CO2 flux from tundra lichen, moss, and tussock, Council, Alaska: Assessment of spatial representativeness

CO2 flux-measurement in dominant tundra vegetation on the Seward Peninsula of Alaska was examined for spatial representativeness, using a manual chamber system. In order to assess the representativeness of CO2 flux, a 40 m * 40 m (5-m interval; 81 total points) plot was used in June, August, and September of 2011. Average CO2 fluxes in lichen, moss, and tussock tundra were 3.4 +- 2.7, 4.5 +- 2.9, and 7.2 +- 5.7 mgCO2/m2/m during growing season, respectively, suggesting that tussock tundra is a significant CO2 source, especially considering the wide distribution of tussock tundra in the circumpolar region. Further, soil temperature, rather than soil moisture, held the key role in regulating CO2 flux at the study site: CO2 flux from tussock increased linearly as soil temperature increased, while the flux from lichen and moss followed soil temperature nearly exponentially, reflecting differences in surface area covered by the chamber system. Regarding sample size, the 81 total sampling points over June, August, and September satisfy an experimental average that falls within +-10% of full sample average, with a 95% confidence level. However, the number of sampling points for each variety of vegetation during each month must provide at least +-20%, with an 80% confidence level. In order to overcome the logistical constraints, we were required to identify the site's characteristics with a manual chamber system over a 40 m * 40 m plot and to subsequently employ an automated chamber for spatiotemporal representativeness.本研究针对阿拉斯加州苏厄德半岛优势苔原植被的二氧化碳通量展开空间代表性分析，采用手动箱式测量系统开展观测。为评估二氧化碳通量的代表性，研究团队于2011年6月、8月及9月，在一块40米×40米的样地（采样间隔5米，共设81个采样点）进行观测。生长季内，地衣、苔藓与丛状苔原的平均二氧化碳通量分别为3.4±2.7、4.5±2.9及7.2±5.7 mgCO₂/(m²·m)，结果显示丛状苔原是重要的二氧化碳源，考虑到其在环极地区的广泛分布，这一结论尤为关键。此外，本研究样地中调控二氧化碳通量的关键因素为土壤温度而非土壤湿度：丛状苔原的二氧化碳通量随土壤温度升高呈线性增长，而地衣与苔藓的通量则随土壤温度变化近似呈指数关系，这一现象反映了手动箱式测量系统覆盖的地表面积存在差异。关于采样规模，2011年6月、8月及9月的81个总采样点，可满足在95%置信水平下，实验平均值落在全样本平均值±10%范围内的要求。然而，针对每类植被在每个月的采样点数，需在80%置信水平下将误差控制在±20%以内。为克服后勤保障限制，本研究需先通过手动箱式系统对40米×40米样地的站点特征进行测定，后续再采用自动箱式系统开展时空代表性研究。