Abstract: To understand the influence of enclosure duration on diversity of large soil animals in degraded typical steppe of Inner Mongolia, the community composition of large soil animals at soil depths of 0-10, 10-20, and 20-30 cm in the enclosing 32 years plot (A), 19 years plot (B) and grazing grassland (C) were investigated in the Inner Mongolia Grassland Ecosystem Research Station, Chinese Academy of Sciences. A total of 984 individuals from 39 groups, belonging to two phyla, four classes and nine orders, were collected. The dominant groups were Carabidae, Chrysomelidae larva, and Cicadellidae for plot A; Cicadellidae, Carabidae, and Elateridae larvae for plot B; and Elateridae larvae, and Anthicidae for plot C. Species richness, Shannon index, evenness index and density-groups index were the highest in plot B and the lowest in plot C, while it was opposite for the dominance index. The numbers of individuals and groupsdecreased with increasing soil depth. Soil water content, pH, total phosphorus and organic matter contents were changed significantly (P<0.05) after exclosed, but no significant change was found in bulk density, porosity and total nitrogen content (P>0.05). The results of correlation analysis showed that the density, Shannon index and evenness index of large soil animals were significantly positively correlated with soil water (P<0.01). In conclusion, enclosure substantially influenced the horizontal and vertical distribution of large soil animals in the degraded typical steppes of Inner Mongolia, with greater numbers of individuals and groups than that in grazed plots. Moreover, enclosure is beneficial to the improvement of soil physicochemical properties.

Key words: simulated rainfall addition, morphological characteristics, spatial correlation, point pattern, desert plant