, the response function slope was much steeper than literature values for soil moisture effects on photosynthesis and stomatal conductance. Specifically, we found stem growth stops at soil moisture potentials of −0.47 MPa for larch and −0.66 MPa for spruce, whereas photosynthesis in trees continues down to −1.2 MPa or lower, depending on species and measurement method. These results are strong evidence that the response functions of source and sink processes are indeed very different in trees, and need to be considered separately to correctly assess vegetation responses to environmental change. The results provide a parameterization for the explicit representation of growth responses to soil water in vegetation models.
中文翻译：
树木生长对土壤水分的直接响应及其对陆地碳循环模型的影响
木材生长是植被长期保持大气中碳固存的主要过程。但是，我们对木材生长过程及其对环境驱动因素的反应的理解是有限的。当前的动态全球植被模型（DGVM）主要由光合作用驱动，因此没有明确包括对树木生长的直接环境影响。然而，生理证据表明，要在增加的气候胁迫条件下真实地模拟植被碳分配，独立于光合作用处理生长响应至关重要。缺乏适用于DGVM中全局仿真的合理的增长响应函数。在这里，我们介绍了落叶和常绿针叶树的第一个土壤水分生长响应函数和参数范围。针对欧洲落叶松和挪威云杉在瑞士阿尔卑斯山的干燥温带森林中校准了响应曲线。我们提出了一种新的数据驱动方法，该方法基于树环宽度（TRW）记录，生长季节长度和模拟的次日土壤水文学的组合来参数化环宽度增量模拟。我们发现，用于生长模拟的简单线性响应函数在零水分应力下具有截距，分别再现了落叶松和云杉的观察到的TRW变异性的62.3％和59.4％，重要的是，响应函数斜率比文献值陡得多土壤水分对光合作用和气孔导度的影响 具体来说，我们发现在落叶松的土壤湿度为-0.47 MPa，云杉的土壤湿度为-0.66 MPa时，茎的生长停止了，而树木的光合作用则持续降低至-1.2 MPa或更低，具体取决于种类和测量方法。这些结果是有力的证据，表明树木中源和汇过程的响应功能确实有很大不同，因此需要单独考虑以正确评估植被对环境变化的响应。结果为植被模型中对土壤水的生长响应的明确表示提供了参数化。
更新日期：2020-12-09
中文翻译：
树木生长对土壤水分的直接响应及其对陆地碳循环模型的影响
木材生长是植被长期保持大气中碳固存的主要过程。但是，我们对木材生长过程及其对环境驱动因素的反应的理解是有限的。当前的动态全球植被模型（DGVM）主要由光合作用驱动，因此没有明确包括对树木生长的直接环境影响。然而，生理证据表明，要在增加的气候胁迫条件下真实地模拟植被碳分配，独立于光合作用处理生长响应至关重要。缺乏适用于DGVM中全局仿真的合理的增长响应函数。在这里，我们介绍了落叶和常绿针叶树的第一个土壤水分生长响应函数和参数范围。针对欧洲落叶松和挪威云杉在瑞士阿尔卑斯山的干燥温带森林中校准了响应曲线。我们提出了一种新的数据驱动方法，该方法基于树环宽度（TRW）记录，生长季节长度和模拟的次日土壤水文学的组合来参数化环宽度增量模拟。我们发现，用于生长模拟的简单线性响应函数在零水分应力下具有截距，分别再现了落叶松和云杉的观察到的TRW变异性的62.3％和59.4％，重要的是，响应函数斜率比文献值陡得多土壤水分对光合作用和气孔导度的影响 具体来说，我们发现在落叶松的土壤湿度为-0.47 MPa，云杉的土壤湿度为-0.66 MPa时，茎的生长停止了，而树木的光合作用则持续降低至-1.2 MPa或更低，具体取决于种类和测量方法。这些结果是有力的证据，表明树木中源和汇过程的响应功能确实有很大不同，因此需要单独考虑以正确评估植被对环境变化的响应。结果为植被模型中对土壤水的生长响应的明确表示提供了参数化。
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