The Ecology of Nitrogen Fixation

固氮生态学

• 批准号: RGPIN-2015-05278
• 负责人: Markham, John
• 金额: $ 1.53万
• 依托单位: University of Manitoba
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=678526
• 关键词: Ecology; Nitrogen; Fixation

Plant growth in temperate ecosystems is limited by nitrogen availability. Indeed, the success of modern agriculture is due primarily to the invention of nitrogen fertilizers. However, the use of nitrogen fertilizer requires intensive energy inputs and can result in eutrophication of the environment. Nitrogen can also be supplied to ecosystems by nitrogen fixing microbes. The symbiotic interaction between plants and nitrogen fixing bacteria frees plants from the limitations of soil nitrogen availability. The development of new nitrogen fixing symbioses could free us from our reliance on nitrogen fertilizer. However, this long sought goal of plant breeders has yet to be realized. Understanding the ecology of existing nitrogen fixing organisms may help us not only to understand their roles in natural systems, but also guide us in developing new nitrogen fixing systems and applications for them. ***The fundamental problem in the ecology of nitrogen fixing plants is explaining why they are not more common. In many nitrogen-limited ecosystems nitrogen fixing plants tend to be rare, whereas they often dominate systems where nitrogen does not limit growth. The proposed research will look at factors that can potentially limit the success of symbiotic nitrogen fixing plants. Theory predicts that nitrogen fixation is limited by its cost relative to the acquisition of other elements. Lab and field experiments will therefore determine if making carbon acquisition more difficult (by altering light levels), or soil nutrient uptake more efficient (using fertilizer and adjusting soil temperatures) reduces the effectiveness of the nitrogen fixation. Comparing nitrogen fixing plants with and without their symbionts will allow us to quantify the benefit of the symbiosis under varying environmental conditions. Plants typically harbor symbiont genotypes that vary in their effect on nitrogen fixation. I will manipulate interactions between bacterial genotypes of varying nitrogen fixing capability to understand how mutualistic relationships are maintained, rather than displaced by less mutualistic interactions. I will also determine how symbiotic nitrogen fixation contributes to the productivity of boreal forests across a regional transect. Comparing productivity and nitrogen fixation from the driest edge of the boreal forest to the center of its range will not only give us insight into conditions that favor nitrogen fixation, but will also help us understand how this may be modified with a changing climate. Finally, I will determine the input of fixed nitrogen by cyanolichens and mosses where they are super abundant, to determine if they can displace the role of symbiotic nitrogen fixation in a tropical cloud forest. Overall, this research will allow us to predict conditions that promote nitrogen fixation and discover new methods to manage nitrogen and ecosystem productivity.

温带生态系统中植物的生长受到氮素有效性的限制。的确，现代农业的成功主要归功于氮肥的发明。然而，使用氮肥需要密集的能源投入，并可能导致环境富营养化。氮也可以通过固氮微生物提供给生态系统。植物与固氮菌的共生作用使植物摆脱了土壤氮素有效性的限制。新的固氮共生体的开发可以使我们摆脱对氮肥的依赖。然而，这一植物育种者长期追求的目标尚未实现。了解现有固氮菌的生态，不仅可以帮助我们了解它们在自然系统中的作用，还可以指导我们开发新的固氮系统和应用。*固氮植物生态中的根本问题是解释为什么它们不更常见。在许多氮素有限的生态系统中，固氮植物往往很少，而在氮素不限制生长的系统中，它们往往占据主导地位。这项拟议的研究将着眼于可能限制共生固氮植物成功的因素。理论预测，固氮受到其相对于获得其他元素的成本的限制。因此，实验室和田间实验将确定，是使碳获取变得更加困难(通过改变光照水平)，还是使土壤养分吸收更有效(使用化肥和调整土壤温度)降低固氮效果。比较有无共生体的固氮植物将使我们能够量化在不同环境条件下共生的好处。植物通常含有不同的共生体基因，它们对固氮的影响不同。我将操纵不同固氮能力的细菌基因型之间的相互作用，以了解如何维持互惠关系，而不是被较少互惠的相互作用所取代。我还将确定共生固氮对整个区域样带的北方森林生产力的贡献。比较从北方森林最干燥的边缘到其范围中心的生产力和固氮，不仅可以让我们洞察有利于固氮的条件，而且还有助于我们理解这种情况可能会如何随着气候变化而改变。最后，我将确定超级丰富的蓝藻和苔藓对固定氮的输入，以确定它们是否可以取代热带云雾森林中共生固氮的作用。总体而言，这项研究将使我们能够预测促进固氮的条件，并发现管理氮素和生态系统生产力的新方法。