SRA

The hyperarid Atacama Desert in northern Chile is believed to be the most hostile habitat for microbial life. Vascular plants, which may provide nutrients and resources via litter deposition are mostly absent in the barren landscape. However, isolated patches of vegetation exist across the coastal mountain range, which are related to fog corridors. Unique dune ecosystems dominated by rootless Tillandsia landbeckii exist at elevations of ca. 900-1200 m asl and receive water and nutrients exclusively from the Pacific Ocean via fog deposition. This study aims at investigating the relative importance of fog moisture on plants and microbial interactions in a fossil sand dune located at the Rio Loa canyon. Our interdisciplinary approach combines sedimentological, geochemical and microbial techniques. Relict plant material was 14C-dated to develop a chronology of past dune growth events. The bacterial community composition was analysed based on 16S rRNA gene sequencing and lipid biomarker analysis (PLFAs, GDGTs). Compound-specific hydrogen isotope analysis of leaf wax n-alkanes was used to characterize changes in hydrological conditions. Moreover, variations in grain sizes and elemental composition were used to reconstruct changes in depositional regime. Our results point to multiple stages of plant growth and dieback during the past ~1,200 years. We find that the soil microbial abundance, richness and diversity was generally higher in core sections with elevated amounts of plant material. Recurrent rewetting events during specific climate periods in the past may have supported active microbial communities in the sand dune sustained by nutrients released from plant litter. This is further supported by significant changes in d15N pointing to increased biological nitrogen cycling. Due to the extreme aridity, the sand dune retains a well-preserved environmental record that reflects concomitant changes in hydrological conditions, plant growth and microbial abundance and diversity during periods of climate extremes.