Phosphorus uptake kinetics and nitrogen fractions in maize grown in nutrient solutions

The analysis of ion uptake kinetics is the key experimental procedure for determining the uptake efficiency of different species and varieties. The principal goal of this study was to evaluate phosphorus (P) uptake and its effect on nitrogen (N) metabolism in two maize varieties (Sol da Manha and Eldorado) and one improved maize cultivar (AG 122 (R)) exposed to a resupply of 10 or 100 mu M of P following a period of P deprivation. The experiment was based on a completely randomized design with four replicates, with treatments arranged in a 3x2 factorial scheme consisting of three genotypes and two P doses. The treatments were applied at 16 days after germination (DAG), and samples of nutrient solution were collected over time to estimate the kinetics of P uptake (V-max, K-M and C-min). At the end of the experiment, a portion of the total fresh weight was stored to determine N fractions and soluble sugars. Under the experimental conditions, the AG 122 (R) cultivar showed the lowest K-M and C-min values for both P doses, indicating a higher uptake efficiency for these plants. In contrast, the Eldorado and Sol da Manha varieties showed the highest V-max values. An absence of P from the nutrient solution for one day, followed by the addition of 10 mu M of P for the same period, did not result in alterations in N metabolism in any of the genotypes. However, it was observed that the Sol da Manha and Eldorado varieties concentrated their NO3--N metabolism in their roots, whereas the AG 122 (R) cultivar concentrated its NO3--N metabolism in its shoots.