Net Nitrate Uptake by Red Maple Is a Function of Root‐Zone Temperature

Abstract

Previous studies show that nutrient acquisition increases with root‐zone temperature to an optimum, but the response may be unique to the nutrient and species combination investigated. The objective was to determine the influence of root‐zone temperature on the kinetics of net nitrate uptake by using solution‐grown “Autumn Flame” and “Franksred” (Red Sunset®) ramets as representatives of red maple (Acer rubrum L.). Red maple was exposed to root‐zone temperatures of 14, 24, or 34°C for 3, 4, or 6 weeks during three experiments. Standard solution‐depletion techniques were then used to assess nitrate uptake for 14 h. Averaged over both cultivars and all experiments, means for root‐surface area were 0.129, 0.141, 0.120 m2 (SE 0.0080 m2) for root zones at 14, 24, and 34°C, respectively. Means for uptake differed by cultivar only in experiment 1. A linear, concentration‐independent estimate of I max dominated net uptake below 540 µM. Averaged over both cultivars in all experiments, apparent I max estimates were 120, 150, and 170 nmol m−2 s−1 (SE 8.8 nmol m−2 s−1) for the root‐zone treatments 14, 24, and 34°C, respectively. Apparent K m and C min could be estimated only for experiment 3. K m increased with root‐zone temperature and had means of 88, 140, and 190 µM (SE 51 µM) whereas C min decreased and had means of 66, 38, and 18 µM (SE 17 µM) for the 14, 24, and 34°C treatments, respectively. It was concluded that it is necessary to account for root‐zone temperature when estimating nitrate uptake in red maple, and these results suggest that only a single concentration‐independent constant for nitrate uptake is necessary for uptake calculations below 540 µM.