Studies On Effect And Mechanism Of Silicon On Shade Tolerance,Lodging-resistance And Yield Improvement In Relay Strip Intercropped Soybean

In the maize-soybean intercropping mode,soybean seedling stage is affected by maize shade,which results in the decrease of photosynthetic rate of leaves,bending resistance of stems,root activity and lodging easily,and ultimately reduces soybean yield.For this reason,pot experiment and field experiment were set up from 2017 to 2018.Two soybean varieties Nandou 12 and Nan 032-4 were used as materials in pot experiment.The shade environment of maize-soybean intercropping was simulated by black shading net with 50%transmittance.Two cultivation models of soybean mono-cropping and maize-soybean intercropping were set up with Nandou 12 and semi-compact maize varieties?Chengdan 30and Chuandan 418?.In order to improve the lodging resistance of soybean stalks,different silicon concentration gradient spraying during soybean seedlings was carried out,which was divided into four levels.The four levels of silicon application were 0 mg/kg,100mg/kg,200 mg/kg and 300 mg/kg,respectively.Silicon accumulation in different parts of soybean plants,photosynthetic parameters of leaves,chlorophyll content,stem diameter and stem bending resistance,root morphological characteristics,injury flow rate,root-shoot ratio,dry matter accumulation and so on were measured at the early?V6?and late?R5?growth stages of soybean.Soluble sugar content,anatomical structure of transverse section of stem,lignin content,activity of related enzyme and gene expression were used to determine yield and yield components of soybean during harvest period.The mechanism of silicon on improving shade resistance,lodging resistance and yield of soybean was analyzed,which provided theoretical basis for promoting soybean growth,lodging resistance,yield increasing and application of silicon fertilizer in agricultural production.The main results are as follows:1.Suitable silicon application increased the silicon accumulation in all parts of plant.After spraying Na₂SiO₃·9H₂O solution on the leaf surface,it could be absorbed by soybean leaves under normal light and shade,and transferred to roots and stems smoothly,thus significantly increasing the silicon content in the body.However,there were differences among organs,which were as follows:root>leaf>stem.Under normal light environment,spraying 100 mg/kg Na₂SiO₃·9H₂O aqueous solution on the leaf surface,the silicon content in Nandou 12 was the highest,while under shade environment,200 mg/kg was the optimum concentration;For Nan032-4,under normal light and shade environment,the optimum concentration was 200 mg/kg and 100 mg/kg respectively.2.Applying appropriate silicon concentration increased net photosynthetic rate?Pn?,stomatal conductance?Gs?and transpiration rate?Tr?of soybean,and decrease intercellular carbon dioxide concentration?Ci?.The net photosynthetic rate of Nandou 12 under normal light and shade increased by 46.4%and 33.3%respectively compared with CK treatment in 200 mg·kg^-1treatment.Silicon application also increased chlorophyll content,soluble sugar content and fresh weight of leaves,reduced leaf area and enhanced photosynthesis of soybean.3.Silicon application increased root length,root surface area,root volume,root-shoot ratio and root dry weight of soybean.Silicon application can also significantly increase root injury flow.With the increase of silicon application,soybean injury flow shows a trend of first increasing and then decreasing,specifically 200 mg·kg^-1>300 mg·kg^-1>100mg·kg^-1>0 mg·kg^-1.The increase of injury flow can explain that silicon application enhances root vitality of intercropping soybean.4.Suitable application of silicon increased the stem diameter,bending resistance,fresh weight and lodging resistance index of soybean,and further enhanced the transport of nutrients and water in plant.Silicon application also increased the thickness of xylem and phloem in the anatomical structure of cross section of soybean stem intercropped with silicon.And then increased the proportion of xylem and phloem,reduce the proportion of pith and strengthen the density of stem.Silicon application also enhanced the activity of POD,CAD,4CL and PAL,increased the expression of POD,CAD and PAL genes in pre-growth period of soybean,increased lignin accumulation in vivo,and improved lodging resistance of soybean stalks.5.Silicon application significantly increased the accumulation of some carbohydrates in stems and leaves of plants,such as soluble sugar and sucrose,and show a trend of increasing first and then decreasing with the increase of silicon concentration;Silicon increased the starch content in stems and reduces the starch content in leaves.Silicon application significantly increased the dry matter accumulation of soybean organs and promoted the yield.6.Silicon application significantly increased the yield of soybean by increasing the number of effective pods per plant,the number of grains per plant and the weight of grains per plant.The yield increased by 10%-30%.The yield increased by 200 mg·kg^-1>100 mg·kg^-1>300 mg·kg^-1.Medium silicon concentration(100 mg·kg^-11 and 200 mg·kg^-1)was more conducive to the improvement of soybean yield.In conclusion,silicon application had significant effects on silicon uptake and accumulation,photosynthesis,root growth,stem morphology and anatomical structure,lignin synthesis and activity and expression of related enzymes,lodging resistance and yield of soybean.Silicon could effectively improve the growth of soybean under shade stress,enhance photosynthesis and root absorptive capacity of soybean,promote material accumulation,facilitate lignification of plant cells,enhance stem strength and lodging resistance,thereby improving soybean yield.