Shade effect on carbohydrates dynamics and stem strength of soybean genotypes

We selected four genotypes from the recombinant inbred lines based on their agronomic traits in terms of lodging resistance. Then, we investigated the morphological characteristics and stem carbohydrate accumulation of different soybean (Glycine max L.) genotypes under different light environments (normal light, low light and shading stress). Based upon metabolic accumulation of carbohydrates in the stem, we explored the reasons for the differences in stem strength of different soybean genotypes and expounded the relationship between accumulation and distribution of carbohydrates. Results of the present study showed that with the advancement of soybean growth period, the cellulose and lignin contents in soybean stem increased while the hemicellulose, sucrose and soluble sugars contents decreased. Compared with normal light conditions, the lignin, cellulose, soluble sugar and sucrose contents in the soybean plants under shading stress were reduced to different levels. Moreover, low light significantly reduced non-structural carbohydrate content in soybean stem while the lignin and cellulose contents were not significantly changed. The correlation analysis showed that there was a significant positive correlation among the stem snapping resistance, cellulose and lignin contents. The results showed that the stem strength was mainly determined by lignin and cellulose contents. The lignin content in the stem had a greater effect on the stem strength compared to cellulose. The xylose in soybean stem was also significantly reduced under the shading stress, which reduced lignin synthesis substrates. Under low light and shading stress, the minimum decrease in sucrose and structural carbohydrates content of a genotype (B23) was noticed indicating that B23 had high stem strength and increased decomposition of sucrose into cellulose synthesis. This trait of increased decomposition reduces the plant’s inefficient decomposition of sucrose thus most of the sucrose is used to synthesize cellulose. Conclusively, these results suggested that deposition of a relatively large amount of structural carbohydrates (e.g. lignin, cellulose, hemicellulose and monosaccharides) leads to thicker stem tissues which could be helpful to reduce lodging due to shading stress under multiple cropping systems.