Temporary lake sustains active heterotrophic microbial communities in poly-extreme high-altitude environments of the Atacama Desert

The Puna de Atacama is a high-altitude desert region renowned for its extreme environmental conditions, resulting in limited biological activity and low organic carbon availability. This study investigates the influence of a temporary lake on bacterial communities in the Barrancas Blancas plain, a previously understudied region of this mountain desert. A 70-m moisture transect was established from the lake margin to a dry reference site. Comprehensive analyses were conducted, including physicochemical and enzymatic analyses, ATP content, a specific DNA extraction method targeting intact microbial cells, amplicon sequencing, and multivariate statistics. The results show that the temporary lake supports high bacterial abundance and microbial activity, particularly on soil surfaces located 8-23 m from the shoreline (the "middle of the transect"). Here, bacterial abundance ranged between 10⁷ and 10⁸ 16S rRNA gene copies g^-1 soil, ATP content between 10^-12-10^-11 mol g^-1 soil, and fluorescein diacetate hydrolytic activity between 49 and 127 μg fluorescein g^-1 soil 3 h^-1 - values comparable to those reported in non-desert environments such as forest, and semi-arid soils. High surface activity correlates with the presence of Bacteroidota (classes Chitinophagales and Sphingobacteriales) and Proteobacteria (classes Caulobacterales and Xanthomonadales), key heterotrophic recyclers in oligotrophic ecosystems, that may degrade complex organic polymers derived from aquatic crustaceans and microbial mat-like structures. These specialised functions likely link microbial activity to higher trophic levels via the microbial loop, indicating that the lake and its surrounding soils sustain an active food web with complex interactions despite the prevailing oligotrophic conditions. Overall, this study underscores the crucial role of temporary lakes as ecological hotspots supporting life in extreme environments.