Microbial aerobic methane oxidation is an important sink for aquatic methane worldwide. Despite its importance to global methane fluxes, few aerobic methane oxidation rates have been obtained in freshwater or marine environments without imposing changes to the microbial community through use of ex situ methods. A novel in situ incubation method for continuous time‐series measurements was used in Jordan Lake, North Carolina, during 2020–2021, to determine reaction kinetics for aerobic methane oxidation rates across a wide range of naturally varying methane (55–1833 nM) and dissolved oxygen (DO; 28–366 μM) concentrations and temperatures (17–30°C). Methane oxidation began immediately at the start of each of 21 incubations and methane oxidation rates were 1st order with respect to methane. The data density allowed for accurate calculation of 1st‐order rate constants, k, that ranged from 0.018 to 0.462 h−1 (R2 > 0.967). Addition of ammonium (20–45 μM) to natural concentrations ranging from 0.057 to 2.4 μM did not change aerobic methane oxidation rate kinetics, suggesting that the natural population of aerobic methane oxidizers in this eutrophic lake was not nitrogen limited. Values of k inversely correlated most strongly with initial DO concentrations (R2 = 0.82) rather than temperature. Values for k increased with Julian day throughout our sampling period, suggesting seasonal influences on methane oxidation via responses to geochemical changes or shifts in microbial community abundance and composition. These experiments demonstrate a high variability in the enzymatic capacity for 1st‐order methane oxidation rates in this eutrophic lake that is tightly and inversely coupled to oxygen concentrations. Measurements of in situ aerobic methane oxidation rate constants allow for the direct quantification and modeling of the microbial community's capacity for methane oxidation over a wide range of natural methane concentrations.

中文翻译：

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分层湖中原位需氧甲烷氧化速率


微生物需氧甲烷氧化是全球水生甲烷的重要汇。尽管其对全球甲烷通量很重要，但在不通过使用异位方法对微生物群落进行改变的情况下，在淡水或海洋环境中获得的有氧甲烷氧化率很少。 2020 年至 2021 年期间，北卡罗来纳州乔丹湖使用了一种用于连续时间序列测量的新型原位培养方法，以确定各种自然变化的甲烷 (55-1833 nM) 和溶解氧（DO；28–366 μM）浓度和温度（17–30°C）。甲烷氧化在 21 次孵化的每一次开始时立即开始，并且甲烷氧化速率相对于甲烷而言是一阶。数据密度允许精确计算一阶速率常数 k，范围从 0.018 到 0.462 h−1 (R2 > 0.967)。添加铵（20-45 μM）至自然浓度范围为 0.057 至 2.4 μM 不会改变需氧甲烷氧化速率动力学，表明该富营养化湖泊中需氧甲烷氧化剂的自然种群不受氮限制。 k 值与初始 DO 浓度 (R2 = 0.82) 而不是与温度呈负相关。在整个采样期间，k 值随着儒略日的增加而增加，表明季节性通过对地球化学变化或微生物群落丰度和组成的变化的响应对甲烷氧化产生影响。这些实验表明，在这个富营养化湖泊中，一阶甲烷氧化速率的酶能力存在很大的可变性，与氧浓度紧密且成反比。 原位需氧甲烷氧化速率常数的测量可以直接量化和建模微生物群落在广泛的天然甲烷浓度范围内的甲烷氧化能力。