| Solar radiation is one of the important factors which effect yield and quality of crops.Global dimming(reduction in global radiation)has been observed throughout the world over the past few decades and become a new challenge to crop production.Therefore,identifying the spatial-temporal changes of reduced solar radiation and quantifying its impacts on crop yield are of prime importance for developing adaptation and mitigation strategies for crop production under future changed climate conditions.In China,soft wheat is mainly grown in the Middle-Lower Reaches of Yangtze River Basin,where solar radiation declined during wheat growth period,which was harmful to wheat yield and quality.For this purpose,daily data of sunshine hours of 50 years(1961-2010)from 73 meteorological stations in the Middle-Lower Reaches of Yangtze River Basin were first used to identify the spatial-temporal changes of low light during the key growth period of wheat(March to May)and the relationship between low light and wheat yield was analyzed.Secondly,experiments of soft wheat(Triticum aestivum L.,cvs ’Yangmai 15’,’Yangmai 13’ and ’Ningmai 9’)with different shading levels and durations at three key growth periods(jointing,booting and post-anthesis)were conducted at the experimental station of Jiangsu Academy of Agricultural Sciences located at Nanjing(32°02′ N and 118°53’ E)during 2008-2011.Based on the experimental data,the effects of low light on growth processes,yield components and grain quality of soft wheat were quantified and incorporated into a generic crop growth model(SUCROS)to develop a dynamic model MSPWYQ-L(Modelling System for Predicting Wheat Yield and Quality under Low Light)for predicting the effects of low light during key growth periods on the yield and grain quality of wheat.The model was validated using independent data from both shading experiments and agrometeorological stations,and then used for assessing low light induced yield loss of soft wheat in the Middle-Lower Reaches of Yangtze River Basin during 1961 to 2010 and identifying its spatial-temporal changes.The main research results are as follows:1.Low light was an important factor that affected solar radiation level in the Middle-Lower Reaches of Yangtze River Basin,and significant negative correlations were observed between wheat yield and four low light indices.Daily data of sunshine hours for 50 years(1961-2010)at 73 meteorological stations located in the Middle-Lower Reaches of Yangtze River Basin were used to identify spatial-temporal changes of accumulated sunshine hours and four low light indices(frequency of low light,accumulated days of low light,average days of a low light event,and maximum days of a low light event)during the key growth period of wheat(March to May).The results show that,accumulated sunshine hours displayed a gradual decrease from the Northeast to the Southwest,while values of the four low light indices displayed a gradual increase from the Northeast to the Southwest in the Middle-Lower Reaches of Yangtze River Basin.Lower values of accumulated sunshine hours(<350 h)were found in most area of Hunan and Jiangxi provinces where severer low light occurred,while higher values of accumulated sunshine hours(>519 h)were observed in the northeast of Jiangsu Province and the north of Anhui Province where milder low light occurred.During 1961-1990,accumulated sunshine hours decreased while values of the four low light indices increased.During 1991-2010,accumulated sunshine hours increased while values of the four low light indices decreased.The spatial-temporal changes of accumulated sunshine hours and the four low light indices indicated that low light was an important factor that affected solar radiation level during key growth periods of wheat in the Middle-Lower Reaches of Yangtze River Basin.Significant negative correlations were observed between wheat yield and four low light indices,which indicated that low light was harmful to wheat production in this region.The research results should provide a theoretical basis for assessing the impact of low light on wheat production.2.A sunshine hour based low light index was proposed and a dynamic model MSPWYQ-L for predicting the effects of low light on wheat yield and quality was developed.Based on the data of shading experiments,the effects of low light on wheat growth processes,yield components and grain quality were quantified.These quantitative relationships were then incorporated into a generic crop growth model(SUCROS)to develop a dynamic model MSPWYQ-L for predicting the effects of low light during key growth periods on wheat yield and quality.Independent data from both shading experiments and agrometeorological stations were used to validate the model.Compared with SUCROS model,our model improved predictions of wheat yield,i.e.increased prediction accuracy by 28%due to its ability in capturing the changes of leaf photosynthetic capacity,photosynthetic initial light-use efficiency,specific leaf area,partitioning index for green leaf dry weight and harvest index under low light conditions.The determination coefficient(r2)between the predicted and measured values of grain number per spike,thousand grain weight,test weight,falling number,protein content and wet gluten content were 0.82,0.82,0.80,0.75,0.74 and 0.78,respectively,and the corresponding relative root mean squared errors(rRMSE)were 0.02,0.04,0.01,0.03,0.04 and 0.04,respectively.By simulation analysis,the threshold low light index for MSPWYQ-L model were determined as 9.3,4.1 and 9.2 when low light occurring between jointing and anthesis,between anthesis and maturity,and between jointing and maturity.The model developed in this study gave satisfactory predictions of the effects of low light on yield and grain quality of soft wheat,hence,can be used for assessing the impacts of reduced solar radiation on soft wheat production under future changed climate conditions.3.Low light induced yield loss of wheat was simulated to increase first then decrease during 1961-2010 and display a gradual increase from the Northeast to the Southwest in the Middle-Lower Reaches of Yangtze River Basin.Daily data of sunshine hours,minimum and maximum temperature of 50 years(1961-2010)from 73 meteorological station in the Middle-Lower Reaches of Yangtze River Basin were used as input to simulate low light induced yield loss of wheat under historical weather conditions by MSPWYQ-L model developed in this study.The results show that,low light induced yield loss of wheat was simulated to display a gradual increase from the Northeast to the Southwest in the Middle-Lower Reaches of Yangtze River Basin.The largest yield loss was found in the south of Hunan and Jiangxi provinces where yield loss was over 44%,while the smallest yield loss was found in the north of Hubei and Anhui provinces,the south of Henan Province and the most area of Jiangsu Province where yield loss was less than 10%.During 1961-1990,an increasing trend of yield loss was observed across most of the studied region,especially for the south of Hunan and Jiangxi provinces where yield loss significantly increased(9.3%10a-1,P<0.01).During 1991-2010,a significant decreasing trend was observed across most of the studied region.Yield loss was increased first then decreased during 1961-2010,especially in the regions where yield loss was large.The spatial-temporal changes of low light induced yield loss were similar with that of accumulated low light index from jointing to anthesis,and from jointing to maturity,which indicated that the spatial-temporal changes of wheat yield loss was closely related to that of low light occurring in the key growth periods,specially during the periods between jointing and anthesis.The simulation results in this study can be used for assessing the impacts of reduced solar radiation on wheat yield and developing adaptation and mitigation strategies for wheat production under future changed climate conditions. |
