Microbial methanogenesis in the sulfate-reducing zone of sediments in the Eckernforde Bay, SW Baltic Sea
Microbial methanogenesis in the sulfate-reducing zone of sediments in the Eckernforde Bay, SW Baltic Sea
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DOI：
10.5194/bg-15-137-2018
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发表时间：
2018-01-10
期刊：
影响因子：
4.9
通讯作者：
Treude, Tina
中科院分区：
文献类型：
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作者：
Maltby, Johanna;Steinle, Lea;Treude, Tina
底栖微生物产甲烷是海洋系统中甲烷的已知来源。在大多数沉积物中，大部分甲烷生成位于硫酸盐还原区以下，因为硫酸盐还原剂在主要底物氢和乙酸盐的竞争中胜过产甲烷菌。甲烷生成和硫酸盐还原的共存之前已经被证明，并且可能通过产甲烷菌使用非竞争性底物，如甲醇或甲基化胺。然而，知识的大小，季节性和环境控制的这种非竞争性甲烷生产是稀疏的。在本研究中，在硫酸盐还原带（SRZ产甲烷）的存在下，在沉积物（海底以下0-30厘米，厘米b. s.f.）进行了调查。波罗的海西南部季节性缺氧的埃克恩福德湾。2013年3月至2014年9月，在采样区“Boknis Eck”每季度测定一次水柱参数，如氧、温度和盐度，以及孔隙水地球化学和底栖甲烷生成速率，以调查季节性环境变化对SRZ甲烷生成速率和分布的影响，估计其对底栖甲烷排放的潜在贡献，并确定负责SRZ产甲烷的潜在产甲烷基团。在存在或不存在硫酸盐还原剂的情况下，在添加非竞争性底物后，在四个实验设置中研究了产甲烷的代谢途径：（1）未改变的沉积物分批孵育（净产甲烷），（2）C-14-碳酸氢盐标记实验（氢营养产甲烷），（3）添加两种甲烷的操作实验，（硫酸盐还原剂抑制剂）、2-溴乙烷磺酸盐（产甲烷菌抑制剂）或甲醇（非竞争性底物，潜在的产甲烷），和（4）添加C-13标记的甲醇（潜在的甲基营养型产甲烷）。与甲醇孵育后，进行分子分析，以确定甲基营养型产甲烷过程中的关键功能产甲烷基团。还为了比较SRZ产甲烷与硫酸盐还原区（>30 cm b. s.f.）以下的产甲烷的幅度，在2013年9月采集的样品中，通过C-14-碳酸氢根放射性示踪剂培养来确定氢营养型甲烷生成。SRZ甲烷生成在上部30 cm b. s.f.（0.2 nmol cm（-3）d（-1））至2013年11月（1.3 nmol cm（-3）d（-1））和2014年3月（0.2 nmol cm（-3）d（-1））至9月（0.4 nmol cm（3）d（-1））。其幅度和分布似乎是由有机质的可用性，C / N，温度和氧气在水柱，揭示了较高的利率在温暖，分层，缺氧的季节（9月至11月）相比，寒冷，含氧的季节（3月至6月）每年。大多数SRZ产甲烷可能是由非竞争性底物的使用驱动的（例如，甲醇和甲基化的化合物），以避免与硫酸盐还原剂竞争，如在甲醇添加后观察到的潜在产甲烷活性增加1000-3000倍所示。因此，竞争性的氢营养甲烷增加的沉积物中只有低于硫酸盐渗透的深度（>30厘米b. s.f.）。使用甲烷八叠球菌科特异性引物通过PCR检测到甲烷八叠球菌科的成员，这些成员可能与所观察到的SRZ甲烷生成有关。本研究表明，SRZ甲烷生成是埃克恩福德湾底栖甲烷收支和碳循环的重要组成部分。虽然它的贡献，从沉积物到水柱的甲烷排放量可能是轻微的，SRZ产甲烷可以直接喂到甲烷氧化以上的硫酸盐-甲烷过渡带。
Benthic microbial methanogenesis is a known source of methane in marine systems. In most sediments, the majority of methanogenesis is located below the sulfate-reducing zone, as sulfate reducers outcompete methanogens for the major substrates hydrogen and acetate. The coexistence of methanogenesis and sulfate reduction has been shown before and is possible through the usage of noncompetitive substrates by methanogens such as methanol or methylated amines. However, knowledge about the magnitude, seasonality, and environmental controls of this noncompetitive methane production is sparse. In the present study, the presence of methanogenesis within the sulfate reduction zone (SRZ methanogenesis) was investigated in sediments (0-30 cm below seafloor, cm b.s.f.) of the seasonally hypoxic Eckernforde Bay in the southwestern Baltic Sea. Water column parameters such as oxygen, temperature, and salinity together with porewater geochemistry and benthic methanogenesis rates were determined in the sampling area "Boknis Eck" quarterly from March 2013 to September 2014 to investigate the effect of seasonal environmental changes on the rate and distribution of SRZ methanogenesis, to estimate its potential contribution to benthic methane emissions, and to identify the potential methanogenic groups responsible for SRZ methanogenesis. The metabolic pathway of methanogenesis in the presence or absence of sulfate reducers, which after the addition of a noncompetitive substrate was studied in four experimental setups: (1) unaltered sediment batch incubations (net methanogenesis), (2) C-14-bicarbonate labeling experiments (hydrogenotrophic methanogenesis), (3) manipulated experiments with the addition of either molybdate (sulfate reducer inhibitor), 2-bromoethanesulfonate (methanogen inhibitor), or methanol (noncompetitive substrate, potential methanogenesis), and (4) the addition of C-13-labeled methanol (potential methylotrophic methanogenesis). After incubation with methanol, molecular analyses were conducted to identify key functional methanogenic groups during methylotrophic methanogenesis. To also compare the magnitudes of SRZ methanogenesis with methanogenesis below the sulfate reduction zone (>30 cm b.s.f.), hydrogenotrophic methanogenesis was determined by C-14-bicarbonate radiotracer incubation in samples collected in September 2013.SRZ methanogenesis changed seasonally in the upper 30 cm b.s.f. with rates increasing from March (0.2 nmol cm(-3) d(-1)) to November (1.3 nmol cm(-3) d(-1)) 2013 and March (0.2 nmol cm(-3) d(-1)) to September (0.4 nmol cm(3) d(-1)) 2014. Its magnitude and distribution appeared to be controlled by organic matter availability, C / N, temperature, and oxygen in the water column, revealing higher rates in the warm, stratified, hypoxic seasons (September-November) compared to the colder, oxygenated seasons (March-June) of each year. The majority of SRZ methanogenesis was likely driven by the usage of noncompetitive substrates (e.g., methanol and methylated compounds) to avoid competition with sulfate reducers, as was indicated by the 1000-3000-fold increase in potential methanogenesis activity observed after methanol addition. Accordingly, competitive hydrogenotrophic methanogenesis increased in the sediment only below the depth of sulfate penetration (>30 cm b.s.f.). Members of the family Methanosarcinaceae, which are known for methylotrophic methanogenesis, were detected by PCR using Methanosarcinaceae-specific primers and are likely to be responsible for the observed SRZ methanogenesis.The present study indicates that SRZ methanogenesis is an important component of the benthic methane budget and carbon cycling in Eckernforde Bay. Although its contributions to methane emissions from the sediment into the water column are probably minor, SRZ methanogenesis could directly feed into methane oxidation above the sulfate-methane transition zone.