Abstract
Soil organic carbon (SOC) availability is determined via a complex bio-mediated process, and Pb-Zn tailings are toxic to the soil microbes that are involved in this process. Here, Pb-Zn-tailings- contaminated karst soils with different levels (paddy field > corn field > citrus field > control group) were collected to explore the intrinsic relationship between Pb-Zn tailings and microbes due to the limited microbial abundance in these soils. The SOC concentration in the paddy fields is the highest. However, based on the soil microbial diversity and sole-carbon-source utilization profiles, the rate of SOC availability, McIntosh index, Shannon-Wiener diversity index, Simpson’s diversity index and species richness are the lowest in the rice paddy soils. According to the results of Illumina sequencing of the 16S rRNA gene, Acidobacteria and Proteobacteria are the dominant phyla in all samples, accounting for more than 70% of the reads, while the majority of the remaining reads belong to the phyla Verrucomicrobia, Chloroflexi, Actinobacteria, Bacteroidetes, and Nitrospirae. We also observed that their class, order, family, genus and operational taxonomic units (OTUs) were dependent on SOC availability. Pearson correlation analysis reveals that L-asparagine utilization profiles show significant positive correlation with OTUs 24, 75, and 109 (r = 0.383, 0.350, and 0.292, respectively), and malic acid utilization profiles show significant positive correlation with OTUs 4, 5, 19, 27 (Bradyrhizobium), 32 (Burkholderia), 75 and 109 (r = 0.286, 0.361, 0.387, 0.384, 0.363, 0.285, and 0.301, respectively), as also evidenced by the redundancy analysis (RDA) biplot and heat map. These results indicate that the most abundant groups of bacteria, especially the uncultured facultative Deltaproteobacteria GR-WP33-30 (OTU 24), after long-term acclimation in heavy metal-contaminated soil, are associated with the variance of labile carbon source such as L-asparagine and may have considerable control over the stability of the vast SOC pool in karst surface soils with different agricultural land-use practices. These findings can expand our understanding of global soil-carbon sequestration and storage via changes in microbial community structure of the most abundant species.
Highlights
Almost 3000 Pg C is stored as soil organic carbon (SOC) (Köchy et al, 2015), which is equivalent to three times the carbon content of the Earth’s atmosphere (Pries et al, 2017)
To reduce this knowledge gap, we mainly investigated the effect of toxic Pb-Zn tailings on variance in Soil organic carbon (SOC) availability and soil microbial activity under long-term field conditions by using realtime PCR (Denman and McSweeney, 2006) and high-throughput community sequencing data (Li et al, 2017); the V3–V5 region (515F-909R for bacteria and archaea) of the 16S rRNA genes (Tamaki et al, 2011) was amplified and was used for taxonomic analyses of their communities in our soil samples
Taxonomic assignment of operational taxonomic units (OTUs) was obtained by using the Ribosomal Database Project (RDP) pyrosequencing pipeline2
Summary
Almost 3000 Pg C is stored as soil organic carbon (SOC) (Köchy et al, 2015), which is equivalent to three times the carbon content of the Earth’s atmosphere (Pries et al, 2017). It is necessary to test the influence of Pb-Zn-tailingscontamination on microbial communities and the microbial feedback to SOC availability In this context, we hypothesized that (i) toxic Pb-Zn tailings alter the structure and/or function of soil microbial communities; (ii) the altered structure and/or function of soil microbial communities in turn affect SOC availability and alter the stability of the SOC in surface soils of Pb-Zn-tailings-contaminated karst regions; and (iii) the altered structure and/or function of soil microbial communities can be used as a key to understand the process described above. Based on the results of this study, the large 16S rRNA gene dataset coupled with the ecological features of these soil samples will help us understand how these communities change with SOC availability in Pb-Zn-tailings-contaminated surface soils of karst regions
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