Abstract: Drying-rewetting of soil is a common phenomenon in arid and semiarid region. In recent years, the impacts of dryingrewetting events on soil C and N cycling have been given widely attention considering the increasing occurrences of extreme precipitation and drought. In this study, we used a laboratorial incubation method to study the responses of soil C and N mineralization rates to soil drying-rewetting and the timedelay effects in a Mongolian pine (Pinus sylvestris var. mongolica) plantation in Keerqin Sandy Land, a semiarid region in northern China. We found that the soil CO₂ release rate gradually decreased with the increasing soil drought. However, the soil respiration rate could recover to its original level when rewetting the drying soil. Soil cumulative CO₂ release and NO₃^--N concentration were lower in dryingrewetting treatment compared to the wet treatment (keeping continuously moist conditions), but soil cumulative CO₂ release, NO₃^--N concentration and net nitrification rate were higher than that in drought treatment (keeping continuously dry conditions). During the delay stage, there were timedelay effects of soil drying-rewetting events on the soil CO₂ release rate and its accumulation, but not for the soil net nitrification rate. Our results indicated that soil water was an important environmental factor controlling soil C and N cycles, and different timedelay effects of soil drying-rewetting events existed on soil C and N mineralization rates in the Mongolian pine plantation in the semiarid region.

Key words: urban building land, non-point source pollution, simulation, area thre-shold., prediction