DISSERTATION RESEARCH: Tracking Ecosystem Nitrogen Cycling in Black Spruce Forests with Novel15N Measurements

许多陆地和水生生态系统的动态受氮（N）的可用性控制，而氮在环境中往往供应不足。 人类活动增加了生态系统中氮的有效性，通过增加肥料添加或大气沉积增加氮的输入，并通过加速内部循环的N作为结果气候变暖或景观改造。虽然更多的N可以提高生物生产力，但这对数千年来由低营养条件形成的自然生态系统的结构和功能产生了重大影响。 最近，研究人员试图使用氮的稳定同位素-一种可以区分植物叶片中不同形式氮的测量方法-来了解生态系统氮的动态。 相对简单的测量叶氮同位素在一个单一的时间点记录的净效应，随着时间的推移发生的多个复杂的生物和物理的转变，N在整个生态系统中移动。这个博士论文研究项目将在阿拉斯加黑云杉森林的范围内进行N循环的机械测量，为在同一地点进行的叶N同位素的解释提供基础。在这里，结合实验施肥和分析模型的土壤肥力的自然梯度将被用来探索和解释叶片氮同位素的模式。这些结果将有助于通知自然生态系统的响应不断变化的N循环。 研究生，除了进行研究，将指导和本科研究助理。 这项研究将有助于更好地了解气候变化对自然生态系统的影响。

The dynamics of many terrestrial and aquatic ecosystems are controlled by the availability of nitrogen (N), which is often in short supply in the environment. Human activities are increasing N availability in ecosystems both by increasing N inputs through fertilizer addition or atmospheric deposition, and by speeding up internal recycling of N as a result climate warming or landscape modification. While more N can increase biological productivity, this has a significant impact on the structure and function of natural ecosystems that have been shaped by low nutrient conditions for thousands of years. Recently, researchers have sought to use stable isotopes of N --a measurement method that can distinguish between different forms of N-- in plant leaves to understand ecosystem N dynamics. Relatively straightforward measurements of leaf N isotopes at a single point in time record the net effect of multiple complex biological and physical transformations that occur over time as N moves throughout whole ecosystems. This doctoral dissertation research project will make mechanistic measurements of N cycling across a range of Alaskan black spruce forests to provide an underpinning to the interpretation of leaf N isotope made at the same sites. Here, natural gradients of soil fertility in combination with experimental fertilizer additions and analytical modeling will be used to explore and interpret the patterns of leaf N isotopes. These results will help inform the response of natural ecosystems to a changing N cycle. The graduate student, in addition to performing research, will be mentoring and undergraduate research assistant. This study will help better understand the impact of climate change on natural ecosystems.