Deterministic processes vary during community assembly for ecologically dissimilar taxa

The continuum hypothesis states that both deterministic and stochastic processes contribute to the assembly of ecological communities. However, the contextual dependency of these processes remains an open question that imposes strong limitations on predictions of community responses to environmental change. Here we measure community and habitat turnover across multiple vertical soil horizons at 183 sites across Scotland for bacteria and fungi, both dominant and functionally vital components of all soils but which differ substantially in their growth habit and dispersal capability. We find that habitat turnover is the primary driver of bacterial community turnover in general, although its importance decreases with increasing isolation and disturbance. Fungal communities, however, exhibit a highly stochastic assembly process, both neutral and non-neutral in nature, largely independent of disturbance. These findings suggest that increased focus on dispersal limitation and biotic interactions are necessary to manage and conserve the key ecosystem services provided by these assemblages

Suppressed N fixation and diazotrophs after four decades of fertilization

Background: N fixation is one of the most important microbially driven ecosystem processes on Earth, allowing N to enter the soil from the atmosphere, and regulating plant productivity. A question that remains to be answered is whether such a fundamental process would still be that important in an over-fertilized world, as the long-term effects of fertilization on N fixation and associated diazotrophic communities remain to be tested. Here, we used a 35-year fertilization experiment, and investigated the changes in N fixation rates and the diazotrophic community in response to long-term inorganic and organic fertilization. Results: It was found that N fixation was drastically reduced (dropped by 50%) after almost four decades of fertilization. Our results further indicated that functionality losses were associated with reductions in the relative abundance of keystone and phylogenetically clustered N fixers such as Geobacter spp. Conclusions: Our work suggests that long-term fertilization might have selected against N fixation and specific groups of N fixers. Our study provides solid evidence that N fixation and certain groups of diazotrophic taxa will be largely suppressed in a more and more fertilized world, with implications for soil biodiversity and ecosystem functions

Effect of electrolytes on electrochemical properties of MmNi(5)-based hydrogen storage alloy

This Project is financially supported by the National Natural Foundations of China (51261003), the Natural Foundations of Guangxi Province (2012GXNSFGA060002; 2011GXNSFD018004; 201201ZD009) Guangxi Experiment center of information science (20130113) and National students’ Innovative Project (101059530) and National students’ Innovative Project (101059530).The effect of electrolytes on the electrochemical properties of MmNi(3.68)Co(0.72)Mn(0.43)Al(0.17) hydrogen storage alloy electrodes has been investigated at 303 K and 273 K. Three electrolytes (EL1, EL2, EL3) were obtained by adding 2 wt%, 4 wt% and 6 wt% LiOH into the original electrolyte EO (6 M/ L KOH), respectively. The results indicate that the addition of LiOH improves the discharge capacity and cycle life at 303 K and 273 K. The highest maximum capacity and capacity retention (after 50th cycles) have been observed in electrolyte EL2. However, the high-rate dischargeability (HRD) decreases gradually from EO to EL3 at the two temperatures because of the addition of LiOH. The corrosion current I-corr from Tafel Polarization curves (TP) and the resistance of the oxide layer R-ol from electrochemical impedance spectroscopy (EIS) indicates that the alloy electrode worked in EL1 has a better anti-corrosion ability. The real surface area of the electrodes estimated with EIS analysis, decrease from 51.95 cm(2) in EO to 15.6 cm(2) in EL2, but increase to 31.59 cm(2) in EL3 after being fully activated. The additional LiOH improves the anti-pulverization ability of alloy powders, delay the loss of active elements within the alloy electrode, resulting in an inproved capacity retention of alloy electrode. Meanwhile, the electrochemical kinetics analysis suggests that the charge-transfer reaction at the interface of electrode surface and electrolyte is the rate-determining step when tested at 303 K and 273 K.Publisher PDFPeer reviewe

