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Global climate change is characterized by altered global atmospheric composition, including elevated CO

The abundance, community composition and activity of key nitrogen (N)-cycling functional guilds were monitored at a site where coniferous Cunninghamia lanceolate and broadleaved Mytilaria laosensis were planted in 1993. Leaf cellulose, litter C/N ratio, leaf dry matter content, soil inorganic N content were significantly higher under C. lanceolata, while specific leaf area, litter production, litter magnesium, soil C and soil C/NO3− ratio were higher under M. laosensis. The 15N tracing experiment together with quantitative PCR revealed that autotrophic nitrification rates, as well as the abundances of ammonia-oxidizing archaea and comammox Nitrospira were significantly higher under C. lanceolate than M. laosensis. However, M. laosensis exhibited substantially higher nitrate retention capacity via dissimilatory nitrate reduction to ammonium (DNRA), accompanied by a significantly higher abundance of nrfA gene than C. lanceolate. The Illumina sequencing indicated that tree species markedly affected soil bacterial community composition regardless of the soil layers. Redundancy analysis suggested that litter C/N ratio was the most influential factor explaining functional gene abundances and bacterial communities. Taken together, our findings showed that M. laosensis improved soil N retention capacity mainly through inhibiting autotrophic nitrification while enhancing DNRA activity. This study highlights the importance of tree species identity in influencing the microbially-mediated N cycling and bacterial community composition.

Aims Soil nematode community is an important component of the soil food web, which has been widely recognized as a key bio-indicator for assessing the influence of nature restoration on ecological functions. However, the dynamics of the abundance, diversity and function of soil nematode community remain unclear under different forest succession phases. Methods The soil nematode community of natural secondary forests was investigated using a chronosequence approach. Nature restoration for five succession stages were sampled in this study to represent a wide range of stand age groups.Results Soil nematode abundance gradually increased with forest stand age, which reached a peak value (574 individuals 100 g-1 dry soil) in the older age classes. In contrast, soil nematode diversity was not affected by forest stand age. Soil available nitrogen and phosphorus were key factors influencing soil nematode abundance and diversity during forest secondary succession. The plant parasite index decreased with forest stand age, which indicated that ecosystem function and health would be improved as nature restoration progresses. In addition, the structure of soil nematode community was more sensitive to forest secondary succession compared to plant community and soil microbial community. The bottom-up effects of the plant and microbial communities on soil nematode community were important drivers of nematode community structure in subtropical forests. Conclusions Overall, this study demonstrates the active responses of soil nematode community to nature restoration, and highlights the importance of the above-ground and below-ground interactions to the soil food web.

Owing to the similar mechanisms of antibiotic and metal resistance, there is a growing concern that metal contamination may select for antibiotic resistance genes (ARGs) in the environment. Here, we constructed short-term laboratory microcosms to investigate the dynamics of a wide range of ARGs and two copper (Cu) resistance genes in an agricultural soil amended with a gradient of Cu concentrations (0~1000 mg kg-1). Mobile genetic elements (MGEs) were also quantified as a proxy for the horizontal gene transfer potential of ARGs. We detected 126 unique ARGs across all the soil samples using the high-capacity quantitative PCR array, and multidrug and β-lactam resistance were the most abundant ARG categories. The copper amendments significantly enhanced the absolute and relative abundances of ARGs and MGEs, which gradually increased along the gradient of increasing Cu concentrations. The two Cu resistance genes (copA and pcoR) were highly enriched in low-level Cu treatment (50 and 100 mg kg-1), and their abundances decreased with the increasing Cu concentrations. The level of metal and antibiotic resistance gradually declined over time in all Cu-amended treatments but was still considerably higher in contaminated soils than untreated soils after 56 days' incubation. Significant associations among ARGs and MGEs were revealed by the network analysis, suggesting the mobility potential of antibiotic resistance in Cu-amended soils. No significant positive correlations were found between ARGs and copper resistance genes, suggesting that these genes are not located in the same bacterial hosts. Taken together, our results provide empirical evidence that short-term copper stress can cause evolution of high-level antibiotic and metal resistance and significantly change the diversity, abundance, and horizontal transfer potential of soil ARGs.

Soil ecosystem represents the largest contributor to global nitrous oxide (N2 O) production, which is regulated by a wide variety of microbial communities in multiple biological pathways. A mechanistic understanding of these N2 O production biological pathways in complex soil environment is essential for improving model performance and developing innovative mitigation strategies. Here, combined approaches of the 15 N-18 O labelling technique, transcriptome analysis, and Illumina MiSeq sequencing were used to identify the relative contributions of four N2 O pathways including nitrification, nitrifier-induced denitrification (nitrifier denitrification and nitrification-coupled denitrification) and heterotrophic denitrification in six soils (alkaline vs. acid soils). In alkaline soils, nitrification and nitrifier-induced denitrification were the dominant pathways of N2 O production, and application of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) significantly reduced the N2 O production from these pathways; this is probably due to the observed reduction in the expression of the amoA gene in ammonia-oxidizing bacteria (AOB) in the DMPP-amended treatments. In acid soils, however, heterotrophic denitrification was the main source for N2 O production, and was not impacted by the application of DMPP. Our results provide robust evidence that the nitrification inhibitor DMPP can inhibit the N2 O production from nitrifier-induced denitrification, a potential significant source of N2 O production in agricultural soils.

