Abstract: To investigate the effects of nitrogen nutrition on the growth of P. frutescens in salted stress and provide a theoretical basis for rational regulation of nitrogen fertilizer in production, we examined the effects of different forms and ratios of nitrogen on the growth, antioxidant enzyme system, soluble protein content and nitrogen metabolism of Perilla frutescens under 60 mmol·L^-1 salt stress. The results showed that under the treatment of no NaCl supplied, the total fresh and dry weights of aboveground part, total chlorophyll content, nitrate reductase (NR) and glutamine synthetase (GS) activities, soluble protein content and antioxidant enzyme activity of P. frutescensat NH₄⁺-N/NO₃^--N ratio of 25∶75 were higher than those in other treatments. Under the NaCl stress, P. frutescens biomass was inhibited, chlorophyll content was decreased, soluble protein and MDA content was increased, antioxidant enzyme activity was enhanced, and NR and GS activities were also increased. At NH₄⁺-N/NO₃^--N ratio of 25∶75, P. frutescens leaves had the highest chlorophyll content, SOD activity, CAT activity and soluble protein content, and with the lowest MDA content. The activity of POD was the highest at the NH₄⁺-N/NO₃^--N ratio of50∶50. Under the salt stress, with the increased proportion of NO₃^--N, the activities of NR and GS showed an upward trend, and the highest activity at the NH₄⁺-N/NO₃^--N ratio of 0∶100. The activities of NR and GS in the amido nitrogen treatment were lower than those in the purenitrate treatment but higher than those in the pure ammonium treatment. Under the salt stress, different nitrogen forms and ratios had significant effects on chlorophyll content, nitrogen metabolism, anti retrogradation regulation and yield of P. frutescens. All the results indicated that under the salt stress, the combined applications of ammonium and nitrate were more effective than pure nitrate, pure ammonium, and amidenitrogen applications. Furthermore, the NH₄⁺-N/NO₃^--N ratio of 25∶75 was more favorable to maintain the activities of antioxidase and nitrogen metabolism enzyme, alleviate the salt stress on seedling growth, and increase seedling weight, and thus could achieve high salt tolerance.

Key words: Juglans mandshurica, polymorphic site index model, natural secondary mixed forest, guide curve