Effects of Different Inorganic Nitrogen Sources of Iris pseudacorus and Iris japonica on Energy Distribution, Nitrogen, and Phosphorus Removal

Abstract

High- and low-affinity transport systems are the main pathways for the transportation of NO3– and NH4+ across intracellular membranes. NO3− and NH4+ are assimilated through different metabolic pathways in plants. Fifteen ATP molecules are hydrolyzed in the metabolic process of NO3–; however, only five ATP molecules are hydrolyzed in that of NH4+. In this research, seedlings of Iris pseudacorus and Iris japonica were used as the experimental materials in the NO3–:NH4+ = 30:0, NO3–:NH4+ = 28:2, NO3–:NH4+ = 27:3, NO3–:NH4+ = 15:15, NO3–:NH4+ = 3:27, and NO3–:NH4+ = 0:30 treatments at the 7.5 mmol·L−1 the total nitrogen content (TN). The intracellular free energy was represented by physiological resistance (R) and physiological impedance (Z) according to the Nernst equation and could conveniently and comprehensively determine the cellular metabolic energy (GB). The maximum absorption rate (Vmax) and Michaelis constant (Km) for NH4+ and NO3– uptake were calculated according to the kinetic equation. The results showed that the cellular metabolic energy (GB) of I. pseudacorus was 1 to 1.5 times lower than that of I. japonica at each treatment on the 10th day. The GB values of I. pseudacorus and I. japonica seedlings increased with increasing NH4+ concentration. However, there was a turning point at the NO3–:NH4+ = 15:15 treatment for the cellular metabolic energy of I. pseudacorus and I. japonica. Correlation analysis showed that the value of cellular metabolic energy was negatively correlated with the Vmax and Km for NO3– uptake, whereas it was positively correlated with that for NH4+ uptake. These results demonstrate that the NO3–:NH4+ = 27:3 treatment level was the most suitable for I. pseudacorus and I. japonica. This indicates that the greater cellular metabolic energy is the most suitable for plant growth when the concentration of ammonium or nitrate had no significant difference at treatment. These results provide a simple and rapid solution for removal of nitrogen by determination of cellular metabolic energy.