The Effects Of Shading On Carbohydrates In Soybean Stalk And The Relationship Of Carbohydrates With Stem Strength

Lodging is an important factor which restricts the intercropping of high quality and high yield of soybean,and its degree of occurrence is closely related to the intensity of soybean stalk under shaded environment.The study was explored the effects of shading on carbohydrate accumulation and the differences between different genotypes from the aspect of improving the stalk strength,which has an important role in revealing the shade-tolerance mechanism of soybean.In this experiment,27 soybean varieties with strong shade tolerance cultivar-Nandou 12,weak shade-tolerant cultivar-Nan 032-4,and their recombinant inbred lines were used to study the relationship between the accumulation and distribution of the carbohydrates in soybean stems and the stem strength.We select four materials with significant differences in stalk strength from the recombinant inbred lines.Then through the corn-soybean intercropping and monocropping two planting patterns and shading and shading signal(low R/FR)two light environments,system study on the morphological characteristics and carbohydrate accumulation of soybean stems.From the point of metabolic accumulation of carbohydrates in stems,we analysis the reasons for the differences in stem strength of different soybean materials,and expound the relationship between the accumulation and distribution of carbohydrates and the strength of stems under the shaded environment.The main results are as follows:1.Intercropping planting and shading stress environment significantly increased the main stem length,internode length,and the ratio of internode length and diameter of soybean,and reduced the accumulation of stem and stem unit length biomass,resulting in the folding of stems.Soybean morphology was relatively less affected by the shading signal.Different soysbean materials morphology and stalk strength were affected by shaded stress and shaded signals.The materials with strong stalk strength,B23 and B24,are insensitive to the shaded signal,and all the morphological indicators have less variation in the shaded environment,which can maintain the strong stem strength and superior stalk morphology.2.Carbohydrate synthesis studies showed that with the advancement of soybean growth period,the content of cellulose,lignin and starch in the stems of soybeans increased;the content of hemicellulose,sucrose and soluble sugars decreased.Compared with monocropping,the contents of lignin,cellulose,soluble sugar and sucrose in the soybean cultivars of intercropping system were reduced to varying degrees;compared with normallight,the carbohydrate content of soybean stems decreased under shading,but the stalks decreased.The material with high stem strength had a lower decrease,and the stalk tissue was denser which had a better stalk strength。The non-structural carbohydrate content in soybean stems decreased significantly under shaded signals,while the lignin and cellulose content did not change significantly.Therefore,the soybean stem resistance maintained a higher level under shaded signals.3.The correlation analysis showed that there was a very significant positive correlation between the stem snapping resistance and its cellulose and lignin content(r=0.749,r=0.897,P<0.01).The results showed that the stem strength was determined mainly by lignin and cellulose content,and the lignin content in the stem had a greater effect on the strength of the stem compared to cellulose.4.Compared with monocropping and normal light,the xylose in the structural carbohydrates of soybean stems was significantly reduced under the intercropping and shading stress,which reducing lignin synthesis substrates,lowering of lignin content,and less stalk filling,eventually resulting in decreased stem strength at the seedling stage of soybeans.Under the shaded environment,the sucrose content of material B23 with high stem strength decreased,while the change of cellulose content was the smallest,which indicates that B23 with high stalk strength can effectively increase sucrose utilization efficiency,and sucrose can be more efficiently decomposed into cellulose synthesis.,which reduces the inefficient decomposition of sucrose and more sucrose is used to synthesize a relatively large amount of cellulose,so that the stem tissue is denser and the stem strength is maintained at a higher level.5.Under intercropping system,the effective number of pods,the number of seeds per plant,the grain weight per plant and the yield were significantly reduced;the uneffective number of pods and 100-seed weights did not change significantly.The B23 decreasing rate of effective pod number,the number of seeds per plant,and the weight of seeeds per plant were the smallest under intercropping,and the yield was the highest.The interaction of planting patterns with soybean genotypes had a significant effect on soybean yield.