Acton lake sediment: Bioturbation Microcosms Raw sequence reads

Methane emissions from aquatic ecosystems are increasingly recognized as substantial, yetvariable contributions to global greenhouse gas emissions. This is in part due to the challenge of modeling biologic parameters that affect methane emissions from a wide range of sediments. For example, the impacts of fish bioturbation on methane emissions in the literature have been shown to result in a gradient of reduced to enhanced methane emissions from sediments, however, it is likely that variation in experimental fish density, and consequently the frequency of bioturbation by fish likely impacts this outcome. To explore how the frequency of disturbance impacts the levels of methane emissions and the corresponding microbial communities associated with producing methane, we quantified greenhouse gas emissions and microbial community composition in sediment microcosms treated with various frequencies of mechanical disturbance, analogous to different levels of activity in benthic feeding fish. Greenhouse gas emissions were largely driven by methane ebullition and were highest for the intermediate disturbance frequency (disturbance every 7 days). The lowest emissions were for the highest frequency treatment (3 days). In terms of total microbial community structure, no statistical difference was observed in the community structure of any disturbance treatment (0, 3, 7, 14 days) or sediment depth (1 cm, 3 cm) measured. Looking specifically at methanogenic Archaea however, a shift towards greater relative abundance of a putatively oxygen-tolerant methanogenic strain (ca. Methanothrix paradoxum) was observed for the highest frequency treatments and at depths impacted by disturbance (1 cm). This was further supported by a linear decrease in quantitative abundance of methanogens (assessed by qPCR of the mcrA gene) with increased disturbance frequency in bioturbated sediments (1 cm) opposed to those below the zone of bioturbation (3 cm). This suggest that the disturbance treatments affected methanogen populations, likely through oxygen exposure. However, total methane emissions were not simply a function of methanogen populations and were likely impacted by the residence time of methane in the lower frequency disturbance treatments. Low frequency mechanical disruption results in lower methane ebullition compared to higher frequency treatments which in turn resulted in reduced overall methane release and likely enhanced methanotrophic activities. The impacts of disturbance on methanotrophic communities will be the subject of follow up work

水生生态系统的甲烷排放对全球温室气体排放的贡献既可观又存在显著波动，这在一定程度上源于对广泛分布沉积物中影响甲烷排放的生物学参数进行建模的挑战。例如，已有研究表明，鱼类生物扰动（bioturbation）对沉积物甲烷排放的影响可呈现从排放减弱到增强的梯度变化，但实验所用鱼类密度的差异，以及由此导致的鱼类生物扰动频率差异，很可能会影响这一实验结果。为探究扰动频率如何影响甲烷排放水平以及与之相关的产甲烷微生物群落，本研究通过设置不同频率的机械扰动（模拟底栖摄食鱼类的不同活动强度）处理沉积物微宇宙（sediment microcosms），对温室气体排放与微生物群落组成进行了定量分析。实验结果显示，温室气体排放主要由甲烷气泡喷发驱动，且在中等扰动频率（每7天扰动一次）组中排放水平最高，而最高扰动频率（每3天扰动一次）组的排放水平最低。在整体微生物群落结构方面，所有扰动处理组（0、3、7、14天扰动周期）以及不同沉积物深度（1cm、3cm）的群落结构均未观测到统计学差异。然而，针对产甲烷古菌（methanogenic Archaea）的分析显示，在最高扰动频率组以及受扰动影响的沉积物表层（1cm深度），一种推测具有耐氧性的产甲烷菌株（约为Methanothrix paradoxum）的相对丰度显著升高。这一结果进一步得到了定量分析的支持：在受生物扰动影响的表层沉积物（1cm）中，产甲烷菌的定量丰度（通过针对mcrA基因的定量PCR（qPCR）检测）随扰动频率升高呈线性下降，而在未受生物扰动影响的深层沉积物（3cm）中则未出现该趋势。这表明扰动处理可能通过氧气暴露影响产甲烷菌种群。然而，总甲烷排放并非仅由产甲烷菌种群决定，低频扰动组中甲烷的停留时间可能也对排放水平产生了影响。相较于高频扰动组，低频机械扰动会降低甲烷气泡喷发效率，进而减少整体甲烷释放量，并可能增强甲烷氧化微生物的活性。有关扰动对甲烷氧化微生物群落的影响将作为后续研究的主题