The Uptake of Nitrate by Lolium perenne from Flowing Nutrient Solution

Abstract

Experiments with simulated swards of perennial ryegrass (Lolium perenne L.) grown in flowing nutrient solution with NOj held at 0-1 mg N l-1 show that the rate of NOj uptake was related to diurnal, day-to-day, and seasonal changes in radiation. In summer the diurnal variation in NO7 uptake ranged from 25 to 50 mg N m 2 h-1 and the day-to-day variation ranged from 500 to 1500 mg N m~2 d_1. Mean daily rates of uptake over 12 d periods in summer and in winter averaged 908 and 44 mg N m~2, respectively. The pattern of NO7 uptake followed that of C02 flux with the maximum rate of the former occurring 5 or 6 h after the maximum CO, influx. After defoliation, NOj uptake was severely curtailed for 2 d concomitant with a very small influx of C02. Analysis of the changes that occurred in the rate of NOj uptake immediately after the switching on or off of artificial light suggests that two reversible processes may be involved in the relation between NOj uptake and radiation, one with a longer and the other with a shorter time constant.