Generally, with increasing elevation, there is a corresponding decrease in annual mean air and soil temperatures, resulting in an overall decrease in ecosystem carbon dioxide (CO2) exchange. However, there is a lack of knowledge on the variations in CO2 exchange along elevation gradients in tundra ecosystems. Aiming to quantify CO2 exchange along elevation gradients in tundra ecosystems, we measured ecosystem CO2 exchange in the peak growing season along an elevation gradient (9–387 m above sea level, m.a.s.l) in an arctic heath tundra, West Greenland. We also performed an ex-situ incubation experiment based on soil samples collected along the elevation gradient, to assess the sensitivity of soil respiration to changes in temperature and soil moisture. There was no apparent temperature gradient along the elevation gradient, with the lowest air and soil temperatures at the second lowest elevation site (83 m). The lowest elevation site exhibited the highest net ecosystem exchange (NEE), ecosystem respiration (ER) and gross ecosystem production (GEP) rates, while the other three sites generally showed intercomparable CO2 exchange rates. Topography aspect-induced soil microclimate differences rather than the elevation were the primary drivers for the soil nutrient status and ecosystem CO2 exchange. The temperature sensitivity of soil respiration above 0 °C increased with elevation, while elevation did not regulate the temperature sensitivity below 0 °C or the moisture sensitivity. Soil total nitrogen, carbon, and ammonium contents were the controls of temperature sensitivity below 0 °C. Overall, our results emphasize the significance of considering elevation and microclimate when predicting the response of CO2 balance to climate change or upscaling to regional scales, particularly during the growing season. However, outside the growing season, other factors such as soil nutrient dynamics, play a more influential role in driving ecosystem CO2 fluxes. To accurately upscale or predict annual CO2 fluxes in arctic tundra regions, it is crucial to incorporate elevation-specific microclimate conditions into ecosystem models.

中文翻译：

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北极苔原生态系统中沿海拔梯度的土壤呼吸的二氧化碳交换和温度敏感性


一般来说，随着海拔的增加，年平均空气和土壤温度会相应降低，导致生态系统二氧化碳 （CO2） 交换总体减少。然而，对于苔原生态系统中 CO2 交换沿海拔梯度的变化缺乏了解。为了量化苔原生态系统中沿海拔梯度的 CO2 交换，我们测量了西格陵兰岛北极荒原苔原沿海拔梯度（海拔 9-387 m，m.a.s.l）的生态系统 CO2 交换。我们还根据沿海拔梯度收集的土壤样本进行了异位孵化实验，以评估土壤呼吸对温度和土壤水分变化的敏感性。沿海拔梯度没有明显的温度梯度，第二低海拔地点 （83 m） 的空气和土壤温度最低。海拔最低的地点表现出最高的生态系统净交换 （NEE）、生态系统呼吸 （ER） 和生态系统总生产 （GEP） 率，而其他三个地点通常表现出可比的 CO2 汇率。地形方面引起的土壤小气候差异而不是海拔是土壤养分状况和生态系统 CO2 交换的主要驱动因素。0 °C以上土壤呼吸的温度敏感性随海拔升高而增加，而海拔对0 °C以下的温度敏感性和水分敏感性没有调节。土壤全氮、全碳和铵态氮含量是 0 °C 以下温度敏感性的控制因素。 总体而言，我们的结果强调了在预测 CO2 平衡对气候变化的响应或扩大到区域尺度时考虑海拔和小气候的重要性，尤其是在生长季节。然而，在生长季节之外，土壤养分动态等其他因素在驱动生态系统 CO2 通量方面发挥着更重要的作用。为了准确放大或预测北极苔原地区的年度 CO2 通量，将特定海拔的小气候条件纳入生态系统模型至关重要。