Research Of Physiological Mechanism Of Effect Of Increased Canopy Temperature On Yield And Quality Of Cotton Plant

Cotton growth is very sensitive to environment temperature. High temperature can decrease photosynthesis rate, make the physiological senilism and subsequently reduce fiber quality and yield. The time from July to October is the critical period of cotton yield formation, in which extreme high temperature weather frequently occurs in a year. Therefore, cotton yield reduction caused by high temperature stress at blooming-boll forming stage occurred frequently in all cotton belt of China. Researches on the mechanism and trend of cotton fiber quality and yield under high temperature conditions can provide theoretical basis to develop cultivation techniques to ensure cotton fiber yield and quality. The experiment was carried out in the half-open-top greenhouse in Pailou experiment site of Nanjing Agricultural University (118°50’E,32°02’N) in the year of2010. Cotton cultivar Simian3and Siza3which had similar genetic background were applied in the research. Effect of increased2-3℃canopy temperature on cotton plant photosynthesis and its physiological mechanism during blooming-bolling stage were studied in this research.Our study focused on (1) effect of increased canopy temperature on photosynthesis characters in the functional leaf of main stems,(2) effect of increased canopy temperature on cotton yield and fiber quality and (3) effect of increased canopy temperature on antioxidant enzyme activities in the subtending leaf and fiber of cotton. The main results were as follows:1. Effect of the increased canopy temperature on photosynthesis characters in the functional leaf of the main stemsThe results indicated that in the2-3℃increased canopy temperature condition (average boll period temperature was33.5-35.2℃), the chlorophyll SPAD readings and net photosynthetic rate (Pn) of the functional leaf on the main stems reduced, while the stomata conductance (Gs), intercellular CO2concentration (Ci) and transpiration rate (Tr) increased. Soluble protein content increased significantly while soluble sugar content, soluble amino acid content and C/N decreased. Siza3presented less variation range in the above indexes than that for Simian3. The results suggested that in the2-3℃increased canopy temperature (average boll period temperature was33.5-35.2℃) condition, the cotton plant suffered a serious temperature stress, the plant photosynthesis and dry matter accumulation rate reduced, accompany with the reduction of the carbohydrates supplication capacity in the leaf subtending the boll. The cotton plant also suffered water deficiency stress in leaf but the reduction of the photosynthesis rate was mainly due to non-stomatic restrictions, and it might be caused by the damage of cell membrane. The thermal tolerance of Siza3is higher than Simian3.2. Effect of the increased canopy temperature on cotton yield and fiber quality.Effect of2-3℃increased canopy temperature (average boll period temperature was33.5-35.2℃) on cotton yield and fiber quality of bolls of different fruiting branches at blooming-bolling stage was studied, the results showed that the most significant effects on expulsion rate and fiber qualities were from the bolls setting on the upper fruiting branches, which were different in various cotton cultivars. The number of bud, young boll, maturing boll were significantly reduced, and the abscission rate rose, these lead to yield reduction. Fiber length increased, while the strength reduced, the trend of fineness and micronaire value varied among different branches; As viewed from fruit branches, fiber from bolls setting on upper branches is longer than that on the lower branches, and longer than the middle ones, the fiber fineness of lower branch decreased significantly, the derease degree (△%) of Simian3and Siza3of which were4.38%and11.26%, while fineness from the upper branches and the middle branches rose. Micronaire value of the lower branches rose, while the middle and the upper branches decreased; the effects of increased canopy temperature on fiber yield and fiber strength of upper branches (△%) are the most, while the effect on boll weight from the bolles from the middle branches was the most. The results above showed that the2-3℃increased canopy temperature affected cotton yield more, while affected fiber quality differently in different branches, it likely optimize fiber length and reduce fiber strength.3. Effect of the increased canopy temperature on antioxidant enzymes activity in the subtending leaf and fiber of cotton. The results indicated that in the2-3℃increased canopy temperature condition (average boll period temperature was33.5-35.2℃), activities of antioxidant enzyme POD and CAT in the subtending leaf of cotton both reduced, while MDA content increased. Dynamic changes of antioxidant enzyme and MDA content in the fiber of cotton is similar with that in the subtending leaves of the boll. The effect of increased canopy temperature varied with branches positions on cotton plant. It’s more obvious that the reduction of enzyme activity and MDA content of lower branch than that of middle and upper. There was significant positive correlation between POD and CAT (P<0.05), and antioxidant enzyme was significantly negative correlated with soluble protein content (P<0.05). Comparing relationship between photo synthetic rate, biomass different enzymes and osmoregulation substance, we discovered that photosynthetic rate was significantly related with POD, CAT and MDA content, and had no correlation with osmoregulation substance content, while biomass had significant correlation relationship with POD, CAT and MDA content. All the results suggested that the balance of antioxidant enzyme system in the subtending leaf was broken under the2-3℃increased canopy temperature condition, and it was the major reason that caused the reduction in cotton fiber yield and fiber quality.