Lichens Bite the Dust – A Bioweathering Scenario in the Atacama Desert

Bioweathering mediated by microorganisms plays a significant role in biogeochemical cycles on global scales over geological timescales. Single processes induced by specific taxa have been described but could rarely be demonstrated for complex communities that dominate whole landscapes. The recently discovered grit crust of the coastal Atacama Desert, which is a transitional community between a cryptogamic ground cover and a rock-bound lithic assemblage, offers the unique chance to elucidate various bioweathering processes that occur simultaneously. Here, we present a bioweathering scenario of this biocenosis including processes such as penetration of the lithomatrix, microbial responses to wet-dry cycles, alkalinolysis, enzyme activity, and mineral re-localization. Frequently occurring fog, for example, led to a volume increase of microorganisms and the lithomatrix. This, together with pH shifts and dust accumulation, consequently results in biophysical breakdown and the formation of a terrestrial protopedon, an initial stage of pedogenesis fueled by the grit crust.