Effects of nitrogen on cotton fiber strength formation under water stress and re-watering during the flowering and boll-forming stage

Pot eexperiments were conducted to study the effects of nitrogen on the cotton fiber strength formation under water stress and after re-watering during the flowering and boll-forming stage in Nanjing Agricultural University in 2005 and 2006. Within each water treatment, three nitrogen levels were imposed: N 0, 240 and 480 kg /ha. The results showed that water stress significantly reduced soluble protein content in cotton fiber, increased the antioxidant enzyme activities of SOD, CAT and POD and MDA content at the end of soil water stress, but reduced the fiber thickening key enzymes activities of sucrose synthetase, β-1,3-glucanase, sucrose phosphate synthetase, and IAA oxidase. On the 10th day after re-watering, there was no significant difference of SOD, CAT and POD activity between water-stressed and well-watered cotton. However, MDA content declined, and the fiber thickening related key enzymes activities were still lower than well-watered treatments. The fiber strength was also reduced. The result of 2-year experiment showed that N 240 kg/ha was the optimal nitrogen application rate for forming high-strength fibre under soil water stress and afterward re-watering because the antioxidant enzymes activities and the fiber thickening key enzymes activities were highest, and MDA content were the lowest, thus leading to the greatest fibre strength. In our experiments, deficient (N 0 kg/ha) and excessive (N 480 kg/ha) nitrogen supply are of disadvantaged to the fiber thickening key enzymes activities and cotton fibre strength.