Doctoral Dissertation Research: Mechanisms of shrubification in a changing Arctic

北极苔原由各种植物组成，包括苔藓、草、开花草本植物和木本灌木，它们保护着大量冻结在北极土壤中的地下碳。随着北极变暖，灌木正在取代其他植物物种，改变碳循环。这种转变对北极土壤碳的驱动机制和影响尚不清楚。这项研究通过测试三种可能解释灌木在温暖气候中的竞争优势的假设机制来探索这种转变背后的原因。这些假设包括光合作用增加，对变暖提供的营养物质的反应更大，以及从更长的生长季节中获得更大的收益。该项目采用数学模型，实地实验，并在阿拉斯加苔原景观灌木调查，以测试这些机制。这项研究将提高我们对迅速变暖的北极地区植被变化和碳循环的理解。结果将通过一个面向公众的互动网站分享，并纳入K-12和大学课程。这项研究的目标是确定气候变化使灌木在异质性北极生态系统中占主导地位的机制。该研究方法结合了基于特征的模型的竞争冻原物种通知与现场实验操作的温度，养分供应和融雪日期。这三个环境因素的全析因实验操作将使研究人员能够解开假设机制对灌木化的相对贡献。由于不同的机制可能会在广阔而多变的北极景观中推动灌木化，研究人员将在阿拉斯加北坡的自然环境梯度中对灌木种群和变暖实验进行调查。通过澄清在当地和景观尺度上驱动灌木化的机制，这项研究将有助于未来在地球系统模型中准确地代表北极灌木的努力，并减少气候变化预测的不确定性。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

Arctic tundra is made up of a variety of plants, including mosses, grasses, flowering herbs, and woody shrubs, which guard vast quantities of underground carbon frozen in Arctic soils. As the Arctic warms, shrubs are replacing other plant species, altering the carbon cycle. The driving mechanisms and impacts of this shift on Arctic soil carbon remains unclear. This research explores the reasons behind this shift by testing three hypothesized mechanisms that may explain shrubs' competitive advantage in a warmer climate. These hypotheses include increased photosynthesis, greater response to nutrients made available by warming, and larger gains from longer growing seasons. The project employs mathematical models, field experiments, and surveys of shrubs across Alaskan tundra landscapes to test these mechanisms. This research will improve our understanding of vegetation changes and carbon cycling in the rapidly warming Arctic. Results will be shared via a public-facing interactive website and incorporated into K-12 and college courses. The goal of this research is to determine the mechanisms by which changing climate enables shrub dominance in heterogeneous Arctic ecosystems. The research approach combines trait-based models of competing tundra species informed with field experimental manipulations of temperature, nutrient availability, and snowmelt date. The full factorial experimental manipulation of these three environmental factors will allow researchers to untangle the relative contribution of the hypothesized mechanisms to shrubification. Since different mechanisms may be driving shrubification across vast and variable Arctic landscapes, researchers will conduct surveys of shrub populations and warming experiments across natural environmental gradients on the North Slope of Alaska. By clarifying mechanisms driving shrubification at local and landscape scales, this research will aid future efforts to represent Arctic shrubs accurately in Earth System Models and reduce uncertainties in climate change projections.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.