Search

Methylmercury (MeHg) is the most toxic organic matter of all mercury (Hg) compounds. Its toxicity is far higher than that of inorganic Hg. Methylmercury can enter the human body through food, threatening human health. Based on the Nanweng River National Nature Reserve in the Greater Xing'an Mountains, the differences in the distribution of MeHg in soil samples collected from four types of wetlands, including medium swamp, low swamp, island forest, and forest soil, and the effect of the soil properties on the MeHg content were investigated in this study. The results show that:① the trends of the total Hg and MeHg levels are inconsistent. The order of the mean total Hg content is island forest (138.76 mg·kg -1 ±101.97 mg·kg -1 ) > forest soil (117.57 mg·kg -1 ±32.44 mg·kg -1 ) > low swamp (71.8 mg·kg -1 ±1.42 mg·kg -1 ) > median swamp (65.11 mg·kg -1 ±26.69 mg·kg -1 ), while the mean MeHg content is in the order of island forest (1.14 μg·kg -1 ±1.15 μg·kg -1 ) > medium swamp (0.87 μg·kg -1 ±1.06 μg·kg -1 ) > low swamp (0.28 μg·kg -1 ±0.06 μg·kg -1 ) > forest soil (0.1 μg·kg -1 ±0.05 μg·kg -1 ); ② the contents of MeHg in the island forest and medium swamp were relatively high and fluctuated dramatically, whereas the contents of MeHg in the low swamp and forest soil were lower and showed little change between each sampling point; ③ the longer the marsh wetland formation was, the higher was the MeHg content, that is, median swamp (0.87 μg·kg -1 ±1.06 μg·kg -1 ) > low swamp (0.28 μg·kg -1 ±0.06 μg·kg -1 ); the soil pH was positively correlated with MeHg ( P <0.05); in the medium swamp area, the content of MeHg was positively related to the water content (WC), organic matter (OM%), carbon (C%), and total mercury (THg; P <0.05); in the island forest areas, the MeHg content showed a linear relationship with the soil pH and NH 4 + -N ( P <0.05). This study reveals the distribution characteristics of MeHg and its influencing factors for different wetland ecosystems, providing data supporting the comprehensive evaluation of MeHg accumulation in wetland ecosystems.

To investigate the coupling mechanism between naphthalene degradation and denitrification using a liquid media containing naphthalene (sole carbon source) and nitrate, a naphthalene degradation bacterial consortium under denitrification was enriched from a soil with potential risk of PAH (polycyclic aromatic hydrocarbon) contamination. The bacterial community composition of the enriched consortium was analyzed by Illumina MiSeq Sequencing. Subsquently, the enriched consortium was cultured under anaerobic conditions for 9 days, and the concentrations of electron acceptors (nitrate and nitrite) for denitrification, gaseous reduction products (N 2 O and N 2 ) involved in denitrification, and abundances of denitrification concerned genes ( narG :periplasmic nitrate reeducates gene; nirS : cd 1 -nitrite reductase gene) were detected at days 1, 3, 7, and 9. The result of Illumina MiSeq Sequencing showed that Pseudomonas (Proteobacteria) was the most dominant genus in this enriched consortium. Under anaerobic conditions, the naphthalene removal rate of this enriched consortium was 49.11% within 9 days. Relative higher naphthalene degradation rates were found both at the beginning (day 1-3) and the end (day 7-9) of incubation, and these were significantly higher than at the middle (day 3-7) of the incubation stage ( P <0.05). The concentration of nitrate decreased during the whole culture period, while the concentration of nitrite increased during the initial incubation (day 1-3) and rapidly decreased from day 3 to 9. Furthermore, obvious productions of N 2 O[3.39 μg ·(L ·h) -1 ] and N 2 [8.97 μg ·(L ·h) -1 ] were only measured at the end of incubation (day 7-9). The abundances of both narG and nirS increased during the incubation, indicating the continuous growth of denitrifiers in the enriched consortium during the incubation period. In summary, this study illustrated that both the nitrate reducing stage and gas producing steps of denitrification could be coupled with anaerobic naphthalene degradation, which might be helpful for a deeper investigation regarding the coupling mechanism between denitrification and anaerobic PAH degradation.

The degradation of soil polycyclic aromatic hydrocarbons (PAHs) under denitrification is one of the most important pathways for anaerobic PAH elimination, but little is known about the effect of nitrate (the terminal electron acceptor for denitrification) on soil denitrification activity and PAH degradation under anaerobic conditions. In this study, the effect of nitrate on soil anthracene anaerobic degradation and denitrification activity was investigated through an anaerobic microcosm experiment. Two groups of treatments without (N 0 ) and with (N 30 ) nitrate (30 mg·kg -1 ) amendment were conducted. Each group contained three treatments with different anthracene concentrations (0, 15, and 30 mg·kg -1 , denoted as A 0 , A 15 , and A 30 , respectively). Therefore, a total of six treatments (N 0 A 0 , N 0 A 15 , N 0 A 30 , N 30 A 0 , N 30 A 15 , and N 30 A 30 ) were incubated in darkness at 25℃ for 45 days, and the production rates of N 2 O and CO 2 , abundances of denitrification related genes ( narG :periplasmic nitrate reductase gene; nirK :copper-containing nitrite reductase gene; and nirS : cd 1 -nitrite reductase gene), and soil anthracene content were measured at 3, 7, 14, and 45 days. The results indicated that the intensive denitrification enzyme activity in each treatment was only detected at day 3, which could be significantly enhanced by both nitrate and anthracene amendments. Subsequently, a sharp decline of denitrification enzyme activity was observed in each treatment, while anthracene showed an obvious inhibition of soil denitrification enzyme activity. The result of a two-way ANOVA also indicated that nitrate, anthracene, and their interactions had significant effects on soil denitrification enzyme activity. The result of a quantitative-PCR indicated that, during the incubation, the abundances of narG and nirS exhibited an increasing tendency, but the abundance of nirK was relatively constant compared with its former counterparts. The final removal rate of anthracene under anaerobic soil environment was in the range of 33.83%-55.01%, and neither the final removal rate nor the degradation rate of anthracene could be significantly affected by nitrate amendment during incubation. The anthracene degradation rates in the higher anthracene containing treatments (N 0 A 30 and N 30 A 30 ) were significantly higher than those in the lower anthracene containing treatments (N 0 A 15 and N 30 A 15 ). In summary, nitrate amendments had no effect on soil anthracene anaerobic degradation but could significantly affect soil denitrification enzyme activity and the abundance of denitrification related narG and nirS genes.

