Influence of Nitrogen Form and Nitrogen Absence on Utilization of Assimilates for Growth and Maintenance in Tops and Roots of Lolium multiflorum

Utilization of assimilates for growth and maintenance of tops and roots of Lolium multiflorum was determined for plants supplied with either nitrate or ammonium. Carbon dioxide exchange rates were measured continuously for tops and roots separately. Three-day periods were applied for two irradiation levels. On the last day of each three-day period no nitrogen was supplied to the two treatments. In the nitrate treatment, the coefficient of utilization for converting assimilates into constructive growth (Y_G) remained unaffected in absence of nitrate. However, in absence of nitrate the maintenance respiration (M) for both tops and roots was only one third of that in presence of nitrate. In the treatment with ammonium the maintenance respiration of the plants was not influenced by the absence of ammonium. However, especially for the tops Y_G increased in absence of ammonium. In both the treatments, growth respiration of the roots was inefficient compared to that of the tops. Only in the case of absence of nitrate, maintenance respiration of the roots was similar to that of the tops.