When spring and autumn frosts coincide: their limited impact on ecosystem carbon fluxes

Abstract Frosts, increasingly prevalent due to global warming, have the potential to negate the carbon storage benefits of an extended growing season, thus exacerbating global warming. However, existing research primarily targets dominant species, with limited evidence on carbon fluxes at the ecosystem scale. Using a manipulative experiment simulating 7-day frosts in a temperate grassland, we found that, frosts produced minimal impact on gross ecosystem productivity (GEP) and ecosystem respiration (ER), but altered their difference (i.e., net ecosystem productivity, NEP), and this effect persisted throughout the growing season. During the growing seasons excluding frost periods, spring frosts increased NEP, while autumn frosts decreased it, and the combination of both frosts neutralized NEP. The early-stage (2018-2020) impacts of frosts on NEP may be attributed to plant eco-physiological changes, whereas late-stage (2021-2023) impacts were explained by shifts in plant community structure. Our findings suggest that more frequent frosts in both seasons may not increase carbon emissions in temperate grasslands. Understanding these patterns is crucial for predicting carbon balance and developing effective climate-change mitigation strategies in response to the future warmer climate.