The nitrification inhibitor 3,4-dimethylpyrazol-phosphate (DMPP) and the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) can mitigate N losses through reducing nitrification and ammonia volatilization, respectively. However, the impact of repeated applications of these inhibitors on nitrogen cycling microorganisms is not well documented. This study aimed to investigate the changes in the abundance and community structure of the functional microorganisms involved in nitrification and denitrification in Australian pasture soils after repeated applications of DMPP and nBTPT. Soil was collected in autumn and spring, 2014 from two pasture sites where control, urea, urea ammonium nitrate, and urea-coated inhibitors had been repeatedly applied over 2 year. Soil samples were analyzed to determine the potential nitrification rates (PNRs), the abundances of amoA, narG, nirK and bacterial 16S rRNA genes, and the community structure of ammonia oxidizers. Two years of urea application resulted in a significantly lower soil pH at Terang and a significant decrease in total bacterial 16S rRNA gene abundance at Glenormiston and led to significantly higher PNRs and abundances of ammonia oxidizers compared to the control. Amendment with either DMPP or nBTPT significantly decreased PNRs and the abundance of amoA and narG genes. However, there was no fertilizer- or inhibitor-induced change in the community structure of ammonia oxidizers. These results suggest that there were inhibitory effects of DMPP and nBTPT on the functional groups mediating nitrification and denitrification, while no significant impact on the community structure of ammonia oxidizers was observed. The application of nitrification or urease inhibitor appears to be an effective approach targeting specific microbial groups with minimal effects on soil pH and the total bacterial abundance.

The effluents from wastewater treatment plants have been recognized as a significant environmental reservoir of antibiotics and antibiotic resistance genes (ARGs). Reclaimed water irrigation (RWI) is increasingly used as a practical solution for combating water scarcity in arid and semiarid regions, however, impacts of RWI on the patterns of ARGs and the soil bacterial community remain unclear. Here, we used high-throughput quantitative PCR and terminal restriction fragment length polymorphism techniques to compare the diversity, abundance and composition of a broad-spectrum of ARGs and total bacteria in 12 urban parks with and without RWI in Victoria, Australia. A total of 40 unique ARGs were detected across all park soils, with genes conferring resistance to β-lactam being the most prevalent ARG type. The total numbers and the fold changes of the detected ARGs were significantly increased by RWI, and marked shifts in ARG patterns were also observed in urban parks with RWI compared to those without RWI. The changes in ARG patterns were paralleled by a significant effect of RWI on the bacterial community structure and a co-occurrence pattern of the detected ARG types. There were significant and positive correlations between the fold changes of the integrase intI1 gene and two β-lactam resistance genes (KPC and IMP-2 groups), but no significant impacts of RWI on the abundances of intI1 and the transposase tnpA gene were found, indicating that RWI did not improve the potential for horizontal gene transfer of soil ARGs. Taken together, our findings suggested that irrigation of urban parks with reclaimed water could influence the abundance, diversity, and compositions of a wide variety of soil ARGs of clinical relevance.Irrigation of urban parks with treated wastewater significantly increased the abundance and diversity of various antibiotic resistance genes, but did not significantly enhance their potential for horizontal gene transfer.

Heavy metal contamination is assumed to be a selection pressure on antibiotic resistance, but to our knowledge, evidence of the heavy metal-induced changes of antibiotic resistance is lacking on a long-term basis. Using quantitative PCR array and Illumina sequencing, we investigated the changes of a wide spectrum of soil antibiotic resistance genes (ARGs) following 4–5 year nickel exposure (0–800 mg kg–1) in two long-term experimental sites. A total of 149 unique ARGs were detected, with multidrug and β-lactam resistance as the most prevailing ARG types. The frequencies and abundance of ARGs tended to increase along the gradient of increasing nickel concentrations, with the highest values recorded in the treatments amended with 400 mg nickel kg–1 soil. The abundance of mobile genetic elements (MGEs) was significantly associated with ARGs, suggesting that nickel exposure might enhance the potential for horizontal transfer of ARGs. Network analysis demonstrated significant associations between ARGs and MGEs...

