Vegetation structure and function are key design choices in terrestrial models that affect the relationship between carbon uptake and environmental drivers. Here, we investigate how representing canopy vertical structure in a terrestrial biosphere model—that is, micrometeorological, leaf area, and leaf water profiles—influences carbon uptake at five U.S. temperate deciduous forest sites in July. Specifically, we test whether the interannual variability (IAV) of gross primary productivity (GPP) responds differently to four abiotic environmental drivers—air temperature, relative humidity, incoming shortwave radiation, and soil moisture—using either a Community Land Model multilayer canopy model (CLM‐ml) or a big‐leaf model (CLM4.5/CLM5). We conclude that vertical leaf area and microclimatic profiles (temperature, humidity, and wind) do not impact GPP IAV compared to a single‐layer model when plant hydraulics is excluded. However, with a mechanistic representation of plant hydraulics there is vertically varying water stress in CLM‐ml, and the sensitivity of carbon uptake to particular climate variables changes with height, resulting in dampened canopy‐scale GPP IAV relative to CLM4.5. Dampening is due to both a reduced dependence on soil moisture and opposing climatic forcing on different leaf layers. Such dampening is not evident in the single‐layer representation of plant hydraulic water stress implemented in the recently released CLM5. Overall, both model representations of the canopy fail to accurately simulate observed GPP IAV and this may be related by their inability to capture the upper range of observed hourly GPP and diffuse light‐GPP relationships that cannot be resolved by canopy structure alone.

中文翻译：

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冠层微环境垂直非均质性对温带落叶林碳吸收年际变化的影响

植被结构和功能是影响碳吸收和环境驱动因素之间关系的陆地模型的关键设计选择。在这里，我们研究了如何在陆地生物圈模型中表示冠层垂直结构（即微气象学，叶面积和叶水剖面）如何影响7月美国五个温带落叶林站点的碳吸收。具体来说，我们使用“社区土地模型”多层冠层模型（），测试了总初级生产力（GPP）的年际变化（IAV）对四种非生物环境驱动因素（气温，相对湿度，传入的短波辐射和土壤湿度）的反应是否不同（ CLM-ml）或大叶模型（CLM4.5 / CLM5）。我们得出的结论是，垂直叶面积和微气候特征（温度，湿度，如果不包括工厂液压系统，则与单层模型相比，风和风不会对GPP IAV产生影响。但是，用植物液压的机械表示法，CLM-ml中的水分胁迫在垂直方向上发生变化，并且碳吸收对特定气候变量的敏感性随高度而变化，从而导致相对于CLM4.5的冠层尺度GPP IAV衰减。潮湿是由于减少了对土壤水分的依赖以及不同叶层上相反的气候强迫。在最近发布的CLM5中实现的工厂液压水压力的单层表示中，这种阻尼并不明显。总体，