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.

热带森林是高生产的生态系统，占陆地初级生产的三分之一，但需要氮才能支持植物的生长。氮固定是由微生物进行的一种过程，可以使热带森林补充这种养分。在热带森林中发现了最高的氮固定率，但是在世界上最大的热带森林的所在地，亚马逊盆地的测量很少。磷和钼是在氮固定过程中起重要作用的两个元素。 实际上，已知磷的可用性限制氮固定，但没有人确定钼在自然界中是否具有相似的作用。 由于钼很少见，并且很容易从土壤中浸出，因此它的低浓度可能会导致亚马逊盆地的氮固定速率低，那里的土壤是养分的养分，而区域几乎没有得到钼的新输入。亚马逊盆地中的这些所谓的“风化”土壤也很酸，这种情况可能使氮固定微生物难以进入钼。该博士学位论文改进的研究将调查这些因素如何相互作用以限制氮的固定，这影响了热带森林对环境变化的响应方式。亚马逊东南部是一个研究的但重要的森林生态系统，在该系统中，（1）氮固定尚未量化，以及（2）钼和磷浓度较低，可能是由于这些元素的大气输入低。该奖项的资金将支持实验，以测试亚马逊东南部的自由生活土壤微生物固定的氮直接受到低磷或钼的限制，还是通过对土壤中磷和钼络合的pH效应而间接限制。研究人员将进行磷，钼和石灰图添加实验，并将衡量氮固定速率的长期变化以及磷和钼的可用性。结果将在审查论文中传播，以推断地球系统模型的全球氮固定率。此外，研究人员将与巴西学生进行培训和合作，并利用结果为年度扩展您的地平线研讨会的教学模块开发一个对科学感兴趣的中学女孩的工作室。