Linking Biocrust Architecture and Dispersal: Reproductive Ecology of Lichens of the Grit Crust in the Coastal Atacama Desert

Abstract

Biological soil crusts are essential components of arid ecosystems, yet the establishment and dispersal of lichen-dominated crusts remain poorly understood. In the coastal Atacama Desert, a unique biocrust type—the grit crust—is formed by minute chlorolichens colonising mobile quartz particles. We investigated the developmental stages and dispersal mechanisms of these micro-lichens using high-resolution digital microscopy, scanning electron microscopy and micro-manipulative direct PCR. Microscopic structures on individual quartz grains included melanised fungal micro-colonies, exploratory hyphal networks, free-living green algal colonies and developing lichen thalli. Molecular analyses identified mycobionts of the Caliciaceae alongside photobionts of the green algal genus Trebouxia, occurring in both lichenised and non-lichenised states. The presence of free-living algal cells on grit surfaces suggests that unassociated photobionts function as environmental reservoirs priming symbiosis formation. Our findings support a sequential assembly model in which airborne fungal spores colonise mineral substrates before encountering compatible photobionts. Multiple dispersal vectors—including fungal spores, lichen fragments and algal cells carried by wind and dust—confer high colonisation and recovery potential to grit crust communities, likely driving the rapid turnover, spatial heterogeneity and productivity characteristic of this exceptional lichen-dominated desert biocrust.