Nutrient inflows into apple roots. II. Nitrate uptake rates measured on intact roots of mature trees under field conditions
1982
BHAT, K. K. S.
The rates of uptake of nitrate‐N per unit length; surface area and volume of root were measured in solution depletion experiments conducted in a root laboratory, using intact roots of two 4.5‐year‐old apple trees (Discovery/M.9 and Worcester Pearmain/M.9) at two different depths in the soil profile. In Discovery/M.9, NO₃ ⁻ uptake rate per unit root was constant over the 20‐200 mmol m⁻³ range of solution concentration. In Worcester/M.9, the uptake rate per unit root over the 200‐150 mmol m⁻³ range (corresponding to a ‘lag’ phase) was lower than that over 150‐20 mmol m⁻³. The uptake rates after the lag phase at depths of 46 and 104 cm were ca. 1.3 and 5.0 times greater than those in Discovery/M.9 at the 46 and 110 cm depths, respectively. The concentration below which net uptake was zero was ca. 1 mmolm⁻³. In Discovery/M.9, the uptake rate per unit root at the 46cm depth was about 2.8 times that at 110 cm whereas in Worcester/M.9, the uptake rates at 46cm depth were about 1.8 and 1.4 times lower than those at 104cm over the solution concentration ranges 200‐150 and 150‐20 mmol m⁻³, respectively. Only small differences were observed in uptake rates per unit root between 1400‐1700 h, 2400‐0400 h, and 0700‐1100 h. For successive 5°C‐increments in root temperature between 5 and 25° C, the nitrate uptake rate per unit root increased by 130, 10, 30 and 5%, respectively. A major change in the activation energy for nitrate uptake was observed at a transition temperature located between 5°and 10°C.
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