Atacama Desert soils as potential habitat for life at the extreme dry limit

In the soils of the Atacama Desert its evolutionary history is buried and thus memorized. This is because of the extreme and prolonged dryness, which enabled the preservation of organic residues of life. Until now it is not known if and how life has survived under such conditions. Therefore, we aimed at quantifying and identifying different sources and hotspots of organic matter (OM) along four west-east directed transects, spanning the Atacama Desert from north to south and selected soil profiles which were dug to 0.6-3.4 m depth. Soil organic carbon (SOC) concentrations were determined by temperature-dependent differentiation; n-alkane and PAH signatures, as markers for plant residues and atmospheric, external inputs of OM, respectively, were detected using gas-chromatographic separation and mass-sensitive detection; potential hotspots of OM accumulation were identified by soil moisture content, electric conductivity and microbial community structure. We found that with increasing aridity SOC stocks decreased from 53±53 to 4±1 t ha-1 in the topsoil. In the subsoil, SOC concentrations peaked between 40 and 150 cm depth, also in hyper-arid regions, adding 74.0-94.3% of subsoil SOC to the topsoil SOC stock. Biomarker analyses revealed that OM was partly derived by plant growth, some came by atmospheric transport and that there exist habitats of life at greater soil depth. Now further studies are needed to investigate how much of this OM is derived from the atmosphere or was built in-situ and what keeps the deep biosphere alive and who is colonizing it.