The Importance of Molybdenum Speciation to Nitrogen Fixation and Assimilation in Lakes

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。许多水生生态系统的生产力往往受到关键营养物供应的限制。在海洋和一些湖泊中，氮通常是关键的限制性营养物质。氮对生命至关重要，它以多种化学形式存在，包括氮气、铵、硝酸盐和各种有机物质，如氨基酸（蛋白质的组成部分）和核酸（DNA的组成部分）。氮可以通过各种微生物在这些物种之间进行转化，从而影响对植物（例如硝酸盐和铵）和高等生物有用的氮形式的相对可用性。氮循环过程本身可能受到其他营养因素的限制。例如，生物氮循环中的许多关键酶反应都需要金属来维持其活性。特别是，钼是参与硝酸盐吸收（硝酸盐同化）和氮气（固氮）的氮循环途径中酶的必需成分。在湖泊生态系统中，一个主要的未知因素是通常以极低浓度存在的营养微量金属如何控制氮的循环。这项研究的主要目的是确定营养微量金属，如钼（以及铁和铜）的化学形式如何影响生物体吸收它们的能力。将在加利福尼亚州和内华达州的三个湖泊进行研究，对比生产率和微量金属浓度。然而，在海洋系统中，硝酸盐和氮气的吸收通常由铁的可用性控制，据推测，在湖泊中，这些过程的限制性微量元素是钼。为了验证这一假设，PI开发了新的分析技术来测量这些湖泊中钼的不同化学种类。该项目将为控制关键氮循环过程中金属可用性和形态的重要性提供相当多的新信息。关于湖泊中金属丰度的高质量数据很少。因此，这些研究将提供关于金属载荷如何随着时间的推移而改变和影响这些系统的信息。自从在其中一些湖泊的流域进行了较早的深入研究以来，已经发生了广泛的发展和随后的人为干扰。该项目将为本科生、研究生和博士后提供最先进的技术和方法的就业和培训。pi教授研究生和本科水平，并积极参与K-grey教育和推广项目。他们都是环境科学中增加性别和种族多样性的积极分子。研究结果将通过演讲和出版物广泛传播。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The productivity of many aquatic ecosystems is often limited by the availability of a key nutrient. In the oceans and in some lakes nitrogen is often that key limiting nutrient. Nitrogen, which is critical for life, occurs in diverse chemical forms including nitrogen gas, ammonium, nitrate and various organic species such as amino acids (the building blocks of proteins) and nucleic acids (the building blocks of DNA). Nitrogen can be converted among these species by various microbes which thereby affect the relative availability of forms of nitrogen useful to plants (e.g. nitrate and ammonium) and higher organisms. Nitrogen cycle processes may themselves be limited by other nutrient factors. For instance, many of the key enzyme reactions in the biological nitrogen cycle require metals for their activity. In particular, molybdenum, is a required component of the enzymes of the nitrogen cycle pathways involved in the uptake of nitrate (nitrate assimilation) and nitrogen gas (nitrogen fixation). In lake ecosystems, a major unknown is how nutrient trace metals that generally exist at very low concentrations control the cycling of nitrogen. The main objective of this study is to determine how the chemical form of nutrient trace metals, such as molybdenum (as well as iron and copper), affect the capacity of organisms to take them up. Studies will be undertaken in three lakes in California and Nevada with contrasting productivity and trace metal concentration. Whereas the uptake of nitrate and nitrogen gas is often controlled by iron availability in marine systems, it is hypothesized that in lakes the limiting trace element for these processes is molybdenum. To test this hypothesis, the PI's have developed new analytical techniques that measure the different chemical species of molybdenum in these lakes. This project will provide considerable new information on the importance of metal availability and form in controlling key nitrogen cycle processes. High quality data on metal abundance in lakes is scarce. These studies will therefore provide information on how metal loading has changed and affected these systems over time. Extensive development and subsequent human perturbations have occurred since the earlier intensive studies were conducted in the watersheds of some of these lakes. The project will provide employment and training in state of the art techniques and approaches for undergraduate, graduate students and postdoctoral associates. The PIs teach at both the graduate and undergraduate levels and are active in K-grey education and outreach programs. Both are activists in increasing gender and ethnic diversity in the environmental sciences. The results will be widely disseminated through presentations and publications.