Nitrogen Fixation Ability Of Stylosanthes Rhizobia And Their Tolerance To Acid Soils

Stylosanthes is the important leguminosae forage in south China. Legume-rhizobium symbiotic nitrogen (N) fixation is an important character of stylo and also the base of improving soil fertility. But there is barely rhizobium inoculant adapted to acid soils. This research included collecting stylo nodules from planting-area in China and isolating and purifying rhizobial strains from fresh nodules, screening high effective strains for stylo utilizing soil in Hainan province and testing response to the inoculation of selecting strains. To adapt aci soil, some stress tolerant test including pH, aluminum and phosphorus factor were done to select highly effective acid-tolerant rhizobium. The results will give theoretical foundation to inoculation practice in south China, and to promote bacterial fertilizer development, maintain the economical-ecological-environmental benefits.1) Results from the inoculation pot experiment indicated that rhizobial nitrogenase activity varied significantly with originated areas and with different strains of stylo. but not soybean genotypes. This suggested that the activity of rhizobial nitrogenase is more closely related to the environmental conditions than the characteristics of the host plants. Whether highly ability of nitrogen fixation or not was not correlate closely to nodule number, nodule weight. This suggested that the activity of rhizobial nitrogenase is more closely related to the environmental conditions than the characteristics of the host plants.2) The results of experiment was that inoculation could increase stylo shoot fresh weight, nodule weight and nitrogen (N) content. And 5 rhizobial strains with highly efficiency were gotten, RJS9-2, YM11-1, BS1-1, LZ3-2 and PN13-3 by shoot fresh weight and N content.3) The outcome of acid resistance and salt tolerance was told that all the strain process acid tolerance ability, grow better under pH 6.00 medium than pH7.0. At the same time, the pH of liquid culture did rise after rhizobia growing. And all are sensitive to salt, but strain RJS9-2 could resist little concentration of sodium chloride.4) Phosphor(P) favored nodule formation and increased nitrogen fixation activity of the nodule symbiosis as indicated by the increased nitrogen drawn and P content.5) There are significant differences between strains to pH and aluminum duress. Inoculation strains YM11-. LZ3-2, RJS9-2 grew well under low pH 3.5, higher N content than 5.8. Aluminium chloride did not decrease stoly yields, but increase. All these indicate that Legume-rhizobium symbiotic system could resist more serious environment. All the 5 strains would adjust to popularize in south ChinaAbove all, inoculation effective acid-tolerant rhizobium could increase stylo yields in acid soil, at the same time, the system of rhizobium-legumes will play more tolerant ability to acid soil, and improve the condition of red soil in southern China. The 5 strains isolated from stylo nodule will be popularized for acid soil. And they promote high yield and high quality of stoly output.