Screening for Al-tolerant rhizobium and a study on its characters

【Objective】The resistant aluminium strains of wild soybean rhizobia in Southern China were screened to set up a system of isolating and identifying aluminum-tolerant rhizobium, and to establish the foundation of effective inoculant for soybean planting areas in South China. 【Method】The nodules of wild soybean which grew in Hunan Province and Guangzhou area were isolated by using technique of strains activated culture method. The tolerance of aluminum was detected by spectrophotometer. The growth characteristics of aluminum-tolerant rhizobium were analyzed using the method of inoculation. The effects on growth and nodulation of the cultivated-soybean were explored by inoculating with aluminum-tolerant strains.【Result and conclusion】 The results showed that the isolated rhizobium could grow with 200 μmol·L^-1 Al³⁺ distinct from the other strains, showing some special features of tolerance to aluminum. The boundary pH that W20 could not survive was 4.0, while the favorite pH was 6.0. In the Proton flux assay, W20 had the ability to prevent more H⁺ from penetrating the cytomembrane than W14, which could make W20 avoid some damage caused by H⁺. Inoculating with the effective rhizobium could significantly increase soybean biomass, nodulation, N content and reduce the content of Al³⁺ with aluminum addition. The shoot and root biomass of soybean increased by 60.9% and 14.8% respectively, while the nodule number and nodule weight increased by 66% and 209% with the rhizobium of W20 strain inoculants at 200 μmol ·L^-1 Al³⁺, respectively. Meanwhile NH₄-N content of shoot and root was stimulated by 25.7% and 9.4% respectively.