The effect of root and shoot temperature of 8°C or 24°C on the uptake and distribution of nitrogen in white clover (Trifolium repens L.)

Limited information is available on the factors influencing the uptake and distribution of nitrogen (N) at low temperatures. This experiment quantified the distribution of N in white clover at root and shoot temperatures of 8°C or 24°C. Stolon tip cuttings of white clover (Trifolium repens L.) were grown in silica sand. After 62 days, plants were transferred to an 8°C or 24°C controlled environment room and, to quantify the distribution of N, a pulse of 15KNO3 was applied. Thereafter, plants were supplied with a complete nutrient solution containing NH4NO3 at a concentration calculated to provide plants with 20% of their N requirement. Plants were harvested at 0, 1, 4, 8, 24, 168, or 336 h. Leaf area and dry weights plus 14N/15N distribution in all fractions and total N concentration were measured. At both temperatures, the dry weights in all fractions increased significantly (P < 0.05) with time. After 336 h the amount of labelled 15N contained in the laminae and petioles was lower at 8°C than at 24°C. The higher 15N recovery in the laminae and petioles, and the higher lamina N%, indicated more N had been transported from the roots to the laminae at 24°C. This investigation suggests that temperature does affect the movement of N around the plant, with a consequent effect on N pool sizes and, hence, growth.