Organic Matter Dynamics and Microbial-Mineral Interaction across Aridity Gradients in the Atacama Desert

The Atacama Desert in Northern Chile, one of the driest places on Earth, provides a unique setting for studying organic matter preservation and microbial resilience in extreme aridity. Our project investigates the relationships among organic compounds, microbial communities, and mineral substrates across aridity gradients from the Coastal Cordillera via the hyperarid core to the foothills of the Andes. Its focus is on investigating surface crust formation, organic matter dynamics within these crusts, and the role of lithobiotic and endolithic communities in stabilising soil through interactions with mineral matrices. We combined gas chromatography-mass spectrometry (GC-MS) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) to analyse lipid biomarkers and microorganisms, biofilms, and biominerals, respectively. First results reveal that surface crusts from areas receiving more than 5 mm of annual rainfall show a much higher diversity and concentration of sterols and fatty acids compared to areas with less than 2 mm of rainfall, reflecting differences in biological diversity, crust composition, and organic degradation. Halite crusts display lower lipid contents than adjacent soil crusts. Samples from the hyperarid core exhibit abundant aromatic hydrocarbons, suggesting atmospheric input and microbial degradation. SEM images reveal close microbial-mineral interactions and their agglutinating effect on mineral particles. Integrating biomarker data with mineral and microbial analyses aims at unravelling how biogeochemical processes, past hydrological episodes, and microbial activity simultaneously shaped the desert landscape, contributing to a broader understanding of carbon dynamics in extreme environments.