Genetic improvement of yield shapes the temporal and spatial root morphology of soybean (Glycine max) grown in north-east China

In north-east China, a major region of soybean production in China, soybean yield has increased mainly from long-term application of genetic selection procedures for high yield. Most previous investigations into soybean yield improvement have focused on above-ground morphological and physiological characteristics. Root morphology, in contrast, is much less documented. In this study, eight soybean genotypes are assigned to two pools, based on yield potential performance. The root morphologies of plants from these high- and low-yielding pools are compared temporally and spatially. The high-yielding soybean pool exhibits significantly higher root growth rates from the R1 to R4 stages and lower root senescence rates after the R5 stage compared with the low-yielding pool. Plants from the high-yielding pool not only accumulate more shoot biomass, but also allocate greater biomass to the roots, leading to a 14.5% rise in root-to-shoot ratio. Root length in the high-yielding soybean pool after R5 is 24.2% greater than that in the low-yielding pool. Greater root length duration contributes to the longer leaf life span. These findings indicate that more biomass used in root production and slower root senescence during the reproductive stage play important roles in supporting higher yields. Spatially, the densities of biomass and length of roots from 0 to 45 cm of soil depth at the plant position and halfway between plants from the high-yielding soybean pool are significantly greater than the low-yielding. Thicker root diameters in deeper soil depths are observed in the high-yielding soybean pool. The characteristics of root morphology for high-yielding soybean in north-east China are summarized diagrammatically.