Climate change in the Arctic is leading to shifts in vegetation communities, permafrost degradation and alteration of tundra surface–atmosphere energy and carbon (C) fluxes, among other changes. However, year-round C and energy flux measurements at high-latitude sites remain rare. This poses a challenge for evaluating the impacts of climate change on Arctic tundra ecosystems and for developing and evaluating process-based models, which may be used to predict regional and global energy and C feedbacks to the climate system. Our study used 14 years of seasonal eddy covariance (EC) measurements of carbon dioxide (CO₂), water and energy fluxes, and winter soil chamber CO₂ flux measurements at a dwarf-shrub tundra site underlain by continuous permafrost in Canada’s Southern Arctic ecozone to evaluate the incorporation of shrub plant functional types (PFTs) in the Canadian Land Surface Scheme Including Biogeochemical Cycles (CLASSIC), the land surface component of the Canadian Earth System Model. In addition to new PFTs, a modification of the efficiency with which water evaporates from the ground surface was applied. This modification addressed a high ground evaporation bias that reduced model performance when soils became very dry, limited heat flow into the ground, and reduced plant productivity through water stress effects. Compared to the grass and tree PFTs previously used by CLASSIC to represent the vegetation in Arctic permafrost-affected regions, simulations with the new shrub PFTs better capture the physical and biogeochemical impact of shrubs on the magnitude and seasonality of energy and CO₂ fluxes at the dwarf-shrub tundra evaluation site. The revised model, however, tends to overestimate gross primary productivity, particularly in spring, and overestimated late-winter CO₂ emissions. On average, annual net ecosystem CO₂ exchange was positive for all simulations, suggesting this site was a net CO₂ source of 18 ± 4 g C m⁻² yr⁻¹ using shrub PFTs, 15 ± 6 g C m⁻² yr⁻¹ using grass PFTs, and 25 ± 5 g C m⁻² yr⁻¹ using tree PFTs. These results highlight the importance of using appropriate PFTs in process-based models to simulate current and future Arctic surface–atmosphere interactions.

中文翻译：

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使用包括生物地球化学循环的加拿大陆地表面计划 (CLASSIC) 模拟加拿大低北极地区的灌木及其能量和二氧化碳通量

北极的气候变化正在导致植被群落的变化、永久冻土退化和苔原地表-大气能量和碳 (C) 通量的改变，以及其他变化。然而，在高纬度地区的全年 C 和能量通量测量仍然很少见。这对评估气候变化对北极苔原生态系统的影响以及开发和评估基于过程的模型提出了挑战，这些模型可用于预测区域和全球能源和碳对气候系统的反馈。我们的研究使用了 14 年的二氧化碳 (CO ₂ )、水和能量通量以及冬季土壤室 CO ₂的季节性涡旋协方差 (EC) 测量值在加拿大南部北极生态区连续多年冻土之下的矮灌木苔原场地进行通量测量，以评估灌木植物功能类型 (PFT) 在包括生物地球化学循环 (CLASSIC) 的加拿大陆地表面计划中的纳入，加拿大陆地表面组成部分地球系统模型。除了新的 PFT 之外，还对水从地表蒸发的效率进行了修改。这一修改解决了地面蒸发偏高的问题，当土壤变得非常干燥时，该偏差会降低模型性能，限制热量流入地面，并通过水分胁迫效应降低植物生产力。与之前 CLASSIC 用来代表北极永久冻土影响地区植被的草和树 PFT 相比，₂矮灌木苔原评估地点的通量。然而，修订后的模型往往高估了初级生产力总额，尤其是在春季，并高估了晚冬的 CO ₂排放量。平均而言，年度净生态系统 CO ₂交换对于所有模拟都是正值，表明该站点是使用灌木 PFT的 18 ±  4 g C m ^-2  yr ^-1净 CO ₂源 ，15  ±  6 g C m ^-2  yr ^{- 1}使用草 PFT，和 25  ±  5 g C m ^-2  yr ^-1使用树 PFT。这些结果强调了在基于过程的模型中使用适当的 PFT 来模拟当前和未来北极表面 - 大气相互作用的重要性。