Collaborative Research: Importance of Heterotrophic and Phototrophic N2 Fixation in the McMurdo Dry Valleys on Local, Regional and Landscape Scales

南极洲的麦克默多干谷被认为是地球上最干燥、最寒冷、可能也是最恶劣的环境之一。除了缺水之外，山谷里的生物群面临着非常有限的营养物质供应，比如氮化合物——蛋白质合成所必需的。干谷的冰川溪流有广泛的蓝藻（蓝绿藻）垫，这是该地区生物群碳和氮化合物的主要来源。虽然溪流中的蓝藻是这些化合物的重要来源，但其他非光合细菌也为山谷生物群贡献了相当一部分（~50%）的固定氮化合物。这项研究工作将包括检查哪些非光养细菌参与固氮，以及哪些环境因素负责控制这些微生物的固氮。这项工作将解决控制麦克默多四个干谷中固氮微生物活动、丰度和多样性的环境因素。这将允许在不同纬度、温度、海拔和暴露于水的地点之间进行比较。这些结果将被整合到景观湿度模型中，该模型将有助于确定蓝藻和非光合固氮微生物在这种非常恶劣的环境中的影响。干谷在很多方面与火星环境相似，了解干谷的原始生命和非常简单的营养循环对于了解其他星球上的生命曾经是如何存在的有重要意义。此外，对极端环境中微生物的研究已经导致了许多生物技术的应用，如扩增DNA的聚合酶链反应和农作物抗冻机制。因此，这项研究应该能够深入了解生物群如何在极端环境中生存，而这些见解可能会导致其他商业应用。

The McMurdo Dry Valleys in Antarctica are recognized as being the driest, coldest and probably one of the harshest environments on Earth. In addition to the lack of water, the biota in the valleys face a very limited supply of nutrients such as nitrogen compounds - necessary for protein synthesis. The glacial streams of the Dry Valleys have extensive cyanobacterial (blue green algae) mats that are a major source of carbon and nitrogen compounds to biota in this region. While cyanobacteria in streams are important as a source of these compounds, other non-photosynthetic bacteria also contribute a significant fraction (~50%) of fixed nitrogen compounds to valley biota. This research effort will involve an examination of exactly which non-phototrophic bacteria are involved in nitrogen fixation and what environmental factors are responsible for controlling nitrogen fixation by these microbes. This work will resolve the environmental factors that control the activity, abundance and diversity of nitrogen-fixing microbes across four of the McMurdo Dry Valleys. This will allow for comparisons among sites of differing latitude, temperature, elevation and exposure to water. These results will be integrated into a landscape wetness model that will help determine the impact of both cyanobacterial and non-photosynthetic nitrogen fixing microorganisms in this very harsh environment. The Dry Valleys in many ways resemble the Martian environment, and understanding the primitive life and very simple nutrient cycling in the Dry Valleys has relevance for understanding how life might have once existed on other planets. Furthermore, the study of microbes from extreme environments has resulted in numerous biotechnological applications such as the polymerase chain reaction for amplifying DNA and mechanisms for freeze resistance in agricultural crops. Thus, this research should yield insights into how biota survive in extreme environments, and these insights could lead to other commercial applications.