Vertical-scale spatial influence of radial oxygen loss on rhizosphere microbial community in constructed wetland.

Complex interactions between plants and microorganisms form the basis of constructed wetlands (CWs) for pollutant removal. In the rhizosphere, radial oxygen loss (ROL) plays a key role in the activity and abundance of functional microorganisms. However, little has been done to explore how ROL would influence the niche differentiation of microbial communities at different vertical spatial scales. We demonstrate that ROL decreases with depth, promoting an oxidation-reduction rhizosphere microecosystem in CWs. The high level of ROL in the upper layer could support the oxygen supply for aerobic bacteria (Haliangium), facilitating the COD (60%) and NH4+-N (50%) removal, whereas the enrichment of denitrifiers (e.g., Hydrogenophaga and Ralstonia) and methanotrophs (Methanobaterium) in the lower layer could stimulate denitrification. The function prediction results further certified that the abundance of genes catalyzing nitrifying and denitrification processes were significantly enhanced in the upper and bottom layers, respectively, which was attributed to the oxygen concentration gradient in the rhizosphere. This study contributes to further unraveling the rhizosphere effect and enables an improved understanding of the decontamination mechanisms of CWs.

Microbial mediated reaction of dimethylarsinic acid in wetland water and sediments.

The biogeochemical reactions of dimethylarsinic acid (DMAs(V)) were investigated using simulated wetland systems in a laboratory. DMAs(V) was injected into the wetland water, and the As concentrations in the water, plants, and sediments were monitored. Aqueous and solid-phase As speciation was evaluated, and the results revealed that the DMAs(V) was completely transported to the sediments and plants. X-ray absorption spectroscopic measurement of the As in the sediment revealed that approximately 85-95% of As existed as inorganic As species, demonstrating the important role of microorganisms in the biogeochemical reaction of DMAs(V). The influences of microbes were further investigated in smaller batches under aerobic and anaerobic conditions. The microbial batch results showed that DMAs(V) demethylation reduced the total aqueous As concentration, demonstrating that As(V) has higher affinity to wetland sediment than DMAs(V). The redox conditions were also revealed as an important controlling factor of the As reaction and, under anaerobic conditions, we observed the presence of the most toxic form of inorganic As(III) in the aqueous phase. Although this study reports one example from a specific wetland, the important roles of the redox conditions and microbial influences were identified from the comprehensive analysis of As speciation and mass balance.

[Rhizosphere Microbial Diversity in Different Wetland Microcosms].

To investigate the rhizosphere microbial community structure characteristics in varying combinations of plants and filter materials in the process of aquaculture pond water treatment, six types of wetland microcosms were established using two kinds of plants (Zizania latifolia Turcz. and Sagittaria graminea) and two types of filter materials (garnet and magnetite). High-throughput sequencing technology was used to analyze the microbial structural features and composition diversity of the wetland rhizosphere. The results were as follows. The microorganisms recovered belonged to 52 phyla, 118 classes, 455 families, 905 genera, and 1426 species. Based on the Shannon index, Zizania latifolia Turcz. (average value: 5.77) had a higher capacity than Sagittaria graminea(average value: 5.29) in terms of microbial enrichment. However, the rate of Proteobacteria in the rhizosphere microorganism communities of the Sagittaria graminea and Zizania latifolia Turcz. microcosms were 61.97% and 51.78%, respectively, further showing that the roots of Sagittaria graminea in the wetland microcosms better enriched the Proteobacteria during the experimental period. The major bacterial groups of different plant roots were enriched with ß-Proteobacteria in the experiment. The results of this study provide a theoretical basis for species optimization in artificial wetland systems and best combination of wetland construction that will be useful for future investigations.

Rapid chiral separation of atenolol, metoprolol, propranolol and the zwitterionic metoprolol acid using supercritical fluid chromatography-tandem mass spectrometry - Application to wetland microcosms.

A method for enantiomeric separation of the three ß-blocking agents atenolol, metoprolol, propranolol and the zwitterionic metoprolol acid, a major metabolite of both metoprolol and in environmental matrices also atenolol, has been developed. By use of supercritical fluid chromatography and the polysaccharide-based Chiralpak(®) IB-3, all four compounds were simultaneously enantiomerically separated (Rs>1.5) within 8min. Detection was performed using tandem mass spectrometry, and to avoid isobaric interference between the co-eluting metoprolol and metoprolol acid, the achiral column Acquity(®) UPC(2) BEH 2-EP was attached ahead of to the chiral column. Carbon dioxide with 18% methanol containing 0.5% (v/v) of the additives trifluoroacetic acid and ammonia in a 2:1 molar ratio were used as mobile phase. A post column make-up flow (0.3mL/min) of methanol containing 0.1% (v/v) formic acid was used to enhance the positive electrospray ionization. Detection was carried out using a triple quadrupole mass spectrometer operating in the selected reaction monitoring mode, using one transition per analyte and internal standard. The method was successfully applied for monitoring the enantiomeric fraction change over time in a laboratory scale wetland degradation study. It showed good precision, recovery, sensitivity and low effect of the sample matrix.