Abstract:

【Objective】 The objective of the experiment is to clarify the effects of the subtending leaf nitrogen concentration on strength formation of cotton fiber. 【Method】 Five nitrogen rates were applied to set up varying leaf-nitrogen content treatments and three cotton cultivars with a great difference in fiber quality were employed. The study focused on the relationship between nitrogen concentration in subtending leaf of boll and the content of saccharide compounds, and their relationship with fiber strength formation. 【Result】 Results showed that the changes of optimal nitrogen concentration in subtending leaf of cotton boll followed the equation: YN＝αt-β(YN is nitrogen concentration in the subtending leaf of cotton boll (%); t is boll age (d); α and β are the parameters). At fiber thickening stage, the content of sucrose, and cellulose all changed as a parabola-like curve according to the increasing nitrogen content in the leaf subtending boll. The curve of the leaf nitrogen for fiber strength increasing was very close to the curve of the optimum leaf nitrogen for sucrose or cellulose accumulation, while it was significantly apart from the curve of the leaf nitrogen for β-1, 3-glucan accumulation. 【Conclusion】 The nitrogen content of the leaf subtending bolls reflects the special nitrogen status for fiber development precisely. At fiber thickening stage, there exists an optimum leaf nitrogen curve for sucrose, β-1,3-glucan and cellulose accumulation and for fiber strength formation. The higher the sucrose exist, the higher fiber strength formed. At the early stage of fiber thickening, higher content of β-1,3-glucan is benefit for fiber strength formation, while at later stage, the higher content of β-1,3-glucan will make less contribution to fiber strength formation. It is concluded that the optimum leaf nitrogen content for fiber strength formation in different cotton culitivars is different, and the nitrogen concentration in the subtending leaf of cotton boll affects obviously the cotton fiber thickening and strength formation in cotton fiber.

Key words: cotton, subtending leaf of cotton boll, leaf nitrogen concentration, saccharide compounds, fiber strength