Characterization of diverse soybean genotypes for phosphorus uptake and use efficiency

Abstract

Soybean (Glycine max L. Merrill) is one of the most important legume crops grown worldwide. However, without phosphorus (P) fertilization, soybean yields often are limited by phosphorus availability. Phosphorus is an essential macronutrient and P uptake ability and P use efficiency (PUE) of a crop critically influence its productivity. To improve soybean yields under low-P conditions, a better understanding of the mechanisms underlying P uptake and PUE is needed. The first part of this study was aimed at identifying and characterizing soybean genotypes which contrast in their ability to take up P and in their PUE. Results from pot and field experiments with diverse soybean genotypes, including SoyNAM parents, obsolete cultivars, commercial cultivars, and plant introduction lines, revealed significant differences among genotypes for numerous P-related traits. Significant differences in shoot P concentration, shoot P content used as surrogate measure for P uptake, physiological PUE, and root complexity were observed among genotypes. Phosphorus use efficiency was much higher under low-P conditions compared to P-sufficient conditions. Positive correlations between biomass production and P uptake and top-soil root architecture and P uptake were observed. In a subset of five contrasting genotypes, soybean root symbiosis with arbuscular mycorrhizal fungi (AMF) was investigated to explore whether mycorrhizal infection levels were related with genotype differences in P uptake and PUE. All five genotypes displayed high AMF colonization percentages ([greater than] 80 percent) and no significant differences in mycorrhizal colonization were detected among genotypes and between low-P and P sufficient treatments. Arbuscular mycorrhizal fungi colonization did not explain observed differences in P uptake, and approaches aimed at increasing levels of AMF infection in soybean do not appear promising, at least not for environments like the one used in this study. This research identified soybean genotypes contrasting for shoot P concentration, shoot P content, PUE, and topsoil root system architecture. Further, it confirmed differential sensitivity of diverse soybean genotypes to P availability. The identified genotypes can serve as a resource for physiological and genetic studies as well as in breeding efforts aimed at improving P uptake and PUE in elite germplasm.