| Since 1950,the amount of solar radiation received by the global surface has decreased significantly(i.e."global dimming"),which has become one of the important stress of crop production.Increasingly frequent fine particle aerosol pollution(i.e.haze)is the main cause of the decrease of solar radiation in China.Solar radiation is the energy source of crop growth and development.On the one hand,haze weather led to the decrease of the total solar radiation,which reduced the photosynthetic productivity of crops and led to the decline of crop yield.On the other hand,the proportion of diffuse radiation increased when haze occurred,which made the distribution of light in the canopy more uniform and the proportion of high light intensity leaf area reduced,thus increasing the crop radiation use efficiency and causing the corresponding compensation effect to the decrease of crop yield caused by the decrease of total solar radiation,that is,the diffuse radiation is used to produce crop yield called "fertilizer effect".Crop canopy light interception is the necessary information to calculate crop radiation use efficiency.The influence of the increase of the proportion of diffuse radiation in haze weather on canopy light interception ratio can be used to accurately estimate the crop canopy radiation use efficiency in haze weather,and to provide a basis for further revealing the reasons for the "fertilizer effect" of crop yield by diffuse radiation.The field experiment carried out in this study use field haze simulator in open field with wheat(Triticum aestivum L.cv Ningmai 13)in 2014-2016 years in Jiangsu Academy of Agricultural Sciences(32.03°N,118.87°E).This study measured the photosynthetic active radiation at the top and bottom of the wheat canopy and leaf area index under different treatment conditions,calculated the canopy extinction coefficient,the canopy light interception and the light interception ratio,and further analyzed the effects of the solar radiation on the wheat canopy light interception and the light interception ratio quantitatively.The main results are as follows.(1)The decrease degree of photosynthetically active radiation interception in wheat canopy was basically consistent with that of photosynthetically active radiation under haze conditions.When solar global radiation declined by 14.09%and the ratio of diffuse radiation increased by 9.76%(Simulation of mild haze),the photosynthetically active radiation above wheat canopy decreased 21.20%,the interception of photosynthetically active radiation decreased 23.0%from treatment to maturity.When solar global radiation declined by 15.06%-20.93%and the ratio of diffuse radiation increased by 11.56%-12.96%(Simulation of moderate haze),the photosynthetically active radiation above wheat canopy decreased 13.60%-19.70%,the interception of photosynthetically active radiation decreased 16.70%-20.20%from treatment to maturity.When solar global radiation declined by 25.93%-31.47%and the ratio of diffuse radiation increased by 10.61%-21.13%(Simulation of heavy haze),the photosynthetically active radiation above wheat canopy decreased 25.20%-43.20%and the interception of photosynthetically active radiation decreased 30.20%-43.80%from treatment to maturity.(2)Under different haze treatments,the canopy leaf area index increased and the extinction coefficient decreased,which resulted in no significant difference in the interception ratio of photosynthetically active radiation in wheat canopy during the growth stages.When total radiation declined by 14.09%and the ratio of diffuse radiation increased by 9.76%(Simulation of mild haze),wheat canopy leaf area index increased 3.27%-5.0%,extinction coefficient decreased 0.64%-7.51%,and the light interception radio decreased 1.55%.When total radiation declined by 15.06%-20.93%and the ratio of diffuse radiation increased by 11.56%-12.96%(Simulation of moderate haze),wheat canopy leaf area index increased 1.11%-4.77%,extinction coefficient decreased 1.40%-6.25%,and the light interception radio decreased 0.45%-2.32%.When total radiation declined by 25.93%-31.47%and the ratio of diffuse radiation increased by 10.61%-21.13%(Simulation of heavy haze),wheat canopy leaf area index increased 4.39%-10.52%,extinction coefficient decreased 2.98%-10.60%,and the light interception radio decreased 0.78%-4.26%.(3)Under different haze treatments,the variation of light interception ratio between different leaf positions decreased with the deepening of the degree of haze,which makes the light permeation at the bottom of the canopy increase,and the distribution of light in the canopy is even more uniform.When total radiation declined by 14.09%and the ratio of diffuse radiation increased by 9.76%(Simulation of mild haze),compared with the flag leaf,the interception ratio of the second leaf from the top increased 0.02%-1.87%,and the interception ratio of the third leaf from the top decreased 3.92%-9.32%.When total radiation declined by 15.06%-20.93%and the ratio of diffuse radiation increased by 11.56%-12.96%(Simulation of moderate haze),compared with the flag leaf,the interception ratio of the second leaf from the top increased 0.41%-3.03%,and the interception ratio of the third leaf from the top decreased 2.23%-6.57%.When total radiation declined by 25.93%-31.47%and the ratio of diffuse radiation increased by 10.61%-21.13%(Simulation of heavy haze),compared with the flag leaf,the interception ratio of the second leaf from the top increased 1.35%-3.35%,and the interception ratio of the third leaf from the top decreased 2.73%-5.58%.This present study determined the influence of solar radiation changes caused by haze on canopy light interception and the interception ratio through field observation.However,the uniformity of the distribution of photosynthetically effective radiation in the canopy was improved,which indicated that the improvement of the uniformity of light distribution in the canopy of wheat under the haze,not the amount of light interception or the interception ratio,was one of the contributors to the "fertilizer effect" of the wheat yield. |
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