The Distribution And Photosynthetic Characteristics Of Effective Radiation In Different Soybean Canopy

Soybean is an important legume crop,its growth and development metabolism can not be separated from light energy,improving the utilization rate of light energy of soybean population is the key to increase soybean yield.Changes in canopy structure of soybean population will directly affect the distribution of photosynthetic effective radiation in the canopy,thus affecting physiological functions such as photosynthesis of soybean,leading to changes in yield.Therefore,it is of great significance to make clear the reasonable canopy structure and improve the utilization of light energy and soybean yield.This experiment was carried out in 2018-2019.Dongnongdou252,Kenfeng 16 and Henong 60 with suitable densities of 150000,300000 and 450000 plants/hm² were selected as the experimental materials to study the distribution of photosynthetic effective radiation in different soybean varieties canopy,To explore the influence of shading on Photosynthetic related indexes and chlorophyll fluorescence parameters of soybean,And to explore the photosynthetic effective radiation using the method of artificial shading The relationship between canopy photosynthetic rate and photosynthetic rate,fitting correlation curve,was used to estimate the canopy photosynthetic rate of soybean in the field.The test results show that:The leaf area index of soybean canopy increased first and then decreased with the increase of growth period,reaching the maximum at R₄,and there was significant difference among tested varieties.The leaf area distribution of the three varieties was mainly concentrated in the upper layer,and that of Kenfeng 16 and Dongnongdou 252 were mainly concentrated in the middle and upper layer.The photosynthetic effective radiation of Kenfeng 16 and Dongnongdou 252 were significantly higher than that of Henong 60 at noon on sunny days,and there was no significant difference between the tested varieties at cotyledon mark.The photosynthetic effective radiation at the canopy growth point of the tested varieties was significantly higher than that at the middle of the stem and the cotyledon mark,and there was no significant difference between the latter two.With the development of soybean growth period,the photosynthetic effective radiation in the canopy first decreased and then increased.The relationship between the photosynthetic effective radiation（Y）and the leaf area index（x）of soybean canopy at noon was in accordance with the equation:Y=116.0815+1377.64×0.37421^x.There was a significant positive correlation between PAR and Pn of tested soybean varieties.The relationship between Pn and PAR of Dongnongdou 252 was in accordance with the equation:y=2.73164+0.00478x,Henong60:y=2.18355+0.00711x,Kenfeng 16:y=2.99273+0.00639x.The average net photosynthetic rate of the upper and middle layer of the canopy was higher than that of the lower layer.The average net photosynthetic rate of the upper and middle layers of Kenfeng16 was higher than that of Dongnongdou252 and Henong60,but there was no significant difference among the lower layers.With the development of growth period,the average photosynthetic rate of each layer of soybean canopy first decreased and then increased.The assimilation rate of CO₂ is the highest in the upper layer,the lowest in the middle layer and the lowest in the lower layer.The assimilation rate of CO₂ in the upper layer of Henong 60 was significantly higher than that of Kenfeng 16 and Dongnongdou252.The assimilation rate of CO₂ in the middle and lower layers of the canopy of Kenfeng16 and Dongnongdou252 was significantly higher than that of Henong60.With the development of the growth period,the assimilation rate of CO₂ in the upper layer of Henong60 gradually increased,while that in the middle and lower layers gradually decreased.With the increase of shading level,Phi2 increased,Phi NO changed little,Phi NPQ and NPQ decreased,Fm,Fv/Fm,F₀ increased.With the gradual development of the growth period,the relative chlorophyll content of Kenfeng 16 and Henong 60 showed an increasing trend,reaching the maximum in R₆,but no significant change in Dongnong bean.The changes of Fs and Fv/Fm of each variety showed a single peak curve,reaching the maximum in R₄,and the changes of different shade treatments were the same.The grain weight and number of the tested varieties were mainly concentrated in the upper layer and less in the lower layer.The order of grain weight of each layer was Dongnongdou 252>Kenfeng 16>Henong 60.The number of grains in the upper layer of Kenfeng 16 was significantly higher than that of Dongnongdou 252 and Henong 60.The order of grain number in the lower layer of the tested varieties was Dongnongdou 252>Kenfeng 16>Henong 60.The yield and accumulation rate of Kenfeng16 and Henong60 were significantly higher than that of Dongnongdou 252.There was no significant difference between Kenfeng 16 and Henong 60.