Abstract:

【Objective】 The aim of the experiment is to study the responses of carbohydrate metabolism to nitrogen application levels in cotton fiber development and its relationships with fiber strength formation. 【Method】 A field experiment was carried out in three nitrogen application levels: N0 (0 kg N?hm-2) as deficient application nitrogen level, N1(240 kgN?hm-2)as optimal nitrogen application level and N2 (480 kgN?hm-2) as high nitrogen application level, and cotton cultivar NuCOTN 33B (AC-33B) and Kemian 1 (KC-1) were used as materials. The study focused on the time course changes of the important matters (sucrose and β-1, 3-glucan) contents and the enzymes (sucrase, sucrose synthetase, sucrose phosphate synthetase and β-1, 3-glucanase, which were key enzymes in carbohydrate metabolism) activities in different nitrogen application levels. 【Result】 The 2-year experiment showed that under the optimal nitrogen application level, the sucrase activity was the highest, which bring abundant energy for carbohydrate metabolism in a long time. Sucrose synthetase and sucrose phosphate synthetase presented the highest activities, which lead to the greater decrease of sucrose content during the 5-24 DPA (Day Post Anthesis) and the greater increment of sucrose content during the 24-31DPA than in the two other nitrogen application levels. The total transformation rate of sucrose in cotton fibers during whole boll age was the highest. The β-1, 3-glucanase activity was the highest that made β-1, 3-glucan transformation rate high. The changes of which mentined above could result in a longer period and more tempered cellulose accumulation process, which was benefit to higher strength fiber formation. While under the deficient nitrogen application level, the carbohydrate metabolism process presented the opposition changes as in the preceding nitrogen application level, and this deteriorated cellulose accumulation led to low strength fiber formation. Lastly, things operated in the high application nitrogen level were between those in the optimal nitrogen application level and in the deficient nitrogen application level. 【Conclusion】 There were notable differences in carbohydrate metabolism among the three nitrogen application levels in cotton fiber development, and these differences were important factors causing the variety in fiber strength development. Under the optimal nitrogen application level, the enzymes activities and the chief matters were preferably accommodated in the fiber development and these could beneficial to high strength fiber formation.

Key words: cotton, cotton fiber development, carbohydrate metabolism, nitrogen, fiber strength