Study On Characteristics And Physiological Mechanism Of Cotton Senescence With The Different Levels Of Nitrogen Nutrition

Cotton is very important economic crop, but premature senescence recently becomesa severe problem. Moreover, premature senescence can't be reasonably regulated for lessresearch on this problem.The difference of configuration, physiological and biochemical characteristics ininsect-resistant transgenic Bt gene cotton 33B variety treated with three levels of nitrogen:low nitrogen (LN) 0kg·hm^-2; middle nitrogen (MN) 189.5 kg·hm^-2; high nitrogen (HN)395.0kg·hm^-2. The effects of Nitrogen Fertilizer on Cotton Senescence could be obtainedby analysis of above results, to provide scientific reference for regulation of cottonpremature senescence and high yield cultivation.The results as follows:1. The cotton was premature senescence by low nitrogen for: (1) boll load in unit leafarea was the highest; (2) the contents of chlorophyll and dissolvable protein,photosynthesis ratio in low nitrogen treated group were lower than those in middle andhigh nitrogen treated groups, but MDA had a contrary result. The physiological andbiochemical characteristics started to be different from bloom growth stage or earlier.2. Different levels of nitrogen could affect the activities of SOD and POD in axial leaf:HN＞LN, MN＞LN.3. From physiological characteristics of fruit branch leaves on the upper, middle andlower position of axial. High nitrogen could accelerate lower leaves senescence, lowernitrogen could induce whole plant senescence, and middle nitrogen could delay leaves orwhole plant senescence.4. The contents of chlorophyll and dissolvable protein and SOD activity from the firstto the tenth axial leaves decreased. MDA and POD increased.6. Different levels of nitrogen affected water quantity of cotton tissues. The beginningof water quantity decreasing was later than that of physiological characteristics. Thenutritional and procreation organs had the same trend: HN＞MN＞LN, the differencebegan at boll opening stage.7. Dry matter accumulation of whole overground plant was well fitted by the logisticequation. Dry matter accumulation of nutrition organ was HN＞MN＞LN, and dry matter accumulation of procreation organ of LN was lower than that of the others.8. LN treatment decreasod the contonts of Zinc and Manganese in cotton plant. HNhad the contrary results. MN could control excessive absorbing to copper.