中文摘要：

为揭示毛乌素沙地沙漠化逆转过程中土壤颗粒的固碳效应,选择陕北榆林治沙区从流沙地、半固定沙地到林龄为20～55年生的灌木和20～50年生的乔木固沙林地,采用物理分组法分析了土壤砂粒、粉粒、黏粒结合碳的演变特征和累积速率.结果表明：对比流沙地,土壤总有机碳及各颗粒碳含量在两种固沙林地均呈显著增加趋势,并以表层0～5 cm土壤碳含量增幅最高.从流沙地到55年生灌木和50年生乔木固沙林地,0～5 cm土层砂粒碳密度增速均为0.05 Mg·hm^（-2）·a^（-1）,粉粒碳密度增速分别为0.05和0.08 Mg·hm^（-2）·a^（-1）,而黏粒碳密度增速分别为0.02和0.03 Mg·hm^（-2）·a^（-1）.0～20 cm土层,两种林地各颗粒碳密度增速平均为0～5cm土层的2.1倍.按此增速到50～55年生的固沙林地时,两种林地0～20 cm土层的砂粒碳、粉粒碳和黏粒碳密度分别比流沙地平均提高6.7、18.1、4.4倍,并且颗粒碳对总有机碳的累积贡献率平均为粉粒碳（39.7%）≈砂粒碳（34.6%）〉黏粒碳（25.6%）.综上,毛乌素沙地沙漠化逆转过程土壤颗粒均表现出显著的固碳效应,且以砂粒和粉粒为主要固碳组分.

英文摘要：

The aim of this study was to investigate the effects of carbon sequestration in soil particle- sized fractions during reversion of desertification at Mu Us Sand Land, soil samples were collected from quicksand land, semifixed sand and fixed sand lands that were established by the shrub for 20-55 year-old and the arbor for 20-50 year-old at sand control region of Yulin in Northern Shaanxi Province. The dynamics and sequestration rate of soil organic carbon （SOC） associated with sand, silt and clay were measured by physical fractionation method. The results indicated that, compared with quicksand area, the carbon content in total SOC and all soil particle-sized fractions at both sand-fixing sand forest lands showed a significant increasing trend, and the maximum carbon con- tent was observed in the top layer of soils. From quicksand to fixed sand land with 55-year-old shrub and 50-year-old arbor, the annual sequestration rate of carbon stock in 0-5 cm soil depth was same in silt by 0.05 Mg· hm-2 · a-1. The increase rate of carbon sequestration in sand was 0.05 and 0.08 Mg·hm-2 · a-1, and in clay was 0.02 and 0.03 Mg· hm-2 · a-1 at shrubs and arbors land, respec- tively. The increase rate of carbon sequestration in 0-20 cm soil layer for all the soil particles was averagely 2.1 times as that of 0-5 cm. At the annual increase rate of carbon, the stock of carbon in sand, silt and clay at the two fixed sand lands were increased by 6.7, 18.1 and 4.4 times after 50- 55 year-old reversion of quicksand land to fixed sand. In addition, the average percentages that contributed to accumulation of total SOC by different particles in 0-20 cm soil were in the order of silt carbon （39.7%）≈ sand carbon （34.6%） 〉 clay carbon （25.6%）. Generally, the soil particlesized fractions had great carbon sequestration potential during reversion of desertification in Mu Us Sand Land, and the slit and sand were the main fractions for carbon sequestration at both fixed sand lands.