Abstract: The responses of soil ciliate communities to the returning of cropland to forest were investigated to examine whether ciliates can be used to evaluate the effects of ecological restoration. Four sampling sites were selected, with three different returned forest types and an abandoned land as control in Hui County of Longnan City, Gansu Province, China. At each site, the community characteristics of soil ciliates and vegetation, along with physical and chemical parameters of the soil, were analyzed. Ciliates were isolated from the soil using nonflooded Petri dish method and in vivo observation. Enumeration was carried out using direct-culture counting method. A total of 127 soil ciliate species belonging to 9 classes, 18 orders, 28 families, and 47 genera were identified. The species richness, density, and species diversity index of soil ciliates in the ecologically restored sites were significantly higher than those of the control site. The dominant group changed from Colpodida in control site to Sporadotrichida in ecologically restored sites, indicating that soil ciliate communities tended to complicate with the progress of the returning cropland to forest project. Soil ciliate community characteristics were closely related to vegetation type. Soil water content, organic matter content, total nitrogen content, and electrical conductivity were the dominant factors affecting soil ciliate community composition. After returning cropland to forest, the vegetation gradually recovered, soil physical-chemical factors changed, and soil ciliate communities showed positive response to the restoration of ecological environment. These findings suggest that ciliate community composition can be used as an indicator for the successful restoration of cropland to forest.

Key words: Hunan, double-rice cropping, carbon efficiency, life cycle assessment.