Collaborative Research on Shrub-Snow Interactions in Alaskan and Canadian Tundra and their Potential for Positive Feedbacks to Vegetation and Climate Change

在北极，从苔原到以灌木为主的植被的广泛转变似乎正在进行中。冬季过程可能对这种苔原到灌木的转变至关重要，因为更大、更密的灌木能捕获更多的雪，这导致冬季土壤温度升高，并允许土壤有机质中氮的更大分解和动员。本研究项目的目标包括确定1)灌木冬季捕获的积雪是否促进了土壤中氮的生物学意义上的动员，2)灌木是否吸收了冬季动员的氮并增加了其生长，从而促进了灌木的扩张，3)灌木扩张是否促进了土壤中的碳损失，正如之前在已成为灌木主导的肥沃苔原地块中所看到的那样。4)了解灌木如何从冬季积雪中恢复过来，以及积雪如何影响它们的生长和死亡。这些目标将通过操纵积雪和灌木结构的现场实验，以及通过测量过去50年来灌木自然扩张的植物和土壤碳氮来实现。随着气候变暖，灌木的扩张可能是北极地区最普遍的陆地表面变化。我们的研究结果将有助于揭示灌木扩张的机制及其对生态系统碳氮循环的影响。北极和北方地区有大量的土壤碳储存，如果释放出来，可能会大大增加大气中的二氧化碳浓度，从而进一步加剧气候变暖。

In the Arctic, a widespread transition from tundra to shrub-dominated vegetation appears to be underway. Winter processes could be critical to this tundra-to-shrub transition, because larger and denser shrubs trap more snow, which leads to warmer soil temperatures during winter and could permit greater decomposition and mobilization of nitrogen from soil organic matter. The goals of this research project include determining 1) whether snow trapped by shrubs in winter promotes biologically significant mobilization of nitrogen from soil, 2) whether shrubs take up nitrogen mobilized during winter and increase their growth, thus promoting shrub expansion, 3) whether shrub expansion promotes carbon loss from soil, as has been seen previously in fertilized tundra plots that have become dominated by shrubs, and 4) understanding how shrubs recover from being laid down by winter snow, and how snow affects their growth and mortality. These goals will be addressed by field experiments manipulating snow accumulation and shrub architecture, and by measuring plant and soil carbon and nitrogen where shrubs have naturally expanded over the last 50 years. Expansion of shrubs may be the most widespread land surface change in the Arctic as climate warms. Our results will help reveal the mechanisms underlying shrub expansion and their consequences for ecosystem cycling of carbon and nitrogen. Arctic and boreal regions have large stores of soil carbon that could greatly increase atmospheric CO2 concentration if released, promoting further climate warming.