Effects Of Shading On Growth And Nitrogen Metabolism In Cotton Plant (Gossypium Hirsutum L.) During Flowering And Boll-Forming Stage

Cotton (Gossypium hirsutum L.) plant is a light favoured crop which were grew under suitable light intensity and the compensation point and light saturation point of leaves is 750-1,000 lux,70,000-80,0001ux respectively. During growth process of cotton plant, flowering and boll-forming stage is the key yield determinant period and environment-sensitive stage of cotton. Light is one of the most important environmental factors, providing plants with both a source of energy and information signals that control their growth and development. In recent years, with the change of global climate and growth districts, low light intensity in the cotton canopy that caused by adverse weather occurred frequently in our country during flowering and boll-forming stage, and it made a reduction in yield and poor fibre quality. Cotton yield is closely related to growth condition, so we need a study on growth and development of cotton under shading.Nitrogen as a mineral nutrient has an important effect on yield and fibre quality of cotton, and utilization of nitrogen is closely related to growth condition of cotton root. During flowering and boll-forming stage, the growth and development of cotton root would affected by shading, which suppressed the capacity of enroll nitrogen. Then study the effects of shading on growth and nitrogen metabolism in cotton plant is required.The experiment was conducted in the summer season of 2009 at the pailou experimental station of the Nanjing Agricultural University. Cotton cultivars (Sumian 15, Kemian 1) were grew in pots, and three light levels (100%,80%,60% of natural light) were Performed at the flowering day of the bolls at 1st-2nd fruiting node on 6-8th fruiting branches. Sampling was conducted 4 times for 15-day intervals from onset to bolls open. Then study the effect of shading on the dynamic growth both in shoot and root, the response of nitrogen metabolism to shade, and its physiological mechanism was also investigated. The main results were as follows:(1) The effects of shading on organs and yield and fibre quality of cotton shoot during flowering and boll-forming stageWith the increment of shading level, the leaf area of main stem leaf and the fruiting branch leaf were larger than those under natual light. The height of cotton plant was increased by the shading while the number of fruiting branches was inhibited, but there are some slight variances among the three shading levels. Under shading, the distribution proportion of reproductive organs was less than those vegetative organs. All the dry matter accumulations of different organs were decreased with the increament of shading level.The cotton yield per plant was decreased with the increment of shading level. The effects of shading on the cotton yield and fiber quality depended upon the position of fruiting branch and fruiting bud. The shading had a bad effect on the bolls at low (2-4 fruiting branches) inside (1-2 fruiting buds) and outside (≥3 fruiting buds) parts less than those at middle (6-8 fruiting branches) or upper (9-11 fruiting branches) positions. The shading prolonged the fiber length at all position, but there were some slight variances among the three shading levels. Fiber micronaire and fiber strength were decreased with the increament of shading level during the flowering and boll-forming stage, the bolls which at the middle (6-8 fruiting branches) parts were affected largely than those at low(2-4 fruiting branches) and upper (9-11 fruiting branches) positions. The fiber uniformity index and the was unaffected or affected slightly by the shading.(2) The effects of shading on cotton root growth and its physiological characteristics during flowering and boll-forming stageThe shading had an inhibition on dry matter accumulation of root biomass; and last root dry matter accumulation was reduced about 20% under severe shading compared with those in natural light. Root vigor, total absorption area and active absorption area were also decreased with the increment of shading level. There was some confusion in scavenging system of active oxygen of cotton root. The content of Malondialdehyde (MDA) was significantly (P<0.05) increased by the shading. Summary, all that had some adverse effects on root growth and its physiological mechanism which suppressed the ability to absorption, synthesis and transportation of nitrogrn.(3) The effects of shading on nitrogen metabolism of cotton(Gossypium hirsutum L.) during flowering and boll-forming stageWith the shading time extended, the activities of nitrate reductase (NR), glutamate synthase (GOGAT) in root and glutamate synthase (GOGAT) in the functional leaves decreased. With the increment of shading level, the activities of the nitrogen metabolize enzymes, such as NR, GS, GOGAT were seriously inhibited, and had a more sensitive response to shade at the 15th day after shading. Under shade treatment, the contents of amino acid, soluble protein and nitrogen accumulation were reduced both in root and in stem functional leaves. The descending of nitrogen absorption in cotton root was result from the drop of GS/GOGAT activity mostly and the drop of NR activity took the second place, but in stem functional leaves the drop of NR activity was the major while the drop of GS/GOGAT activity was secondary.