Ecological and Environmental Benefits of Planting Green Manure in Paddy Fields

Soil fertility management is one of the most important factors affecting crop production. The use of organic manures, including green manure, is an important strategy to maintain and/or improve soil fertility for sustainable crop production. Green manure generally refers to crops that can provide fertilizer sources for agricultural cash crops and improve soil productivity. The application of green manure is a traditional and valuable practice for agroecosystem management, particularly in paddy systems where green manure is rotated with rice. This paper systematically reviews the effects of green manure on soil microenvironments and greenhouse gas emissions, and the role of green manure in the phytoremediation of paddy fields. The paper concludes that green manure can not only affect soil nutrients and the microbial community, but also reduce greenhouse gas emissions and enhance soil remediation to some extent. Moreover, this review provides theoretical guidance on the selection of green manure germplasm and tillage methods for paddy fields of different climates and textures. However, this review only provides a macro-overview of the effects of green manure on soil nutrients, greenhouse gas emissions, and soil remediation in rice paddies based on a large number of previous studies, and does not provide a comprehensive quantitative assessment due to differences in green manure varieties and soil texture. The prospects for quantitative analysis of the ecological and economic effects of the sustainable development of green manure cultivation are discussed

Prevalence of Antibiotic Resistance Genes in Air-Conditioning Systems in Hospitals, Farms, and Residences

High-throughput quantitative PCR combined with Illumina sequencing and network analysis were used to characterize the antibiotic resistance gene (ARG) profiles in air-conditioning filters from different environments. In total, 177 ARGs comprising 10 ARG types were determined. The detectable numbers and the relative abundance of ARGs in hospitals and farms were significantly higher than those in city and village residences. Compared to hospitals, farms had a higher level of tetracycline, multidrug, integrase, and macrolide⁻lincosamide⁻streptogramin (MLS) B resistance genes but a lower level of beta-lactam resistance genes. The bl3_cpha gene was the most abundant resistance gene subtype in hospital samples with an abundance of 2.01 × 10−4 copies/16S rRNA, while a level of only 5.08 × 10−12 copies/16S rRNA was observed in farm samples. There was no significant difference in bacterial diversity among the hospitals, farms, and residences, and Proteobacteria was the most abundant phylum. Network analysis revealed that Proteobacteria and Actinobacteria were possible hosts of the beta-lactam, MLSB, aminoglycoside, multidrug, sulfonamide, and tetracycline resistance genes. The results demonstrate that ARGs exist in indoor environments and that farms and hospitals are important sources. This study provides a useful reference for understanding the distribution patterns and risk management of ARGs in indoor environments

Plasmid-Mediated Transfer of Antibiotic Resistance Genes in Soil

Due to selective pressure from the widespread use of antibiotics, antibiotic resistance genes (ARGs) are found in human hosts, plants, and animals and virtually all natural environments. Their migration and transmission in different environmental media are often more harmful than antibiotics themselves. ARGs mainly move between different microorganisms through a variety of mobile genetic elements (MGEs), such as plasmids and phages. The soil environment is regarded as the most microbially active biosphere on the Earth’s surface and is closely related to human activities. With the increase in human activity, soils are becoming increasingly contaminated with antibiotics and ARGs. Soil plasmids play an important role in this process. This paper reviews the current scenario of plasmid-mediated migration and transmission of ARGs in natural environments and under different antibiotic selection pressures, summarizes the current methods of plasmid extraction and analysis, and briefly introduces the mechanism of plasmid splice transfer using the F factor as an example. However, as the global spread of drug-resistant bacteria has increased and the knowledge of MGEs improves, the contribution of soil plasmids to resistance gene transmission needs to be further investigated. The prevalence of multidrug-resistant bacteria has also made the effective prevention of the transmission of resistance genes through the plasmid-bacteria pathway a major research priority

Effects of Elevated CO2 on Tomato (Lycopersicon esculentum Mill.) Growth and Rhizosphere Soil Microbial Community Structure and Functionality

Although elevated CO2 (eCO2) in the atmosphere is one of the main factors influencing climate and ecosystem stability, less research on eCO2 in greenhouse soil systems has been conducted, despite their prevalence. In this article, phospholipid fatty acid (PLFA) profiling, 16S rRNA and Internally Transcribed Spacer (ITS) gene sequencing and high-throughput quantity polymerase chain reactions (HT-qPCRs) for 72 biogeochemical cycling-related genes were used to reveal the comprehensive responses of microbes to 23 days eCO2 fumigation in the soil of a tomato greenhouse. Our results indicated that eCO2 significantly increased microbial biomass (p < 0.05). The fungal community was more susceptible to eCO2 than the bacterial community; the fungal alpha diversity indices decreased significantly under eCO2 (p < 0.05) and the abundance of Ascomycota and its lower level taxa also increased significantly (p < 0.01). The absolute abundance of numerous C, N, P, S and methane cycling related genes increased significantly (p < 0.05) under eCO2. Furthermore, the microbial community structure and function were correlated with certain measured plant characteristics. Hence, the microbial ecosystem of the tomato greenhouse soil system was stimulated under eCO2. These results contribute to a greater understanding of how eCO2 in the atmosphere affects terrestrial ecosystem stability

