| description |
Aquifer ecosystems, typically dark and oligotrophic, are thought to rely on lithoautotrophs as primary producers of organic carbon, especially when the input of fresh material from the surface soils is limited. In this study we followed the archaeal 16S rRNA gene diversity from surface soils to the groundwater and to the rock matrix of aquifer and aquitard rocks in the carbonate-rock Hainich Critical Zone Exploratory in Thuringia/central Germany. The RNA-based sequence data suggested that the archaeal communities in each three habitats were totally distinct. The archaeal groups detected in the surface soils composed less than 0.1 % of the groups found in the groundwater suggesting a limited input from the surface to the subsurface. The sequence data indicated that the main archaeal metabolism in the groundwater was heterotrophy mostly carried out by the Woesearchaeota phylum, whereas most archaea detected in the rocks (Thaumarchaeota, Bathyarchaeota, and Hadesarchaea) were predicted autotrophs. 13C-CO2 stable isotope probing (SIP) using filtered groundwater also identified ammonia-oxidizing Thaumarchaeota, Bathyarchaeota and methanogens as potential lithoautotrophs; but these groups composed only a miniscule fraction of the archaea in the initial groundwater samples. Prepared aquifer rock material, exposed in one groundwater well for 6 months were colonized mainly by two ammonia-oxidizing Thaumarchaeotal groups, who were potentially labelled during subsequent 13C-CO2 SIP incubations. These results suggest that archaeal CO2 fixation is mainly occurring in the aquifer rocks rather than in the groundwater. |