Soil salinization has rapidly encroached from the coastline to inland areas over the past two decades in the Yellow River Delta (YRD). Soil samples were collected from low-(LSW), medium-(MSW), and high-(HSW) salinity wetlands at a depth of 0-20 cm for 16S rRNA sequencing and bioinformatic analyses. The richness and α-diversity indices were significantly lower in saline soils (ECe > 15 dS/m, HSW) than in soils those were not saline (ECe < 15 dS/m, LSW and MSW) (p < 0.05), generally showing a decreasing trend with increasing salinities. The phyla, Proteobacteria, Bacteroidetes, Chloroflexi, Acidobacteria and Planctomycetes, represented more than 70% of the bacterial community in the three wetlands, indicating the wide adaption of these phyla to salinity changes. Specifically, Proteobacteria was recognized as the most dominant (35.30%-38.59%) phylum regardless of salinity. Furthermore, bacterial composition was different among the wetlands, as revealed by β-diversity indices and analysis of similarities. Linear discriminant analysis (LDA) effect size revealed the presence of 11, 2, and 10 discriminating bacterial taxa (LDA > 4) among LSW, MSW, and HSW, respectively, implying that they can serve as bioindicators of soil salinization. Redundancy analysis, Spearman correlation analysis, and the Mantel test suggested that salinity parameters (EC, Na + , K + , Mg 2+ , Ca 2+ , Cl − , and SO 4 2−) prominently structured the bacterial community in the current study. These results suggest that the changes of bacterial composition would be induced in these LSW and MSW soils once seawater intrusion occurs.
Intensive use of atrazine and extensive dispersal of lead (Pb) have occurred in farmland with chemical agriculture development. However, the toxicological effect of their presence on soil microorganism remains unknown. The objective of this study was to investigate the impacts of atrazine or Pb on the soil microbiota, soil net nitrogen mineralization, and atrazine residues over a 28-day microcosm incubation. The Shannon-Wiener diversity index, typical microbe species, and a Neighbor-joining tree of typical species from sequencing denaturing gradient gel electrophoresis (DGGE) bands were determined across periodical sampling times. The results showed that the existence of atrazine or Pb (especially high concentration) in soils reduced microbial diversity (the lowest H value is 2.23) compared to the control (H = 2.59) after a 28-day incubation. The species richness reduced little (from 17~19 species to 16~17 species) over the research time. But soil microbial community was significantly affected by the incubation time after the exposure to atrazine or Pb. The combination of atrazine and Pb had a significant inhibition effect on soil net nitrogen nitrification. Atrazine and Pb significantly stimulated soil cumulative net nitrogen mineralization and nitrification. Pb (300 and 600 mg kg(-1)) accelerated the level of atrazine dissipation. The exposure might stimulate the significant growth of the autochthonous soil degraders which may use atrazine as C source and accelerate the dissipation of atrazine in soils.
BACKGROUND: Although electro-bioremediation (EK-Bio) is effective at removing organic contaminants from soil, the role of electrical intensity (EI) and polarity-reversal (PR) remains unclear. Two electrokinetic reactors (ER I and II) with six treatments (EK-I, EK-PR-I, Bio-I, EK-Bio-I, EK-Bio-PR-I and EK-PR-II) were applied for 42 days to examine the effect of EI and PR on oil EK-Bio remediation. RESULTS: The final oil degradation rate in EK-Bio-PR-I was 27.8%, representing an increase of 18.4%, 11.3% and 7.6% compared with EK-I, Bio-I and EK-Bio-I, respectively. Soil pH remained at around 6.6, and the average bacterial counts increased from 7.66 to 8.41 log 10 cfu g -1 dry soil by the end of EK-Bio-PR-I. There was a significant positive linear correlation between EI and the oil degradation rate in EK-I (y = 0.6919x + 9.2278; Pearson correlation coefficient = 0.9887). The simulated oil degradation rate was assessed according to the above equation in an amplification experiment (EK-PR-II), and the observed oil degradation rate showed no significant difference with the simulated data (P > 0.05).CONCLUSION: EI and PR have positive effects on oil degradation efficiency and soil bacteria, indicating that EK-Bio with appropriate EI and periodic PR is the best approach for removing oil from soil.
Nanomaterials such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) may repeatedly enter the soil environment with unknown adverse consequences. To provide the information on the effects of repeated exposure of CNTs, we determined the response of soil enzyme activity and soil basal respiration (SBR) through a twoweek incubation of farmland soil repeatedly treated with different concentrations of CNTs (100, 200, 500 mg kg -1 for SWCNTs and 100, 500, 1000 mg Kg -1 for MWCNTs). The activities of catalase, alkaline phosphatase, and invertase and SBR were measured after one and two-time treatments. The repeated contamination of SWCNTs and MWCNTs repressed the activity of alkaline phosphatase and invertase in the 14-day incubation. Alkaline phosphatase and invertase were more sensitive indicators of CNTs contamination than catalase and soil basal respiration.High concentration of the SWCNTs stimulated SBR while the lower concentration suppressed SBR. The recurred exposure of SWCNTs and MWCNTs repressed the activity of catalase and invertase. The obtained results indicated the soil microorganisms were suppressed under repeated pollution, as suggested by the same suppressed response of SBR between SWCNTs and MWCNTs treatment except for the concentration of 500 mg kg -1 .
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