Short Period Uptake of Nitrate by Rice Seedlings

Abstract

Uptake of low concentrations of nitrate by rice seedlings was studied from two points of view: changes in the uptake during the seedling growth and the influence of temperature. At all stages, seedlings took up nitrate at a constant rate for 6h after the roots being immersed in the solution of 250μM potassium nitrate plus 500μM calcium sulfate. Nitrate uptake by 20 day old seedlings was obviously lower than that of 10-and 14-day-old seedlings, suggesting that the uptake depended on the growth rate of the seedlings. Nitrate uptake was greatly influenced by temperature. At 28°C, there was almost no difference in nitrate uptake by 14-day-old seedlings for the 10 varieties used in this experiment. Nitrate uptake was depressed by low temperatures, but the extent differed for each variety. The uptake ratios (16°C/28°C) for Indica paddy varieties and a Japonica upland variety were less than 0.50, while those for other Japonica paddy varieties were more than 0.50. In particular, Akage showed the highest ratio of 0.75. Compared with nitrate uptake, potassium uptake was less influenced by temperature. Potassium uptake in Indica varieties was higher than that in Japonica varieties.