Nitrate uptake kinetics for rooted cuttings of Acer rubrum L

Red maple (Acer rubrum L.) occurs in a broad spectrum of both woodland and managed landscapes in much of eastern North America. Earlier work has indicated considerable plasticity within the species in water use efficiency, as well as dry mass accumulation and tertiary root extension when grown in a solution in which all N was supplied as NO₃⁻. Nitrogen uptake is largely a function of N supply, soil water availability and root surface area. Therefore, compensatory mechanisms could have evolved among cultivars to compensate for site differences. The objective of this study was to define $NO_3^ - $ uptake parameters for red maple in a hydroponic system through the use of two cultivars known to differ in root production and water use efficiency. Green wood stem cuttings of two red maple cultivars, 'Autumn Flame' and 'Franksred', were rooted and then transferred to solution culture. Using established techniques, three separate experiments were conducted to define ranges of Imax, Km and Cmin values and to determine root mass, length, mean radius and surface area. Estimates of Imax exhibited considerable variation between experiments with means ranging from 1.57E-5 to 5.91E-5 µmol cm⁻² s⁻¹. However, cultivar differences in Imax were statistically significant in only one of the three experiments. Means for Km ranged from 2.04E-1 to 5.23E-1 µmol cm⁻³, while Cmin values were consistent at 0.001 µmol cm⁻³ (the limit of analytical detection) across all experiments. While data on variation among red maple cultivars are not conclusive, some evidence exists for genotype differences that may relate to the broad range of site conditions under which red maple is successfully grown.