Effects of nitrogen forms and proportions of nitrogen forms on the growth and physiological characteristics of Elymus sibiricus

To clarify the effects of different nitrogen forms and different ratios of nitrate nitrogen (NO₃^–-N) and ammonia nitrogen (NH₄⁺-N) on the growth and physiological characteristics of Elymus sibiricus, the seeds of wild E. sibiricus were collected from an alpine meadow and used in an experiment. Different ratios of nitrate nitrogen (NO₃^–-N) and ammonia nitrogen (NH₄⁺-N) (0∶10, 3∶7, 5∶5, 7∶3 and 10∶0) were tested using the nutrient solution sand culture method. The results showed that the mixed nitrogen forms promoted the growth of E. sibiricus more than did single nitrogen forms. Plant height, nitrate reductase activity, and the soluble protein content of leaves had the highest values when the ratio of NO₃^–N and NH₄⁺-N was 7∶3, while nitrate reductase activity increased by 48.54% and 74.71% when compared with either effects of nitrate or ammonium, respectively, and the content of soluble protein content increased by 10.16% and 7.30% when compared with effects of nitrate or ammonium alone, respectively. The root vigor was the highest at the ratio of NO₃^–-N and NH₄⁺-N of 5∶5, which increased by 31.05% and 8.08% when compared with effects of nitrate or ammonium nitrogen alone, respectively. In addition, when the ratio of NO₃^–-N and NH₄⁺-N was 3∶7, the root length and total nitrogen content improved significantly and increased to 43.90% and 29.76% when compared with effects of nitrate and ammonium nitrogen alone, respectively. Through a comprehensive analysis using the membership function method, it was found that the ratio of 7∶3 NO₃^–-N∶NH₄⁺-N had the most obvious effects on the growth and physiological characteristics of E. sibiricus.