Collaborative Research: Influence of phosphorus deficiency on enigmatic biological methane production in oxic freshwater lakes

自工业革命以来，大气中的甲烷含量已经上升了150%，而且还在继续增加。虽然能源部门和农业来源是主要来源，但天然微生物来源约占全球甲烷排放总量的一半。长期以来，微生物甲烷生产一直被认为是一个缺氧过程，只有在极低到零氧的条件下才能进行。最近的研究表明，在湖泊和海洋的含氧上层水域中，微生物可能通过一种以前未被认识到的微生物代谢途径产生甲烷。在缺磷的条件下，某些细菌可以利用甲基膦酸盐这种不活跃的有机分子来满足它们对磷的需求，并在这个过程中释放甲烷。这种机制在多大程度上支持甲烷从湖泊排放到大气中是未知的，环境条件变化对甲烷的影响也是未知的。该项目将通过调查Flathead湖和蒙大拿州其他18个不同缺磷状态的湖泊的好氧甲烷生产的分布、速率和控制来解决这一知识差距。由于大气中氮污染物的沉积和刻意减少湖泊磷输入的措施都可能导致磷缺乏，因此我们必须知道这些因素是否会导致意想不到的甲烷排放增加。这项研究还将直接支持研究生和本科生的教育、实地和实验室经验，并将为来自美洲原住民（库特奈和萨利什）部落土地的当地高中教师提供培训。该项目将评估蒙大拿州西部不同磷可用性湖泊中微生物介导的氧化甲烷产量的时空变异性。它是由一个总体假设指导的：含氧淡水湖的甲烷弥漫性流出直接受到生态系统营养（氮、磷）缺乏的性质和严重程度的影响。采用化学、稳定同位素、宏基因组和基于pcr的基因分析相结合的观察和实验方法，将研究：1)蒙大拿州淡水湖甲烷浓度、稳定同位素组成和净产量的时空变化，重点是弗拉特海德湖；2)微生物甲基膦酸盐降解对这些湖泊甲烷净生产量的影响程度；3)参与膦酸盐和甲烷循环的微生物的功能多样性、丰度和转录活性；4)水生营养物（无机和总）池的化学计量（特别是氮磷比）如何影响氧化甲烷的产生和甲烷循环功能基因的表达。该研究将对微生物甲烷来源和甲基膦酸盐降解作为含氧淡水湖甲烷来源的潜在贡献进行系统评价。该项目的研究结果将为目前对淡水湖生境中碳和磷循环耦合相互作用的理解提供新的见解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Atmospheric levels of methane have risen 150% since the Industrial Revolution, and continue to increase. Although energy sector and agricultural sources are major contributors, natural microbiological sources account for roughly half of total global methane emissions. Microbial methane production has long been assumed to be an anoxic process, carried out only under conditions of extremely low to zero oxygen. Recent research has demonstrated the potential for microbial methane production to occur in oxygenated upper waters of lakes and oceans through a previously unappreciated metabolic pathway present in microorganisms. Under conditions of phosphorus deficiency, certain bacteria can utilize otherwise unreactive organic molecules known as methylphosphonates to meet their phosphorus requirements, releasing methane in the process. The extent to which this mechanism supports the out-gassing of methane from lakes to the atmosphere is unknown, as are the consequences of changing environmental conditions upon it. This project will address this knowledge gap by investigating the distributions, rates of and controls on aerobic methane production in Flathead Lake and 18 other Montana lakes of varying phosphorus deficiency status. Because atmospheric deposition of pollutant nitrogen and deliberate measures to curtail phosphorus inputs to lakes can both lead to phosphorus deficiency, it is crucial that we know whether these factors may have the unexpected consequence of enhancing methane emissions. This research will also directly support the education, field and laboratory experiences of graduate and undergraduate students and will provide training to local high school teachers from Native American (Kootenai and Salish) tribal lands.This project will evaluate temporal and spatial variability in microbially-mediated, oxic methane production across lakes with varying phosphorus availability in western Montana. It is guided by the overarching hypothesis: diffusive effluxes of methane from oxic freshwater lakes are directly influenced by the nature and severity of ecosystem nutrient (nitrogen, phosphorus) deficiencies. A combination of observational and experimental approaches employing chemical, stable isotopic, metagenomic and PCR-based gene analyses will be used to examine: 1) time and space variability in the concentration, stable isotope composition, and net production of methane in freshwater lakes in Montana, focusing on Flathead Lake; 2) The extent to which microbial methylphosphonate degradation results in net production of methane in these lakes; 3) The functional diversity, abundances, and transcriptional activities of microorganisms involved in both phosphonate and methane cycling; and 4) How the stoichiometry (specifically nitrogen:phosphorus ratios) of aquatic nutrient (inorganic and total) pools influences oxic methane production and expression of methane cycling functional genes. The study will provide a systematic evaluation of microbial methane sources and the potential contribution of methylphosphonate degradation as a source of methane in oxic freshwater lakes. Results from this project will provide new insights and advance current understanding of coupled interactions between carbon and phosphorus cycling in freshwater lake habitats.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.