Research On Adaptation Of Soybean To Low-light Stress Under Intercropping

Corn-soybean strip hybrid planting can ensure maize yield and increase soybean yield in one season.The key to give full play to population yield advantage is to select soybean varieties with shade tolerance.Soybean germplasm resources in guizhou,cultivation has a long history,is the southwest mountain spring soybean and maize strip intercropping cultivation of main areas,but the production suitable for intercropping soybean variety few,yield is low,affect the output of the whole intercropping system and cultivation patterns of a wide range of application,this study based on corn-strip intercropping soybean planting technology development of soybean varieties in urgent demand,The rich soybean germplasm resources in low light area of Guizhou were fully utilized to screen soybean materials suitable for low light stress intercropping,which laid a foundation for breeding soybean resistant varieties,so as to further give play to the advantages of intercropping.In this study,net intercropping soybean was cultivated in different ecological environments to analyze the effects of low light stress on the growth,development and yield of soybean,and the adaptability evaluation system of soybean to low light stress was established by cluster analysis,principal component analysis and membership function evaluation.And through in-depth analysis of the shadow resistance: strong,middle or weak three varieties under the net interplanting of morphological and physiological characteristics,find out the shadow of resistance to adapt to the intercropping soybean morphological effect and physiological mechanism of weak light stress for breeding shade-tolerance soybean varieties and shadow resistance evaluation to provide theoretical basis for the development of corn,soybean belt compound planting technology is of great importance.The main results are as follows:1.Effects of low light stress on morphological characteristics of soybean: in terms of stem morphology,compared with net cropping,plant height increased by 17.2%,stem diameter decreased by 36.1%,plant lodging rate increased by 29.3%,and effective branch number decreased by 33.8%,and plant height and effective branch number were significantly correlated with yield.In leaf morphology,leaf area per plant decreased by27.9%,leaf area index(LAI)decreased by 28.1%,and dry matter weight decreased by39.4%.In terms of yield characters,the effective pod number per plant decreased by 36.6%,the grain number per plant decreased by 39.5%,the 100-grain weight decreased by 17.7%,and the yield decreased by 52.4%.The change rate of effective pod number per plant,the effective grain number per plant,the 100-grain weight per plant was significantly correlated with the yield change rate.Under the experimental conditions,the yield of the same material had no significant difference among the three ecological points.The results showed that the main factor affecting yield was intercropping low light stress,and the yield was significantly reduced by intercropping low light stress for different ecological points.2.Effects of intercropping low light stress on physiological characteristics of soybean:the net photosynthetic rate under intercropping low light stress was significantly lower than that under net cropping low light stress,with an average decrease of 48.5%.The main factor affecting the photosynthetic rate under this experimental condition was intercropping low light stress,and the net photosynthetic rate of leaves was significantly reduced under intercropping low light stress for different ecological points.The relative content of chlorophyll(SPAD value)decreased by 17.5%,SOD activity increased by55.9%,CAT activity increased by 126.4%,and POD activity increased by 15.3%.The activities of SOD and CAT were greatly affected by the ecological environment,which were sensitive to weak light stress in intercrop,and the variation coefficient was large,while POD activity was relatively stable.It was mainly affected by the genetic characteristics of each material and the variation range was small under the intercropping weak light stress.3.Comprehensive evaluation of soybean adaptability to intercropping low light stress:D values of all the tested materials were obtained through correlation analysis,principal component analysis and membership function analysis,and then cluster analysis was conducted to finally divide the 30 materials into three categories:Qiandou 08014,Qiandou 2011-1,Qiandou 2011-3,Qiandou 2011-5,Qiandou 2011-19,Qiandou 2011-20 and other six materials were classified into the first class,and their comprehensive evaluation value of shade tolerance was high.These materials had lower plant height,more effective branching number,larger leaf area per plant,lower CAT enzyme activity,more pod number per plant and smaller 100-grain weight.It belongs to shade-resistant material;Qiandou 08002,Qiandou 7,Qiandou 2011-7,Qiandou 2011-24 and other 10 materials belong to the second class.The comprehensive evaluation value of shade-tolerance was higher,such as lower plant height,fewer effective branches,larger leaf area per plant,higher CAT enzyme activity,more pod number per plant,and moderate100-seed weight.The other 14 materials belong to the third class,which have the lowest comprehensive evaluation value of shade tolerance.They are sensitive materials with higher plant height,less effective branching number,smaller leaf area per plant,higher CAT enzyme activity,less pod number per plant and larger 100-seed weight.Using the comprehensive evaluation value of shade tolerance(D value)as the dependent variable,the plant height,stem diameter,effective branch,plant lodging rate,leaf area per plant,leaf area index,biological yield,pod number per plant,seed number per plant,100-seed weight,photosynthetic rate and CAT enzyme activity were significantly correlated with D value(X1,X2......)X12 represents)and other 12 indicators as independent variables for stepwise regression analysis to establish the optimal regression equation:D= 0.99-0.001-0.002-0.002X3-0.005X5-0.004X8-0.003X10-0.0003 X12(R2 =0.9853,F=127.5720,P=0.0001).The results showed that plant height,effective branch,leaf area per plant,pod number per plant,100-seed weight and CAT activity represented by the six indexes in the equation had obvious response to Low-light stress under intercropping,and could be used as the evaluation indexes of soybean shading tolerance.4.shadow resistance soybean intercropping morphological effect of weak light stress and photosynthetic physiological mechanism analyses:Compared with the net cropping system,soybean with strong shade tolerance had more stable plant height and stem diameter,higher resistance to falling,effective branching and leaf area index,which could maintain reasonable canopy structure.Leaf net photosynthetic rate and Rub Pcase activity decreased slightly,which laid a foundation for maintaining high intercropping yield.Under intercropping,cultivars with strong shade tolerance could significantly increase leaf apparent quantum efficiency,reduce light compensation point,light saturation point and leaf carboxylation efficiency(CE),and increase CO2 compensation point.With the increase of shading degree,the utilization ability of weak light was improved,while the utilization ability of high CO2 was decreased.The Fv/Fm,Yield,QP and Retr values were significantly decreased,while the NPQ values were increased,indicating that the potential activity of PS reaction center was significantly reduced by low light stress.The electron transfer rate and activity of PSⅡ were decreased,and the amount of the primary electron acceptor QA reoxidized to form QA was reduced.The value of NPQ significantly increases the absorption of excess light energy dissipated in the form of heat,which is a self-protection mechanism and plays a certain role in protecting the photosynthetic apparatus.