Title: Comparative studies on physiological and ecological characteristics of solanaceous fruit vegetables. (7). Effects of applied nitrogen form on chemical constituents of xylem exudate.
Abstract: Tomato (cv. Fukuzyu No. 2), eggplant (cv. Hayabusa) and sweet pepper (cv. Shinsakigakemidori) were grown in sand culture under glasshouse conditions, in order to clarify the effects of various concentration ratios of nitrate nitrogen (N03-N) to ammonium nitrogen (NH4-N) in the cultural solution on the exudation rate and chemical constituents of xylem exudate.1. The application of concentration ratio of N03-N: NH4-N (7: 3) greatly promoted growth in each vegetable, but the higher concentration ratio of NH4-N remarkably suppressed growth of plants. The plants applied with the concentration ratio of NO3-N to NH4-N (7: 3) showed the highest exudation rate and conversely the plants grown under the application of higher concentration ratio of NH4-N had lower exudation rate.2. The NO3-N content in the xylem exudate decreased with increasing the concentration ratio of NH4-N in the cultural solution, while the NH4-N content predominantly increased. Aspartic and glutamic acids remarkably increased with increasing NH4-N concentration ratio of the cultural solution, whereas the other amino acids slightly increased or little changed. Eggplant showed the higher amino acid content in the xylem exudate than tomato and sweet pepper. In spite of the low concentration of NH4-N in the xylem exudate of tomato, the amount of NH4-N in the xylem exudate per plant per hour was greater than those of the other crops, because its exudation rate was much higher.3. The N form in the cultural solution slightly influenced the contents of Fe, Mn, Cu and Zn in the xylem exudate. The application of higher concentration ratio of NH4-N increased P content and conversely reduced K, Ca and Mg contents remarkably, especially in tomato. The large decreases of the total amount of K, Ca, Mg, Fe, Mn, Cu and Zn in the xylem exudate per plant per hour were observed under the application of higher concentration ratio of NH4-N.4. From these results, it may be suggested that the reduction of dry weight due to the application of high concentration ratio of NH4-N in the cultural solution is resulted from the reduction of water and cation uptake and the increase of NH4-N concentration in plant.