Extreme drought–accelerated dissolved carbon metabolism triggers pulsed CO 2 outgassing in karst lakes

Karst aquatic ecosystems are important reservoirs of dissolved carbon (C), supporting dynamic CO 2 fluxes through the biological C pump. However, our current understanding of how sophisticated interactions between aquatic microbiomes and dissolved C turnover constrain the timing of CO 2 sequestration and emission remains limited. Here we capture an extreme drought event and the ensuing relatively wet conditions from systematic investigations in karst lakes, demonstrating that temporally distinct microbiomes are tuned to the metabolic patterns of dissolved C and thereby modulate CO 2 emissions. Specifically, we find that the extreme drought accelerates respiration of dissolved organic C, sharply increasing the CO 2 evasion rate. Wet conditions stimulate photosynthetic uptake of dissolved inorganic C, consuming lake CO 2 while promoting labile organic C formation. We therefore propose that during the observed extreme drought, pulses of CO 2 emissions from the study karst lakes occur after wet conditions end, as a consequence of rapid remineralization of newly produced bioavailable organic C. Our findings highlight the crucial importance of managing periodic CO 2 outgassing from karst waters under drought conditions for the implementation of region-specific C neutrality strategies.