Dry extremes are increasing in frequency. DRYSOM assesses the responses of soil carbon cycling to re-occurring summer drought in a 19 year-long irrigation experiment in naturally drought-prone pine forests (Pfynwald). Results show that irrigation induced a carbon loss in the organic layer but a gain in the mineral soil. Mechanisms for the vertical redistribution of soil organic matter include (1) an increased incorporation of litter into the mineral soil through soil fauna evidenced by a much higher faunal abundance and litter mass loss through macrofauna. (2) In addition, 13C pulse-labeling revealed that belowground carbon inputs were reduced by drought. These SOM shifts have consequences for microbial communities and long-term carbon storage.