Dissertation Research: Does microbial diversity affect ecosystem function? : A denitrification case study

由于人类活动使用农业肥料和化石燃料燃烧产生的沉积物，环境中的氮污染增加了一倍以上。这具有重要的生态后果，但氮在生态系统中的命运知之甚少。以前的氮预算工作发现，很大一部分的氮添加量无法解释。这种氮可能不会出现在预算中的一种方式是，如果它被转化为气体。这可以通过一个称为脱氮的过程发生，该过程产生无害的二氮气体（N2）。然而，这一途径会释放有害的中间产物，如亚硝酸盐、一氧化氮和一氧化二氮，后者是一种强效的温室气体。因此，了解控制渗漏率的因素，其中可能包括微生物群落的性质或土壤性质，是很重要的，如果我们要有一个准确的了解氮添加到土壤系统的命运。在进行这类工作时所面临的挑战之一是量化反硝化中间体，特别是N2，因为很难区分反硝化产生的N2与大气中存在的N2。这里提出的工作将利用一种新型的采样机器人，可以测量和量化所有中间体和N2的生产从土壤中。除了测量中间释放，我们将通过活性基因的测序来确定负责反硝化的活性细菌群落。通过双管齐下的方法，我们可以更准确地确定生态系统中控制氮流动的因素。本项目将探讨活跃的土壤微生物群落与反硝化速率之间的关系，反硝化是一个重要的生态系统过程，对全球气候变化有影响。从这项研究中收集的数据将加强涉及微生物学，生态学，地球化学和生物信息学领域的跨学科研究。微生物测序数据将向公众开放，这些数据将特别有助于为入门级和高级生物信息学培训开发本科课堂材料。该项目还将促进对本科生进行微生物学和地球化学科学方面的培训。最后，该项目将支持与挪威土壤微生物生态学家的国际合作。

Human activities have more than doubled nitrogen pollution of the environment through the use of agricultural fertilizer and deposition from fossil fuel burning. This has important ecological consequences, yet the fate of nitrogen in ecosystems is poorly understood. Previous work on nitrogen budgets have found that a large fraction of added nitrogen cannot be accounted for. One of the ways this nitrogen might not show up in the budget is if it is converted to a gas. This can occur through a process called denitrification, which creates harmless dinitrogen gas (N2). However, this pathway can release harmful intermediates, such as nitrite, nitric oxide and nitrous oxide, with the latter being a potent greenhouse gas. Therefore, understanding the factors controlling the rate of leakage, which could include the nature of the microbial community or the soil properties, is important if we are to have an accurate understanding of the fate of nitrogen added to soil systems. One of the challenges faced in doing this type of work is quantifying denitrification intermediates and, especially, N2, since it is difficult to distinguish the N2 produced from denitrification from that present in the atmosphere. The work proposed here will take advantage of a novel sampling robot that can measure and quantify the production of all intermediates and N2 from soils. In addition to measuring intermediate release we will identify the active bacterial communities responsible for denitrification through sequencing of the active genes. By taking a two-pronged approach we can more accurately define the factors controlling nitrogen flow in ecosystems.This project will explore the relationship between the active soil microbial community and rates of denitrification, an essential ecosystem process which has implications on global climate change. Data collected from this research will strengthen interdisciplinary research that involves the fields of microbiology, ecology, biogeochemistry and bioinformatics. The microbial sequencing data will be made publicly available, and the data will be especially useful for the development of undergraduate classroom materials for bioinformatics training at both the introductory and advanced level. This project will also foster training of undergraduate students in microbiology and biogeochemical sciences. Finally, this project will support international collaborations with soil microbial ecologists in Norway.