| Cotton (Gossypium hirsutum L.) plant is a light favored crop which were grew under suitable light intensity and the compensation point and light saturation point of leaves is750-1,000lux,70,000-80,000lux 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.The cotton flower bell of low temperature oligonucleotide according to affect major ecological factor in cotton production, Yangtze River cotton, flower bell early often not conducive due to the rainy oligonucleotide according the volts before peach and peach volts development, blooming late because of the low temperature oligonucleotide according not conducive to early autumn Peach development; Yellow River River areas there are also late flowering and boll low and groups in the lower part of the phenomenon of light deterioration, limits to increase the yield and quality improvement. Therefore it is necessary to temperature and light as a composite factor of great significance from the level of physiological and biochemical study of temperature and light coupling on leaf photosynthetic characteristics of cotton bolls. In this study Sumian15and Section cotton materials, Nanjing Agricultural University in Nanjing,Jiangsu (118°50’E,32°02’N) archway Experiment Station in2010and2011phased planting shade test, study:(1) Effect of shading on the physiological characteristics and chlorophyll fluorescence kinetics of the cotton leaves during cotton boll formation at different planting dates;(2) Effect of shading on the carbohydrate metabolism of the cotton leaves during cotton boll formation at different planting dates;(3) Effect of shading on cotton yield and yield composition factors during cotton boll formation at different planting dates.The main results were as follows:1. Effect of shading on the physiological characteristics and chlorophyll fluorescence kinetics of the cotton leaves during cotton boll formation at different planting dates.Low temperature and shading resulted in reduction of the chlorophyll content (SPAD), rate of net photosynthesis (Pn) and transpiration (Tr), and stomatal conductance (Gs) of the functional leaves on the main stems, but increased the intercellular CO2concentration (Ci). The decline in Pn of the cotton leaves was related to malfunctioning of the enzymes governing the functioning of photosynthesis and synthesis of chlorophyll, but not related to the stomatal factors and photochemical reactions.Cold stress caused the photochemical efficiency (Fv/Fm) of functional leaves of cotton, but shading conditions increased it. Late sowing and shading conditions resulted in reduction of photochemical efficiency (ΦPSⅡ) and photochemical quenching (qP), but increased non-photochemical quenching (qN). Results of the present study revealed that low light conditions and low temperature changed the chlorophyll fluorescence characteristics of cotton leaves, in order to dissipate energy mainly through non-photochemical quenching. Cold and light stress limits photosynthetic activity, suppresses electron transfer process, reduces electron transport rate, and decreases carbon cycle activity of cotton leaves. Temperature and light stress is also thought to inhibit the photosynthetic carbon metabolism electronic supply, which might result in partial inactivation or injury of PS Ⅱ in cotton leaves, making it difficult to convert light into chemical energy.2. Effect of shading on the carbohydrate metabolism of the cotton leaves during cotton boll formation at different planting dates.Late sowing conditions increases boll leaf of soluble sugar, soluble amino acid content and C/N. Low temperature reduces the consumption of photosynthetic products and block the transport of soluble sugar to sink while it increases the carbon content in the leaves which in turn resulted in an increase in carbon and water compounds (soluble sugar) content. With the severity of shade there were decreasing trends in leaf of soluble sugar, soluble amino acid content and C/N. Low light intensity have inhibiting effects on photosynthesis, the photoelectron transfer capacity and Calvin cycle. Shading reduces the accumulation of carbohydrates in the cotton, thereby reducing the carbon assimilation in cotton leaves, which ultimately results in reduction of synthesis of photosynthetic products in cotton leaves. Late sowing resulted in low leaf sucrose content while specific leaf weight has increased to different degrees, with aggravation of shading degree the sucrose content of leaf increased while specific leaf weight decreased. During late sowing and shade aggravation, the leaf starch content show upward trends while there was a declining trends in sucrose phosphate synthase and sucrose synthase activity in both cotton cultivars.The results in present study suggested that the low temperature and low light intensity resulted in change of sucrose and other non-structural carbohydrate carbon ratio. The different sowing dates and shade treatment significantly affect the boll leaf activity and sucrose metabolism, hinder the accumulation of sugar products, the extended growth period delay the impact of stress on cotton plants, cotton bolls and on sucrose metabolism in leaf is more restrained.3. Effect of shading on cotton yield and yield composition factors during cotton boll formation at different planting dates.Blooming period and the different shading conditions at different planting dates changed the field microclimate, including air, light and light distribution, resulting in reduction of cotton canopy temperature and air flow and humidity. Thus, weakening the plant photosynthetic rate and transpiration caused cooling effect, changed the allocation of carbohydrates in the body of cotton, resulting in reduction of output of photosynthetic products, reduced accumulation of cotton assimilate, led to boll malnutrition, reduced boll volume, number of cotton seeds, grain weight, boll weight, and consequently caused significant loss of cotton production. There were significant interactions between the effect of shade and sowing dates on boll weight and lint percentage. Temperature and shading conditions together have greater degree of influence on boll number, boll weight and lint yield than the temperature-alone or shading-alone, while late sowing under shading conditions has greater impact on the lint. |
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