EFFECTS OF DIFFERENT NITROGEN FORMS ON THE NITROGEN DISTRIBUTION AND UTILIZATION OF TAMARIX RAMOSISSIMA SEEDLINGS UNDER WATER STRESS

In order to explore the influence of drought stress and nitrogen supplementation on changes in growth, photosynthetic physiological traits, and nitrogen distribution and utilization in Tamarix ramosissima seedlings, four soil watering regimes (D-1-20%, D-2-35%, D-3-50%, and D-4-75% of relative field capacity) and supplementation with two nitrogen forms (N-15- KNO3 and N-15-NH4Cl) were evaluated. The results indicated that 1) water was the main factor influencing seedling growth. N-15-NH4Cl was more easily absorbed by the roots for total biomass accumulation, while N-15-KNO3 absorption for total biomass accumulation was promoted under D-4. Under water deficient conditions, N-15-KNO3 increased the root/shoot ratio significantly, and this ratio was significantly increased by N-15-NH4Cl under D-3. 2) The two different nitrogen forms significantly influenced the chlorophyll a content when the seedlings were subjected to severe water stress, while N-15-NH4Cl had a significant effect on the chlorophyll b content under D-2 and D-3. Nitrogen improved the photosystem (PS) II actual photochemical efficiency (phi(PS(II))) of the seedlings, with N-15-NH4Cl significantly effecting phi(PS(II)) under D-1 and D-3, and N-15-KNO3 being more influential under D-2. 3) The nitrogen absorption capacity was diminished under D-1 and D-4, and followed a trend of an initial increase followed by a decrease along with the increase in soil moisture. The distribution of N-15-KNO3 to the seedlings was higher in comparison to N-15-NH4Cl, whereas the utilization of N-15-NH4Cl was higher. The interactive effects of water and nitrogen thus influence the ability of seedlings to adapt to undesirable surroundings.