Abstract: By using open top chambers, this paper studied the physiological and ecological responses of transgenic Bt cotton cv. 33^B and its parent line nontransgenic cotton cv. DP5415 in their growth potential and nitrogen metabolism to doubled CO₂ concentration (750 μl·L^-1 vs. 375 μl·L^-1) and nitrogen fertilization level (200 mg N·kg^-1 vs. 100 mg N·kg^-1). Doubled CO₂ concentration promoted the height and stem growth and the biomass production of the two cultivars significantly, whereas doubled N fertilization level only had significant positive effects on 33^B. The leaf glutamine synthetase activity (GSA) of DP5415 decreased significantly under doubled CO₂ concentration but increased significantly under doubled N fertilization level, while the GSA of 33^B was significantly higher under doubled CO₂ concentration and low nitrogen fertilization level. Both the doubled CO₂ concentration and the doubled nitrogen fertilization level increased the leaf nitrate reductase activity (NRA) of 33^B significantly, and the NRA of DP5415 also had a significant increase under doubled CO₂ concentration. Doubled CO₂ concentration had significant inhibitory effects on the leaf nitrite reductase activity (NiRA) of both 33^B and DP5415. The NiRA of DP5415 decreased significantly under doubled CO₂ concentration and N fertilization level. All the results suggested that under doubled CO₂ concentration, N fertilization level had significant effects on the growth potential of transgenic Bt cotton but lesser effects on its nitrogen metabolism, compared with the control nontransgenic cotton. Therefore, in the planting of transgenic Bt cotton, especially under elevated CO₂ condition, optimized N fertilization should be made.

Key words: Winter wheat, Potassium application stage, Photosynthetic characteristic, Enzyme activity, Starch accumulation