Ecosystem-level Consequences of Mutualist Partner Choice in Alder across a Forest Successional Sequence in Interior Alaska

大多数固氮植物的根与土壤中的微生物形成共生关系。这包括使用植物糖来支持细菌，这些细菌将大气中的氮气捕获到植物的根部，以及支持真菌吸收土壤中的磷并将其转移到根部。这项研究提出，红桤木对两个伙伴的寄主选择的协调变化，使这种固氮物种能够在阿拉斯加内陆森林在火灾等干扰后随着时间的推移而持续发展，并调节这些森林的总体氮输入。细菌和真菌伴侣的身份和生理将在森林林分的年龄序列上进行测量。然后，在已施肥的林分中，微生物伴侣的变化将被记录下来，并用于帮助设计温室中一系列实验的伴侣选择。在温室中测量到的这些变化对氮的生理影响，将通过测量根瘤质量并结合测量的固氮季节性模式，缩小到生态系统中。本项目将首次在生态系统尺度上研究共生伙伴选择对固氮投入的影响。在阿拉斯加，了解原生植物和入侵植物对固氮的控制是一个具有基本科学价值的问题。在过去的150年里，阿拉斯加的入侵固氮树开始出现，桤木的范围已经大大扩展到北方/苔原边界。该项目与Bonanza Creek长期生态研究项目有着密切的联系，在该项目中，教育和公众宣传活动将包括这项研究的组成部分。本项目将培养1名博士后、2名研究生、6名本科生，研究方向为分子与生物信息学方法。

Most nitrogen-fixing plants form mutualistic relationships between their roots and microorganisms in the soil. This involves the use of plant sugars to support bacteria that capture atmospheric nitrogen gas into the roots of the plant, as well as to support fungi that take up soil phosphorus and also move it into the roots. This study proposes that coordinated changes in host selection for both partners by the tree, red alder, enables persistence of this nitrogen-fixing species as interior Alaskan forests develop over time after disturbances such as fire, and regulates the overall nitrogen inputs to these forests. The identity and physiology of the bacterial and fungal partners will be measured over an age sequence of forest stands. Then shifts in the microbial partners in stands that have been fertilized will be documented and used to help design partner choices for a set of experiments in a greenhouse. Physiological consequences of these shifts for nitrogen as measured in the greenhouse will be scaled back to the ecosystem using measurements of the mass of root nodules in combination with seasonal patterns of measured nitrogen fixation. This project will be the first to study the influence of mutualist partner choice on nitrogen fixation inputs at the ecosystem scale. Understanding controls over nitrogen fixation by native and invasive plants is a problem of fundamental scientific value in Alaska, where invasive nitrogen fixing trees are beginning to appear, and where the range of alders has expanded substantially across the boreal/tundra boundary over the past 150 years. The project has strong ties to the Bonanza Creek Long-term Ecological Research program, where education and public outreach activities will include components of this study. This project will also result in the training of one post-doctoral fellow, two graduate students, and six undergraduates in state-of-the art field, molecular and bioinformatics methods.