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Light intensity is one of the important environment factors that affects crop growth and production. Global climate change increases the weak light event. Quantitative predicting the influence of dim light on crop growth and production is the basis of assessing the impact of the dim light event induced by climate change on crop production. Yangtze River valley is the main production region of weak gluten wheat. Cloudy and rainy weather is the harmful event appeared frequently at wheat filling stage. The aim of this study is to quantitatively research the effect of weak light on the wheat growth and production. Experiments of high quality weak gluten wheat, Yangmai 15, Ningmai 9 and Yangmai 13 with different weak light intensity(50%,66%,84%) and duration (2d,4d,6d,8d)of shading treatment were conducted in the farm of Jiangsu Provincial Academy of Agricultural Sciences Nanjing, from November 2008 to June 2010. By analysis of variance on the data, the critical shading conditions was found when shading impact the wheat growth remarkably at the filling stage. Based on the effects of temperature and photo-synthetically active radiation, with PTI as the predicting index, a model for predicting the LAI, yield, dry matter production and distribution at weak light conditions at wheat filling stage was developed.The main research contents are as follow:(1)Definiting the critical shading conditions at wheat filling stage. When shading intensity is more serious than 50% or 66% and shading duration is longer than 4d, shading treatment impacts the LAI of wheat, shoot total dry weight, organ weight, yield, grain number per spike and thousand grain weight significantly. When shading intensity is more serious than 84% and shading duration is longer than 2d shading treatment will effect the LAI of wheat, shoot total dry weight,organ weight, yield, grain number per spike and thousand grain weight significantly.(2)Simulating the impacts of weak light on LAI at filling stage. With PTI after flowering as the predicting index, a model for predicting the LAI under different weak light conditions at filling stage was developed. Independent experimental data was used for validating the model. The results show that the coefficient of determination (r2) and the relative root mean squared error (rRMSE) between the predicted and measured result were 0.68,0.36, respectively. (3)Simulating the impacts of weak light on dry matter production and distribution at wheat filling stage. With PTI after flowering as the predicting index, a model was developed for predicting dry matter contribution under different shading conditions at filling stage. Then with the integrationof LAI simulation model, dry matter contribution model and SUCROS which is based on photosynthesis, the organs dry weight and total shoot dry weight can be predicted. Independent experimental datas were used for validate the model. The results show that coefficient of determination (r2) between the predicted and measured values of dry matter production, dry weight of leaf, stem, seed, awn based on the 1:1 line were 0.72,0.65,0.67,0.70,0.72, respectively; and the relative root mean squared error (rRMSE) between the predicted and the measured values were 0.41,0.39,0.34,0.36,0.31, respectively. The model, combined with the partitioning index of seed and SUCROS model, can preferablely predict the seed dry weight and grain weiht in the mean while.In this study, the model can simulate the light situation at natural condition on the wheat filling stage. According to information, such as flowering date, PAR, temperature, as well as weak light intensity and duration, it can predict the impact of weak light at filling stage. The model, comprehensive consideration of temperature, PAR, and weak light impact factor, can predict the dynamic change of LAI, dry matter production, organ dry weight and yield. This study lays a model foundation for quantitatively researching the impact of wheat production under weak light event.
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