Dissertation Research: Interactions of pH on molybdenum and phosphorus limitation of nitrogen fixation in the Amazon Basin

论文研究：亚马逊流域 pH 值对固氮钼和磷限制的相互作用

• 批准号: 1701092
• 负责人: Robert Howarth
• 金额: $ 2.03万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-07-01 至 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1701092&HistoricalAwards=false
• 关键词: Dissertation; Research; Interactions; pH; molybdenum

Tropical forests are highly productive ecosystems and represent one-third of terrestrial primary production, but require nitrogen to support plant growth. Nitrogen fixation is a process carried out by microorganisms that allows tropical forests to replenish this nutrient. The highest documented nitrogen fixation rates are found in tropical forests, but few measurements have been made in the Amazon Basin, home to the world's largest tropical forest. Phosphorus and molybdenum are two elements that play an important role in the nitrogen fixation process. Indeed, phosphorus availability is known to limit nitrogen fixation, but no one has determined whether molybdenum has a similar effect in nature. Because molybdenum is rare, and is easily leached from soils, it's low concentration could lead to low nitrogen fixation rates in the Amazon Basin, where soils are nutrient depleted, and where regions receive little to no new inputs of molybdenum. These so-called "weathered" soils in the Amazon Basin are also acidic, and this condition can make it even more difficult for nitrogen-fixing microorganisms to access molybdenum. Research for this Doctoral Dissertation Improvement Grant will investigate how these factors interact to constrain nitrogen fixation, which affects how tropical forests will grow in response to environmental change. The southeastern Amazon is an understudied but important forest ecosystem where (1) nitrogen fixation has not yet been quantified and (2) where molybdenum and phosphorus concentrations are low, likely due to low atmospheric inputs of these elements. Funds from this award will support experiments to test whether nitrogen fixation by free-living soil microorganisms in the southeastern Amazon is directly constrained by low phosphorus or molybdenum, or indirectly limited via pH effects on phosphorus and molybdenum complexation in soils. The researchers will conduct phosphorus, molybdenum, and lime plot addition experiments, and will measure long-term changes in nitrogen fixation rates and in the availability of phosphorus and molybdenum. Results will be disseminated in review papers for extrapolation of global nitrogen fixation rates for earth system models. In addition, the researchers will train and collaborate with Brazilian students and use the results to develop a teaching module for the annual Expanding Your Horizons workshop for middle school girls interested in science.

热带森林是高生产力的生态系统，占陆地初级生产力的三分之一，但需要氮素来支持植物生长。固氮是由微生物进行的一种过程，使热带森林能够补充这种养分。有记载的固氮率最高的是热带森林，但世界上最大的热带森林所在的亚马逊盆地几乎没有进行过测量。磷和钼是固氮过程中起重要作用的两种元素。事实上，磷的有效性会限制固氮，但还没有人确定钼在自然界中是否具有类似的效果。由于钼是稀有的，而且很容易从土壤中淋溶出来，它的低浓度可能会导致亚马逊盆地的固氮率较低，那里的土壤养分枯竭，而且那里的地区几乎没有新的钼投入。亚马逊盆地这些所谓的“风化”土壤也是酸性的，这种条件会让固氮微生物更难接触到钼。这篇博士论文的研究将调查这些因素如何相互作用来限制固氮，这会影响热带森林如何生长以应对环境变化。亚马逊东南部是一个研究不足但重要的森林生态系统，在那里(1)固氮作用尚未量化，(2)钼和磷浓度较低，可能是由于这些元素的大气输入较少。这笔资金将用于支持实验，以测试亚马逊东南部自由生活的土壤微生物的固氮是直接受到低磷或钼的限制，还是间接受到土壤中磷和钼络合作用的pH影响的限制。研究人员将进行磷、钼和石灰小区添加实验，并将测量固氮率以及磷和钼的有效性的长期变化。结果将发表在地球系统模型全球固氮率外推的综述论文中。此外，研究人员将与巴西学生进行培训和合作，并利用研究结果为一年一度的为对科学感兴趣的中学女孩举办的扩大你的视野研讨会开发一个教学模块。