Studies On The Nitrogen Fixation And Structure Of Legume-rhzibium Symbioty Grown On The Loess Plateaus, Shaanxi And Gansu

The condition of nodulation and nitrogen fixation of wild and cultural leguminous plants belong to 63 species, 29 genera were field surveyed and indoor analysed. 10 species not reported previously were found nodulated, they were Albizzia kalkora, Astragalus complanatus, A. ellipsoideus, A. scaberrimus, Argyrolobiu argenteum, Glycine soja, Indigofera amblyantha, Lotus orniculatus, Piptanthus nepalensis. During the period of collecting nodules, it was observed that Leguminous plants distributed in region where water is enough, such as beach, field border, woodlot and so on, nodulated easily and nodules grew well, on the contrary, Leguminous plants grown on bareness and sand nodulated less and size of nodules were little. On the other hand, the same leguminous plant nodulated easily under the condition of moist, and nodulated difficultly under the condition of drought. It showed that nodulation condition was related with environment closely and was affected by the environment condition.Comparative studies suggested that with the difference of ecological condition, the life habits of leguminous plants were varied, and there were all kinds of characteristics in the morphology of the nodules. The nodules were divided into two sorts according to the different morphology: one sort was represented by the nodules of Medicago sativa , Melilotus suaveolens, Trifolium repens, Onobrychis viciifolia, which was long round, the size was little, meristem was in the tip cortex, and grew signally or aggregated together to form a palmate or a ginger structure; the other sort was presented by Glycine max, Phaseolus vulgaris, which was round, meristem was barred and in cortex, grew signally. In general, leguminous plants distributed inmountain grassland, native grassland and wet land were mainly annual herb, their nodules were also annual, the form of the nodules was regular, such as round and long round, the color was pink. While, leguminous plants grown in heliophilic area were perennial tree and shrub, their nodules mainly were long round, branched and white, brown or yellow, grew from lateral roots and fibrous root. The diameter of nodules were different, the smallest was the nodule of Lotus orniculatus, about 0.8mm; bigger nodule was one of Cercis chinensis, about 18mm. The morphology of nodules were mainly related with the plant, the nodule morphology of different species belong to the same genera was always similar.From the sample of 25 genera, 46 species, 51 nodules including leguminous pasturage, psammophyte, shrub, tree and field crops, 47 rhizobia were isolated and purified. Then part of them were inoculated to host plants, they nodulated after 27 days. These strains were able to grow in YMA medium well, and secreted glycosaminoglycan. In general, they could form bacterial colonies after 3 days. Colonies were round with luster, the edge were regular, transparent or lacte. The morphology characteristics of 14 strains purified were observed and at the same time physiological and biochemical tests were performed. The results showed there were differences in the morphology of bacteria from different nodules, the Gram staining showed G", An apparent metachromatic granular region was observed under microscope and electron microscope, which indicated there were lipid granular stained with Sudan black in rhizobia.The results of hydrogen ion concentraion experiment of strain showed that 95% of the rhizobia grew on YMA at pH 6.0-6.5, 85% at pH 6.0-7.5,15% at 7.0-7.5. The optimum pH range for rhizobia from Medicago sativa was 5.0-7.5, but most of them could grew at 5.5-7.5. Results above showed that the range of pH for rhizobia collected from the Loess Plateaus were wide. Most of rhizobia for experiment could grow well at the range of 5%~7% NaCl, and the rhizobia from Medicago sativa showed high tolerance, they could grew or grew well at the range of 10%-15% NaCl, which indicated that the tolerance of rhizobia to salt was related with the concentration of salt of soil where the rhizobia were collected. When they were treated for 10...