Objective The study was carried out to explore the effects of low phosphorus stress on root organic acid content and soil phosphatase activity of flue-cured tobacco.

Method By using pot experiment, three different P₂O₅ application amounts of 0 g/plant(P1), 5 g/plant(P2)and 10 g/plant(P3)were set to determine the root exudates, phosphatase activity, soil and tobacco phosphorus content and agronomic traits.

Result The total phosphorus content in the soil was decreased without applying phosphorus. Under the condition of low phosphorus stress, the organic acids secretion capacity of flue-cured tobacco was increased. Compared with P3, the organic acid content in P1 treatment increased by 240.22% in the middle period of prosperous period, and it mainly exuded malic acid, accounting for more than 55%. Different phosphorus application levels had inconsistent effects on the three phosphatase activities. Under the condition of low phosphorus stress, acid phosphatase activity had risen significantly, which increased by 148.75% and 123.97% respectively in the vigorous growing stage period and the budding stage. Neutral phosphatase and alkaline phosphatase were less affected by phosphorus application levels. The correlation analysis showed that, the content of organic acid was positively correlated with acid phosphatase activity. The phosphorus absorption and accumulation of tobacco plants were different. Tobacco plants under P1 treatment had the lowest phosphorus content and phosphorus concentration, the total phosphorus content of tobacco plant was 1 019.39 mg, and the that of P3 treatment was the highest, reaching 1 600.89 mg. P3 treatment had the best agronomic shape, which was significantly better than that of P1 treatment.

Conclusion Without phosphate fertilizer, the flue-cured tobacco could meet the needs of normal growth by regulating the secretion of organic acids and increasing the acid phosphatase activity, but the performance of agronomic traits was poor. The phosphorus absorption capacity of tobacco plants under P3 treatment was improved, while the agronomic traits had no significant difference from those of P2 treatment. The application of P₂O₅ 4 g/plant could reduce the amount of phosphate fertilizer without affecting the growth of flue-cured tobacco, which provided a certain reference for the application amount of phosphate fertilizer in production.