Biological nitrogen uptake and microbial transformations in aquatic ecosystems under conditions of rapid environmental change

氮循环是地球上最复杂、最受扰动的全球性地球化学循环之一。自然地，微生物将气态大气氮“固定”成植物和随后的其他生物体所使用的形式。其他微生物可以通过一系列转化完成循环，将固定的氮以气态形式返回大气。然而，人类通过人工合成肥料来固定大量的氮，从而使地球变得更加肥沃，导致广泛的氮污染。虽然氮污染的内陆沃茨是一个越来越多的关注，在加拿大和地球仪各地，鲜为人知的是微生物多样性和微生物的N速率转换的这一关键的营养循环在新鲜的沃茨的机械控制。湖泊内不平衡的N转化可能对水生生态系统健康产生负面影响，因为在这个复杂的循环中不同N形式的可用性可能会调节浮游植物群落结构，促进讨厌的蓝藻的增殖并产生强效温室气体一氧化二氮。我们建议在几个不同的生态系统类型的调查在不同的尺度上表征多个N代谢率转换以及淡水N循环中的微生物多样性。这种独特的综合性的N循环将通过使用几种新的生理学，同位素，分类学和分子技术，其中许多还没有被用于在淡水系统的方式相结合。我们将研究氮固定，硝化，反硝化和藻类氮营养沿着梯度的湖泊类型的时空变化，并将从群落结构变化的角度，并与其他主要的生态地球化学循环，如碳，将阐述作为气候变化的函数，增加点源和非点源氮污染的N的处理。这项创新计划的研究结果有望改变我们目前的范式N循环在淡水沃茨，提供证据，以帮助证实需要控制氮污染的内陆沃茨，并提供重要的见解，在不同的过程中的变化，以帮助指导未来的海洋学研究。

The nitrogen (N) cycle is one of the most complex and heavily perturbed global biogeochemical cycles on earth. Naturally, microorganisms "fix" gaseous atmospheric N into a form used by plants and subsequently other organisms. Other microorganisms can return this fixed N to the atmosphere in gaseous form through a series of transformations completing the cycle. Humans however are enriching the earth by artificially fixing large amounts of N through fertilizer synthesis resulting in widespread N pollution. Although N pollution to inland waters is a growing concern in Canada and around the globe, little is known about the microbial diversity and the mechanistic controls of the microbial N rate transformations of this critical nutrient cycle in freshwaters. Unbalanced N transformations within lakes may have negative repercussions on aquatic ecosystem health as the availability of different N forms within this complex cycle may regulate phytoplankton community structure, contribute to the proliferation of nuisance cyanobacteria and produce the potent greenhouse gas nitrous oxide. We propose to characterize multiple N metabolic rate transformations as well as the microbial diversity in the freshwater N cycle at different scales of inquiry across several different ecosystem types. This unique integrative look into the N cycle will be done by using a combination of several novel physiological, isotopic, taxonomical and molecular techniques, many of which have yet to be used in a systematic fashion in freshwaters. We will examine the spatial and temporal variation of N-fixation, nitrification, denitrification and algal N nutrition along a gradient of lake types and will characterise the processing of N, as a function of climate change, increased point and non-point source N pollution, from a perspective of changes in community structure and in relation to other major biogeochemical cycles like carbon. The findings of this innovative program are expected to alter our current paradigms of N cycling in freshwaters, supply evidence to help substantiate the need to control N pollution to inland waters and provide important insights in the variability of the different processes to help direct future oceanographic studies.