Accumulation and Distribution of Cadmium in Flue-Cured Tobacco and Its Impact on Rhizosphere Microbial Community

To explore the accumulation and distribution of Cadmium (Cd) in flue-cured tobacco and the effect on soil microbial community structure in the rhizosphere, pot experiments were conducted with different treatment levels of Cd (0, 2, 4, 8, and 16 mg.kg(-1)). The Cd accumulation in different organs of flue-cured tobacco was analyzed, and the bacteria and fungi community structures in the rhizosphere were examined using PCR-DGGE fingerprinting with universal bacteria and fungi primers. Results showed that the order of Cd contents in different organs of flue-cured tobacco was: leaf > stem > root. Increasing Cd concentration in the pot soil elevated Cd contents in different organs of flue-cured tobacco. As to the soil microbial community, the bacterial fingerprinting bands in rhizosphere with 4 mg.kg(-1) Cd level were significantly less than other treatments. Some bacteria disappeared with increasing soil Cd concentrations. Nevertheless, some special bacteria apparently had a strong restoration capability in the rhizosphere at a high Cd contamination level (16 mg.kg(-1)). Among the 8 clusters of bacterial communities identified by the sequencing, the Bacterium elfin, Acidobacteria bacterium elfin, and Mycobacterium had strong resistance and adaptability to Cd contamination of different concentrations, whereas the Leptolyngbya had strong adaptability to Cd contamination of moderate concentration, which could become the dominant population at this level. The fungi community diversity in the rhizosphere with different concentrations of Cd was significantly different from the pattern of bacteria. Some fungi appeared with the increase of Cd concentration, but some fungi disappeared at the moderate Cd concentration (4 mg-kg-'). Among the 4 clusters of fungal communities identified by the sequencing, the Fusarium and unknown species were the dominant species in the fungi community, which existed in all treatments and had strong adaptability to different Cd concentrations. The Acremonium sclerotigenum was sensitive to Cd contamination and disappeared at Cd concentrations greater than 2 mg.kg(-1), but Rhizopus appeared at Cd concentrations greater 8 mg.kg(-1), suggesting its preference for high Cd concentrations. Flue-cured tobacco had a strong ability to absorb and accumulate Cd. A proper concentration of Cd might have a positive effect on the soil bacteria and fungi community structure of flue-cured tobacco rhizosphere.