Effects of zinc (zinc sulfate) on rhizobia-earleaf acacia (Acacia auriculaeformis) symbiotic association

This project was aimed at investigating the feasibility of using a legume woody plant Acacia auriculaeformis to reclaim Zn-contaminated areas. The effects of different concentrations of Zn, applied as zinc sulfate, on nodulation (%) and nitrogen fixation activity of the A. Auriculaeformis symbiont Rhizobium strain (AA9108) and on growth of the host plant in solution culture conditions were studied. The EC₁₀ and EC₅₀ values (effective concentration to reduce the growth by 10% and 50%, respectively) for AA9108 were 373.6 mg l^-1 and 638.9 mg l^-1, respectively. Nodule formation was inhibited by 10% and 50% at Zn levels of 62.9 mg l^-1 and 115.6 mg l^-1, respectively. EC₁₀ and EC₅₀ values for N₂-fixation activity were 4.7 mg l^-1 and 38.6 mg l^-1, respectively. Growth of the host plant was the most sensitive (EC₁₀ and EC₅₀ values were 0.6 mg l^-1 and 18.3 mg l^-1, respectively). Screening Zn-tolerant varieties of the genus Acacia is therefore a prerequisite for using this genus in revegetation of Zn-contaminated areas.