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，从冻土带到以灌木为主的植被的广泛过渡似乎正在进行中。冬季过程可能对冻土带到灌木的转变至关重要，因为更大、更密的灌木可以捕获更多的雪，这会导致冬季土壤温度更高，并可以更大程度地分解和动员土壤有机质中的氮。这项研究项目的目标包括：1)确定冬季被灌木困住的雪是否促进了从土壤中生物意义上的氮素的动员；2)灌木是否吸收了冬季动员的氮素并增加了它们的生长，从而促进了灌木的生长；3)灌木的扩张是否促进了土壤中的碳损失，正如以前在以灌木为主的肥沃苔原地块中所看到的那样；以及4)了解灌木如何从冬季的积雪中恢复过来，以及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田间实验来实现，并通过测量灌木在过去50年中自然扩张的植物和土壤碳和氮来实现。随着气候变暖，灌木的扩张可能是北极最广泛的陆地表面变化。我们的结果将有助于揭示灌木扩展的潜在机制及其对生态系统碳和氮循环的影响。北极和北方地区拥有大量的土壤碳储量，如果释放出来，可能会极大地增加大气中的二氧化碳浓度，从而进一步促进气候变暖。

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.