Effect of exogenous hormone IAA or 6-BA combined with nitrogen on the above-ground growth and physiological characteristics of Elymus sibiricus

This study aimed to elucidate the effects of IAA or 6-BA and nitrogen and different ratios of IAA or 6-BA and nitrogen on the above-ground growth and physiological characteristics of Elymus sibiricus and to thus provide a theoretical basis for improving the development of E. sibiricus seedlings. Seeds of E. sibiricus from Qinghai alpine grassland were collected as experimental materials, which were tested using the nutrient solution sand culture method. The results showed that different ratios of nitrogen combined with IAA or 6-BA can better promote the growth of E. sibiricus seedlings than single nitrogen, IAA, or 6-BA. When the ratios of nitrogen and IAA were 5 ꞉ 5, the leaf area, chlorophyll, and soluble protein content of E. sibiricus increased significantly (P < 0.05) compared with the control (12 mg·L⁻¹ single nitrogen). Compared with the control treatment, the leaf area increased by 12.31%, the chlorophyll content increased by 1.2%, and the soluble protein content increased by 17.72%. When the ratios of nitrogen and 6-BA were 5 ꞉ 5, the peroxidase activity of leaves was the highest, and the peroxidase activity of E. sibiricus leaves increased significantly compared with single 12 mg·L⁻¹ or 20 mg·L⁻¹ nitrogen treatment, which increased by 9.1% and 19.72%, respectively (P < 0.05). In addition, when the ratio of nitrogen and 6-BA was 3 ꞉ 7, the leaf area increased significantly by approximately 16.77% and 19.41% than single 12 mg·L⁻¹ or 20 mg·L⁻¹ nitrogen, respectively (P < 0.05). Through principal component analysis and membership function methods, it was found that the ratio of nitrogen ꞉ IAA at 5 ꞉ 5 had obviously affected the above-ground growth and physiological characteristics of E. sibiricus.