Nitrogen absorption by alpine forage species based on ¹⁵N tracer technique in a hydroponic culture

Based on ¹⁵N tracer technique, absorption of different concentrations of ammonium nitrogen (N-NH⁴⁺), nitrate nitrogen (N-NO^3-) and glycine (N-Gly) by root of six species of alpine forage (Puccinellia tenuiflora, Poa crymophila, Festuca sinensis, Elymus nutans, Elymus sibiricus and Bromus inermis) was studied in a hydroponic culture. The uptake kinetic parameter was analyzed according to Michaelis-Menten equation. The Michaelis-Menten equation represents the velocity equation for the relationship between the initial rate of an enzymatic reaction and the substrate concentration. The result showed that the absorption range of ammonium nitrogen, nitrate nitrogen and glycine by root of six species of alpine plant were 1.1-20.9 µmol·g^-1·h^-1, 0.4-3.4 µmol·g^-1·h^-1 and 0.1-3.7 µmol·g^-1·h^-1, which accounts for 68.8%-74.7%, 12.0%-27.0% and 4.3%-13.4% of total absorptivity, respectively. The six kinds of P. tenuiflora, P. crymophila, F. sinensis, E. nutans, E. sibiricus and B. inermis showed significant difference in nitrogen absorption. At the same concentration, the absorption of nitrogen in different forms of the same herbage is different. The absorptive amount of ammonium nitrogen was the highest among them, then the glycine, the nitrate nitrogen was least absorbed. The results could provide a theoretical basis for nitrogen utilization in alpine forages. For example, P. tenuiflora showed a much higher ability of absorbing nitrogen nutrition in a high salt environment and could be a more suitable herbage to be planted in saline-alkali soil in the Qinghai-Tibet Plateau as compared with E. nutans.