In arid and semi-arid regions, the climate is characterized by long dry periods interspersed by occasional precipitation, owing to which the soil surface undergoes frequent cycles of drying and rewetting (D/RW). This influences underground carbon (C) mineralization and produces a transient CO₂ pulse after each rewetting. Although the rewetting event is short-lived, the CO₂ production that it triggers may constitute a significant portion of the carbon released annually because little carbon is released in dry periods. The aim of this paper is to understand the response of CO₂ efflux to repeated D/RW cycles and to elucidate the mechanisms that regulate carbon cycling in dry lands. As a case study, we examined the soil from a sand-fixed vegetation area in the southeastern fringe of the temperate Tengger Desert of northern China. We subjected soil samples to laboratory incubation at a constant temperature of 25℃, with simulated rainfalls occurring at 10-day intervals. Three treatment conditions differed in terms of precipitation volume (5, 10, or 20 mm). Soil respiration rate and soil water content were measured 1 h before rewetting (baseline); 0.5, 2, 12, and 24 h after rewetting; and every 24 h until the next cycle. We analyzed the changes in soil CO₂ efflux and moisture after each cycle by comparing peak and average respiration rates and total CO₂ production. The results showed that all cycles stimulated soil respiration, which peaked at 0.5 h after rainfall and then gradually decreased to baseline level. Respiration rates and carbon release both increased with increasing precipitation. As the D/RW cycles proceeded, the peak and average soil respiration rates and amounts of carbon released tended to decrease. Although peak respiration rates following the first rewetting increased with precipitation volume, peak respiration rates of the second and third rewetting of soils with different precipitation amounts did not vary with precipitation volume but did correlate with antecedent moisture.
Our results indicate that rewetting of dry soil significantly accelerates soil CO₂ efflux, but the magnitude of this effect gradually decreases as D/RW cycles are repeated. Furthermore, the intensity of drying and rewetting and the soil water present before precipitation both influence the soil respiration response in temperate desert soil. This implies that the soil respiration response depends not only on rainfall but also on antecedent soil conditions. Climate models predict that precipitation patterns will likely intensify in mid-latitude regions, with increases in total precipitation, drought period duration, and frequency of extreme precipitation events. The water environment of these soils will become more severe, which will intensify the effects of pulsed precipitation events and further impact soil C storage and fertility due to the relatively low levels of organic C content.