Abstract:

【Objective】 Soil labile organic matter and carbon management index are important parameter representing carbon cycle in soil ecosystem. Study on dynamics of them in the artificial Robinia in loess hilly area so as to understand the change and effect evaluation during process of ecological restoration is of great importance. 【Method】 The research regarded Zhifanggou small watershed in typical erosion environment as a study plot, the selected artificial Robinia grown in different times were used as objects of study, the interchangeablely space-time method was adopted and the sloping cropland and the plot where the Platycladus orientailis are grown were used as contrasts. Several indexes were analyzed such as TOC, LOC, NLOC and evolution characters of carbon management index in the period of ecological restoration. 【Result】 The study indicates that the content of soil carbon is on the low side because human behavior has a negative effect on sloping cropland. However, the content of every group soil carbon increased drastically by planting Robinia. With the increasing of the time of conservation, the relationship is very remarkable. After 50 years of restoration, the content of TOC, LOC, NLOC and AI in the study plot increased by 271%，174%, 467%, and 271%, respectively, compared with sloping cropland. The increasing speed of NLOC was faster than LOC. It is assumed that the increased carbon by restoration is stored in an inactive form to produce active matter which is necessary for biont. And the soil carbon must keep active to fulfill the balance of carbon dynamic transformation. At initial stages, soil carbon management index increased remarkably. Later it increased but is then declined eventually. The rate of the content of TOC, LOC and NLOC in the study plot grown with Robinia was 49%, 34% and 61% of the control respectively. 【Conclusion】 The results suggested that it is impossible to increase the content of every group soil carbon by planting Robinia in the loess hilly area, but much longer time, compared with degradation of soil fertility after deforestation, is required to reach to the climax before vegetation destruction.

Key words: hilly loess plateau, artificial Robinia, soil active carbon, carbon management index