Cumulative respiration in two drying and rewetting cycles depends on the number and distribution of moist days

• Two DRW cycles were imposed with varying numbers of moist or dry days in either the first or second cycle.
• Respiration flush size upon rewetting increased with increasing number of prior dry days.
• Cumulative respiration in the moist period increased with number of moist days.
• Effect of varying the number of dry or moist days on respiration: first > second cycle
• Distribution and length of moist and dry periods in DRW are important for respiration.

Surface soils in arid and semi-arid climates are exposed to drying and rewetting (DRW) which can influence soil organic matter decomposition. However, factors influencing cumulative respiration in DRW treatments remain unclear, as total cumulative respiration compared to constantly moist control (CM) has been found to be higher, lower or not different. An incubation experiment was conducted to determine the influence of the number of dry and moist days and their distribution in two DRW cycles on respiration rate and cumulative respiration in each DRW cycle and at the end of the experiment. The number of moist or dry days ranged in either the first or second DRW cycle between 10 and 35. The other cycle consisted of 5 dry and 5 moist days. The CM treatment was maintained at 70% of field capacity throughout. Cumulative respiration in CM was greater than that in DRW treatments with the difference stronger in treatments with varying numbers of dry days than those with varying numbers of moist days. In DRW treatments, cumulative respiration in the dry period differed little between treatments. The size of the respiration flush upon rewetting increased with increasing number of prior dry days with a stronger effect in the first DRW cycle. Cumulative respiration in the moist period increased with number of moist days, particularly when the number of moist days varied in the first cycle. It is concluded that in DRW, the respiration flush upon rewetting increases with the number of dry days whereas cumulative respiration is a function of the number of moist days. Further, varying the number of dry or moist days has a greater effect in the first than in the second cycle.