Antimicrobial Peptides from Black Soldier Fly (Hermetia illucens) as Potential Antimicrobial Factors Representing an Alternative to Antibiotics in Livestock Farming

Functional antimicrobial peptides (AMPs) are an important class of effector molecules of innate host immune defense against pathogen invasion. Inability of microorganisms to develop resistance against the majority of AMPs has made them alternatives to antibiotics, contributing to the development of a new generation of antimicrobials. Due to extensive biodiversity, insects are one of the most abundant sources of novel AMPs. Notably, black soldier fly insect (BSF; Hermetia illucens (Diptera: Stratiomyidae)) feeds on decaying substrates and displays a supernormal capacity to survive under adverse conditions in the presence of abundant microorganisms, therefore, BSF is one of the most promising sources for identification of AMPs. However, discovery, functional investigation, and drug development to replace antibiotics with AMPs from Hermetia illucens remain in a preliminary stage. In this review, we provide general information on currently verified AMPs of Hermetia illucens, describe their potential medical value, discuss the mechanism of their synthesis and interactions, and consider the development of bacterial resistance to AMPs in comparison with antibiotics, aiming to provide a candidate for substitution of antibiotics in livestock farming or, to some extent, for blocking the horizontal transfer of resistance genes in the environment, which is beneficial to human and animal welfare

Effects of Metal Oxide Nanoparticles on Nitrous Oxide Emissions in Agriculture Soil

Metal oxide nanoparticles (NPs) have been widely used in industrial and agricultural production and introduced into soils. The impact of these nanoparticles on soil nitrous oxide (N2O) emission is unclear. We conducted a microcosm experiment to investigate the effects of titanium oxide nanoparticles (TiO2 NPs), copper oxide nanoparticles (CuO NPs), and aluminum oxide nanoparticles (Al2O3 NPs) on soil N2O emissions and the abundance of functional genes related to N2O production/reduction. Compared to the soil without NPs addition, TiO2 NPs applied to the soil produced no significant effect on N2O emissions. The denitrification process in the soil exposed to CuO NPs was inhibited by reducing the functional genes related to nitrite reductase (nirK) and increasing N2O reductase (nosZ), while CuO NPs added to the soil stimulated the cumulative N2O emissions by 92.7%. After the application of Al2O3 NPs to the soil, the nitrification process was inhibited by inhibiting the functional genes of ammonia-oxidizing bacteria (AOB amoA), and soil N2O emission was reduced by 48.6%. Large-scale application of CuO NPs in agricultural soils may stimulate the N2O emissions resulting in potential environmental risks

Soil Texture Alters the Impact of Salinity on Carbon Mineralization

Soil salinization typically inhibits the ability of decomposer organisms to utilize soil organic matter, and an increase in soil clay content can mediate the negative effect of salinity on carbon (C) mineralization. However, the interactive effects of soil salt concentrations and properties on C mineralization remain uncertain. In this study, a laboratory experiment was performed to investigate the interactive effects of soil salt content (0.1%, 0.3%, 0.6% and 1.0%) and texture (sandy loam, sandy clay loam and silty clay soil with 6.0%, 23.9% and 40.6% clay content, respectively) on C mineralization and microbial community composition after cotton straw addition. With increasing soil salinity, carbon dioxide (CO2) emissions from the three soils decreased, but the effect of soil salinity on the decomposition of soil organic carbon varied with soil texture. Cumulative CO2 emissions in the coarse-textured (sandy loam and sandy clay loam) soils were more affected by salinity than those in the fine-textured (silty clay) soil. This difference was probably due to the differing responses of labile and resistant organic compounds to salinity across different soil texture. Increased salinity decreased the decomposition of the stable C pool in the coarse-textured soil, by reducing the proportion of fungi to bacteria, whereas it decreased the mineralization of the active C pool in the fine-textured soil through decreasing the Gram-positive bacterial population. Overall, our results suggest that soil texture controlled the negative effect of salinity on C mineralization through regulating the soil microbial community composition