Highly Active Biogenic Ice-Nucleating Particles of the West Greenland Phyllosphere may Impact Arctic Weather and Climate

Biogenic ice-nucleating particles (INPs) are widely detected in the Arctic atmosphere, where they potentially modulate Arctic mixed-phase clouds and consequently impact the regional climate. However, limited data on source environments, abundance, diversity, and atmospheric concentrations of biogenic INPs give rise to substantial uncertainties in aerosol-cloud interactions. As Arctic warming reduces snow and ice cover, accelerates greening, and increases periods of vegetation exposure, the aerosolization of plant-associated biogenic INPs may be enhanced. To better constrain the role of the phyllosphere microbiota and INPs in Arctic mixed-phase clouds, we collected quantitative data on INP and microbial community composition across three sites in western Greenland (Kangerlussuaq, Ilulissat, and Disko Island). Sampling was conducted from June to September, with each site visited two to three times. We combined freezing assays with bacterial community profiling and cultivation-based approaches. In addition, atmospheric samples were collected on filters (0.8 pore size) continuously from May to September on Disko Island to monitor variation in bioaerosol types and concentrations across the summer season. We further investigated phyllosphere-associated microbial communities and biogenic INPs. Highly active INPs were detected across all locations, with onset freezing temperatures ranging from -3°C to -7°C. The highest INP concentration per gram of plant material active at -10°C was observed in Kangerlussuaq in September, when temperatures drop to subzero degrees, suggesting that environmental factors, such as temperature, trigger INP production. Members of the genus Pseudomonas were consistently present in the plant samples, and cultivation studies yielded eight ice-nucleation active (INA) isolates, all affiliated with this genus. Whole genome sequencing revealed that the isolates represented novel species and contained genes that encode ice-nucleation active proteins (INpro). Our findings show that the Arctic phyllosphere can serve as a source of highly active biogenic INPs and thus may contribute to regional atmospheric INP levels and further impact cloud processes. We conclude that biogenic INPs derived from the Arctic phyllosphere need to be included in atmospheric models to improve predictions of Arctic climate feedback.