Waterlogging of cotton calls for caution with N fertilization

Abstract

The main objective of this investigation was to evaluate the effects of nitrogen on waterlogging resistance in terms of changes in dry-matter accumulation, root antioxidant enzyme activities, root vigor, and photosynthesis under waterlogging during the flowering and boll-development stage. Cotton plants grown in pots with three N levels (0, 4.5, and 9.0 g N pot−1, equivalent to 0, 240, and 480 kg N ha−1, respectively) were subjected to waterlogging for eight days and then permitted to recover for fifteen days. The dry weights of root and shoot were decreased by waterlogging, and were highest at 240 kg N ha−1. In waterlogged root, the activities of superoxide dismutase and catalase decreased and that of peroxidase increased in comparison with the control. The application of N increased the activities of catalase and peroxidase of both waterlogged root and the control, but decreased superoxide dismutase activity. Malondialdehyde content, an indicator of membrane lipid peroxidation, was significantly increased, and was lowest in the 240 kg N ha−1 N treatment during waterlogging. Both root vigor and canopy apparent photosynthesis rate, which were weakened by waterlogging, reached a peak at 240 kg N ha−1. At the 15th day after termination of waterlogging, N application promoted root vigor and canopy apparent photosynthesis rate of waterlogged cotton plants. These results indicated that an appropriate N supply (240 kg N ha−1) may contribute to waterlogging resistance of cotton by adjusting the antioxidant enzyme activities of root, reducing lipid peroxidation and boosting root vigor; however, excessive N supply (480 kg N ha−1) may lead to an adverse impact on waterlogging resistance of cotton. Therefore, the application of N should be reduced to decrease stress when waterlogging occurs, and additional N fertilizer may be used to promote cotton growth after waterlogging.