The diel vertical migration of microbes within snowpacks driven by solar radiation and nutrients

Seasonal snowpacks are inhabited by various microbes despite their ephemeral and cold environments. Physicochemical conditions in snowpacks drastically change with day–night cycles; however, their effect on the microbial community is largely unknown. This study described the diel vertical migration (DVM) of microbes within a snowpack in an alpine forest in northern Japan. Periodic sampling revealed that motile microbes were distributed near the surface at night but actively migrated to a depth of 10 to 20 cm during the day, whereas immotile microbes remained near the snow surface. The vertical migration of microbes was synchronized with the intensity of solar radiation, suggesting that the microbes moved downward to avoid intense solar radiation. Soluble nutrients were the highest at the snow surface, suggesting that surface snow provides a favorable environment for microbial growth. These results indicated that motile microbes migrate diurnally within the snowpack to remain under the best conditions for their growth. Snow core sampling revealed that microbes were mostly present above a depth of 30 cm in the snowpack. Therefore, the snow layer above this depth, referred to as the microbial active snow surface (MASS) layer, is important for the life cycles of microbes and biogeochemical cycles within snowpacks.