Low Phosphorus Tolerance Mechanisms in Soybean Cultivars Grown in Soil

Low P availability in soil limits soybean growth. However, the mechanisms by which different soybean cultivars adapt to low P availability in soil have yet to be elucidated. In this study, we aimed to describe the root system architecture and physiological traits for P acquisition of six soybean cultivars under soil culture. Three P-efficient soybean cultivars (Maetsue, Kurotome, and Fukuyutaka) and three P-inefficient soybean cultivars (Ihhon, Chizuka, and Komuta) were grown in 0 g P kg(-1) soil (- P) and 0.44 g P kg(-1) soil (+ P) for 7 and 14 days after transplanting (DAT). Rhizosphere samples were collected, and metabolites were analyzed using capillary electrophoresis time-of-flight mass spectrometry. The low P tolerance scores of the six soybean cultivars grown under soil culture were 38%-122% at 7 DAT and 26%-151% at 14 DAT. Under - P treatment, the P-efficient cultivars had greater root lengths, acid phosphatase activities, and organic acid exudation in the rhizospheres than the P-inefficient cultivars. The rhizosphere of each soybean cultivar contained 120 metabolites, including amino acids, organic acids, phosphate esters, carbohydrates, homologs, and nucleic acids. Moreover, the concentrations of 37 of these 120 metabolites increased in the rhizospheres of the P-efficient cultivars under - P treatment. Soybean cultivars released variety of metabolites into the rhizosphere and number of metabolites were different among cultivars. P-efficient soybean cultivars release acid phosphatase, organic acids, and other metabolites which increase soil P availability into the rhizosphere and acquire more soil P.