Uptake and Transport of Calcium and Phosphorus in Lolium perenne in Response to N Supplied to Halves of a Divided Root System

The uptake and transport of Ca 2+ and HPO 4 2− from roots of Lolium perenne L. was studied using variable N nutrition supplied to halves of a divided root system. Plants were grown for 4 weeks in solution containing 0.11 m M NO 3 − –N; then one‐half of the root system was supplied with either 4.0 m M NO 3 − –N or 0.28 m M NH 4 + –N while the other half of the root system remained in low‐N solution. Uptake and transport of Ca 2+ increased and uptake of HPO 4 2− declined in root halves supplied with high NO 3 − –N for 16 h. After supply of high NO 3 − –N or NH 4 + –N to half the root system for 6 days, the roots supplied with high‐N exhibited significantly higher rates of uptake and percentage transport to shoots of both Ca 2+ and HPO 4 2− –. However, in neither the 16‐h nor 6‐day treatment did Ca 2+ or HPO 4 2− uptake of the root half supplied with low N differ significantly from the control (low N supplied to both halves of the root). Significantly higher N concentrations were found in low‐N supplied roots (compared to the control) as a result of internal translocation of N from high‐N supplied roots to low‐N supplied roots. Although N concentration in the low‐N supplied roots increased, uptake rates of Ca 2+ or HPO 4 2− did not change implying that external N concentration may be the important factor which influences or governs N mediated uptake responses. This would further suggest that the site of uptake regulation for Ca 2+ and HPO 4 2− exists on the outer plasma membrane which is in direct contact with the external solution. Transport of Ca 2+ and HPO 4 2− to the shoot was generally increased in low‐N root halves after 6 days of high‐N supply to the other half of the root. This implies that plant growth demand may be a major factor in regulating rates of Ca 2+ and HPO 4 2− transport from roots to the shoot. It also reinforces the hypothesis that uptake and transport of ions out of the root are separately controlled or regulated in the plant.