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）两种强效温室气体排放的主要来源。由于人口增长，富氮肥料的使用及其径流是淡水湖中氮(N)和磷(P)日益失衡的主要原因。这些关键的营养物质限制了藻类的生长，限制了水生野生动物所需的能量，也限制了全球范围内这一重要生态系统的温室气体释放。近40年来，人为氮径流的快速增加使得磷的输入量减少，使全球氮磷比的平衡从19:1转变为30:1，使越来越多的湖泊生态系统受到磷可用性的限制。虽然这一趋势很可能会继续下去，但我们对这将如何影响淡水生态系统内以及这些生态系统与大气之间二氧化碳和甲烷的运动的了解仍然不确定。利用我们最近的发现，低磷可用性似乎降低了蓝藻（有时称为“蓝绿藻”）处理二氧化碳和甲烷氧化菌（一组细菌）处理CH4的能力，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；对全球气候变化有重大影响的影响。

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.