Groundwater environments provide habitats for diverse microbial communities, and although Archaea usually represent a minor fraction of communities, they are involved in key biogeochemical cycles. We analysed the archaeal diversity within a mixed carbonate-rock/siliciclastic-rock aquifer system, vertically from surface soils to subsurface groundwater including aquifer and aquitard rocks. Archaeal diversity was also characterized along a monitoring well transect that spanned surface land uses from forest/woodland to grassland and cropland. Sequencing of 16S rRNA genes showed that only a few surface soil-inhabiting Archaea were present in the groundwater suggesting a restricted input from the surface. Dominant groups in the groundwater belonged to the marine group I (MG-I) Thaumarchaeota and the Woesearchaeota. Most of the groups detected in the aquitard and aquifer rock samples belonged to either cultured or predicted lithoautotrophs (e.g., Thaumarchaeota or Hadesarchaea). Furthermore, to target autotrophs, a series of ¹³CO₂ stable isotope-probing experiments were conducted using filter pieces obtained after filtration of 10,000 L of groundwater to concentrate cells. These incubations identified the SAGMCG Thaumarchaeota and Bathyarchaeota as groundwater autotrophs. Overall, the results suggest that the majority of Archaea on rocks are fixing CO₂, while archaeal autotrophy seems to be limited in the groundwater.

中文翻译：

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碳酸盐/硅质岩岩石地下水生态系统中的古细菌多样性和二氧化碳固定剂。

地下水环境为各种微生物群落提供了栖息地，尽管古生菌通常仅占群落的一小部分，但它们参与了重要的生物地球化学循环。我们分析了碳酸盐-岩石/硅质碎石-岩石混合含水层系统中古细菌的多样性，垂直地从表层土壤到地下含水层，包括含水层和阿奎达岩石。沿监测井断面也表征了古细菌的多样性，该断面覆盖了从森林/林地到草地和农田的地表土地用途。对16S rRNA基因的测序表明，地下水中仅存有少量表层土壤居住古细菌，这表明表层的输入受到限制。地下水中的主要群体属于海洋I类群（MG-I）Thaumarchaeota和Woesearchaeota。在水母和含水层岩石样品中检测到的大多数组属于培养的或预测的岩石自养生物（例如Thaumarchaeota或Hadesarchaea）。此外，针对自养生物，一系列使用10,000 L地下水过滤浓缩细胞后获得的滤片，进行了^13个CO ₂稳定同位素探测实验。这些温育确定了SAGMCG Thaumarchaeota和Bathyarchaeota是地下水自养生物。总体而言，研究结果表明，岩石上的古细菌大多数固定了CO ₂，而古细菌的自养作用似乎仅限于地下水。