The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is a powerful tool that can be used to promote nitrogen (N) use efficiency and reduce N losses from agricultural systems by slowing nitrification. Mounting evidence has confirmed the functional importance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in nitrification and N 2 O production; however, their responses to DMPP amendment and the microbial mechanisms underlying the variable efficiencies of DMPP across different soils remain largely unknown. Here we compared the impacts of DMPP on nitrification and the dynamics of ammonia oxidizers between an acidic pasture soil and an alkaline vegetable soil using a 15 N tracing and 13 CO 2 -DNA–stable-isotope probing (SIP) technique. The results showed that DMPP significantly inhibited nitrification and N 2 O production in the vegetable soil only, and the transient inhibition was coupled with a significant decrease in AOB abundance. No significant effects on the community structure of ammonia oxidizers or the abundances of total bacteria and denitrifiers were observed in either soil. The 15 N tracing experiment revealed that autotrophic nitrification was the predominant form of nitrification in both soils. The 13 CO 2 -DNA–SIP results indicated the involvement of AOB in active nitrification in both soils, but DMPP inhibited the assimilation of 13 CO 2 into AOB only in the vegetable soil. Our findings provide evidence that DMPP could effectively inhibit nitrification through impeding the abundance and metabolic activity of AOB in the alkaline vegetable soil but not in the acidic pasture soil, possibly due to the low AOB abundance or the adsorption of DMPP by organic matter. IMPORTANCE The combination of the 15 N tracing model and 13 CO 2 -DNA–SIP technique provides important evidence that the nitrification inhibitor DMPP could effectively inhibit nitrification and nitrous oxide emission in an alkaline soil through influencing the abundance and metabolic activity of AOB. In contrast, DMPP amendment has no significant effect on nitrification or nitrifiers in an acidic soil, potentially owing to the low abundance of AOB and the possible adsorption of DMPP by organic matter. Our findings have direct implications for improved agricultural practices through utilizing the nitrification inhibitor DMPP in appropriate situations, and they emphasize the importance of microbial communities to the efficacy of DMPP.

Land application of agricultural wastes is considered as a promising bioremediation approach for cleaning up soils contaminated by aged polycyclic aromatic hydrocarbons (PAHs). However, it remains largely unknown about how microbial PAH-degraders, which play a key role in the biodegradation of soil PAHs, respond to the amendments of agricultural wastes. Here, a 90-day soil microcosm study was conducted to compare the effects of three agricultural wastes (i.e. WS, wheat stalk; MCSW, mushroom cultivation substrate waste; and CM, cow manure) on the dissipation of aged PAHs and the abundance and community structure of PAH-degrading microorganisms. The results showed that all the three agricultural wastes accelerated the dissipation of aged PAHs and significantly increased abundances of the bacterial 16S rRNA and PAH-degrading genes (i.e. pdo1 and nah). CM and MCSW with lower ratios of C:N eliminated soil PAHs more efficiently than WS with a high ratio of C:N. Low molecular weight PAHs were dissipated more quickly than those with high molecular weight. Phylogenetic analysis revealed that all of the nah and C12O clones were affiliated within Betaproteobacteria and Gammaproteobacteria, and application of agricultural wastes significantly changed the community structure of the microorganisms harboring nah and C12O genes, particularly in the CM treatment. Taken together, our findings suggest that the three tested agricultural wastes could accelerate the degradation of aged PAHs most likely through changing the abundances and community structure of microbial PAH degraders.

The emerging environmental spread of antibiotic-resistance genes (ARGs) and their subsequent acquisition by clinically relevant microorganisms is a major threat to public health. Animal manure has been recognized as an important reservoir of ARGs; however, the dissemination of manure-derived ARGs and the impacts of manure application on the soil resistome remain obscure. Here, we conducted a microcosm study to assess the temporal succession of total bacteria and a broad spectrum of ARGs in two contrasting soils following manure application from cattle that had not been treated with antibiotics. High-capacity quantitative PCR detected 52 unique ARGs across all the samples, with β-lactamase as the most dominant ARG type. Several genes of soil indigenous bacteria conferring resistance to β-lactam, which could not be detected in manure, were found to be highly enriched in manure-treated soils, and the level of enrichment was maintained over the entire course of 140 days. The enriched β-lactam resistance genes had significantly positive relationships with the relative abundance of the integrase intI1 gene, suggesting an increasing mobility potential in manure-treated soils. The changes in ARG patterns were accompanied by a significant effect of cattle manure on the total bacterial community compositions. Our study indicates that even in the absence of selective pressure imposed by agricultural use of antibiotics, manure application could still strongly impact the abundance, diversity and mobility potential of a broad spectrum of soil ARGs. Our findings are important for reliable prediction of ARG behaviors in soil environment and development of appropriate strategies to minimize their dissemination.

An intense current RF-linac for the far-infrared FEL is now under construction at CIAE. The normalized brightness of 3.4 x 10{sup 9} A/(m-rad) was obtained from the injector of the linac. An acceleration section with 9 cells will be connected with the injector to provide an electron beam for the 200 {mu}m FEL oscillator. In this paper, the late results from the injector beam test will be reported. The physical design and research progress in the acceleration section, beam transport, undulator as well as optical cavity will be introduced respectively.