The Effects of Temperature and Form of Nitrogen Supply on the Relative Contribution of Root Uptake and Remobilization in Supplying Nitrogen for Laminae Regrowth ofLolium perenneL.

Abstract

Plants of Lolium perenne L. cv. S23 were grown in sand culture supplied with either ammonium (NH4+) or nitrate (NO3−) in an otherwise complete nutrient solution at 12°C or 20°C. Three weeks after germination, plants were clipped weekly to simulate grazing. After 10 weeks growth all nitrogen (N) was supplied enriched with 15N to quantify the effects of form of N supply and temperature on the relative ability of current root uptake and remobilization to supply N for laminae regrowth. The form of N supply had no effect on the dry matter partitioning, while at 20°C more dry weight was allocated to laminae regrowth and less to the remaining plant material. The current root uptake of N, which subsequently appeared in the laminae regrowth, was similar for plants supplied with NH4+ or NO3−, and both were equally reduced at the lower temperature of growth. Remobilization of N to laminae regrowth was greater for plants receiving NH4+ than NO3−; remobilization with either form of N supply was reduced at the lower temperature of growth. Remobilization was reduced to a lesser extent at 12°C than current root uptake. It was concluded that remobilization became relatively more important in supplying N for regrowth of laminae at lower temperatures.