Study On The Effect Of Waterlogging On Cotton Plant And The Recovery Mechanism During Flowering And Boll-Forming Stage

Cotton(Gossypium hirsutum L.), the world’s foremost important cash crop, has poor resistance on waterlogging stress. Flowering and boll-forming stage, the critical water sensitive period of cotton, is the key period for increasing lint yield and improving fiber quality. However, seasonal waterlogging happens at this stage occasionally, which affects the cotton growth and yield development seriously, and then results in the decrease of yield and quality. The objective of this study was to screen suitable evaluation indexes indicating the stress and recovery degree after waterlogging, which would provide a theoretical basis for taking appropriate cultivation measures to reduce the impact of flood disasters on cotton production. In2011, by using cotton cultivars Siza3as material and four waterlogging treatments (0,6,9,12days, respectively), field experiments were carried out in Dafeng, Jiangsu province (120°28’E,33°12’N, middle lower reaches of Yangtze River Valley). The study focused on:(1) Effect of waterlogging on the accumulation and distribution of dry matter and yield for cotton during the flowering and boll-forming stage;(2) Effect of waterlogging on the photosynthetic characteristics of cotton function leaf during the flowering and boll-forming stage;(3) the physiological indexes indicating the stress and recovery level in cotton plant after waterlogging. The main results were as follows:1. Effect of waterlogging on the accumulation and distribution of dry matter and yield for cotton during the flowering and boll-forming stageThe biomasses of different organs decreased significantly, and the distributive indices of dry matter in different organs changed under waterlogging. After the release of waterlogging, stress indexes of root and bud, flower and boll decreased, in which the distributive indices of biomass increased. However, stress indexes of stem and leaf increased, in which the distributive indices of biomass decreased. The yield and fiber quality of cotton were also significantly affected. The seed cotton yield and lint decreased, and the reduced degree was increased with increasing the stress degree. Through the analysis of yield component and yield spatial distribution found that the main difference between waterlogging six days and waterlogging nine days is boll number in5to8fruit branch of coton, the main difference between waterlogging nine days and waterlogging twelve days is boll weight in more than13fruit branch of coton, boll number and boll weight in waterlogging six days and waterlogging twelve days are all different. The effect of waterlogging on micronaire value and uniformity were not significant, but strength and length were significantly decreased.2. Effect of waterlogging on the photosynthetic characteristics of cotton function leaf during the flowering and boll-forming stageThe net photosynthetic rate of cotton function leaf was decreased significantly under waterlogging, of which the stress index is0.28,0.39,0.55as waterlogging for6,9,12days, respectively. In the progress of recovery after waterlogging, the cotton function leaf of waterlogging for6,9days, of which the stomatal limitation value (Ls) decreased gradually. The Ls of cotton of waterlogging for12days increased, but the non stomatal limitation value (NLs) decreased. At the time of terminating waterlogging, chlorophyll fluorescence parameters of cotton waterlogging for6days had no significant change in compared with the control. When waterlogging for9,12days respectively, the quantum yield of electron transport, maximum photochemical efficiency of open photosystem and photochemical quenching were decreased, while non-photochemical quenching coefficient increased significantly. After the release of waterlogging for12days, the cotton of waterlogging for9days, of which chlorophyll fluorescence parameters recover to the control level, but there were still some major differences between the cotton of waterlogging for12days and the control. In conclusion, when the stress index of net photosynthetic rate was less than0.28, the main factor of photosynthetic performance degradation was stomatal limitation. As it was0.39, both stomatal limitation and non-stomatal limitation worked together to reduce the cotton photosynthetic performance, but stomatal limitation accounted for the major factor. At the time it was greater than0.55, non-stomatal limitation was the main reason that why the photosynthesis of cotton reduced after waterlogging.3. Research of the physiological indexes indicating the stress and recovery level in cotton plant after waterloggingEach of the14stress relating physiological indexes of cotton functional leaf, such as net photosynthetic rate (Pn), stomatal conductance (Gs), MDA content, had significant difference under different stress levels or at different recovery stage after waterlogging, and significant difference was also observed in the correlation degree between the indexes and the recover level. The relative correlation degree of the stress relating physiological indexes and the stress level in different recovery stage were very similar, indicated that the14indexes can be grouped by the correlation degree and those indexes presented higher correlation degree with stress level could be used as key physiological indexes to indicate the stress or recovery level in cotton plant after waterlogging. With the data in this research, it was concluded that Pn and MDA content presented higher correlation degree and lower variation in different stages than other physiological indexes. They could be used as key physiological indexes in evaluating the strain and recovery degree after waterlogging.