Abstract:Soil ciliates are some of the most complex and highly differentiated soil unicellular eukaryotes and play an important role in soil ecosystems. The species richness and individual abundance of soil ciliates, and their unique cell structures and physiological characteristics means that soil ciliate communities are highly sensitive to environmental conditions and therefore can be used as bioindicators in natural and human-influenced soil ecosystems.In order to understand the response of soil ciliate communities to the soil environmental changes after the implementation of the Conversion of Cropland to Forest and Grassland Program, from March to September 2010, the community characteristics of soil ciliates in five sampling sites(Platycladus orientalis forests) at different stages of restoration, together with a control sampling site(a wild grass slope). The sites were located in Wudu District, Longnan City, and were studied using the non-flooded petri dish method, observation in vivo, protargol impregnation, and Foissner's counting method. A total of 71 soil ciliate species were identified in this study, which belonged to 3 classes, 10 orders, 22 families, and 29 genera. Hierarchical cluster analysis showed significant differences in the distribution of soil ciliate species among the soils collected from forests at different restoration stages. Furthermore, the analysis indicated that as restoration progressed, the composition of soil ciliate species became more and more complex. The diversity of soil ciliate species in the soil samples collected from the restoration sites were all higher than that in the control soil sample. Multiple linear regression analysis revealed that there was a significant correlation between the ciliate species number and restoration stage(ŷ=2.714x2-10.820x+28.400, R2=0.940), and that there was an increase in the number of ciliate species as the restoration progressed. A statistical analysis of the number of the soil ciliate species showed a gradual succession of dominant soil ciliate groups over the course of ecological restoration. The dominant soil ciliate group Colpodida in earlier restoration soils was substituted by Hypotrichida in later restoration soils.In this study, the soil environmental conditions including pH, soil temperature, soil water content, soil available phosphorus, available potassium, ammonium nitrogen, organic matter, and organic carbon in different soil samples were also investigated using potentiometric determination, angle stem earth thermometer,high-temperature drying, Olsen's method, sodium tetraphenylboron turbidimetry, indophenol blue colorimetry, and hydration heat-photoelectric colorimetry, respectively. The results of physicochemical analysis of the soil samples suggested that soil quality improved during the conversion from cropland to forestland. Bivariate correlation analysis showed that soil organic matter and ammonium nitrogen had the most important influence on soil ciliate community diversity. Finally, the redundancy analysis results suggested that the variation between soil ciliate communities had a significant correlation with changes to soil environmental conditions during the conversion from cropland to forestland. Therefore, the soil ciliates could be considered as indicator organisms for assessing the effects of ecological restoration after conversion of cropland to forest.