Microbial hotspots related to fog-dependent Tillandsia landbeckii dunes in the Atacama  Desert
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.