Zhengnan Cao

Responses of Scirpus triqueter, soil enzymes and microbial community during phytoremediation of pyrene contaminated soil in simulated wetland

The aim of this study was to determine the enhancement of Scirpus triqueter in the dissipation of pyrene and the interaction of pyrene with plant, soil enzymes and microbial community. The results indicated that the dissipation ratios of pyrene in the rhizospheric and non-rhizospheric soil were 64.65 ± 3.86% and 54.49 ± 2.74%, respectively, and were higher than that in the unplanted soil (42.60 ± 0.71%) at 80 d after planting S. triqueter. The pyrene was toxic to S. triqueter, as evidenced by growth inhibition in height, diameter, shoot number and biomass during the planting period. The activities of dehydrogenase decreased significantly at the presence of pyrene in soils, and increased remarkably with the introduction of S. triqueter. It was found that the pyrene addition increased the ratios of fungal/total fatty acids and gram-positive/gram-negative, but the presence of S. triqueter decreased the ratios of gram-positive/gram-negative. A larger stress level was found in the pyrene treated soils without S. triqueter. The ratio of aerobic/anaerobic bacteria decreased with increasing pyrene concentration, but increased when S. triqueter was planted. The principal analysis of phospholipid fatty acid signatures revealed that microbial community structures in the rhizospheric and non-rhizospheric soil were similar, but different from those in the unplanted and control soil.

Degradation of diesel-originated pollutants in wetlands by Scirpus triqueter and microorganisms.

The wetland ecological environment near Huangpu-Yangtze River Estuary (HYRE) is deteriorating more and more seriously due to oil spills. In this paper, the simulation experiment of degradation was conducted to restore the diesel pollution in soils where the decontaminating potential of indigenous hydrocarbon-degrading microorganisms (HDMs) was evaluated with pot experiments and the co-activation between HDMs and native plant, Scirpus triqueter L.(STL), was investigated. The experimental results indicated that HDMs isolated from HYRE wetland had a degradation effect on diesel pollutants. Within 60 days, the removal ratio of diesel compared with initial amount could be up to 57.27 ± 8.18% in the HDMs inoculated soils at different concentrations of diesel. It was also found that the growth of Scirpus triqueter could enhance the degradation and remediation of diesel pollutants by increasing the populations of microorganisms. A community of STL and HDMs showed a remarkable capability of degrading hydrocarbon components in diesels. Under the combined effects of HDMs and STL (STL-Ms), the removal ratio of diesel pollutants could reach 67.42 ± 8.92%. For example, at 15,000 mg kg(-1) diesel concentration the removal ratios in the HDMs and STL-Ms soils were 67.41% and 72.62%, respectively. Moreover, the saturated hydrocarbons were more readily degraded than the aromatic hydrocarbons in treated soils showing a good degradation effect on the range of C(16)-C(24)n-alkanes, especially C(19). Positive correlations between microbial populations and diesel removal ratios were observed during the experiment. Microbial populations were found significantly higher in the HDMs soils and rhizosphere soils than in the control ones. The results confirmed that the HDMs and plant improved the biodegradation ability for diesel pollutants and they could be reasonably matched to cure and restore the ecological environment of oil-contaminated wetlands.

Response Characteristics of Scirpus Triqueter and Its Rhizosphere to Pyrene Contaminated Soils at Different Growth Stages

Scirpus triqueter (Triangular club-rush), a typical wetland species, is used to study the response characteristics to pyrene. A pot experiment was conducted to investigate the growth parameters (height, diameter, shoot number, total volume, underground biomass, aboveground biomass and total biomass), and enzymes (catalase and superoxide dismutase) of S. triqueter. The characteristics of soil enzymes (catalase and polyphenol oxidase) and microorganisms (bacteria and fungi) were also assessed after pyrene treatment. Elevated pyrene concentration (80 mg·kg−1) in the soil reduced the shoot number and biomass significantly, especially at the early growth stage. In root tissue, the enzyme catalase was activated at 80 mg·kg−1 of pyrene. Compared to roots, shoots had higher enzyme activities. Catalase activities in the rhizosphere increased throughout the growth period of S. triqueter. Polyphenol oxidase activities in the rhizosphere were higher than those in the bulk soil and unplanted soil. The populations of bacteria (total bacteria, pyrene-tolerant bacteria, and actinomyces) and fungi decreased under the stress of high pyrene concentration, while that of pyrene-tolerant bacteria increased with the increasing pyrene concentration. The presence of pyrene did not benefit the growth of S. triqueter. S. triqueter and soil enzymes varied within the growth stages. The presence of S. triqueter could improve the activity of soil enzymes and facilitate the propagation of microorganisms which could help eliminate pyrene contamination.