Lichen species across Alaska produce highly active and stable ice nucleators

Forty years ago, lichens were identified as extraordinary biological ice nucleators (INs) that enable ice formation at temperatures close to 0 & LCIRC;C. By employing INs, lichens thrive in freezing environments that surpass the physiological limits of other vegetation, thus making them the majority of vegetative biomass in northern ecosystems. Aerosolized lichen INs might further impact cloud glaciation and have the potential to alter atmospheric processes in a warming Arctic. Despite the ecological importance and formidable ice nucleation activities, the abundance, diversity, sources, and role of ice nucleation in lichens remain poorly understood. Here, we investigate the ice nucleation capabilities of lichens collected from various ecosystems across Alaska. We find ice nucleating activity in lichen to be widespread, particularly in the coastal rainforest of southeast Alaska. Across 29 investigated lichen, all species show ice nucleation temperatures above -15 & LCIRC;C, and & SIM;30 % initiate freezing at temperatures above -6 & LCIRC;C. Concentration series of lichen ice nucleation assays in combination with statistical analysis reveal that the lichens contain two subpopulations of INs, similar to previous observations in bacteria. However, unlike the bacterial INs, the lichen INs appear as independent subpopulations resistant to freeze-thaw cycles and against temperature treatment. The ubiquity and high stability of the lichen INs suggest that they can impact local atmospheric processes and that ice nucleation activity is an essential trait for their survival in cold environments.

Automated summary

Forty years ago, lichens were found to possess extraordinary ice nucleation abilities, allowing them to thrive in freezing environments. The ice nucleators in lichens have the potential to impact cloud glaciation and atmospheric processes in the warming Arctic. This study investigates the ice nucleation capabilities of lichens collected from different ecosystems in Alaska, and finds widespread ice nucleating activity, particularly in the coastal rainforest of southeast Alaska. These findings suggest that the ice nucleation activity is an essential trait for the survival of lichens in cold environments and can influence local atmospheric processes.