Nutrient uptake rules of Polygala tenuifolia and its relationship with accumulation of bioactive components

Objectives Polygala tenuifolia, a Chinese medicine herb whose root is the harvested part, is one of the main commoditized raw materials. The rules of nutrient absorption and its relationship with the accumulation of bioactive components were studied, in order to provide theory for scientific fertilizer application in Polygala tenuifolia.

Methods The 3-year-old P. tenuifolia plants were taken as the research material. Since turning green on March 26 of 2017, plant samples were collected at the 40, 60, 80, 100, 120, 140, 160, 180 and 195 days after revival. The dry matter accumulations, the contents of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), copper (Cu), zinc (Zn) in roots and the aboveground parts were analyzed. At the same time, the contents of saponins, flavonoids and phenols in roots of different growth periods of P. tenuifolia were measured.

Results The dry matter accumulation in the aboveground parts of P. tenuifolia increased first and then decreased, and that in roots kept a linear increasing during the whole growing period. The dry matter accumulation of the aboveground parts was greater than that of roots from 40 days to 140 days after turning green. With the growth center transferred to roots from the 160 days to 195 days after revival, the dry matter accumulation of roots was greater than that of the aboveground parts. The maximum N absorption capacity of P. tenuifolia was from 100 days to 140 days after revival with the absorption amount of 18.77 g/m², and the maximum P and K absorption capacity was 140 days after revival, with the absorption amounts of 3.07 g/m² and 3.36 g/m², respectively. The accumulation of saponins and flavonoids in the whole growth period in roots of P. tenuifolia all showed two peaks, for saponins they appeared at 140 days (6.28 g/m²) and 180 days (6.43 g/m²) and for phenols at 80 days (2.37 g/m²) and 180 days (4.31 g/m²) after revival. The accumulation of flavonoids appeared one peak at 180 days revival green (2.35 g/m²). The economic yield of root bioactive components reached the highest at the 180 days after revival. A positive and significant correlation was found between flavonoid content and Zn content in root (P < 0.05), and it was extremely significant between phenol content and Zn content in root (P < 0.01).

Conclusions The rapid dry matter accumulation in roots is from 140 days to 195 days after the revival of P. tenuifolia plants, which is more than 40 days behind the peak accumulation of N P and K by the plants. Zinc content plays very important role in the contents of the bioactive components. For the highest economic profits, balanced fertilization of NPK with Zn should be paid more attention, and the proper harvest time of P. tenuifolia is also very important, which is at about 180 days after the revival (25 th, September) under the experimental condition.