Research For The Colonization Of Acid-tolerant Rhizobium Of Alfalfa

Alfafa is a high quality leguminous pasture, which is known as "kingdom of pasture". Recent years, the industrialization of alfafa is developing quickly with the increasing requirement, thus the demand is more that planting alfafa on the acid soil. In our country, alfafa mainly grow on the neutral and alkalescent soil in the north. With western exploition and the development of returning farmland to forestry and grassland, our county implied the plan of "bringing north pasture to south". This implement is an important action to boost the planting of alfafa. However, acid soils have a wide distribution and vast area in the south of China, in addition, alfafa is the most sensitive leguminous pasture, the existence of acid soils badly hampered the implement of "bringing north pasture to south" and the industrialization of alfafa. So it is important to establish a accrete system of highly effective and adversity resistance.The symbiosis of rhizobium and alfafa is an important aspect in the field of alfafa research, inoculating highly effective acid-tolerant rhizobium of alfalfa will help to establish an alfafa accrete system of highly effective and adversity resistance in the south of our country. With the increasingly spread of leguminous plant on acid soil, inoculating acid-tolerant rhizobium has already been an important approach to improve the yield and quality of leguminous pasture on the acid soil. However, the degree of viability and rhizobium colonization directly affects the inoculating effect. At the same time, rhizobium will affects other microorganism or microbial biomass to some distance after inoculating in the soil. So, it has a very important significance to strengthen the research of rhizobium colonization on the root, and it will help to discover the microecology characters of plant growth-promoting rhizobacteria, improve the adaptability in . rhizosphere and the stability of increase production.Meanwhile, as an ingredient that can transfer signal, Ca²⁺ is a vital factor which can promote the acid-tolerant ability of rhizobacteria. Thus, we studied that acid-tolerant rhizobium was inoculated on the acid soil in Jinyun mountain, and Ca²⁺ solution of three concentrations were applied on the soil, and discussed the rhizobium colonization on the acid soil and the effect that applying Ca²⁺ affected the soil microecological environment, then analyzed the affection of applying Ca²⁺ and inoculating acid-tolerant rhizobium to the symbiosis effect of rhizobium and alfafa. These can supply some theory and technology gist on the inoculating highly effective acid-tolerant rhizobium on the new south alfafa plantation. The main results followed:1.Bifida zone design which was lack of three zones was used, three strains of acid-tolerant rhizobium of alfalfa (91522,91512,91532) our lab had got were inoculated on the alfalfa, while Ca²⁺ solution of three concentrations (0mmol/L,5mmol/L,10mmol/L) were applied on the soil(pH4.6). The results showed that all the three strains of acid-tolerant rhizobium of alfalfa could colonize on the acid soil, and the trends of colonization were basically consistent. Compared with the control, the colonization amount of all the three strains had no significant difference, but the three strains in the experiment all had higher colonization amount than that of control, the best effects appeared in inoculating the strains named 91512 and 91532. The treatments which were applied Ca²⁺ didn't affect the rhizobium colonization significantly, but applying 5mmol/LCa²⁺ showed a best colonization effect. These indicated that inoculating acid-tolerant rhizobium and applying Ca²⁺ of suitable concentration will promote the colonization of rhizobium on the acid soil.2.Applying Ca²⁺ and inoculating acid-tolerant rhizobium of alfalfa could evidently affected the number of microorganism and microbial biomass in the .rhizosphere. The difference reaches a significant and very significant level. After inoculating acid-tolerant rhizobium of alfalfa, the number of bacteria,fungi and biomass increased significantly, actinomycetes increased a little but didn't reaches the significant level. The difference among the three strains wasn't significant. Applying Ca²⁺ only increased the number of bacteria significant, but not affected other microorganism significantly. It is obvious that inoculating acid-tolerant rhizobium of alfalfa and applying Ca²⁺ changed the nutrition ingredient of rhizosphere on the acid soil, it helped the microorganism to grow and propagation, so the microecological environment in the soil was meliorated, the number of microorganism and microbial biomass has also been increased.3.Compared to the control, after inoculating acid-tolerant rhizobium of alfalfa, the number of microorganism and microbial biomass had significant and very significant difference in most of the evaluating months. The number of microorganism and microbial biomass of three big types in the four treatments reached the maximum in June. It was obvious that with the colonization of rhizobium and the growth of plant roots, the increasing rhizosphere secretion provide large energy for rhizosphere microorganism, addition with the warm and wet condition of soil, all kinds of microorganism could grow and propagate quickly. Thus the number of microorganism and microbial biomass reached the maximum.4.Test the symbiosis of rhizobium and alfafa by inoculating acid-tolerant rhizobium and applying Ca²⁺. The results showed that inoculating acid-tolerant rhizobium and applying Ca²⁺ affected significantly on root fresh weight, plant height, fresh weight upground and nodule weight. Strain 91512 affected greatly on plant height, fresh weight upground and nodule weight, root fresh weight was affected greatly by strain 91532; by applying calcium 5mmol/L, the best symbiosis effect on alfalfa were gained, which showed that moderately calcium and acid-tolerant rhizobium of alfalfa were able to improve yield and quality of alfalfa.5.Inoculating acid-tolerant rhizobium and applying Ca²⁺can ameliorated the nutrition condition in the acid soil, acid-tolerant rhizobium and Ca²⁺ 5mmol/L greatly affected the total nitrogen of soil. In every treatment, exchangeable calcium of acid soil decreased, the least of decreased exchangeable calcium of acid soil was discovered in the Ca²⁺ 5mmol/L treatment. All soil nutrition increased not significantly, except that exchangeable calcium decreased and total P keep the number. It indicated that acid-tolerant rhizobium and Ca²⁺ ameliorated the nutrition condition that alfafa needed during their growing, promoted the growth and metabolism of alfafa roots, thus accelerated the upgrowth and propagation of rhizosphere microorganism, which can ameliorated the microecologica! environment and speed up the accumulation of soil nutrition, accompanied the improvement of soil fertility.