The Uptake of Nitrate byLolium perennefrom Flowing Nutrient Solution

Abstract

Experiments with simulated swards of perennial ryegrass (Lolium perenne L.) grown in flowing nutrient solution with NO₃- held at 0.1 mg N I⁻¹ show that the rate of NO₃- uptake was related to diurnal, day-to-day, and seasonal changes in radiation. In summer the diurnal variation in NO₃-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 NO₃- uptake followed that of CO₂ flux with the maximum rate of the former occurring 5 or 6 h after the maximum CO₂ influx. After defoliation, NO₃- uptake was severely curtailed for 2 d concomitant with a very small influx of CO₂. Analysis of the changes that occurred in the rate of NO₃- uptake immediately after the switching on or off of artificial light suggests that two reversible processes may be involved in the relation between NO₃-uptake and radiation, one with a longer and the other with a shorter time constant.