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Soil methane generation mainly driven by soil prokaryotic microbes can be coupled with the degradation of petroleum hydrocarbons (PHCs); however, the relationship between prokaryotic community structure and methane production activity in soil with the potential risk of PHC contamination is seldom reported. In this study, 3 soil samples (CS-1 to CS-3) in the area nearby an exploratory gas well and 5 soil samples (DC-1 to DC-5) in a drill cutting dump area were obtained from the Fuling shale gas field (Chongqing City, China). Then, the prokaryotic community structure was examined by Illumina Miseq sequencing, and the linkage between soil methane production rate (MPR) and prokaryotic community composition was analyzed. The results indicated that 2 samples (DC-4 and DC-5) collected from the drill cutting dump area had significantly higher MPR than the other samples, and a significant and positive relationship (r = 0.44, P < 0.05) was found between soil MPR and soil organic matter (OM) content. The prokaryotic community composition in the sample (DC-5) with the highest MPR was different from those in the other samples, and soil OM and MPR were the major factors significantly correlated with the prokaryotic community structure in this soil. The samples (DC-4 and DC-5) with higher MPR had a higher relative abundance of Archaea and different archaeal community structures from the other samples, and the MPR was the sole factor significantly correlated with the archaeal genus composition in this soil. Therefore, both the prokaryotic and archaeal community structures are essential in the determination of soil MPR, and the bacterial genus of Saccharibacteria and the archaeal genus of Methanolobus might be the key contributors for methane generation in this soil from the shale gas field.

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 -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 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 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 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 ). 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 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.

It has previously been confirmed that polycyclic aromatic hydrocarbons (PAHs) could be degraded by soil microbes coupling with denitrification, but the relationships among soil denitrifiers, PAHs, and nitrate under obligate anaerobic condition are still unclear. Here, co-effects of pyrene and nitrate on the activity and abundance of soil denitrifiers were investigated through a 45-day incubation experiment. Two groups of soil treatments with (N 30 ) and without (N 0 ) nitrate (30 mg kg -1 dry soil) amendment were conducted, and each group contained three treatments with different pyrene concentrations (0, 30, and 60 mg kg -1 dry soil denoted as P 0 , P 30 , and P 60 , respectively). The pyrene content, abundances of denitrification concerning genes (narG, periplasmic nitrate reductase gene; nirS, cd 1 -nitrite reductase gene; nirK, copper-containing nitrite reductase gene), and productions of N 2 O and CO 2 were measured at day 3, 14, 28, and 45, and the bacterial community structures in four represented treatments (N 0 P 0 , N 0 P 60 , N 30 P 0 , and N 30 P 60 ) were analyzed at day 45. The results indicated that the treatments with higher pyrene concentration had higher final pyrene removal rates than the treatments with lower pyrene concentration. Additionally, intensive emission of N 2 O was detected in all treatments only at day 3, but a continuous production of CO 2 was measured in each treatment during the incubation. Nitrate amendment could enhance the activity of soil denitrifiers, and be helpful for soil microbes to sustain their activity. While pyrene seemed had no influence on the productions of N 2 O and CO 2 , and amendment with pyrene or nitrate both had no obvious effect on abundances of denitrification concerning genes. Furthermore, it was nitrate but not pyrene had an obvious influence on the community structure of soil bacteria. These results revealed that, under anaerobic condition, the activity and abundance of soil denitrifiers both were insensitive to pyrene, but nitrate could improve the activity of soil denitrfiers and induce the shifts in soil bacterial community structure.

The responses of soil ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) to mercury (Hg) stress were investigated through a short-term incubation experiment. Treated with four different concentrations of Hg (CK, Hg25, Hg50, and Hg100, denoting 0, 25, 50, and 100mgHg/kg dry soil, respectively), samples were harvested after 3, 7, and 28day incubation. Results showed that the soil potential nitrification rate (PNR) was significantly inhibited by Hg stress during the incubation. However, lower abundances of AOA (the highest in CK: 9.20×10(7)copies/g dry soil; the lowest in Hg50: 2.68×10(7)copies/g dry soil) and AOB (the highest in CK: 2.68×10(7)copies/g dry soil; the lowest in Hg50: 7.49×10(6)copies/g dry soil) were observed only at day 28 of incubation (P<0.05). Moreover, only the community structure of soil AOB obviously shifted under Hg stress as seen through DGGE profiles, which revealed that 2-3 distinct AOB bands emerged in the Hg treatments at day 28. In summary, soil PNR might be a very useful parameter to assess acute Hg stress on soil ecosystems, and the community structure of soil AOB might be a realistic biological indicator for the assessment of heavy metal stress on soil ecosystems in the future., (Copyright © 2015. Published by Elsevier B.V.)

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.

Purpose: Denitrification is an important biochemical process in global nitrogen cycle, with a potent greenhouse gas product N(2)O. Wastewater irrigation can result in the changes of soil properties and microbial communities of agricultural soils. The purpose of this study was to examine how the soil denitrification genes responded to different irrigation regimes., Materials and Methods: Soil samples were collected from three rural districts of Beijing (China) with three different irrigation regimes: clean groundwater (CW), reclaimed water (RW), and wastewater (WW). The abundance and diversity of three denitrification microbial genes (nirS, nirK, and nosZ) were examined by real-time polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) molecular approaches., Results and Discussion: The abundance of nirS in the WW treatment was higher than that in the CW treatment, and no significant difference was found between the RW and CW or WW treatments. The abundance of nirK gene of the RW and WW treatments was higher than that of the CW treatment. There was no difference for nosZ gene among the three treatments. Correspondence analysis based on the DGGE profiles showed that there was no obvious difference in the nosZ gene composition, but nirS and nirK genes changed with different irrigation regimes., Conclusions: Irrigation with unclean water sources enhanced the soil NO (3) (-) content and changed the abundance and composition of soil denitrifiers, and different functional genes had different responses. Irrigation with unclean water sources increased the abundance of nirK gene and changed the community structures of nirS and nirK genes, while nosZ gene was relatively stable in the soil. These results could be helpful to explore the mechanisms of the variation of denitrification processes under long-term wastewater irrigation and partially explain the reason of more N(2)O output in the field with wastewater irrigation.