Isolation Of Effective And Acid-Tolerant Rhizobium Meliloti And Effects On Capacity Of Symbiosis System Tolerant To Acidity And Aluminum

Alfalfa (Medicago sativa L.) is a fine forage legume, gaining the name of "king of pasture". In recent years, with the area of alfalfa plantation increasing, necessity to plant alfalfa on acid soils increases. In China, alfalfa mainly grows on northern neutral and alkali soils. As the program of developing western China and removing furrow to forest of grass progressing, industry structure regulating, and the growth area of alfalfa extending, planting on southern soils became important for the industrialization of alfalfa. However, there's a lot of acid soil in South of China, and acid-tolerant rhizobia are in short. So, isolating acid-tolerant R. meliloti is necessary.The foreign experience of planting alfalfa on moderately acid soil showed that inoculating acid-tolerant rhizobium could improve the yield and quality of alfalfa. According to foreign experience, we started with the soil type and alfalfa growth on southwestern China, studied isolation of acid-tolerant R. meliloti, explored the growth characteristic of acid-tolerant rhizobium, and the effects on growth and nodulation of alfalfa, probed the acid-tolerance mechanism with the addition of calcium. In addition, field experiments were carried to examine influence on lucerne's growth, yield and quality by applying calcium and inoculating acid-tolerant R. meliloti. All the measures taken above were in order to set up a system isolating and identifying acid-tolerant rhizobium, and to establish the foundation of effective inoculant for new planting areas in southwest Main results were listed as follows:1. Several R. meliloti were isolated from nodules of alfalfa grown on acid soils (pH5.2), six could grow on the solid media with pH4.8 steadily. The six rhizobia were numbered 91511, 91512, 91521, 91522, 91531, 91532, which could nodulate alfalfa in about 9d, make alfalfa gain high number of nodules (above 10 per plant) and high nodulation occupancy (about 66.67%-100%).2. Growth curve of the six R. meliloti were examined under different acidity (pH7.0, pH6.0, pH5.5, pH5.2, pH5.0, pH4.8). The results indicated that acidity slowed Rhizobia's growth significantly, which made the rhizobia exhibit a longer lag phase, a lagged log phase and a delayed stationary phase. When incubated in liquid medium, the six strains showed the ability to grow at pH5.0 and above but could not grow at pH4.8 except strain 91532. So we can conclude that under low acidity, the acid-tolerant...