Soybean is often intercropped with maize, sugarcane, and sorghum.  Because of the shade coming from the latter, the soybean stem lodging is often a very serious problem in intercropping systems.  The aim of this study is to characterize the possible mechanisms in the stem of shade-induced promotion of seedling soybean lodging in intercropping systems at the proteome level.  We found that the soybean stem became slender and prone to lodging when it was planted with maize in an intercropping system.  The inhibition of lignin biosynthesis and lack of photosynthate (soluble sugar) for the biosynthesis of the cell wall led to the lower internode breaking strength.  A total of 317 proteins were found to be affected in the soybean stem in response to shade.  Under the shade stress, the down-expression of key enzymes involving the phenylpropanoid metabolic pathway inhibited lignin biosynthesis.  The up-regulation of expansin and XTHs protein expression relaxed the cell wall and promoted the elongation of internodes.  Although the expression of the enzymes involving sucrose synthesis increased in the soybean stem, the lack of a carbon source prevented rapid stem growth.  This metabolic deficit is the principal cause of the lower cellulose content in the stem of intercropped soybean, which leads to weakened stems and a propensity for lodging.

Soil with low phosphorus (P) availability and organic matter contents exists in large area of southwest of China, but some soybean genotypes still show well adaptations to this low yield farmland.  However, to date, the underlying mechanisms of how soybean regulates soil P availability still remains unclear, like microbe-induced changes.  The objective of the present study was to compare the differences of rhizosphere bacterial community composition between E311 and E109 in P-sufficiency (10.2 mg kg^–1) and P-insufficiency (5.5 mg kg^–1), respectively, which then feedback to soil P availability.  In P-sufficiency, significant differences of the bacterial community composition were observed, with fast-growth bacterial phylum Proteobacteria, genus Dechloromonas, Pseudomonas, Massilia, and Propionibacterium that showed greater relative abundances in E311 compared to E109, while in P-insufficiency were not.  A similar result was obtained  that E311 and E109 were clustered together in P-insufficiency rather than in P-sufficiency by using principal component analysis and hierarchical clustering analysis.  The quadratic relationships between bacterial diversity and soil P availability in rhizosphere were analyzed, confirming that bacterial diversity enhanced the soil P availability.  Moreover, the high abundance of Pseudomonas and Massilia in the rhizosphere of E311 might increased the P availability.  In the present study, the soybean E311 showed capability of shaping rhizosphere bacterial diversity, and subsequently, increasing soil P availability.  This study provided a strategy for rhizosphere management through soybean genotype selection and breeding to increase P use efficiency, or upgrade middle or low yield farmland.