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

近年来北极灌木扩张的气候驱动因素和景观尺度模式已经得到了很好的理解，而控制灌木补充和生长的生物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生物地球物理特征可能解释有文献记载的通过广泛的永久冻土退化和地下流量增加的潜在过程，从大型北极河流输出的碳和营养物质增加。此外，利用遥感，高灌木的出现可以作为跨空间和时间的地下性质的易于测量的代用品。如果我们的观察结果在其他河流环境中也是正确的，那么这些信息有可能提供新的水文、永久冻土和生物过程见解，以补充关于增加北极灌木覆盖的大量文献。北极冻土带差异径流的初步测量将沿河岸走廊的高灌木与失去的河流段（下游流量减少的河流）联系起来，而获得或维持的河流段（下游流量增加）则缺乏高灌木。该奖项将支持测量，以测试塔里克（永久冻土）的形成和向下的水文梯度是否创造了一个有利于灌木补充和生长的生物地球化学地下环境，这反过来又导致高灌木分布模式与失去的河流流域一致。该团队将测量具有不同坡度、河床形态和基质的额外溪流，以检验他们初步观察的统计意义，即高灌木表明溪流正在消失，并将测量范围扩大到包括灌木高度、覆盖度、生物量、叶面积指数（LAI）、永久冻土和土壤微生物群落。该奖项将支持三位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，为研究灌木、永久冻土、水文和微生物学之间的联系过程奠定基础。这项工作的结果将直接分发给土地管理部门和私人组织。

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.