干旱区沙漠化逆转过程植被–土壤碳储量的恢复演变规律研究

Restoration Changes in Organic Carbon Stocks of the Vegetation and Soil Ecosystems in the Reversion Process of Desertification in Arid Areas

摘要: 碳汇作用是陆地生态系统的重要生态功能之一，也是生态修复关注的重要方面。以地带性植被区为对照，应用空间代替时间的方法，在石羊河中游选择流动沙丘及造林恢复5年、15年和25年沙化土地样地，研究了沙漠化逆转过程沙地生态系统植被–土壤有机碳储量的恢复演变过程、规律及其影响因素。结果表明：固沙植被碳储量随沙漠化逆转过程先增加后降低，造林恢复25年平均固碳速率仅达到0.05 Mg/hm²•a。尽管沙漠化逆转过程的不同恢复阶段地上植被碳储量大，但是造林恢复5年、15年和25年沙化土地地下植被总碳储量也仅占到地带性植被的22.6%、54.9%和45.3%。0~1 m土壤和生态系统有机碳储量均随沙漠化逆转过程持续增加，造林恢复25年平均固碳速率分别达到0.48 Mg/hm²•a和0.53 Mg/hm²•a，远远高于固沙植被的固碳速率，而且0~5 cm表层土壤是有机碳储量为增长最快的层次。土壤有机碳储量所占比例均在87.5%以上，是沙漠化逆转不同恢复阶段沙化土地和地带性植被区的主要碳库。上述结果证明，固沙造林加速了沙漠化逆转过程，快速提高了沙化土地植被和表层土壤的碳储量，是固定大气CO2于沙地植被和土壤中的有效途径。但是，造林恢复25年沙化土地碳储量与地带性植被间依然存在明显差距，特别是地下植被和深层土壤有机碳储量还存在较大的增长潜力。

Abstract: Carbon sequestration is one of the important ecological functions of land ecosystem, and it is also an important aspect of ecological restoration. An unrestored shifting sand dune and three formerly shifting sand dunes that had been afforested for 5, 15 and 25 years were selected in the middle reaches of Shiyang River to study restoration changes in biomass carbon (BC) and soil organic carbon (SOC) stocks of the desertified lands in the reversion process of desertification and their influence factors. Results showed that BC stocks of the desertified lands was increased and then reduced in the reversion process of desertification, and the average vegetation carbon se-questration rate reached only 0.05 Mg/hm²•a in 25 years. Total BC stocks of the desertified lands afforested for 5 years, 15 years and 25 years only accounted for 22.6%, 54.9% and 45.3% of native zonal vegetation, respectively. SOC in 0 - 1 m layer and ecosystem stocks increased gradually in the reversion process of desertification, and the average carbon sequestration rate reached 0.48 Mg/hm²•a and 0.53 Mg/hm²•a in 25 years, respectively. 0 - 5 cm topsoil was the fastest layer for restoration of SOC stocks. SOC stocks accounted for more than 87.5% of the ecosystem organic C stocks, and soil was major C stocks of the different restoration stages in the reversion process of desertification and native zonal vegetation. Therefore, sand-fixation afforestation not only promoted the reversal of desertification, but also increased BC and topsoil SOC stocks rapidly, which proved that sand-fixation afforestation was the effective way to fix atmospheric CO2 in the desertified lands. However, C stocks of the desertified lands at the different restoration stages were lower than native zonal vegetation obviously and there was still a growth potential for BC of underground vegetation and SOC stocks of deep soil of the desertified lands afforested for 25 years.