The variation in microbial community structure under different heavy metal contamination levels in paddy soils

As a global pollution problem, heavy metal contamination poses a serious hazard to soil microorganisms which play an extremely important role in soil chemical cycling and ecological persistence. However, the effects that different levels of heavy metal contamination in soils have on microorganisms and the interactions between them are still unclear. The purpose of this research is to analyze the microbial structure under different levels of heavy metal contamination, find out heavy metal tolerant species under different environmental conditions, then provide useful reference for the bioremediation of contaminated farmland. In this study, 16s rRNA high throughput sequencing technology was used to investigate the microbial communities in severe level (SL), moderate level (ML), light level (LL) and clean level (CL) of heavy metal contaminated soils, and the relationships between environment variables and microorganisms were analyzed. The results showed that the concentrations of heavy metals and soil physicochemical properties had various impacts on microbial community composition under different heavy metal contamination levels. Most dominant bacteria were in significant negative correlation with Cd in ML region, and significantly correlated with TN and OM in LL region. However, there was no significant correlation between dominant fungi and the physicochemical properties in LL region. And most of the dominant fungi were significantly correlated with the heavy metal concentrations in SL region. The bacterial phyla such as Proteobacteria, Acidobacteria and Bacteroidetes showed more tolerance with heavy metal contamination in SL, ML and LL regions, respectively. Meanwhile, the dominant fungi of Ascomycota, Basidiomycota, Chytridiomycota, Glomeromycota, Zygomycota and Rozellomycota showed stronger correlations with heavy metal contamination in SL and LL regions. These results indicated that some microorganisms had strong tolerance to heavy metal contamination and had certain heavy metals digestion ability, which can create an appropriate soil environment for the growth of food crops.