Repeated drying and rewetting cycles accelerate bacterial growth recovery after rewetting

Two patterns of bacterial growth response upon drying and rewetting (DRW) of soils have previously been identified. Bacterial growth can either start increasing immediately after rewetting in a linear fashion ("type 1" response) or start increasing exponentially after a lag period ("type 2" response). The effect of repeated DRW cycles was studied in three soils with different response patterns after a single DRW cycle ("type 1", "type 2" with a short lag period and "type 2" with a long lag period). The soils were exposed to seven DRW cycles, and respiration and bacterial growth were monitored after 1, 2, 3, 5, and 7 cycles. Exposure to repeated DRW shifted the bacterial growth response from a "type 2" to a "type 1" pattern, resulting in an accelerated growth recovery to a pre-disturbance growth rate. Bacterial growth in soils that initially had a "type 1" response also tended to recover faster after each subsequent DRW cycle. The respiration patterns after DRW also indicated the same transition from a "type 2" to a "type 1" pattern. Our results show that exposure to repeated DRW cycles will shape the bacterial response to future DRW cycles, which might be mediated by a shift in species composition, a physiological adjustment, evolutionary changes, or a combination of the three.