Severe warming alters biomass allocation and enhances ecosystem respiration in an alpine grassland: evidence from a short-term mesocosm experiment
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Background and aims
Alpine ecosystems are highly sensitive to climate change, with rising temperatures threatening ecosystem structure and function. This study examined the short-term responses of alpine grassland ecosystems (Mont Blanc, Italy) to projected climate scenarios using an Ecotron mesocosm experiment.
Methods
Ecosystem monoliths were exposed to current (~420 ppm CO□) and future CO□ concentrations (~550 and ~800 ppm) under RCP 4.5 and RCP 8.5 scenarios, incorporating changes in temperature, precipitation, humidity, and radiation. CO□ fluxes ( NEP, GPP, R eco ), soil chemistry, vegetation coverage, above- and belowground biomass, and plant functional traits were assessed throughout the experiment.
Results
Alpine grassland ecosystems withstood moderate warming (RCP 4.5), while under severe warming (RCP 8.5), GPP , vegetation cover and biomass increased with a shift toward aboveground allocation, although daytime NEP remained stable as gains were offset by higher R eco , with no detectable water and nutrients limitations. On a diel basis, higher GPP was offset by enhanced R eco , indicating a potential towards net C loss. Salix herbacea exhibited functional trait adjustments—higher LMA and N a , and elevated δ 1 □N—reflecting greater leaf longevity, water-use efficiency, and altered nitrogen metabolism, suggesting potential community reorganization.
Conclusion
Over a single growing season, alpine ecosystems appeared relatively stable under moderate warming. However, under the more severe RCP 8.5 scenario, biomass allocation shifted toward greater aboveground and reduced belowground investment, leading to altered C fluxes that, if sustained over the long-term, could drive the ecosystem C balance from a sink to a source. Responses were plant species-specific, indicating uneven acclimation within the community.
