Identifying Differences in Carbon Exchange among Arctic Ecosystem Types
Identifying Differences in Carbon Exchange among Arctic Ecosystem Types
复制标题
识别北极生态系统类型之间碳交换的差异
作者：
Mathew Williams;L. Street;M. Wijk;G. Shaver
我们的目的是确定在冻土带植被中，C循环对温度和光照的响应有多大的变化。2003年和2004年夏季，我们在阿拉斯加的一个小型北极集水区的23个地点使用了一个大室来测量碳交换。在每个地点，我们用遮荫布测定了C交换的光响应曲线，在生长季节两次。我们用数据拟合了一个简单的光合作用-辐照度，呼吸-温度模型，有四个参数。在给定测量不确定度的情况下，我们使用最大似然技术来确定每个光曲线的可接受参数空间。然后，我们探索了哪些地点和时间段具有共同的参数集——这是功能相似性的指示。我们发现需要七个不同的参数集来解释观测到的C通量在所有地点和时间段对温度和光照变化的响应。估算的最大光合速率（Pmax）的变化与立地叶面积指数（LAI）的测量值密切相关。作为北极冻土带的优势植被，毛毡苔原立地的特征可以用单一的参数集来描述，其Pmax为9.7 μmol m−2 s−1。相应地，灌丛苔原样地的LAI相似（平均值= 0.66）。非灌木林样地（如莎草和灌丛苔原）C动态参数（Pmax为9.7 ~ 25.7 μmol m−2 s−1）和LAI（0.6 ~ 2.0）的时空变化较大。优势非丛植被类型与某一特定参数集之间关系不明显。我们的研究结果表明，阿拉斯加北部酸性tussock苔原斜坡和山顶的C动态在生长旺季相对简单。而坡脚和水迹的LAI和C交换变化模式较多，不单纯与优势植被类型有关。
Our objective was to determine how varied is the response of C cycling to temperature and irradiance in tundra vegetation. We used a large chamber to measure C exchange at 23 locations within a small arctic catchment in Alaska during summer 2003 and 2004. At each location, we determined light response curves of C exchange using shade cloths, twice during a growing season. We used data to fit a simple photosynthesis-irradiance, respiration-temperature model, with four parameters. We used a maximum likelihood technique to determine the acceptable parameter space for each light curve, given measurement uncertainty. We then explored which sites and time periods had parameter sets in common—an indication of functional similarity. We found that seven distinct parameter sets were required to explain observed C flux responses to temperature and light variation at all sites and time periods. The variation in estimated maximum photosynthetic rate (Pmax) was strongly correlated with measurements of site leaf area index (LAI). The behavior of tussock tundra sites, the dominant vegetation of arctic tundra, could largely be described with a single parameter set, with a Pmax of 9.7 μmol m−2 s−1. Tussock tundra sites had, correspondingly, similar LAI (mean = 0.66). Non-tussock sites (for example, sedge and shrub tundras) had larger spatial and temporal variations in both C dynamic parameters (Pmax varying from 9.7–25.7 μmol m−2 s−1) and LAI (0.6–2.0). There were no clear relationships between dominant non-tussock vegetation types and a particular parameter set. Our results suggest that C dynamics of the acidic tussock tundra slopes and hilltops in northern Alaska are relatively simply described during the peak growing season. However, the foot-slopes and water tracks have more variable patterns of LAI and C exchange, not simply related to the dominant vegetation type.