中文摘要：

在干旱／半干旱地区，土壤干湿交替是非常普遍的自然现象。近年来，随着极端降水和极端干旱气候事件增加，干湿交替对土壤C和N循环过程影响受到广泛重视。本研究以我国北方半干旱地区科尔沁沙地樟子松人工林为对象，模拟土壤干湿交替对土壤C和N矿化速率影响及其延时效应。结果表明，土壤呼吸CO2释放速率随土壤干旱化增加不断降低，干旱土壤重新湿润后，土壤呼吸速率能够迅速恢复到初始水平。与恒湿处理相比，干湿交替变化能够降低土壤呼吸CO2释放累积量和土壤硝态氮含量；而干湿交替处理土壤呼吸CO2释放累积量、土壤硝态氮含量和净硝化速率均显著高于恒干处理。在干湿交替结束后延时期间，土壤呼吸CO2释放速率、累积释放量对干湿交替变化表现出延时性，而土壤净硝化速率在不同处理间差异不显著。研究表明，土壤水分是影响半干旱地区沙地樟子松人工林土壤c和N循环的重要环境因子，且土壤C和N矿化速率对土壤干湿交替变化的延时响应存在差异。

英文摘要：

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 mineraliza- tion 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 C02 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 control- ling 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.