| With twelve rhizobium strains that were isolated from nodules of leguminous plants growing naturally in the tailing area of lead-zinc mine in Shangzhou District, Shangluo City, Shaanxi Province as study object, their tolerance to lead salt stress, zinc salt stress and lead-zinc double salt stress was investigated by using solid tablet inoculation culture method, and their physiological and biochemical characteristics were determined by using liquid tube oscillation culture method. The results showed that the rhizobium strains exhibited strong capability to tolerate single lead or zinc salt, but their tolerance capability to lead-zinc double salt was significantly lower than that to single salt. There were considerable differences of physiological and biochemical characteristics among the strains. The stronger the tolerance to lead-zinc stress a rhizobium strain possessed, the more positive physiological and biochemical characteristics it showed. Three rhizobium strains with high tolerance to lead and zinc stress were preliminarily screened out, i.e., CH3 isolated from
nodules of Robinia pseucdoacacia, MX7 isolated from Medicago lupulina and HZ10 isolated from Lespedeza floribunda Bunge. It can be concluded that the tolerance of rhizobia to lead-zinc stress is seemingly built on the basis of their various physiological metabolism reactions, that is to say, the rhizobia are likely to adjust their metabolic pathway to be adaptable to the environment contaminated by lead and zinc. The rhizobium strains with strong tolerance to lead-zinc stress exhibit a potential application value in soil remediation and revegetation in tailing area of lead-zinc mine. |