Climate change alters microbial seasonality in the mountains
During every alpine spring, snowmelt causes remarkable yet unseen changes belowground. As the climate warms, these invisible seasonal transitions will occur earlier in the year, with important implications for nutrient cycles.
Climate change is causing large reductions in winter snow cover and earlier spring snowmelt in alpine ecosystems. Ski resorts are investing vast amounts of money in snow cannons every year just to stay viable. Underneath the disappearing snow another community is also facing challenges due to climate warming. Soil microbial communities, which control key nutrient cycles on which ecosystems depend, are experiencing rapid change in their seasonal dynamics. How they will respond to these changes, and what the consequences will be for nutrient cycles and plant productivity, remains poorly understood.
Snow acts as an insulating blanket that allows soil dwelling microbes to perform important ecosystem functions throughout the alpine winter. In spring, snowmelt causes sudden changes in osmotic potential that lead to microbial cell lysis and death. This is associated with pulses in soil nutrients that coincide with the onset of plant growth. However, it remains unknown how earlier spring snowmelt will affect seasonal transitions in soil microbial communities and the nutrient cycles that they regulate. We set out to test this using a field experiment in alpine grassland high in the Austrian Alps.
We found that earlier snowmelt advances the timing of closely linked seasonal transitions in soil microbial community composition, microbial functioning, and soil biogeochemistry. Snowmelt is predicted to occur 50–130 days earlier in the European Alps by the end of the century. This would allow much less time for soil microbes to perform important ecological functions in winter, such as breaking down plant litter. It could also cause a mismatch between soil nutrient pulses during snowmelt and the onset of plant growth in spring, which would threaten plant productivity and nutrient retention in these globally widespread ecosystems. Mountain regions are experiencing rapid climate warming, the changes in seasonality this brings for belowground life will have far-reaching implications for the nutrient cycles upon which aboveground life depends.
For the UK project team it was a welcome change of scene to be in the beautiful Oetztal Alps. Working high in the mountains came with challenges but assistance was forthcoming from many quarters. The nearby mountain refuge Hohe Mut Alm generously lent us their motorised ‘snow-blower’ to remove snow from the experimental plots in order to simulate reduced winter snow cover and earlier spring. They continued to be very understanding when a small but vital piece of the snow-blower fell off while we were using it and disappeared into the snow! At this point, manual shovelling took over, powered by some very energetic and enthusiastic students from the University of Innsbruck. The Obergurgl resort helped us out with free uplift for fieldworkers, equipment and soil samples. All of this support, together with the lab space, kit and lodgings provided by the Alpine Research Centre Obergurgl, enabled us to sample throughout the winter and spring, as the belowground microbial seasonal transition took place.