Effects Of Exogenous Nitrogen On Conducting Tissue Anatomy, Nitrogen Metabolism And Photosynthetic Characteristics Of Alfalfa

The development of conducting tissue of alfalfa(Medicago sativa L.) can measure the efficiency of operating nutrients. It will have certain significance for clarifying physiological mechanisms of nitrogen transporting and alfalfa yielding that we study the vascular structures of conducting tissue, nitrogen metabolism and photosynthetic characteristics of alfalfa. In this study, according to preliminary test results, the anatomical structure of conducting tissue, nitrogen metabolism and photosynthetic characteristics of alfalfa(Medicago sativa L.) were studied based on two nitrogen forms(nitrate nitrogen and ammonium nitrogen) and five nitrogen levels(0,105,210,315,420 mg·L-1). Two cultivars, Gannong No.3 and Longdong, were selected as materials, and the experiment was conducted outdoors(in flashing net room) using sand culture method. We aim to explore the relationships between its structure and function, and except to reveal the nature that exogenous nitrogen how to promote efficient production of alfalfa from microscopic characteristics of conducting tissue, physiological and photosynthetic characteristics point of view. Thus we can provide a reference for the production of alfalfa nutrient management practices. Conclusions are as follows:1. Nitrogen can significantly promote the alfalfa plant height, biomass, root weight, total root length, root surface area, root diameter and root volume. Except for plant height and biomass peak appeared at 315 mg·L-1 at budding stage, and the rest appeared at 210 mg·L-1 at seeding and budding stage. Compared with two kinds of forms, NH4+-N culture was better than NO3--N. Comprehensive comparison, the combination of NH4+-N and 210 mg·L-1 was the best treatment on the growth of alfalfa under the conditions of this study.2. NO3--N and NH4+-N can both improve the anatomical structure of conducting tissue of alfalfa leaves, stems and roots. The nitrogen treatment on vascular bundle area, xylem area, phloem area and vessel number were significantly higher than those of non-nitrogen treatment. These indexes obtained maximum at 210 mg·L-1. And under that level of NH4+-N treatment, the vascular bundle of conducting tissue of alfalfa leaves, stems and roots was the biggest, both phloem and xylem showed largest area and developed well, and the number of vessel was also the largest.3. Compared with non-nitrogen treatment, nitrogen can promote the activity of alfalfa nitrogen metabolism related enzymes and photosynthetic capacity. In this study of two growth periods, nitrogen content, the activity of nitrogen metabolism-related enzyme and photosynthetic characteristics were highest and strongest at the 210 mg·L-1. Therefore, the combination of NH4+-N and 210 mg·L-1 performed best. The nitrogen metabolism ability and photosynthetic capacity of alfalfa was strongest, then it enhanced capacity of transporting photosynthetic products..4. Compared with cultivar “Longdong”, nitrogen on improving conducting tissue, nitrogen metabolism capacity and photosynthesis performed better in cultivar “Gannong No.3”. That is to say, “Gannong No.3” was more sensitive to nitrogen fertilizer than "Longdong", and it had higher rate of fertilizer returning.In summary, exogenous nitrogen can improve the anatomical structure of conducting tissue, nitrogen metabolism-related enzyme activity and photosynthetic characteristics of alfalfa. Then it promoted photosynthesis of alfalfa, and improved nutrients transporting and organic synthesis capacity, thus improved its production performance and nutritional quality. The treatment of NH4+-210 performed best in this study, and “Gannong No.3” performed better than “Longdong”.