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是由氮(N)的可用性控制的，而氮在环境中往往是供不应求的。人类活动通过施肥或大气沉降增加N输入，以及由于气候变暖或景观改变而加速N的内部循环，增加了生态系统中N的可利用性。虽然更多的氮可以提高生物生产力，但这对数千年来在低营养条件下形成的自然生态系统的结构和功能产生了重大影响。最近，研究人员试图使用植物叶片中N的稳定同位素-一种可以区分不同形式N的测量方法-来了解生态系统N动态。在一个时间点对叶片氮同位素的相对直接的测量记录了随着时间的推移，随着氮在整个生态系统中移动而发生的多种复杂的生物和物理转化的净效应。这个博士论文研究项目将对一系列阿拉斯加黑云杉森林的N循环进行机械测量，为在同一地点制作的叶片N同位素的解释提供基础。在这里，土壤肥力的自然梯度结合实验施肥和分析模型将用于探索和解释叶片N同位素的模式。这些结果将有助于了解自然生态系统对变化的N循环的响应。研究生，除了进行研究，将指导和本科生的研究助理。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.