Physiological Mechanism of Sucrose Metabolism in Cotton Fiber and Fiber Strength Regulated by Nitrogen

Abstract

Two cotton ( Gossypium hirsutum L.) cultivars, KC-1 with average fiber strength of 35 cN tex −1 and AC-33B with average fiber strength of 32 cN tex −1 were used to study effectiveness of nitrogen on fiber strength. Three nitrogen application rates (0, 240, and 480 kg ha −1), standing for low, moderate, and high nitrogen levels, respectively, were applied in field experiments in Nanjing (118°50′E, 32°02′N, middle lower reaches of Yangtze River Valley) and Xuzhou (117°11′E, 34°15′N, Yellow River Valley). The changes of nitrogen concentration in the subtending leaf of cotton boll followed the equation Y N = at − b , where Y N is nitrogen concentration in the subtending leaf of cotton boll (%); t is boll age (d); a and b are parameters. Parameter a was the highest under the high-nitrogen level in both cultivars, explaining the decreases of sucrose inversion amount and enzymes (invertase, sucrose synthetase, and sucrose phosphate synthetase) activities before boll age of 24 d as well as the maximal speed of cellulose accumulation in cotton fiber and fiber strength since the boll age of 24 d. Parameter b was the highest under the low-nitrogen level in both cultivars, indicating negative effects on sucrose metabolism after boll age of 24 d, the shortened duration of cellulose rapid accumulation in cotton fiber, and the reduced increment of fiber strength from boll age of 24 d to boll opening. These changes were important physiological responses to nitrogen concentration in the subtending leaf of cotton boll during cotton fiber development, and ultimately resulted in lower final fiber strength under both high- and low-nitrogen level. In the subtending leaf of cotton boll, boll age of 24 d was a transition point of sucrose metabolism in cotton fiber and fiber strength regulated by nitrogen.