Abstract: The occurrence of overcompensation response of cotton plants after leaf loss and the changes in their protective enzyme system were studied. The 25% leaf removal and 50% leaf removal in standard were imposed on cotton plants respectively with scissors to simulate the process of field pest herbivory. The results showed that the 50% leaf removal could increase the yield of sound boll by 24 .4% that suggested the happening of overcompensation. The 25% leaf removal had no influence on cotton plant height and protein content in leaves, suggesting the 25% leaf removal in standard falling into the category of growth redundancy, but the climax in protein content in cotton leaves postponed about one week. The 50% leaf removal could increase the total area of plant canopy, decrease cotton plant height by 14.5% in two weeks after treatment, increasing protein content by 7 .7%, acquiring 14.1% higher peroxidases activity than the control (CK). Three days after 50% leaf removal treatment, both peroxidases specific activity and in polyphenoloxidases specific activity increased. At the time of two weeks after 50% leaf removal treatment, the specific activities of peroxidases and polyphenoloxidases were more similar to that of CK. All these indicated that the treatment of the 50% leaf removal in standard fell into the category of overcompensation.

Key words: Cotton, overcompensation for leaf removal, leaf removal, protective enzyme, simulated infestation