Exogenous Gibberellin (ga <sub> 3 </ Sub>) On Growth, Development And Biomass Of L. Chinensis,

In this thesis, the effects of exogenous gibberellin (GA3) on seeds germination, seedlings growth, plants development, grass and protein yield of Leymus chinensis, a fine perennial grass species that grows in the Songnen Plain, were carried out. These experiments were designed to determine the role of GA3 in the established stages of Leymus chinensis, to find out the proper applied concentration and time, and to provide theoretical foundation for further research and utilization.Seeds of Leymus chinensis were soaked in GA3 at 0, 50, 100, 150, 200, 300, 500mg/L for 24, 48 and 72 hours. Effects of GA3 on germination rate, germination index, vigor index, relative conductance ratio of seeds and root length, shoot length, root/shoot ratio of seedlings were studied. The results showed that the maximum germination rate was 16.7% when seeds were soaked in GA3 at 300 mg/L for 48 hours, and the relative conductance ratio of seeds was the lowest and shoots of seedlings were the longest in this treatment. Treated with GA3 at 300 mg/L for 72 hours, the germination index was the highest. The vigor index was the highest and roots of seedlings were the longest by soaking the seeds for 72 hours in 200 mg/L GA3. Treated with GA3 for 24 hours or 48, the root/shoot ratio of seedlings increased firstly and then decreased with the enhancement of the GA3 concentration. Treated with GA3 of 300mg/L for 48hours, the drought resistance of seedlings was poor, so it is suggested to irrigate properly. The treatment of 200 mg/L GA3 for 72hours will be more suitable for arid regions.The effects of exogenous GA3 on plants development, grass and crude protein yield of Leymus chinensis were also investigated. GA3 was sprayed on the grass with concentrations of 0, 25, 50, 75 and 100 mg/L at four different stages. Applied at returning green stage, the plant height, total leaf length and total leaf width per plant were larger than those applied at other stages. The highest plant height, the longest total leaf length and total leaf width appeared at concentrations of 75, 25 and 50 mg/L, respectively. The green leaf numbers increased in some treatments, but had no significant differences in contrast with control. Exogenous gibberellin had no significant effects on heading rate, but was helpful for seeds setting.The maximum of individual biomass occurred at the GA3 concentration of 50 mg/L applied at returning green stage. The grass yield per area increased by 20% applied with 50 mg/L at returning green stage or applied with 25 mg/L and 50 mg/L at milky stage. The highest crude protein yield appeared at the GA3 concentration of 50 mg/L applied at returning green stage. Treatment with 50 mg/L GA3 at returning green stage was the best way to improve grass and crude protein yield per area.