中文摘要：

用静态箱法于2012年生长季（5～10月）对黄土高原围封草地常见半灌木铁杆蒿（Artemisia gmelinii）灌丛内外土壤呼吸速率和净生态系统CO2交换速率及其主要环境因子进行实地观测,并对草地土壤基本理化性质进行分析,以揭示铁杆蒿灌丛内外碳交换变化规律及其影响因素。结果显示：（1）铁杆蒿灌丛内的土壤呼吸和净生态系统CO2交换的日交换速率均显著高于灌丛外;灌丛内外土壤呼吸速率和净生态系统CO2交换速率的峰值出现时间一致,且灌丛内显著高于灌丛外;土壤呼吸速率的峰值出现在8月份,净生态系统CO2交换速率的峰值出现在9月份。（2）灌丛内外土壤呼吸速率日动态均呈“单峰型”变化趋势,生长季平均值都接近5月份观测值,分别为（5.49±0.18）和（2.93±0.04） g·m-2·d-1;灌丛内外净生态系统CO2交换速率日动态均以“S”型变化趋势为主,在水分亏缺时期表现为微弱的“双峰”型趋势。（3）灌丛内生长季净生态系统CO2交换速率平均值为（-3.86±0.09） g·m-2·d-1,是灌丛外草地（-1.19±0.07） g·m-2·d-1的3.2倍,灌丛内外均表现为碳汇。研究表明,铁杆蒿灌丛存在“肥岛”现象,有助于该区草地生态系统有机碳的积累,土壤水分和土壤温度是影响灌丛内外土壤呼吸速率的主要因素,而灌丛内外净生态系统CO2交换速率主要受土壤水分的影响。

英文摘要：

Grassland ecosystem is one of the most important terrestrial ecosystems and plays a critical role in global carbon cycle.However,compared with other ecosystems,studies of carbon tock in grassland ecosystem,especially in the Loess Plateau were relatively less.Shrubs are the dominant plant life form in Loess Plateau,Northern China.Based on the continuous measurement of soil respiration and net ecosystems CO2 exchange rate within and outside of the Artemisia gmelinii shrub patch in the grassland of Loess Plateau by using closed chamber method in the growing season of 2012,the temporal variations of soil respiration and net ecosystems CO2 exchange were studied with the effects of temperature and soil water content.The results are as follows：（1）The diurnal variation of soil respiration rate both within and outside of the shrub patch showed an asymmetric single-peak pattern,while that of net ecosystems CO2 exchange rate both showed sigmoid curve under normal circumstances and “twin peaks” type with the water deficit.The peak values of soil respiration rate appear in August while net ecosystems CO2 exchange rate in September.（2）The daily averages of soil respiration and net ecosystems CO2 exchange rate within the shrub patch are significantly higher than that outside.The averages of soil respiration rate within and outside of shrub patch in the growing season are 5.49 and 2.93 g·m-2·d-1,respectively,and are close to the observed value in May.（3）The averages of net ecosystems CO2 exchange rate within and outside of shrub patch in the growing season are -3.86 and -1.19 g·m-2·d-1,close to that observed in May and July,respectively.“fertile island” is observed under the shrub,which can contribute to the carbon accumulation in this region.Soil moisture and soil temperature are the key factors controlling the variation of soil respiration rate,both within and outside of shrub patch,while net ecosystems CO2 exchange rate was mainly controlled by soil moisture.