Spacial characteristics of pyrene degradation and soil microbial activity with the distance from the ryegrass (Lolium perenne L.) root surface in a multi-interlayer rhizobox

The fate of sulfonamides in microenvironments of rape and hot pepper rhizosphere soil system

Sulfonamides (SAs) in agricultural soils can be degraded in rhizosphere, but can also be taken up by vegetables, which thereby poses human health and ecological risks. A glasshouse experiment was conducted using multi-interlayer rhizoboxes to investigate the fate of three SAs in rape and hot pepper rhizosphere soil systems to examine the relationship between the accumulation and their physicochemical processes. SAs mainly entered pepper shoots in which the accumulation ranged from 0.40 to 30.64 mg kg-1, while SAs were found at high levels in rape roots ranged from 3.01 to 16.62 mg kg-1. The BCFpepper shoot exhibited a strong positive linear relationship with log Dow, while such relationship was not observed between other bioconcentration factors (BCFs) and log Dow. Other than lipophilicity, the dissociation of SAs may also influence the uptake and translocation process. Larger TF and positive correlation with log Dow indicate preferential translocation of pepper SAs. There was a significant (p < 0.05) dissipation gradient of SAs observed away from the vegetable roots. In addition, pepper could uptake more SAs under solo exposure, while rape accumulated more SAs under combined exposure. When SAs applied in mixture, competition between SAs might occur to influence the translocation and dissipation patterns of SAs.

Effect of In Situ Bioremediation of Soil Contaminated with DDT and DDE by Stenotrophomonas sp. Strain DXZ9 and Ryegrass on Soil Microorganism

In the present study, the changes in the microbial populations, enzyme activity and bacterial community structure in contaminated soils were investigated during the bioremediation of using Stenotrophomonas sp. strain DXZ9 and ryegrass. The results showed that the removal rates were 81% for DDT and 55% for DDE (69% for DDTs) with ryegrass-microbe. Microbial activity was remarkably improved, and the number of bacteria increased sharply from 7.32 × 106 to 2.56 × 108 cells/g in the 10 days due to successful colonization of the strains and effects of the ryegrass rhizosphere. There was significant difference in fungi number with ryegrass when comparing the 30th and 90th days with the 210th day: The actinomycete number in the soil with ryegrass was higher than without ryegrass, and it indicated that the number of microorganisms significantly increased under the action of ryegrass. The activities of polyphenol oxidase, dehydrogenase and catalase were significantly activated by the combination of ryegrass and microbe, and urease activity was less affected: It has influence on the diversity of bacterial community structure in the soil, but its influence gradually decreased by denaturing gradient gel electrophoresis with an extension in time. The activities represented promising tools for decontaminating and restoring the ecosystem in sustainable ways, and proposing new approaches and technological bottlenecks to promote DDT biodegradation is very significant.

Mechanistic insight into the interactions of EDDS with copper in the rhizosphere of polluted soils

The biodegradable S,S-ethylenediaminedisuccinic acid (EDDS) is a promising chelant for chelant-assisted phytoextraction of trace metals in polluted soil. The interactions between EDDS and trace metals/major elements in the soil affect the metal bioavailability and their subsequent phytoextraction efficiency. This study aimed to investigate the macroscopic and molecular-level interactions of EDDS with Cu in the rhizosphere and non-rhizosphere of a Cu-polluted agricultural soil. A multi-interlayer rhizobox planted with ryegrass was used to simulate the transport of EDDS and Cu from the non-rhizosphere to rhizosphere soils. The results showed that EDDS (5 mM kg^-1) significantly dissociated Cu (285-690 fold), Fe (by 3.47-60.2 fold), and Al (2.43-5.31 fold) from the soil in comparison with a control group. A combination of micro-X-ray fluorescence, X-ray absorption near-edge structure spectroscopy, and sequential extraction analysis revealed that EDDS primarily chelated the adsorbed fraction of Cu by facilitating the dissolution of goethite. Moreover, as facilitated by ryegrass transpiration, CuEDDS was moved from the non-rhizosphere to rhizosphere and accumulated in ryegrass. In situ processes of Cu extraction and transport by EDDS in the rhizosphere were further elucidated with chemical speciation analysis and geochemical modeling methods.

