Effects of different phosphorus applications on growth and platycodin content of Balloon Flower (Platycodon grandiflorum)

• Phosphorus application enhances phosphorus and dry matter accumulation.
• Phosphorus application decreased taproot length and increased its diameter.
• Phosphorus application increased the root yield.
• Phosphorus application increased platycodin content and decreased soluble sugar content.
• Root exterior and interior quality was improved by phosphorus application.

Field experiments were conducted to investigate the effects of different phosphorus (P) rates of 0, 10, 20, 30 and 40 kg P ha−1 on P accumulation, yield, and quality of Balloon Flower (Platycodon grandiflorum) based on a randomized complete block design with four replications. Results indicated that phosphorus application improved the dry matter accumulation but did not change the allocation rate. Of all treatments, the highest proportion of biomass was allocated to the roots, whereas the lowest was allocated to the flowers at full bloom stage (on 20 July, 83 days after planting) and leaves at harvest stage (on 16 October, 139 days after planting). Phosphorus content and accumulation in all treatments exhibited a similar trend, but these parameters differed in terms of growing stage and organs. Phosphorus content and accumulation in the roots were higher at the harvest stage than at the full bloom stage, but these parameters were lower in the leaves and stems. This result indicated that the application of P increased the proportion of P initially stored in the leaves and stems and then translocated to the roots, it increased the taproot diameter, reaching the maximum value at application rate of 20 kg P ha−1; by comparison, the application of P decreased the root branching number. The length of taproots treated with the application rates of 10 and 40 kg P ha−1 was significantly lower than that of the control plants, but no significant differences were observed between P application rates of 20 kg P ha−1, 30 kg P ha−1 and the control plants. Root yield was remarkably higher in P-treated plants than the control plants. Treatment with application rate of 20 kg P ha−1 gained the highest yield of 4683.33 kg ha−1, which was 42.28% higher compared to the control plants. The application of P increased the total platycodin content and decreased the soluble sugar content. No significant effect was observed on the water-soluble extract content. Considering yield and quality, we recommended the optimum P application rate of 20 kg P ha−1 under the specific experimental conditions used in this study.

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