Abstract: Enclosure (fencing) is a fundamental part of China’s current ‘Grain for green’ program, and facilitates both the recovery of vegetation, and the improvement of soil properties. This paper, reports research into the recovery of soil physical and chemical properties and changes in activities of 4 soil enzymes after fencing in Agropyron mongolicum, and Sophora alopecuroides plant communities in the desert steppe of Ningxia province. Adopting the method of space as a substitute for time, the typical sites of two communities were selected and investigated in Yanchi County of Ningxia. The results showed that: 1) After fencing, soil water content, total N and total P increased significantly; while soil bulk density, pH, alkali hydrolysable N and available P contents were significantly reduced in the 0-10 cm soil layer of the A. mongolicum community studied. However, there were no significant differences in soil physical and chemical properties in the 10-40 cm soil depth. In the S. alopecuroides community soil bulk density decreased significantly, while soil water content, pH, organic carbon, total N, total P, available N and available P were significantly increased in the 5-10 cm soil depth. 2) After fencing, in the A. mongolicum community soil urease activity decreased significantly, while soil sucrase activity in the surface layer (0-10 cm) significantly increased, and the activity of catalase and phosphatase did not change significantly. In the S. alopecuroides community soil phosphatase activity decreased significantly, the activities of sucrase and urease were significantly increased, and the activity of catalase changed non-significantly. 3) There were different correlations in the two plant communities between soil enzyme activities and soil physical and chemical properties. In the S. alopecuroides community there was a significant positive correlation between soil sucrase activity, soil urease activity and soil nutrient content (P<0.01), while the activity of phosphatase showed a remarkably negative correlation. In A. mongolicum communities, there were significant positive correlations between urease activity and soil organic carbon, total P and available P content, and also, significant positive correlations between catalase activity and soil organic carbon, total N, and alkali hydrolysable N (P<0.05). In conclusion, although the water content and soil nutrient status of surface soil (0-10 cm) of the two communities were increased by fencing, no consistent changes in activities of the 4 soil enzymes studied were found.

Key words: plant communities, desert steppe, fencing, soil enzyme activity, Agropyron mongolicum, Sophora alopecuroides