本研究采用空间代替时间的方法，以宁夏南部黄土丘陵区紫花苜蓿人工草地以及退化后形成的次生草地为研究对象，针对当地人工草地前期刈割后期撂荒的管理模式，对处于不同退耕年限（0a、2a、10a、30a）的草地植被和土壤碳储量和固碳速率进行了研究，获得主要研究结果如下： 1、在本研究所涉及的年限内，紫花苜蓿始终处于人工草地的主要优势种地位，但随着退耕年限的增加，紫花苜蓿在群落中的重要值下降（由97.33下降到22.20），到退耕30a时，紫花苜蓿人工草地逐步向长芒草草地的方向演替。多样性参数随退耕年限增加的变化情况如下：丰富度、物种多样性和均匀度均呈上升趋势，分别上升了1.22、1.55和0.40，其中均匀度变化较平缓，生态优势度下降了0.70。 2、土壤有机质含量、全氮含量和全磷含量均随着管理模式的变化呈先下降后上升的趋势，土壤容重先增大后减小，转折点均在退耕2a时。其中土壤有机质含量和全氮含量均在0-10cm土层达到最大。 3、随着管理模式的变化，紫花苜蓿地上部分和根系生物量碳储量均呈现先上升后下降的趋势，退耕10a的植被碳储量极显著高于退耕2a和30a，其中退耕10a割草地的根系碳储量比未受到人为干扰草地高出70.3%。 土壤理化性质中，土壤全氮含量和土壤容重与人工草地植被生物量碳储量具有密切关系，三者相互作用共同影响草地碳储量的积累。 4、0-100cm土壤总有机碳储量随退耕年限的增加而增加，变化范围为6.08-12.58kg m-2,退耕30a时已达到全国（11.52-12.04 kg m-2）的平均水平。表层（0-20cm）土壤有机碳储量在退耕初期（0-2a）略有下降，之后不断上升，撂荒后到退耕30a增幅达到123%，在各土层中增幅最大。植被生物量是土壤有机碳储量的重要影响因素，二者存在极显著的相关关系（P＜0.01），且可以用三次多项式函数较好的拟合。 5、人工草地总有机碳储量由坡耕地到退耕2a略有上升约0.1kg m-2，割草地在退耕10a时碳储量增幅最大，达到66.7%，到退耕30a时上升到12.615kg m-2。退耕10a时，未受人为干扰的人工草地总有机碳储量仅为割草地的58.3%，说明一定程度的刈割可以对人工草地碳固存能力的提高起到积极作用。 人工草地在退耕2a-10a间的固碳速率已由退耕初期的0.05 kg m-2 a-1上升到0.52 kg m-2 a-1，退耕10a-30a间固碳速率虽有下降但仍高于退耕初期。利用表征土壤结构的重要指标之一土壤容重与人工草地总有机碳储量进行相关分析得出其与人工草地总有机碳储量存在极显著的线性负相关，R2=0.943。另外，其他种群的出现、群落的演替和群落结构的改变导致的植被生物量的变化对人工草地总有机碳储量具有重要影响。

Alfalfa artificial grassland in loess hilly and gully regions of southern ningxia was studied in a space series of replaced time courses. With the management mode of mowing in the earlier years and abandonment in the later years, the variation of vegetation and soil carbon storage and rate in different restoration years were studied. 1、 During 2a-30a,the alfalfa was still the dominant of the artificial grassland.The importance value of alfalfa decreased from 97.33 to 22.20 with the increase of restoration years.The Margalef, Alatalo and Shannon-Wiener index increased by 1.22,1.55 and 0.40 respectively and the simpson index decreased by 0.70. 2、 With the change of management mode, the organic content, total nitrogen content and phosphorus content declined first and then rose.The changing trend of soil volume weight showed in opposite direction.It changed in 2a in the trends of all of them.Both soil organic content and total nitrogen content reached maximum in the 0-10cm layer. 3、 Both of the above and under ground biomass of alfalfa rose first and then diclined and the root biomass increased.with the change of management mode.The biomass carbon storage in 10a showed significantly higher than that in 2a and 30a.The root carbon storage of mowing field in 10a was above the grassland without artificial thinning at 70.3%. 4、 Soil organic carbon(SOC) of the 0-100cm layer increase with the addition of restoration years and it ranged from 6.08 kg m-2 to12.58kg m-2. SOC in surface soil (layer 0-20cm) fell slightly in early stage (0-2a) and then rose rapidly. In 30a, the increase amplitude turned to be 123% and it reached the maxmum.SOC in this layer.Biomass was an important factor of soil organic storage and there was a significant correlation between them. 5、 The total organic sequestration of artificial grassland increased by 0.1kg m-2 in early stage.The growing rate of it in mowing field reached the maximum 66.7% in 10a.The total organic storage of grassland without artificial thinning reached only 58.3% of mowing field. The organic sequestration rate of grassland during 2a -10a increased from 0.05 kg m-2 a-1 in early age to 0.52 kg m-2 a-1.The average organic sequestration rate decreased but was still higher than early stage.There were significantly negative linear correlation between soil volume weight and total organic sequestration of artificial grassland and R2=0.943.In addition,there was significant correlation between the biomass of other species and total organic storage.The emerge of other species,succession of community and variation of community structure had a great influence on total organic sequestration of artificial grassland.