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流入淡水湖的径流是造成氮(N)和磷(P)日益失衡的主要原因，而氮(N)和磷(P)是在全球范围内限制这一重要生态系统初级生产和温室气体释放的两种关键巨量营养素。近40年来，人为氮径流的快速增加使磷的输入变得矮小，使全球氮磷比的平衡从19:1转变为30:1，促使越来越多的湖泊生态系统走向磷限制。尽管这一趋势可能会继续下去，但我们对这种人为引起的磷限制如何影响淡水生态系统中CO2和CH4通量的了解仍然不确定。利用我们最近发现的磷限制似乎降低了蓝藻固定二氧化碳的能力和甲烷氧化菌氧化CH4的能力，我们提出了一种多学科方法来揭示淡水微生物组合中氮：磷失衡的反应及其对淡水湖温室气体排放的影响。

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 into freshwater lakes as a result of human population growth are major contributors to the growing imbalance of nitrogen (N) and phosphorus (P), two key macronutrients limiting primary production 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 phosphorus limitation. Although this trend is likely to continue, our knowledge of how such an anthropogenically indued phosphorus limitation affects CO2 and CH4 flux in freshwater ecosystems remains uncertain. Capitalising on our recent discovery that P limitation appears to reduce the capacity of both cyanobacteria for CO2 fixation and methanotrophs for CH4 oxidation, we propose a multidisciplinary approach to uncover the response to N:P imbalance in freshwater microbial assemblages and subsequent impact on greenhouse gas emissions in freshwater lakes.