The Study On Symbiotic System Of Frankia And Alnus Rubra

The sense of symbiotic nitrogen fixation between Frankia and non-legume is as important as which between leguminous plants and Rhizobium, and which has a broader research and development prospect. Systematic studies were carried out on Frankia of Alnus rubra root nodules in this paper. The main results were as follows:(1) Frankia of wild Alnus rubra root nodules were separated by the sectioning and squashing methods.The sectioning didn't work. Frankia colony was separated by the sectioning and culture medium BAP,JA,S+T and Qmod. Two pure culture strains were isolated and numbered as LC01,LC02. Morphological characteristic of the two strains were researched,such as shape culture characteristics, nutrient utilization, salt, acid and alkali resistance.The results showed that the two isolates showed a typical Frankia morphology, with filamentous hyphae, multilocular sporangia borne terminally and branching hyphae. Lots of vesicles formed on culture medium without nitrogen. The two strains can use a variety of carbon and nitrogen ;can be survived in a very wide pH and temperature range and a culture medium with 5% NaCl,So the two Frankia strains have strong adaptability to the environment.(2) Inoculation of two Frankia strains on seedlings of Alnus rubra was conducted.Both of them could infect the Alnus rubra and formed nodules.Compare to the control,seedling height,biomass and total nitrogen of seedlings increased distinctly. Greatest growth increment was obtained when Alnus rubra seedings inoculated with strains LCO1.Different means of inoculation have a certain effect on Frankia infect.Experiment results showed that batch inoculation had a better symbiosis effect.(3) Mineral elements,such as nitrogen and phosphorus have very important factors on effect on nodulation nitrogen fixation of Alnus rubra. Inoculation tests with different nitrogen levels showed that low concentration of nitrogen can promote growth and improve nodular number of Alnus rubra.The promote effect on the growth rate and nodulation nitrogen fixation of Alnus rubra. is the best when the nitrogen level is 0.264g/L. when nitrogen level is over 0.264g/L,Alnus rubra growth and the ability of nodulation nitrogen fixation were suppressed. Inoculation tests with different phosphorus levels showed that the best promote effect on nodulation nitrogen fixation when the concentration of phosphorus is 2mM/L.With the increase of phosphorus concentration, The seedling height,biomass and total nitrogen of seedlings are less than the CK.In addition to nitrogen and phosphorus,trace elements molybdenum has an evident influence on nitrogen fixation,too.The test results indicated that when a certain concentration of moderate (2mM/L sodium molybdate) was nourished,it had an evident influence on the growth and nodulation nitrogen fixation of Alnus rubra.But the plant growing will be inhibited when excessive fertilized molybdenum. (4) The nodules formation process and morphological structure characteristic of Alnus rubra were observed by paraffin method. It found that Frankia invaded in through the root hair and epidermis. Frankia stimulate cortexand formed a large number of parenchyma cells and then formed root nodules.Frankia were developed in mediopellis,but there was no hypha formed both in exodermis and endodermis. Early in the period of root nodules formed, there were lot of mycelia in root nodules,but few have sporangiums and sporangiospores.Frankia mainly exists in the form sporangiums and sporangiospores spores rather than mycelia in a mature root nodule.