Tundra shrub effects on growing season energy and carbon dioxide exchange
Tundra shrub effects on growing season energy and carbon dioxide exchange
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苔原灌木对生长季节能量和二氧化碳交换的影响
DOI：
10.1088/1748-9326/aab863
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发表时间：
2018
影响因子：
6.7
通讯作者：
E. Humphreys
中科院分区：
文献类型：
--
作者：
P. Lafleur;E. Humphreys
增加灌木覆盖的北极苔原预计会影响生态系统-大气的碳和能量交换，从而反馈到气候系统，但很少有直接测量灌木苔原-大气交换，以证实预期。在这里，我们提出了能源和二氧化碳（CO2）通量测量使用涡度协方差技术在六个生长季节在三个密切位于加拿大的低北极苔原网站。这些地点以苔原灌木Betula glandulosa为主，但覆盖率从17%-60%不等，平均灌木高度从18-59厘米不等。覆盖率和高度最大的站点积雪量更大，但与一些预期相反，与其他两个站点相比，它具有类似的冬末积雪和积雪融化日期。融雪后立即潜热通量增加更缓慢，在这个网站相比，其他的。然而，在生长季节结束时，在累积潜热通量的网站之间的差异不大，这表明蒸散量并没有增加，更大的灌木覆盖。与此相反，较低的降雨量和土壤解冻较少的贡献较大的夏季感热通量在最大的灌木覆盖的网站，导致更大的总大气加热。净生态系统交换的CO2揭示了更大的灌木覆盖下，提高碳循环速率的潜力。春季CO2排放量最大的灌木覆盖率最高的网站，是夏季的CO2净吸收。季节性净汇CO2是2倍以上的网站与最大的灌木覆盖相比，网站与最少的灌木覆盖。这些结果在很大程度上同意的期望，生长季节反馈到大气中产生的灌木扩张在北极有可能是负的CO2通量，但湍流能量通量为正。
Increased shrub cover on the Arctic tundra is expected to impact ecosystem-atmosphere exchanges of carbon and energy resulting in feedbacks to the climate system, yet few direct measurements of shrub tundra-atmosphere exchanges are available to corroborate expectations. Here we present energy and carbon dioxide (CO2) fluxes measured using the eddy covariance technique over six growing seasons at three closely located tundra sites in Canada’s Low Arctic. The sites are dominated by the tundra shrub Betula glandulosa, but percent cover varies from 17%–60% and average shrub height ranges from 18–59 cm among sites. The site with greatest percent cover and height had greater snow accumulation, but contrary to some expectations, it had similar late-winter albedo and snow melt dates compared to the other two sites. Immediately after snowmelt latent heat fluxes increased more slowly at this site compared to the others. Yet by the end of the growing season there was little difference in cumulative latent heat flux among the sites, suggesting evapotranspiration was not increased with greater shrub cover. In contrast, lower albedo and less soil thaw contributed to greater summer sensible heat flux at the site with greatest shrub cover, resulting in greater total atmospheric heating. Net ecosystem exchange of CO2 revealed the potential for enhanced carbon cycling rates under greater shrub cover. Spring CO2 emissions were greatest at the site with greatest percent cover of shrubs, as was summer net uptake of CO2. The seasonal net sink for CO2 was ~2 times larger at the site with the greatest shrub cover compared to the site with the least shrub cover. These results largely agree with expectations that the growing season feedback to the atmosphere arising from shrub expansion in the Arctic has the potential to be negative for CO2 fluxes but positive for turbulent energy fluxes.