Abstract: 【Objective】Root absorbing ability of soybean is closely related to the yield, while the response of soybean cultivars to seeding rates is not the same. Two pot experiments were conducted to find out the root morphological traits and root vigor of super-high-yield soybean cultivars, and common cultivar under the treatments of different seeding rates and planting pattern. 【Method】Two super-high-yield soybean cultivars Liaodou 14, Zhonghuang 35,and one common cultivar Liaodou 11 were used in the pot experiments to investigate the effects of different seeding rates and planting patterns on soybean root morphological traits, root vigor and bleeding component in 2012 and 2013. The experiment was laid out in a randomized block experiment design with five replications. The treatments consisted of three levels of seeding rate (3, 6 and 9 plants/pot) and two planting patterns (single seeding and mixed seeding). At the stages of R2, R6 and R8, plant roots were selected for measurements. Root length, root surface and root volume were measured by root system scanner WinRhizo Program (Re．gent Instruments Inc．Canada).Root vigor was estimated by TTC method. Bleeding was collected by gravimetric method. The bleeding phosphorus, potassium and soluble sugar were, respectively, determined by molybdenum stibium anti (UV-2450) , flame photometer (PEAA800) and glucose oxidasedetection. Root competition ratio (RCR) of super-high-yield cultivar was calculated by the root character of super-high-yield cultivar at mixed seeding to those at single seeding ratio divided the root character of common cultivar at mixed seeding to those at single seeding ratio. RCR＞1 means that competitiveness of super-high-yield cultivar was stronger.【Result】The result showed that the root morphological traits, root vigor and bleeding components varied with different seeding rates and planting patterns. The whole growth stage, the root morphological traits, root vigor, and the bleeding sap reached maximum at seed filling stage and flowering stage, respectively. Super-high-yield cultivars had higher root length, root volume, root vigor, bleeding sap and bleeding components than those of common cultivar from seed-filling stage to maturity stage. The root length and root volume of super-high-yield cultivar were 8.2% and 10.4%, 53.9% and 34.6% higher than those of common cultivar, respectively, under single seeding and mixed seeding treatments. For another, the bleeding sap of super-high-yield cultivars was 16.9%, 42.0% and 49.1% higher than those of common cultivar at different densities. On the other hand, the root competition ratio of super-high-yield cultivar was higher as well. The root surface and root volume per plant of two cultivars were declined with seeding rates increased, especially the common cultivar which declined about 50.9% and 50.7%. With seeding rates increased the difference of root vigor between super-high-yield cultivar and common cultivar was added, and also the root competition ratio which increased from 1.00 to 1.63. The seed weight per plant of super-high-yield soybean cultivars was higher than that of common cultivar at 6 plants/pot and 9 plants/pot treatments, especially at mixed seeding. The biomass and seed weight per plant of two cultivars were declined with seeding rates increased, especially the common cultivar which declined by 62.5% and 60.0%. There existed significant positive correlation between root morphological characters, root vigor and biomass, seed weight per plant.【Conclusion】The research indicated that super-high-yield soybean had expanded root system under appropriate seeding rate, which maintained stronger absorption capacity and compatibility.

Key words: soybean, density, root morphology, root vigor, bleeding component