Impacts Of Solar Radiation Changes Caused By Haze On Wheat Productivity

Global dimming,defined as reduction in incident global radiation,has been identified as one of the major trends of climate change in addition to the increase of atmospheric CO2 concentration and temperature.Global dimming can be caused by cloud or air pollution.In recent years,with the rapid development of social economy,air pollution in China has become severer and the umber of haze days caused by air pollution has been increasing.The reduction in incident global radiation caused by haze has become a new challenge to crop production since light is one of the most important climate factors that regulate crop growth and development.Wheat is one of the most important food crops in China.Determining the effects of changed incident global radiation under different level of haze conditions on wheat productivity is of importance for assessing the impacts of global dimming on wheat crop production and yield under future global dimming conditions.The objective of this study was to quantify the impacts of changed incident global radiation under different level of haze conditions on winter wheat productivity and to identify its causes.For this purpose,field shedding experiments with wheat(Triticum aestivum L.cv Ningmai 13)were conducted during 2014-2016 at the experimental station of Jiangsu Academy of Agricultural Sciences(32°03’N,118°87’E).Field experiments included shedding treatments with three levels(light,middle and heavy)of simulated haze created using PE film installed(at a height of 2 m above the ground)over plots with each an area of 4x5 m.Plots without shedding were used as Control.The main results are as follows.(1)The total radiation loss caused by haze resulted in a significant decrease in biomass production and yield of wheat,and the decrease of biomass production and yield was less than that decrease of total radiation,which indicated that the increase of scattering radiation had significant effect on wheat dry matter production and yield.Increasing ratio of diffuse radiation under haze conditions on biomass production has significantly "fertilizer effect".When solar global radiation declined by 14.09%and the ratio of diffuse radiation increased by 9.76%(mild haze),biomass accumulation decreased8.03%and yield decreased 8.31%in mature period.When solar global radiation declined byl5.06%-20.93%and the ratio of diffuse radiation increased by 11.56%-12.96%(moderate haze),biomass accumulation decreased8.21%-8.85%and yield decreased 8.95%-9.37%in mature period.When solar global radiation declined by25.93%-31.47%and the ratio of diffuse radiation increased by 10.61%-21.13%(heavy haze),biomass accumulation decreased 13.14%and 14.59%and yield decreasedl3.48%-16.36%in mature period."Fertilizer effect" of diffuse radiation reduced the negative effects of the decreased total radiation on dry matter accumulation by 0.58%(mild haze),0.54%-0.67%(moderate haze)and 0.61%-0.72%(heavy haze),and reduced the negative effects of the decreased total radiation on yield by 0.3%(mild haze),0.3%-0.7%(moderate haze)and 0.4%(heavy haze).(2)Increasing radiation use efficiency under haze is the main reason why increasing ratio of diffuse radiation has significantly "fertilizer effect" on biomass production and yield.Extinction coefficient decreased,light utilization efficiency(ε)increased and leaf area index(LAI)which increased with the increase of specific leaf area(SLA)and leaf partitioning index under haze condition,all these characters raise radiation use efficiency.When solar global radiation declined by 14.09%and the ratio of diffuse radiation increased by 9.76%(mild haze),light utilization efficiency(ε)increased by 16.39%-22.12%extinction coefficient decreased by 1%-7.51%,and radiation use efficiency increased by 5.7%;When solar global radiation declined by 15.06%-20.93%and the ratio of diffuse radiation increased by 11.56%-12.96%(moderate haze),extinction coefficient decreased by 1.4%-5.36%,leaf area index increased by 1.11%-4.77%,light utilization efficiency(ε)increased by 9.88%-25.13%and radiation use efficiency increased by 1%and 8.5%,When solar global radiation declined by 25.93%-31.47%and the ratio of diffuse radiation increased by 10.61%-21.13%(heavy haze),extinction coefficient decreased by 3.45%-10.6%,leaf area index increased by 4.39%-10.52%,light utilization efficiency(ε)increased by 21.5%-43.2%and radiation use efficiency increased by 7.97%-29.12%.(3)The change of solar radiation caused by haze reduces the effective panicles,reduces the spike partitioning index,and the decreasing of spike partitioning index reduces the grain number per spike and thousand grain weight.This is the main reason for the yield reduction under the haze condition.The results showed that the effective panicles,number of grains per spike and the grain weight decreased by 3.81%,9.93%and 4.08%under mild haze.The simulated moderate haze decreased three factors by 2.71%-5.47%,4.13%-6.57%and 2.25%-2.36%respectively;simulated heavy haze,the three factors decreased by 6.42%-9.96%,6.57%-15.63%and 5.04%-8.96%.The results obtained in this study can facilitate the development of a model for assessing the impacts of changed incident solar radiation under different levels of haze conditions on wheat crop productivity,and provide decision support for wheat crop production mitigating global dimming under future changed climate.