Quantifying the impact of anthropogenic nutrient imbalance on C flux from freshwater lakes: cellular mechanisms, community assembly and modelling

淡水湖是地球上最大的生态系统之一，也是二氧化碳(CO2)和甲烷(CH4)排放的主要贡献者，这两种温室气体是强有力的。人口增长导致的富氮化肥及其径流的使用是造成淡水湖氮磷失衡日益严重的主要原因。这些关键营养物质限制了藻类的生长，限制了可用于支持水生野生动物的能源，以及全球范围内这个具有重要生态意义的生态系统的温室气体排放。在过去的40年里，人为氮素径流的快速增加使磷的输入相形见绌，并使全球N：P比例从19：1变为30：1，促使越来越多的湖泊生态系统受到磷有效性的限制。尽管这一趋势可能会继续下去，但我们对这将如何影响淡水生态系统内的二氧化碳和甲烷的移动，以及这些生态系统和大气之间的移动的了解仍然不确定。我们最近发现，磷的低有效性似乎会降低蓝藻(有时称为“蓝藻”)和甲烷养殖菌(一组细菌)处理二氧化碳的能力，利用这一发现，我们建议揭示N：P失衡如何影响淡水微生物群落和淡水湖的温室气体排放；以及对全球气候变化具有重大影响的影响。

Freshwater lakes are amongst the largest ecosystems on Earth, and a major contributor to both carbon dioxide (CO2) and methane (CH4) emissions, two potent greenhouse gases. The use of nitrogen-rich fertilisers and their runoff as a result of human population growth are major contributors to the growing imbalance of nitrogen (N) and phosphorus (P) in freshwater lakes. These key nutrients limit the growth of algae, the energy available to support aquatic wildlife, and greenhouse gas release from this ecologically important ecosystem at a global scale. The much faster increase of anthropogenic nitrogen runoff has dwarfed the input of phosphorus and shifted the balance of the global N:P ratio from 19:1 to 30:1 in the past four decades, driving more and more lake ecosystems towards being limited by the availability of phosphorus. Although this trend is likely to continue, our knowledge of how this will affect the movement of CO2 and CH4 within freshwater ecosystems, and between these ecosystems and the atmosphere, remains uncertain. Capitalising on our recent discovery that a low availability of P appears to reduce the capacity of both cyanobacteria (sometimes called "blue-green algae") to process CO2 and methanotrophs (a group of bacteria) to process CH4, we propose to uncover how N:P imbalance affects freshwater microbial communities and greenhouse gas emissions in freshwater lakes; effects that have major implications for global climate change.