Genotypic variation in phosphorus acquisition from sparingly soluble P sources is related to root morphology and root exudates in Brassica napus

Genotypic variations in the adaptive response to low-phosphorus （P） stress and P-uptake efficiency have been widely reported in many crops. We conducted a pot experiment to evaluate the P-acquisition ability of two rapeseed （Brassica napus） geno- types supplied with two sparingly soluble sources of P, A1-P and Fe-P. Then, the root morphology, proton concentrations, and carboxylate content were investigated in a solution experiment to examine the genotypic difference in P-acquisition efficiency. Both genotypes produced greater biomass and accumulated more P when supplied with A1-P than when supplied with Fe-P. The P-efficient genotype 102 showed a significantly greater ability to deplete sparingly soluble P from the rhizosphere soil be- cause of its greater biomass and higher P uptake compared with those of the P-inefficient genotype 105. In the solution exper- iment, the P-efficient genotype under low-P conditions developed dominant root morphological traits, and it showed more in- tensive rhizosphere acidification because of greater H＋ effiux, higher H＋-ATPase activity, and greater exudation of carbox- ylates than the P-inefficient genotype. Thus, a combination of morphological and physiological mechanisms contributed to the genotypic variation in the utilization of different sparingly soluble P sources in B. napus.