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Quantifying the Responses of Weak Gluten Wheat Leaf Photosynthesis and Chlorophyll Fluorescence Parameters to Weak Light at Filling Stage

Author: ZhangWei
Tutor: LuoWeiHong
School: Nanjing Agricultural College
Course: Crop Cultivation and Farming System
Keywords: Weak gluten wheat Shading Weak light Photosynthetic characteristics Chlorophyll fluorescence parameters Stress diagnosis
CLC: S512.1
Type: Master's thesis
Year: 2011
Downloads: 14
Quote: 1
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Abstract


Light intensity is one of the most important environmental factors which affect the growth and yield of crops. It is increased that weak light events happened in global climate change. Cloudy and rainy days are unfavorable weather events happened frequently during filling stage of wheat at the Yangtze River Region which is the main region of weak gluten wheat in China. Photosynthesis is necessary for guaranteeing the yield and quality of wheat and chlorophyll fluorescence parameters can reflect the variations of photosynthesis system and hence efficient for exploring the status of photosynthesis system. Photosynthesis, hence, yield and quality of crops will be affected significantly due to the variation of light conditions under shading. Therefore, quantifying the effects of shading on photosynthesis and chlorophyll fluorescence parameters is of utmost importance for assessing the effects of weak light events on wheat yield, predicting wheat yield and the loss accurately. For this purpose, field experiments of weak gluten wheat cv. YangMai 15, NingMai 9 (from Oct. 2008 to Jun.2009) and YangMai 15, YangMai 13 (from Oct.2009 to Jun.2010) with different intensities levels and durations of shading to simulate the effects of weak light on growth of wheat were conducted in Jiangsu Academy of Agricultural Sciences (JAAS) (32°07′N,118°62′E). According to the experimental data, the effects of different intensities levels and durations of shading on wheat leaf gas exchange parameters, chlorophyll content and chlorophyll fluorescence parameters were investigated qualitatively. Based on the above analysis, the quantitative relationship between maximum leaf net photo synthetic rate (Pn,max) and chlorophyll fluorescence parameters (φPSⅡ) were determined and the quantitative relationship for diagnosing the shading stress were developed. Independent experimental data were used to validate the quantitative relationship. The main research results are as followed:(1) The effects of each shading treatment on leaf photosynthesis and chlorophyll fluorescence parameters were analyzed. The results demonstrated that when durations above 4 days for each intensities levels of shading, maximum leaf net photosynthetic rate (Pn,max), apparent quantum yield (AQY), stomatal conductance (Cond) and transpiration rate (Trmmol) decreased significantly but intercellular CO2 concentration (Ci) increased of weak gluten wheat leaf. Chlorophyll content was also increased and the decomposing rate of chlorophyll in the later growing stages was slowed down after shading. For the chlorophyll fluorescence parameters, the actual quantum efficiency of PSII (φPSII), photochemical quenching (qP) and relative electron transportation rate of PSII (ETR) decreased but non-photochemical quenching (NPQ) increased after shading. The effects of shading on photosynthetic rate not by stomatal limitations and variation of chlorophyll content but via decreasingφPSII, qP and hence ETR.(2) Using the experimental data of YangMai 15, the effects of different intensities levels and durations of shading on maximum leaf net photosynthetic rate (Pn,max) and actual quantum efficiency of PSII (φPSⅡ) were quantified and quantitative relationships for predicting the effects of weak light on Pn,max andφPSII were developed. Independent data were used for quantitative relationship validation. The results showed that the quantitative relationship gave satisfactory prediction of Pn,max andφPSII. The critical durations for Pn,max and OPSII decreased significantly were, respectively,4 days (50% level of shading), 2 days (66% level of shading) and 2 days (84% level of shading) and the decreasing rate of Pn,max. andφPSII increased with increasing levels of shading. The coefficient of determination (R2) and the root mean square error (RMSE) based on 1:1 line between the estimated and measured values are, respectively,0.71 and 0.75, and 1.9μmolCO2 m-2 s-1 and 0.06.(3) Using the experimental data of YangMai 15, quantitative relationship for diagnosing the weak light stress based on the quantitative relationship between chlorophyll fluorescence parameters and leaf photosynthetic rate was developed. Independent experimental data were used to validate the quantitative relationship. The results demonstrated that the coefficient of determination (R2) and the root mean square error (RMSE) based on 1:1 line between the estimated and measured values are 0.77 and 1.8μmolCO2 m-2 s-1 respectively.Using the quantitative relationship for diagnosing the effects of weak light stress on wheat developed in this study, maximum leaf net photosynthetic rate Pn,max can be predicted according to the values of chlorophyll fluorescence parametersφPSII. It can be used to assess the effects of weak light events on wheat yield and predict wheat yield and the loss accurately.

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CLC: > Agricultural Sciences > Crop > Cereal crops > Wheat > Wheat
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