Carbon flux responses of Alpine ecosystems to combined future climate drivers: Exploring different climate scenarios

During the 21st century, alpine areas are experiencing warming above the global average, making them more sensitive to climate change, with potentially dramatic effects on the release of significant quantities of CO2. Indeed, an expected impact of climate change is the alteration of the balance between carbon assimilation, through photosynthesis, in plant biomass and storage in soils, and its release to the atmosphere via respiration. To predict the effects of climate change on CO2 fluxes, monoliths were collected from an alpine ecosystem (2500m a.s.l.) in the Mont Blanc area (Val Veny, Courmayeur, Italy) and transferred to the Montpellier European Ecotron (CNRS, France) for climate manipulation experiments. Monoliths were exposed to current (~ 420ppm CO2, Control), and 2 future climate scenarios (~ 550ppm CO2 and ~ 800ppm CO2, according to RCP 4.5 and RCP 8.5, respectively) forecasted for 2070. The Ecotron’s experimental chambers allowed to manipulate different climate variables, such as temperature, precipitation, relative humidity, radiation, and CO2 concentration, simultaneously. To assess flux responses, measurements of gross primary productivity (GPP), ecosystem respiration (Reco), and net ecosystem exchange (NEE) were performed twice a week over the summer period. While the differences in terms of fluxes between Control and RCP 4.5 were small, for the RCP 8.5 a greater GPP and more noticeable Reco were observed compared to the other scenarios. Nevertheless, the NEE in RCP 8.5 showed that the alpine ecosystem could work as a sink compared to the other two scenarios, likely attributed to a substantial increase in green canopy.