Effects of ice-wedge degradation and warming on Arctic tundra vegetation across a climatic gradient using a nitrogen-based model

Ice-wedge polygons in Arctic tundra landscapes influence hydrology, nutrients, thermal regimes, and vegetation. Ice-wedges are particularly vulnerable to warming events, and widespread degradation has been observed in recent decades. While increased vegetation growth is predicted to offset some of the nutrient losses from thawing Arctic soils, evolving Arctic vegetation carbon and nitrogen stocks are poorly understood. To explore effects of warming and ice-wedge degradation on Arctic vegetation, we used aboveground plant biomass data from stages of ice-wedge degradation at two northern Arctic tundra sites (Jago River and Prudhoe Bay, AK) to parameterize and test a nutrient-based, plant community and ecosystem model (ArcVeg) incorporating ice-wedges within a landscape for different Arctic tundra locations. Warming increased both aboveground and belowground biomass but introducing ice-wedge degradation led to shrub loss and a shift from terrestrial moss and shrub-dominated communities to aquatic moss and graminoid-dominated communities. In northern locations, degradation reduced vegetation C and N stocks due to biomass loss, whereas at the southern location, total plant C and N increased substantially due to moss proliferation. Model predictions suggest that ice-wedge degradation effects are accentuated under warming, and southern Arctic tundra aquatic moss proliferation may offset or even exceed biomass lost.

北极苔原景观中的冰楔多边形（ice-wedge polygons）会影响水文、养分、热状况以及植被。冰楔对变暖事件尤为敏感，近几十年来已观测到其广泛退化。尽管有预测称植被生长增强可抵消北极冻土融化带来的部分养分流失，但人们对北极植被碳氮储量的动态变化仍知之甚少。为探究变暖与冰楔退化对北极植被的影响，我们利用阿拉斯加北极北部两处苔原站点（亚戈河[Jago River]与普拉德霍湾[Prudhoe Bay]）不同冰楔退化阶段的地上植物生物量数据，对一款面向不同北极苔原区域、在景观尺度中纳入冰楔过程的基于养分的植物群落与生态系统模型（ArcVeg）进行参数化与验证。变暖可同时提升地上与地下生物量，但引入冰楔退化会导致灌木消亡，植被群落从陆生苔藓与灌木主导型转变为水生苔藓与禾草类主导型。在北部站点，冰楔退化因生物量损失降低了植被碳氮储量；而在南部站点，苔藓大量增殖使得植物总碳氮储量大幅提升。模型预测结果显示，变暖会加剧冰楔退化的影响，且北极南部苔原的水生苔藓增殖或可抵消甚至超过流失的生物量。