Minerals loaded with oxygen nanobubbles mitigate arsenic translocation from paddy soils to rice

Inhibiting reductive transformation of arsenic (As) in flooded paddy soils is fundamentally important for mitigating As transfer into the food chain. In this study, oxygen-nanobubble-loaded-zeolites (ZON) and -vermiculites (VON) were tested as a novel approach for supplying oxygen to paddy soils to inhibit As influx into rice. The dynamic physio- and bio-chemical variations in the rhizosphere and bulk soil were profiled in a rhizobox experiment. Upon adding ZON and VON, the redox potential and dissolved oxygen consistently increased throughout the cultivation period. The improved redox environment inhibited As(III) release into porewater and increased As(V) adsorbed on crystalline Fe (hydr)oxides, following the reduction of arsC and arrA gene abundances and enhancement of the aioA gene. Moreover, adding ZON and VON promoted root iron plaque formation, which increased As retention on iron plaque. Both ZON and VON treatments mitigated As translocation from soil to rice, meanwhile increasing root and shoot biomass. ZON was superior to VON in repressing As transfer and promoting rice growth due to its higher oxygen loading capacity. This study provides a novel and environment-friendly material to both mitigate the As translocation from paddy soil to rice and improve rice growth.

Rhizoremediation of a dioxin-like PCB polluted soil by alfalfa: Dynamic characterization at temporal and spatial scale

This study investigates the temporal and spacial dissipation dynamics of a dioxin-like polychlorinated biphenyl (PCB 77) in the rhizosphere of alfalfa. A three-chamber rhizobox was designed to compare the PCB 77 dissipation efficiency in the rhizosphere, near-rhizosphere, and far-rhizosphere zones. Culture-independent techniques, including quantitative PCR (qPCR), Biolog-ECO plate, and denatured gradient gel electrophoresis (DGGE) were employed to investigate the variation of bacterial quantity, metabolic diversity and community structure in the alfalfa-rhizobium symbiosis rhizosphere at different rhizoremediation stages. PCB dissipation rates in different rhizosphere zones were in the order: rhizosphere (90.9%) > near-rhizosphere (80.5%) > far-rhizosphere (31.7%). The number of the bacterial 16S rRNA gene copies in the rhizosphere zone in the polluted treatment reached the highest value of all the treatments. Microbial metabolic diversity, as indicated by average well color development (AWCD) in both rhizosphere and near-rhizosphere zones, had recovered from the PCB 77 pollution. The soil bacterial community diversity improved greatly in the rhizosphere of alfalfa, with some new species appeared in the rhizosphere and near-rhizosphere zones. In conclusion, the dissipation of PCB 77, the quantity of total soil bacteria, soil microbial metabolic diversity, and soil microbial community structure were significantly improved in rhizosphere and near-rhizosphere zones of alfalfa.

Effects of the soil microbial community on mobile proportions and speciation of mercury (Hg) in contaminated soil

The precise characterization of the behavior of individual microorganisms in the presence of increased mercury contents in soil is necessary for better elucidation of the fate of mercury in the soil environment. In our investigation, resistant bacterial strains isolated from two mercury contaminated soils, represented by Paenibacillus alginolyticus, Burkholderia glathei, Burkholderia sp., and Pseudomonas sp., were used. Two differently contaminated soils (0.5 and 7 mg kg(-1) total mercury) were chosen. Preliminary soil analysis showed the presence of methylmercury and phenylmercury with the higher soil mercury level. Modified rhizobox experiments were performed to assess the ability of mercury accumulating strains to deplete the mobile and mobilizable mercury portions in the soil by modification; microbial agar cultures were used rather than the plant root zone. A sequential extraction procedure was performed to release the following mercury fractions: water soluble, extracted in acidic conditions, bound to humic substances, elemental, and bound to complexes, HgS and residual. Inductively coupled plasma mass spectrometry (ICP-MS) and a single-purpose atomic absorption spectrometer (AMA-254) were applied for mercury determination in the samples and extracts. Gas chromatography coupled to atomic fluorescence spectrometry (GC-AFS) was used for the determination of organomercury compounds. The analysis of the microbial community at the end of the experiment showed a 42% abundance of Paenibacillus sp. followed by Acetivibrio sp., Brevibacillus sp., Cohnella sp., Lysinibacillus sp., and Clostridium sp. not exceeding 2% abundance. The results suggest importance of Paenibacillus sp. in Hg transformation processes. This genus should be tested for potential bioremediation use in further research.

Toluene biofiltration enhanced by ryegrass

Toluene biofiltration by microorganisms (an unplanted treatment) and by the combination of ryegrass (Lolium perenne L.) and microorganisms (a planted treatment) was investigated in this study. The results showed that toluene was completely removed by the unplanted and the planted biofilters in less than 0.2 g m⁻³ inlet toluene concentration. Toluene removal capacity for the planted biofilter was significantly higher than that for the unplanted biofilter in the range of 0.2-0.5 g m⁻³ inlet toluene concentration. This study revealed a significant (p < 0.01) increase in the microbial activity in the planted biofilter in comparison with the unplanted biofilter, indicating that ryegrass growing in a biofilter would significantly (p < 0.05) enhance toluene biodegradation.