Microbial community structure in the rhizosphere of Sophora viciifolia grown at a lead and zinc mine of northwest China.

Understanding the effects of heavy metal contamination on microbial activity is important for developing strategies to reclaim sites disturbed by industrial activities. In this study, we investigated arbuscular mycorrhizal (AM) fungi and bacteria associated with Sophora viciifolia growing at a lead and zinc mine in Qinling Mountain, China. Specifically, we measured the extent of AM fungal root colonization, examined microbial community structure by PCR-denaturing gradient gel electrophoresis (PCR-DGGE), and identified the dominant microorganisms. We also measured the amount of glomalin-related soil protein (GRSP) and the association of GRSP with heavy metal ions. We found that AM root colonization decreased, but total GRSP increased with the increase of the lead concentration in soil. The Shannon-Wiener Index (H') of the AM fungal community showed a significant negative correlation with the available lead concentration (r=0.92, P=0.009). Bacterial community H' was also negatively correlated with the total and available lead concentrations in the soil (r=0.97, P=0.007 and r=0.92, P=0.025 for total and available lead, respectively). Both, AM fungal and bacterial community structures differed significantly between sites along the pollution gradient. The specific distributions of the two kinds of organisms indicated their differing tolerances to heavy metal. The dominant AM fungi were identified as Glomeraceae, whereas the dominant bacteria belonged to Proteobacteria. The amount of lead bound to GRSP varied from 3.3 to 172.5 mg kg(-1), which positively correlated with total and available soil lead concentration (r=0.99, P<0.000 and r=0.93, P=0.020 for total soil lead and available soil lead concentration, respectively), thus reducing the bioavailability of heavy metal ions.