Progressive Nitrogen Limitation in Terrestrial Ecosystems: Empirical Test of a Biogeochemical Paradigm

当人类燃烧石油、煤炭和汽油时，二氧化碳会释放到大气中，是全球变暖的主要原因。大气中二氧化碳的增加可能有助于植物通过光合作用更快地吸收二氧化碳。森林的碳吸收是否有助于在下个世纪抵消人类二氧化碳的排放，从而有助于缓解气候变化？一些模型认为有可能，但这些模型假设植物将能够从土壤中获得足够的养分，这一假设很可能是错误的。这项研究项目将确定不断增加的二氧化碳如何影响氮的循环，氮素是一种养分，其短缺最常限制植物的生长。具体地说，这项研究将确定植物对二氧化碳增加的最初积极反应是否最终会因为氮的可获得性下降而消失。该项目还将研究大气中二氧化碳的增加如何改变其他元素的循环，包括钼元素，众所周知，钼元素是生态系统积累有限氮的能力的关键。这些发现对于理解氮循环如何影响二氧化碳继续上升时生态系统可能积累的碳含量将是重要的。该项目将促进教育，并将专门针对参与研究的少数族裔学生。该项目将在研究成果的基础上开发批判性思维练习，旨在用于本科课程。研究和教育的结合在生态系统生态学和生物地球化学中尤为重要，因为这些生态学领域传统上在本科生态学课程中代表性较低，而且这些领域对围绕全球气候变化和碳管理的政策决策具有关键影响。

Carbon dioxide is released to the atmosphere when humans burn oil, coal, and gasoline, and is the major cause of global warming. Increasing carbon dioxide in the atmosphere may help plants take it up faster through the process of photosynthesis. Will carbon uptake by forests help counteract human emissions of carbon dioxide over the next century, and thereby help mitigate climate change? Some models suggest that it might, but these models assume that plants will be able to acquire enough nutrients from the soil, an assumption that may well be faulty. This research project will determine how rising carbon dioxide affects the cycling of nitrogen, the nutrient whose short supply most frequently restricts plant growth. Specifically, this research will determine whether the initial positive responses of plants to increasing carbon dioxide eventually fade away because the availability of nitrogen declines. This project will also examine how increased atmospheric carbon dioxide may alter the cycles of other elements, including the element molybdenum, which is known to be key to the ability of ecosystems to accumulate limiting nitrogen. The findings will be important for understanding how nitrogen cycling influences how much carbon ecosystems might accumulate as carbon dioxide continues to rise. The project will contribute to education and will specifically target minority students for involvement in research. The project will develop critical thinking exercises that build on the research results, designed for use in undergraduate courses. Integration of research and education is particularly important in ecosystem ecology and biogeochemistry, because these fields of ecology are traditionally underrepresented in undergraduate ecology courses, and because these fields have key implications for policy decisions surrounding global climate change and carbon management.