Riparian shrub expansion: Linkages to permafrost, hydrology and soil microbes

最近北极灌木扩张的气候驱动因素和植被规模模式已得到很好的理解，而控制灌木补充和生长的地球化学和物理机制仍不清楚。与溪流附近高大灌木扩张相关的地球物理特征可能解释记录在案的北极大型河流通过广泛的永久冻土退化和地下水流增加的基本过程增加碳和养分出口。此外，高灌木的出现可以作为一个容易测量的代理地下财产跨空间和时间使用遥感。如果我们的观察结果在其他河流环境中成立，则这些信息有可能提供新的水文，永久冻土和生物过程见解，以补充有关增加北极灌木覆盖的广泛文献。北极苔原差异径流的初步测量将沿着河岸走廊的高灌木与流失的河流部分联系起来（下游排放量减少的水流），而获得或保持流段（增加下游的排放量）缺乏高大的灌木。该奖项将支持测量，以测试是否形成一个talik（永冻无霜地面）和向下的水文梯度创造了一个有利于灌木补充和生长的地下地球化学环境，反过来，导致高灌木的分布格局与沿着流失河段相吻合。该团队将测量具有不同梯度、河床形态和基质的其他溪流，以测试其初步观察结果的统计学意义，即高灌木表明溪流正在流失，并将测量范围扩大到灌木高度、覆盖率、生物量、叶面积指数（LAI）、永久冻土和土壤微生物群落。该奖项将支持三名早期职业研究人员收集背景数据，使他们能够探索一个潜在的变革性想法，为研究连接灌木，永久冻土，水文和微生物学的过程奠定基础。这项工作的结果将直接分发给土地管理部门和私营组织。

The climatic drivers and landscape-scale patterns of recent Arctic shrub expansion are well understood, while the biogeochemical and physical mechanisms controlling shrub recruitment and growth remain unclear. The biogeophysical characteristics associated with tall shrub expansion near streams could potentially explain the documented increases in carbon and nutrient export from large Arctic rivers through the underlying processes of widespread permafrost degradation and increased subsurface flow. Additionally, occurrences of tall shrubs could be used as a readily measured proxy for subsurface properties both across space and time using remote sensing. If our observations hold true in other stream environments, the information has the potential to provide novel hydrological, permafrost, and biological process insights to complement the extensive literature on increasing Arctic shrub cover. Preliminary measurements of differential runoff in Arctic tundra link tall shrubs along riparian corridors to losing stream sections (streams with decreasing discharge downstream), whereas gaining or maintaining stream sections (increasing discharge downstream) lack tall shrubs.This award will support measurements to test whether the formation of a talik (permafrost-free ground) and a downward hydrologic gradient creates a biogeochemical subsurface environment that favors shrub recruitment and growth, which, in turn, results in patterns of tall shrub distribution coinciding along losing stream reaches. This team will measure additional streams with differing gradients, bed morphologies, and substrates to test the statistical significance of their preliminary observation that tall shrubs indicate losing streams, and to expand measurements to include shrub height, cover, biomass, Leaf Area Index (LAI), permafrost, and soil microbial communities. The award will support three early career researchers to gather background data to enable them to explore a potentially transformative idea to set the foundation to examine the processes linking shrubs, permafrost, hydrology and microbiology. The results of this work would be disseminated directly to land management and private organizations.