DISSERTATION RESEARCH: Linking Theory and Mechanistic Experiments in Explaining How Nitrogen Fixation Strategies Influence Ecosystem Nitrogen Fertility

在许多温带和北方森林中，氮的有效性限制了植物的生长和碳的储存。生物固氮，将大气中的氮气转化为生物有用的形式，有能力缓解这些生态系统中的氮限制，但固氮树只存在于幼龄林中，而氮限制持续存在于老龄林中。为什么固氮树在温带和北方森林发展的早期被排除在外？最近的理论，包括研究人员开发的数学模型，揭示了这个看似矛盾的一些可能的解释。这些解释中有一些得到了经验主义的支持，但很少有经过实验检验的。该提案描述了一个高度控制的实验，以评估理论强调的四个关键问题。这项实验将侧重于新理论和实地研究的发展，这种方法的结合将解开持续氮限制的看似矛盾。

Nitrogen availability limits plant growth and carbon storage in many temperate and boreal forests. Biological nitrogen fixation, the conversion of atmospheric nitrogen gas into a biologically useful form, has the capacity to alleviate nitrogen limitation in these ecosystems, yet nitrogen fixing trees are only present in young forests, while nitrogen limitation persists in old forests. Why are nitrogen fixing trees excluded early in temperate and boreal forest development? Recent theory, including a mathematical model developed by the investigators, has revealed a number of possible explanations for this seeming paradox. There is empirical support for some of these explanations, yet few have been tested experimentally. This proposal describes a highly controlled experiment to evaluate four of the key issues highlighted by theory. This experiment will focus the development of new theory and field-based studies, and this combination of approaches will unravel the seeming paradox of sustained nitrogen limitation.