中国科学院水利部水土保持研究所机构知识库

黄土高原是我国重要的生态脆弱区，土壤侵蚀和生态系统退化严重。经过近50年的植被恢复，该区土壤侵蚀和水土流失得到显著控制。随着土壤侵蚀的遏制，植被恢复的土壤效应及退耕地碳汇功能逐渐成为该区生态环境建设迫切需要认识的科学问题。本研究以黄土高原退耕刺槐林地为研究对象，通过测定碳氮稳定性同位素丰度，辨识了不同退耕年限土壤和团聚体碳氮来源及其与退耕年限、土层和地点的关系，并分析了土壤碳氮矿化特征及其主要影响因素，从而为准确评价退耕地土壤碳汇功能提供理论依据，并为认识以土壤碳氮循环过程为主导的陆地生态系统地球化学循环奠定基础。所取得的主要结论如下：
（1）农地退耕显著降低了土壤δ¹³C和δ¹⁵N的自然丰度，这种降低随退耕年限的延长而加剧。不同地点土壤δ¹³C和δ¹⁵N自然丰度差异显著，0-10 cm土层显著低于10-20 cm土层。黄土高原农地退耕种植刺槐显著提高了来源于林地的碳氮含量，这种作用随植被恢复年限的延长显著增加，并且主要体现在0-10 cm土层。不同地点间不同来源有机碳和全氮差异显著，并且在0-10 cm土层的差异更为明显。0-10 cm土层土壤中来源于林地的有机碳和全氮含量随土壤质地由细变粗呈降低趋势。
（2）农地退耕显著降低了土壤水稳性团聚体δ¹³C和δ¹⁵N的自然丰度，这种降低作用随退耕年限的延长而加剧。土壤大团聚体和微团聚体中δ¹³C和δ¹⁵N丰度随土壤质地由细变粗呈递增趋势，而来源于林地的有机碳和全氮含量则呈递减趋势。此外，随着粘粒含量降低，退耕刺槐林地团聚体中来源于林地和农地碳氮的差异逐渐减小。0-10 cm土层团聚体来源于林地有机碳和全氮增加幅度要大于10-20 cm土层。
（3）退耕刺槐林地中，团聚体δ¹³C和δ¹⁵N丰度整体表现为大团聚体<微团聚体<粉粘粒，而大团聚体和微团聚体之间差异较小。退耕后新输入的有机碳和全氮主要集中在大团聚体和微团聚体中。
（4）农地退耕显著增加了土壤有机碳和全氮的矿化量，并且受土层、退耕年限和地点的影响。刺槐林地0-10 cm土层有机碳和全氮的矿化量是10-20 cm土

The Loess Plateau is an important ecological fragile area in China, and soil erosion and ecosystem degradation are serious. After nearly 50 years of vegetation restoration, the eco-environment was improved. With the control of soil erosion, the soil effect of vegetation restoration and the function of carbon sink of re-vegetated soil are becoming the urgent scientific problems to be recognized in the ecological environment construction of this area. This study aimed at the re-vegetated soil of Loess Plateau and analyzed the distribution characteristics of soil and aggregate carbon and nitrogen stable isotope distribution and identification of carbon and nitrogen sources, to obtain the contents of carbon and nitrogen deprived from forest or cropland in soil and aggregates. In order to reveal the relationship between re-vegetation ages, soil depth, soil texture and aggregates and the dynamic changes of soil organic carbon and total nitrogen. This study can provide a theoretical foundation to evaluate accurately the function and sustainability of soil carbon sequestration of re-vegetation. And it can also contribute to understanding the terrestrial ecosystem carbon and nitrogen cycle which dominated by soil organic carbon and nitrogen cycling. The main conclusions are as follows:
(1) Re-vegetation can decrease the natural abundance of soil δ¹³C and δ¹⁵N in the 0-10 cm and 10-20 cm soil layer, but the effect differed with re-vegetation age. Re-vegetation can increase the concentrations of soil organic carbon and total nitrogen deprived from forest and both with the increase of vegetation restoration years significantly increased. The changes of soil organic carbon and total nitrogen deprived from forest and cropland were different with sites, and the difference in 0-10 cm soil layer is more obvious. The results show that, with the change from fine soils to coarse soils, the content of organic carbon and total nitrogen in 0-10 cm soil depth deprived from forest decreased.
(2) Re-vegetation can decrease the natural abundance of soil δ¹³C and δ¹⁵N in