Abstract: A pot experiment was conducted with two soybean varieties (Di2003-1 and Hefeng25) and two main soil types (alfisol and mollisol) in Heilongjiang Province to study the interactive effects of variety and soil type on the root morphology and nodule traits of soybean plants. Root samples were collected at the fifth trifoliolate stage, bloombeginning stage, podbeginning stage, full pod stage, seedbeginning stage, full seed stage, and full maturity stage for the analysis of root dry mass, root length, root surface area, average root diameter, nodule number, nodule fresh mass, and mass per nodule. The results showed that soil type had significant effects on the root morphology and nodule traits of test varieties. In alfisol, the root dry mass, root length, and root surface area of test varieties were greater at the fifth trifoliolate stage and bloom-beginning stages while smaller after seedbeginning stage, compared with those in mollisol, and the average root diameter after seedbeginning stage was higher in alfisol than that in mollisol. Soil type did not affect rootshoot ratio. The nodule number after seedbeginning stage was much smaller in alfisol than in mollisol, while the nodule fresh mass and the mass per nodule were in adverse. The root traits in the two soil types varied with soybean variety. Compared with that of Hefeng25, the response of root traits of Di2003-1 to soil type was more sensitive. The interactive effects of variety and soil type on the root morphology and nodule traits of soybean plants were more significant at full seed stage.

Key words: IsoSource model, stable isotope, Three Gorges Reservoir Area, backwater area of Xiaojiang  River fish.