Uptake and utilization of applied phosphorus in oilseed rape (Brassica napus L. cv. Hayola) plants at vegetative and reproductive stages: Comparison of root with foliar phosphorus application

In order to compare plants' response to phosphorus (P) application through roots and leaves, oilseed rape (Brassica napus L. cv. Hayola) plants were cultivated until vegetative or reproductive stages and were pretreated with an adequate (+P) or low (-P) supply of P. Thereafter, these plants were treated with 0.3 mMP as sodium dihydrogen phosphate (NaH2PO4) either through roots (root application, RA) or leaves (leaf application, LA). Shoot biomass was observed to be suppressed under -P conditions at both stages, whereas root growth was comparatively improved in -P plants at the vegetative stage but not at the reproductive stage. Both RA and LA were able to compensate for the growth of vegetative shoot and roots at both stages; however, LA reduced P and dry matter partitioning into the fruits. At the vegetative stage, recovery of applied P was similar between RA and LA treatments, and was extensive in -P plants compared with the +P ones. At the reproductive stage, in contrast, significantly lower recovery of P was observed likely due to the lower capacity of leaves for P absorption and/or their lower re-translocation ability through the phloem. Data of P utilization efficiency showed that -P plants, at both vegetative and reproductive stages, efficiently use leaf-applied P for biomass production when compared with the +P plants. Activity of acid phosphatase was sharply inhibited by RA in -P plants, whereas it was preferably increased by LA in both +P and -P plants. Results indicated that under P-deficiency conditions, plants had higher ability to utilize foliar-applied P, and in contrast to RA, LA may enable plants for a continuous higher capacity of P uptake from P-deficient soil; however, RA was superior to LA in terms of fruit growth.