Impacts Of Solar Radiation Changes Caused By Haze On Rice Biomass Production

In recent years,with the speeding up of industrialization and urbanization,haze days caused by the air pollution is tending to increase year by year.The middle and lower reaches of the Yangtze River region become the zones of high haze frequency in our country.Total radiation decreased and scattering radiation ratio increased when haze occurred.Solar radiation change will affect crop yield because the solar radiation is the energy of photosynthesis and affects the growth of crops.Rice is the main food crops in the food production and consumption.Determining the influence of different solar radiation change situation on rice is the important basis of properly evaluating rice production caused by haze and the important significance to ensure food security in China.In this study,according to air quality index of Shanghai(2012 November-2013 June)and observations of the total radiation and diffuse radiation corresponding to AQI,we determine the relationship between the proportion of scattered radiation and AQI,and then determine the percentage of decrease in total radiation and the ratio of diffuse radiation to global radiation.Field experiments were conducted with rice(Oryza sativa L.)cultivar Nangeng 46 under different levels of solar global radiation and ratio of diffuse radiation to global radiation that were created by shading with plastic film.Based on the experimental data,we had a quantitative analysis of the effect of haze on biomass production of rice and analysed the reasons.The main research results are as follow:(1)Increasing ratio of diffuse radiation under haze conditions on biomass production has significantly "fertilizer effect" and the results showed that the percentage of decrease in biomass and yield are less than the percentage of decrease in total radiation under different levels of haze.When solar global radiation declined by 9.0%and the ratio of diffuse radiation increased by 15.3%(mild haze),biomass accumulation decreased 1.0%and yield decreased 3.9%in mature period.When solar global radiation declined?40.7%and the ratio of diffuse radiation increased by 12.5-47.3%(moderate haze and heavy haze),biomass production decreased by 9.2-15.0%and 17.2%in mature period,and yield decreased by 12.5-19.2%and 24.0%."Fertilizer effect" of diffuse radiation reduced the negative effects of the decreased total radiation on dry matter accumulation by 0.5%(mild haze),0.5-0.8%(moderate haze)and 0.5%(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 condition is the main reason why increasing ratio of diffuse radiation has significantly "fertilizer effect" on biomass production.Extinction coefficient decreased,light utilization efficiency(?)and leaf area index increased under haze condition,all these characters were of benefit to raising radiation use efficiency.When solar global radiation declined by 9.0%and the ratio of diffuse radiation increased by 15.3%(mild haze),extinction coefficient decreased by 0.0-10.6%,light utilization efficiency(?)increased by 20.0-41.3%and radiation use efficiency increased by 9.3%;when solar global radiation declined?40.7%and the ratio of diffuse radiation increased by 12.5-47.3%(moderate haze and heavy haze),extinction coefficient decreased by 4.7-22.8%?20.7-28.2%,leaf area index increased by 5.4-32.9%?9.9-35.7%,light utilization efficiency(?)increased by 5.4-65.7%?64.3-87.2%and radiation use efficiency increased by 3.6-13.7%?22.5%,which were beneficial to improve group photosynthetic productivity.Rice canopy light energy utilization efficiency could be increased by 0.6%when scattered radiation ratio increased 1%,which was consistent with"fertilizer effect" of diffuse radiation on biomass accumulation.(3)Declining harvest index was the main reason why "fertilizer effect" of diffuse radiation on yield was below "fertilizer effect" of diffuse radiation on biomass production.When solar global radiation declined by 9.0%and the ratio of diffuse radiation increased by 15.3%(mild haze),harvest index decreased 2.9%;when solar global radiation declined?40.7%and the ratio of diffuse radiation increased by 12.5-47.3%(moderate haze and heavy haze),harvest index decreased 3.6-5.0%and 8.1%.Because harvest index decreased under haze treatments,so "fertilizer effect" of diffuse radiation on yield was below "fertilizer effect" of diffuse radiation on biomass production.The study proved and quantified "fertilizer effect" of diffuse radiation on biomass production and yield under different levels of haze.Moreover,we explained the reason why diffuse radiation has fertilizer effect.This research laid a certain theoretical basis for analysis of the influence of haze on crop and provided the basis for building model simulations of agricultural production.