Drought memory and vegetation shifts triggered by recurrent extreme drought events in alpine peatlands amplify the sensitivity of carbon sink function to drought

Climate change is expected to intensify the frequency and severity of extreme drought events, profoundly influencing terrestrial ecosystem carbon budgets. Peatlands are crucial carbon reservoirs in the global carbon cycle, storing nearly one-third of the world's soil carbon. However, our understanding of how alpine peatland ecosystems respond to recurrent extreme droughts, particularly in terms of carbon flux dynamics, remains incomplete. Through a six-year in situ experiment, we investigated the effects of sustained extreme drought on carbon flux dynamics in alpine peatlands. Our results demonstrate that extreme drought significantly reduces net ecosystem exchange (NEE), gross ecosystem productivity (GEP), and ecosystem respiration (Reco). These impacts intensified with cumulative drought years due to weakened CO 2 sink resistance. Moreover, extreme drought disrupts the stability of the peatland's CO 2 absorption capacity, with CO 2 and CH 4 fluxes being more sensitive to soil moisture than to temperature. However, as arid conditions intensify, the influence of drought-induced soil moisture alterations on peatland carbon sinks wanes. Notably, temperature exhibits significant negative correlations with the resistance of NEE ( R = −0.530, P < 0.05) and Reco ( R = −0.473, P < 0.05), key indicators defined as the ecosystem's capacity to maintain stable carbon exchange rates despite the perturbations caused by extreme drought. After six years of extreme drought, we observed a shift in plant community composition, with a decline in hygrophyte proportions and an increase in xerophyte species and abundance. NEE demonstrated a unimodal relationship with aboveground biomass, peaking at 450 g/m 2 , while GEP exhibited an inverse pattern. These findings emphasize the importance of integrating plant community dynamics and drought memory effects into Earth system models to enhance predictions of extreme drought impacts on peatland carbon sink functionality under future climate scenarios, thereby amplifying understanding the sensitivity of these ecosystems to drought.