Stomatal conductance, one of the major plant physiological controls within NH₃ biosphere–atmosphere exchange models, is commonly estimated from semi‐empirical multiplicative schemes or simple light‐ and temperature‐response functions. However, due to their inherent parameterization on meteorological proxy variables, instead of a direct measure of stomatal opening, they are unfit for the use in climate change scenarios and of limited value for interpreting field‐scale measurements. Alternatives based on H₂O flux measurements suffer from uncertainties in the partitioning of evapotranspiration at humid sites, as well as a potential decoupling of transpiration from stomatal opening in the presence of hygroscopic particles on leaf surfaces. We argue that these problems may be avoided by directly deriving stomatal conductance from CO₂ fluxes instead. We reanalysed a data set of NH₃ flux measurements based on CO₂‐derived stomatal conductance, confirming the hypothesis that the increasing relevance of stomatal exchange with the onset of vegetation activity caused a rapid decrease of observed NH₃ deposition velocities. Finally, we argue that developing more mechanistic representations of NH₃ biosphere–atmosphere exchange can be of great benefit in many applications. These range from model‐based flux partitioning, over deposition monitoring using low‐cost samplers and inferential modelling, to a direct response of NH₃ exchange to climate change.

中文翻译：

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迈向NH3-CO2生物圈-大气交换模型的耦合范例。

气孔导度是NH ₃生物圈-大气交换模型中的主要植物生理控制之一，通常是根据半经验乘法方案或简单的光响应和温度响应函数来估算的。但是，由于它们固有的对气象代用变量的参数化，而不是直接测量气孔开度，因此它们不适合在气候变化场景中使用，并且在解释实地规模测量方面价值有限。基于H _2的替代方案O流量的测量在湿润地区的蒸散量分配中存在不确定性，并且在叶片表面存在吸湿性颗粒的情况下，蒸腾作用可能与气孔开口解耦。我们认为可以通过直接从CO ₂通量推导气孔导度来避免这些问题。我们重新分析了基于CO ₂衍生的气孔导度的NH ₃通量测量数据集，证实了以下假设：随着植被活动的开始，气孔交换的相关性增加，导致观测到的NH ₃沉积速度迅速降低。最后，我们认为开发更多的NH ₃机理表示生物圈-大气交换在许多应用中都可以带来巨大的好处。这些范围包括基于模型的流量分配，使用低成本采样器进行沉积监测和推论建模，以及NH ₃交换对气候变化的直接响应。