Effect of Nitrogen, Phosphorus and Potassium on Anthocyanin Content of the Seedlings of Polygonum hydropiper L. in Sand Culture

The seedlings of benitade (Polygonum hydropiper L.) are used as the garnish for sliced raw fish of white flesh, due to their purplish red appearance. In connection with their appearance, effects of nitrogen, phosphorus and potassium were studied on the anthocyanin and chlorophyll contents of seedlings grown in pots filled with washed sand. Growth measurements, nitrogen and carbohydrate determinations were also made. Seedlings supplied with deionized water only were the control.1. Seedlings supplied with sodium nitrate, ammonium nitrate and urea, respectively (2, 5 and 10me/l as N), exhibited greenish tinge on their cotyledons and hypocotyls, and had more growth, higher chlorophyll, and lower anthocyanin contents at each nitrogen level, in comparison with the control seedlings exhibiting purplish red appearance. Nitrate seedlings were affected even at 1me. On the other hand, the seedlings supplied with 2me of ammonium sulfate didn′t show any differences compared with the control, and even at 5-10me effects of ammonium nitrogen were less than those of other forms of nitrogen. However, in another experiment ammonium seedlings at 2me had somewhat more growth, higher chlorophyll, and lower anthocyanin contents than the control.2. Application of sodium dihydrogenphosphate (0.75, 1.5 and 3me as PO4-P) or potassium sulfate (0.5, 1 and 3me as K) showed no differences in seedling growth, chlorophyll and anthocyanin contents compared with the control. Even in case they were applied with nitrate or ammonium nitrogen, any additive effects to those of nitrogen were not found.3. Seedlings supplied with 2me of ammonium, nitrate and urea, respectively, had higher total and protein nitrogen contents and lower contents of carbohydrates such as total and reducing sugars and starch, however, the difference from the control was the least in ammonium seedlings. Nitrate seedlings were lower in carbohydrate contents even at 1me. The decrease of anthocyanin in the seedlings supplied with nitrogen was discussed with relation to the decrease of carbohydrate contents due to the increment of nitrogen fractions.