宁夏荒漠草原自然恢复演替过程中土壤有机碳及其分布的变化

Variations in soil organic carbon content and distribution during natural restoration succession on the desert steppe in Ningxia

以宁夏荒漠草原自然恢复的围封草地为对象,通过野外调查和室内分析,研究了未封育、封育3、5、7和10年的草地总有机碳及其在土壤剖面和不同粒级团聚体中的分布。结果表明,土壤有机碳含量随封育年限的增加呈波动性增加,除0~5cm土层外,各土层有机碳含量以封育7年、10年的草地较高;就有机碳在不同粒径团聚体中的分布看,0~10cm表层土壤以封育3年及未封育草地各粒级团聚体有机碳含量较高,而10~40cm土层各粒级团聚体有机碳随封育年限的延长呈增加趋势,各土层团聚体有机碳含量均以1~0.5mm与0.5~0.25mm粒级较高;各粒级团聚体对有机碳的贡献率在0~10cm表层以<0.25mm微团聚体最高,10~20cm土层以>5mm粒级和<0.25mm粒级较高,20~40cm土层以>5 mm粒级最高。综上所述,封育有利于荒漠草原土壤有机碳的固存,退化荒漠草原生态环境恢复在封育7年时出现转折;随土层的加深,团聚体有机碳贡献率对封育的响应减弱,且大团聚体对全土有机碳的贡献率逐渐增大。

Fencing （enclosure） is one of the strategies used to promote the natural restoration of ecological com-munities on the desert steppe in Ningxia. To explore the effects of enclosure on soil organic carbon and its dis-tribution, field studies were conducted at sites with 3, 5, 7, and 10 years of enclosure. Soil samples were col-lected to determine the total organic carbon concentration and its distribution at different soil depths and in soil aggregates. The results showed that the soil organic carbon concentrations were higher in 7-year and l 〇 -year enclosed grasslands than in those enclosed for shorter times, except at 0 - 5 cm depth. The concentrations of soil organic carbon were lower in the 0 -5 cm and 5 -10 cm soil layers than in the 10 -20 cm and 20 -40 cm soil layers. The soil organic carbon concentrations in soil aggregate particles at 0 -10 cm depth were highest in the 3-year enclosed grassland, while those at 10 -40 cm depth increased with longer enclosure times. The max- imum soil organic carbon contents were in aggregates with 1 -0. 5 mm and 0. 5 -0. 25 mm diameters. Aggre-gates of 〈C0. 25 mm, 〉5 mm or 〈C0. 25 mm, and 〉 5 mm made the largest contributions to soil organic carbon content at 0 -1〇 cm depth, 10 -20 cm depth and 20 -4〇 cm depth, respectively. The contribution of aggre-gates to soil organic carbon content decreased with increasing enclosure times. As the soil depth increased, the contribution of aggregates to soil organic carbon content decreased, but the contributions of macroaggregates to soil organic carbon content increased. In conclusion, enclosure was beneficial for carbon sequestration. The restoration of the ecosystem on the degraded desert steppe appeared to undergo a transition at the 7th year of enclosure.