Methane production by microphytobenthos and its contribution to the benthic methane flux from the coastal zone of the Baltic Sea

温室气体甲烷（CH 4）的自然排放量不断增加，对地球气候产生了重大影响。在这方面，近岸沃茨发挥着关键作用，因为与开放沃茨相比，这些地区的水柱甲烷浓度要高得多。然而，鲜为人知的是，甲烷排放源在浅海岸带或其贡献的大气甲烷通量。此外，最近的一系列研究表明，微生物甲烷生产并不限于严格的缺氧条件，并可能广泛存在于好氧水体。这种含氧甲烷的产生使甲烷源靠近水面，从而加强了向大气的通量。基于这些最新的调查和初步生产和甲烷形成之间的联系，我们假设，微型植物底栖生物（MPB）社区，作为主要的初级生产者在许多沿海系统，在浅水CH 4动态中发挥了重要作用。为了探索MPB相关的CH 4生产，我们将调查这个CH 4源的潜力，进行孵化实验，并确定丰富的底栖硅藻物种的初级生产和CH 4生产率。使用一种新的腔衰荡光谱为基础的半连续方法在封闭的孵育实验将使高时间分辨率的白天/黑夜周期的CH 4生产的灵敏测量。实验将在受控的温度和光照条件下进行，并将使用选定的MPB硅藻的纯性/异性克隆培养物，以确定主要效应物和CH 4产生率最高的物种。使用13 C标记的前体底物的实验将进行识别和表征MPB相关的CH 4生产途径。以往的研究，好氧甲烷生产大多是机械的实验室研究，使用培养样品;测量的甲烷生产率是否代表那些在自然系统中没有确定。为了克服这些局限性，在我们的研究中，与克隆培养物的孵化实验将伴随着自然MPB社区采样从浅沃茨在Askö岛（瑞典波罗的海）和内部沿海沃茨的Darss-Zingst Bodden链（德国波罗的海），从而涵盖不同的沉积物类型，水动力条件，和MPB社区。为了使底栖甲烷通量MPB社区与整体底栖和海洋到空气的甲烷通量，我们将确定CH 4通量之间的沉积物，水柱，和大气在这两个研究领域。

Increasing natural emissions of the greenhouse gas methane (CH4) substantially impact the Earth climate. In this context, near-shore waters play a key role because water column CH4 concentrations in these areas are much higher when compared with the open waters. However, little is known about CH4 emitters in shallow coastal zones or their contribution to the atmospheric CH4 flux. Moreover, a series of recent studies indicate that microbial CH4 production is not limited to strictly anoxic conditions and might be widespread in the oxic water column. This oxic CH4 production places the CH4 source close to the water surface, thereby intensifying fluxes to the atmosphere. Based on these recent investigations and a proposed linkage between primary production and CH4 formation, we hypothesize that microphytobenthos (MPB) communities, as major primary producer in many coastal systems, play a significant role in shallow-water CH4 dynamics. To explore MPB-associated CH4 production, we will investigate the potential of this CH4 source, by conducting incubation experiments and determining the rates of both primary production and CH4 production by abundant benthic diatom species. The use of a novel cavity ring-down spectroscopy-based semi-continuous method in closed incubation experiments will enable sensitive measurements of CH4 production in high temporal resolution over day/night cycles. The experiments will be undertaken under controlled temperature and light conditions and will use axenic/xenic clonal cultures of selected MPB diatoms to identify the main effectors and those species with the highest CH4 production rates. Experiments using 13C-labeled precursor substrates will be performed to identify and characterize MPB-associated CH4 production pathways. Previous studies of oxic CH4 production were mostly mechanistic laboratory studies that used culture samples; whether the measured CH4 production rates were representative of those in natural systems was not determined. To overcome these limitations in our study, the incubation experiments with clonal cultures will be accompanied by natural MPB communities sampled from the shallow waters at Askö island (Swedish Baltic Sea) and from the inner coastal waters of the Darss-Zingst Bodden Chain (German Baltic Sea), thus covering different sediment types, hydrodynamic conditions, and MPB communities. To align benthic CH4 fluxes from MPB communities with overall benthic and sea-to-air fluxes of CH4, we will determine CH4 fluxes between the sediment, water column, and atmosphere in both study areas.