Genotypic variation in phosphorus fractions and its relation to phosphorus efficiency in seedlings of Brassica napus L.

Rapeseed (Brassica napus) needs enough phosphorous (P) in its early growth stage and thus is very sensitive to P deficiency. Two genotypes of rapeseed, i.e., a P-efficient cv. 97081, and a P-inefficient cv.97009, were used to study the growth, P uptake and utilization, plant P fractions and the activity of acid phosphatase (APase) under normal and low P nutrient status using soil pot and hydroponic experiments. The results showed that cv. 97081 possessed high effiency of P uptake and utilization since its dry biomass and P accumulation increased by 85.7% and 50.0%, respectively, in comparison with cv. 97009 under P deficient condition. In both rape cultivars, all the P fractions, including insoluble organic P, soluble organic P and inorganic P, increased with P levels in the medium. Low P stress reduced the concentrations of insoluble organic P in the roots of cv. 97009, but not cv. 97081. The ratio of soluble organic P (ester-P) in total P was higher in bottom leaves than upper leaves. Both the concentration and ratio of ester-P of cv. 97081 were higher than that of cv. 97009. The concentration of inorganic P in the roots of cv. 97081 was higher than that of cv. 97009; however, the ratio was much lower compared with cv. 97009. P-efficent cv. 97081 had greater activity of APase in roots and bottom leaves under low P stress than P-inefficient cv. 97009 although there was no significant difference in upper leaves between the two cultivars. The results suggested that the concentrations and distributions of P fractions and the activity of APase were closely related to P uptake and utilization efficiency of Brassica napus.