Nitrate uptake by red maple varies with root-zone temperature
Nutrient uptake is a complex process influenced by plant factors, the growing medium, and interactions between the two. Mathematical models allow researchers to examine, isolate, and manipulate factors that impact uptake. To date, modeling efforts have not assessed the potential impacts of root-zone temperature on nutrient uptake kinetics. Our main objective was to determine the influence of root-zone temperature on nitrate uptake kinetics using solution-grown 'Autumn Flame' and 'Franksred' (Red Sunset[Registered trademark symbol]) ramets as representatives of red maple (Acer rubrum L.). We chose red maple because it is an important forest and landscaping species that occurs in a range of habitats over much of eastern North America. Our secondary objective was to examine the viability of using a modified soil method for determining nitrate uptake kinetics in the greenhouse. Using three solution-depletion experiments, we exposed red maple to root zone temperatures of 14, 24, and 340C for three, four, and six weeks in experiments 1, 2, and 3, respectively. At the end of each treatment period, we used standard solution-depletion techniques to assess nitrate uptake over a 14-hour period. Cultivar uptake means differed only in the first of the three experiments. A linear, concentration-independent estimate of I[Subscript max] dominated uptake below 540 [Mu]m. Averaged over both cultivars in all experiments, I[Subscript max] estimates were 120, 150, and 170 mnol m−2 s−1 for the root-zone treatments 14, 24, 340C, respectively. K[[Subacript m] increased with root-zone temperature and had means of 88, 140, and 190 [Mu]m, while C[Subscript min] decreased and had means of 66, 38, and 18 [Mu]m for the 14, 24, and 340C treatments, respectively. The soil method did not provide valid estimates of kinetic parameters; further modifications to the method are needed. We conclude that it is necessary to account for root-zone temperature when estimating nitrate uptake in red maple, and our results suggest that only I[Subscript max], or a single concentration-independent constant for nitrate uptake, is necessary for uptake calculations below 540 [Mu]m.