Agricultural soils in the oilfields have the potential risk of PAHs (polycyclic aromatic hydrocarbons) pollution, and the denitrification process with nitrate as the terminal electron acceptor might be important for soil PAHs elimination under anaerobic condition. In this study, 9 soil samples listed as JH-1 to JH-9 were collected from the JiangHan oilfield with a history of more than 50 years. Using the functional genes ( nirK: Cu -nitrite reductase gene; nirS: cd 1 -nitrite reductase gene) involved in denitrification as biomarkers, the community structure of soil denitrifiers was investigated by quantitative-PCR and T-RFLP (terminal-restriction fragment length polymorphism) combined with clone library, and the relationship between soil properties and community structure of soil denitrifers was discussed. The result indicated that the copy numbers of nirK were higher than those of nirS in all soil samples, and the lowest copy numbers of nirK and nirS were both detected in the JH-4 with the highest PAHs content. Meanwhile, the correlation analysis also showed a negative correlation between the copy numbers of those functional genes and soil PAHs content ( nirK: R 2 =0.54, P <0.05; nirS: R 2 =0.58, P <0.05). Furthermore, the result of T-RFLP indicated that the nirK community structures in different soil samples varied significantly, which was obviously unique in the sample (JH-4) with the highest PAHs content. The subsequent RDA (redundancy analysis) also demonstrated that soil PAHs content as well as the available nitrogen and phosphorus belonged to the most important factors affecting the nirK community structure in this oilfield soil. Compared with nirK , little variation was shown about the nirS community structure among the soil samples. However, the abundance of nirS -harboring pseudomonas had a remarkably positive relation with the soil PAHs content, which indicated that pseudomonas , a well known bacterial genus with strong ability to degrade organic pollutants, might be an essential driver for PAHs degradation via denitrification process in this oilfield soil.

The present experiment was carried out in order to know the resistance mechanism of the ectomycorrhizal (ECM) fungi under Al stress, to establish the theoretical foundation to alleviate the Al toxicity of trees, to guide the selection of Al-resisted ECM fungi and preserve forest health. The absorption and assimilation of Al3+ by four ECM fungi [Pisolithus tinctorius (Pt 715), Suillus luteus (Sl 08 and Sl 14), Gyroporus cyanescens (Gc 99)], which were isolated from different forest soils, were investigated in pure culture in liquid media. The growths of Pt 715 and Sl 08 were less affected by Al3+, but growths of S114 and Gc 99 were obviously inhibited by Al3+. With the increasing of Al3+ concentration in culture, the absorption and assimilation of Al3+ by four ECM fungi increased. It indicated that the concentration of Al3+ in environments might be the primary factor determining the Al3+ content in the cell of each tested fungi. Amounts of Al3+ absorbed (in total or calculated in unit hyphae) by the Al3+ tolerant strains (Pt 715 and Sl 08) were significantly lower than those by the Al3+ sensitive strains (S1 14 and Gc 99), which illustrated that reducing the absorption of Al3+ under Al3+ stress environment might be an effective approach to alleviate the Al3+ poison for these Al3+ tolerant strains. Furthermore, Al3+ stress could stimulate the ECM fungi to assimilate more N, P, and K, which might indicate that increasing requirement of the nutrients also could be helpful for ECM fungi to fight against the harmful effects caused by Al3+ stress.

In order to investigate the function of Ca2+ in the alleviation of Al3+ stress in ectomycorrhizal fungi, four strains (Bo 02, Bo 15, Pt 715 and Sl 08) were grown in liquid culture media to study the Al resistance of different strains and the effect of exogenous Ca2+ (0, 0.25, 0.5, 1.0 mmol x L(-1)) on the activity of antioxidative protective enzymes under Al3+ stress. It was showed that ectomycorrhizal fungal species varied in resistance to Al3+ stress. Pt 715 and Sl 08 were more tolerant to Al3+ than Bo 02 and Bo 15 in vitro. The activities of CAT and SOD in Bo 02, SOD in Bo 15, CAT and POD in Sl 08 increased significantly under Al3+ stress. It was showed that the activities of these enzymes in ectomycorrhizal fungi had a close relationship with Al3+ stress. The enzymes in Bo 02 were most sensitive to exogenous Ca2+ and the function of Ca2+ in resisting Al3+ stress was the best in the four strains. A high concentration of Ca2+ (> or = 0.5 mmol x L(-1)) could alleviate or offset the increased activities of antioxidative protective enzymes by Al3+ stress in Sl 08.