Modeling and Isotopes Link Mycorrhizal Fungi to Soil Carbon and Organic Nitrogen Use

北极地区的桦树、杨柳和其他灌木正在增加，以减少草和莎草的数量。这种增加的灌木覆盖可以增强冬季积雪的捕获，提高冬季土壤温度，加深夏季土壤解冻，并增加旧碳和氮的释放。从灌木到与灌木相关的共生真菌（称为菌根真菌）的糖通量增加，可以刺激解冻有机物的分解，并释放有机氮供植物吸收，这些有机氮以前被锁定了几千年。这种菌根介导的启动分解可能会影响碳平衡和养分供应进一步灌木生长。为了验证这一点，研究人员将在阿拉斯加北极地区进行长期实验，研究不同苔原类型的植物对变暖的反应。研究人员将使用自然水平的碳和氮同位素来跟踪新的土壤来源的有机氮进入灌木和相关的菌根真菌的结合。 随着新方法的发展，有机氮的使用可以在整个生态系统中进行评估。从计划测量得出的模型可以预测灌木扩张对生态系统过程的影响，如土壤能量平衡，永久冻土融化，旧土壤有机质的释放和循环。来自阿拉斯加和整个北极的真菌和植物的存档样本将扩大研究的时间和地理相关性。该项目将为本科生和研究生提供教育和研究机会。研究人员还将与当地高中教师合作，利用真菌作为生物学教学的工具，并扩大他们在户外教室的工作。

Birch, willow, and other shrubs in the Arctic are increasing in response to warming at the expense of grasses and sedges. This increased shrub cover may enhance winter snow capture, increase winter soil temperatures, deepen summer soil thawing, and increase the release of old carbon and nitrogen. The increased flux of sugars from shrubs to shrub-associated symbiotic fungi (termed mycorrhizal fungi) could stimulate decomposition of thawing organic matter and release organic nitrogen for plant uptake previously locked up for millennia. This mycorrhizally-mediated priming of decomposition may influence carbon balances and nutrient availability for further shrub growth. To test this, researchers will use long-running experiments in Arctic Alaska that are examining plant responses to warming in different tundra types. Researchers will use natural levels of carbon and nitrogen isotopes to track the incorporation of new soil-derived organic nitrogen into shrubs and associated mycorrhizal fungi. With the new methodologies developed, organic nitrogen use can be assessed across ecosystems. Models derived from planned measurements can then predict consequences of shrub expansion for ecosystem processes, such as soil energy balances, permafrost melting, and the release and cycling of old soil organic matter. Archived samples of fungi and plants from Alaska and across the Arctic will expand the temporal and geographic relevance of the studies. The project will provide education and research opportunities to undergraduate and graduate students. Researchers will also work with local high school teachers to use fungi as a tool to teach biology and to expand their work in outdoor classrooms.