利用网格采样法研究了藏北退化高寒草原土壤有机碳变化及与土壤物理性质的关系.结果表明：0～10和11～20 cm土层有机碳含量、有机碳密度及其土层差异均为：轻度退化草地＞正常草地＞中度退化草地＞严重退化草地；有机碳含量、有机碳密度年变化速率则呈相反趋势，且表层土壤有机碳变幅均明显高于其下层土壤.正常草地、轻度退化草地0～10 cm土层有机碳年累积量为0.018和0.003 g·kg.-1，分别为11～20 cm土层年累积量的6.0和2.0倍；中度、严重退化草地0～10 cm土层年损失量达0.150和0.231 g·kg-1，分别为11～20 cm土层年损失量的2.3和2.2倍.中度、严重退化草地有机碳年损失总量为正常草地和轻度退化草地年累积总量的38倍，有机碳年损失总量达7.87×105 t C，且具有较大的潜在退化态势.土壤有机碳与5.0～1.0、1.0～0.5和0.5～0.25 mm团聚体含量，土壤有机碳与土壤容重、土壤含水量间均呈极显著或显著正相关.
By using grid sampling method, the spatialtemporal variation of soil organic carbon (SOC) and its relations to soil physical properties in degraded
alpine grasslands in North Tibet were studied. The SOC content and its density both in surface (0-10 cm) and in subsurface (10-20 cm) layers decreased in order of slightly degraded grassland > normal grassland > moderately degraded grasslands > seriously degraded grasslands, and the differences of SOC content and its density between the two layers showed the same variation trend. An opposite trend was observed in the annual variation rates of SOC content and its density in different grasslands, and the variation was larger in surface than in subsurface layer. The annual accumulation rate of SOC in 0-10 cm layer in not degraded and slightly degraded grasslands was 0.018 and 0.003 g·kg-1, being 6.0 and 2.0 times of that in 10-20 cm layer, while the annual loss rate of SOC in 0-10 cm layer in moderately and seriously degraded grasslands was 0.150 and 0.231 g·kg-1, being 2.3 and 2.2 times of that in 10-20 cm layer, respectively. The total annual loss of SOC in moderately and seriously degraded grasslands was 3.8 times of the total annual accumulation of SOC in not degraded and slightly degraded grasslands. The degraded alpine grasslands in North Tibet had an average annual SOC loss of 7.87×10.7 t C·a-1, and a greater potential to further loss in the future. The SOC content was significantly positively correlated with the contents of 5.0-1.0 mm, 1.0-0.5 mm, and 0.5-0.25 mm soil aggregates, soil bulk density, and soil moisture content.