河西走廊中段绿洲退化土地退耕种植苜蓿的固碳效应

Carbon sequestration effect following retirement of degraded croplands into alfalfa forage land in the middle of Hexi Corridor region,northwest China

土地利用变化和耕作管理是人类影响陆地生态系统碳过程一个重要方面。对河西走廊中段张掖绿洲退化土地退耕种植苜蓿5a后土壤性状的分析表明,49个退耕苜蓿地土壤与相邻未退耕农田土壤配对样本的比较,退耕苜蓿地0～15cm土层土壤粒级组成和容重并未发生显著变化,但土壤pH平均提高了0.11个单位,电导率降低34.8%,土壤有机碳(SOC)和全氮(全N)含量较对照农田土壤平均提高18.5%和9.3%,活性有机碳(labileC)增加53.3%。SOC含量受海拔高度和土壤粒粉粒含量的影响,退耕后SOC和全N的增加幅度沙壤土高于粉壤土,而labileC的增加幅度沙壤土低于粉壤土。退耕苜蓿地0～15cm土层SOC和全N储量较农田土壤分别增加2.84Mghm-2和0.21Mghm-2,土壤C、N的固存率平均为0.57Mghm-2a-1和0.04Mghm-2a-1,表明退化土地由1年生作物向多年生牧草的转变有显著的固碳效应和潜力。活性有机碳的变化较总有机碳的变化更为显著,表明活性有机碳对土地利用变化的响应更为敏感。

Land use change and tillage management is an important aspect for influencing carbon process in terrestrial ecosystem by human. The objective of this study is to identify effects of conversion of degraded cropland to alfalfa forage land on soil carbon sequestration and related soil properties in Zhangye oasis in the middle of Hexi corridor region. We selected 49 sites along altitude gradient as sampling sites where alfalfa were planted for 5 years,and taken paired alfalfa soil and adjacent crop soil in the 015cm depth. The results showed that no changes in soil particle size and bulk density were found following land use change. Compared to adjacent cropland,soil pH value increased in average 0.11 unit but electrical conductivity （EC） decreased by 34.8% in alfalfa field,and the averaged concentrations of SOC,total N and Labile C increased by 18.5%,9.3% and 53.3%,respectively. SOC concentration was influenced by altitude and soil silt and clay content. The sandy loam soils had a greater increase percentage of SOC and total N but a smaller increase percentage of labile C compared to the silt loam soils after land use conversion. SOC and total N storage in the 015 cm depth increased 2.84 Mg hm-2 and 0.21 Mg hm-2,respectively,and the average rates of C and N sequestration were 0.57 Mg hm-2a-1 and 0.04 Mg hm-2a-1 following the retirement of degraded croplands into alfalfa forage land over 5 years. Our results suggest that conversion of annual crops to perennial alfalfa had significant carbon sequestration effect and great potential in the region. Labile C showed a more remarkable increase than SOC following crops to alfalfa conversion,suggesting that it is a more sensitive index of C dynamics under the short-term land use change.