Abstract: Abstract: 【Objective】 The aim of this study was to investigate the genotypic variations for adaptive changes in root morphology and architecture in response to low soil P availability and their relationships to plant growth and phosphorus (P) efficiency. 【Method】Field experiments were conducted in two filed sites located in Boluo and Yingde counties of Guangdong Province in both spring and summer seasons. Totally 51 soybean genotypes contrasting in root architecture and P efficiency were compared for their root morphological and architectural traits and their relationships to plant growth and P efficiency under both low-P and high-P conditions. 【Result】Great genotypic variations were observed for the tested genotypes under low-P conditions; Root architecture and morphology were closely related to plant P efficiency. Genotypes with shallow root architecture had an optimal three-dimensional root configuration and longest total root length, thus having the highest P efficiency and seed yield under low P conditions; Root plasticity of genotypes with either deep or shallow root architecture is lower than those with intermediate root architecture, indicating that root architecture is most stable in the former two groups under low P conditions. 【Conclusion】Low P availability is one of the primary constraints to soybean growth in the experimental soils, and soybean demonstrates a great genetic potential in adaptation to low P soils；Environmental factors, such as P availability of soil, may regulate soybean root architecture；Optimal root morphology and architecture may facilitate absorption of available P and other nutrients in the cultivated soil layer, thus significantly increase P efficiency and seed yield of soybean under low P conditions.

Key words: soybean, low soil P availability, root morphology and architecture, P efficiency