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Chinese fir (Cunninghamia lanceolata) plantation is a dominant forest type and carbon sink in the subtropical region in China. An experiment with simulated nitrogen deposition (addition of 40 kg N ⋅ hm-2 ⋅ a-1) and drought (50% of precipitation exclusion, PE) was established in Chinese fir plantation in 2018. Soil samples (0-15 cm) were collected in summer (July 2020) and winter (January 2021). Soil microbial biomass, colony forming units (CFUs) and carbon source utilization were determined through phospholipid fatty acids (PLFAs), plate count, and Biolog methods, respectively. The results showed significant seasonal variations of PLFAs-related microbial biomass and composition. Soil bacterial and fungal CFUs tended to be decreased by nitrogen addition or precipitation exclusion treatment, and bacterial CFUs were more sensitive to the two treatments than fungal CFUs. Soil microbial function (i. e. carbon source utilization) was not affected by nitrogen addition, but significantly decreased by precipitation exclusion. There was a significant positive correlation between bacterial CFUs and microbial function, indicating the crucial roles of culturable bacteria in microbial carbon transformation. Our results highlight the critical effects of nitrogen deposition and 50% reduced precipitation on microbes in topsoil of fir plantation, with implications for unraveling soil microbial ecological function of subtropical forest ecosystem under global changes in future. [ABSTRACT FROM AUTHOR]

Land application of animal manure is a common agricultural practice potentially leading to dispersal and propagation of antibiotic resistance genes (ARGs) in environmental settings. However, the fate of resistome in agro-ecosystems over time following application of different manure sources has never been compared systematically. Here, soil microcosm incubation was conducted to compare effects of poultry, cattle and swine manures spiked with or without the antibiotic tylosin on the temporal changes of soil ARGs. The high-throughput quantitative PCR detected a total of 185 unique ARGs, with Macrolide-Lincosamide-Streptogramin B resistance as the most frequently encountered ARG type. The diversity and abundance of ARGs significantly increased following application of manure and manure spiked with tylosin, with more pronounced effects observed in the swine and poultry manure treatments than in the cattle manure treatment. The level of antibiotic resistance gradually decreased over time in all manured soils but was still significantly higher in the soils treated with swine and poultry manures than in the untreated soils after 130 days’ incubation. Tylosin-amended soils consistently showed higher abundances of ARGs than soils treated with manure only, suggesting a strong selection pressure of antibiotic-spiked manure on soil ARGs. The relative abundance of ARGs had significantly positive correlations with integrase and transposase genes, indicative of horizontal transfer potential of ARGs in manure and tylosin treated soils. Our findings provide evidence that application of swine and poultry manures might enrich more soil ARGs than cattle manure, which necessitates the appropriate treatment of raw animal manures prior to land application to minimise the spread of environmental ARGs. [ABSTRACT FROM AUTHOR]

Methylmercury (MeHg), a neurotoxin, is a global concern because of its potential risk to human and ecological health. Elevated mercury (Hg) concentrations were recently reported in the Tibetan Plateau (TP) due to increasing Hg input from distant regions, yet little is known about MeHg production and distribution in the terrestrial ecosystems of the TP. Here, we report longitudinal occurrence of MeHg and the factors regulating net MeHg production in 23 grassland sites from eastern to western TP. The soil MeHg content varied from 0.002 to 0.058 ng g −1 , with different distribution patterns between the eastern and western TP. There was a positive correlation between the MeHg concentration and the longitude after 90 °E, which is similar to the distribution patterns of the total mercury (THg), water and organic carbon in this region. Average MeHg concentration in topsoil is generally higher than that in subsoil. Our results show that MeHg concentration in soils of the TP is directly affected by soil water, potential microbial methylators and THg, while indirectly regulated by soil organic carbon through the microbial community and the longitude-dependent precipitation through soil water. Our study suggests that soil water is the most important driver regulating net MeHg production in the grasslands of the TP. These findings have important implications for unraveling the mechanism of net production of MeHg in high-altitude environments. [ABSTRACT FROM AUTHOR]

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. One-sentence summary 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. [ABSTRACT FROM AUTHOR]

Currently, rice straw return in place of burning is becoming more intensive in China than observed previously. However, little is known on the effect of returned rice straw on mercury (Hg) methylation and microbial activity in contaminated paddy fields. Here, we conduct a microcosm experiment to evaluate the effect of rice straw amendment on the Hg methylation and potential nitrification in two paddy soils with distinct Hg levels. Our results show that amended rice straw enhanced Hg methylation for relatively high Hg content soil, but not for low Hg soil, spiking the same additional fresh Hg. methylmercury (MeHg) concentration was significantly correlated to the dissolved organic carbon (DOC) content and relative abundance of dominant microbes associated with Hg methylation. Similarly, amended rice straw was found to only enhance the potential nitrification rate in soil with relatively high Hg content. These findings provide evidence that amended rice straw differentially modulates Hg methylation and nitrification in Hg contaminated soils possibly resulting from different characteristics in the soil microbial community. This highlights that caution should be taken when returning rice straw to contaminated paddy fields, as this practice may increase the risk of more MeHg production. Main finding Rice straw amendment enhanced both Hg methylation and nitrification potential in the relatively high, but not low, Hg soil. [ABSTRACT FROM AUTHOR]

• Microbial residues and plant lignin contributed more to SOC in > 80-year forests. • N addition increased microbial residues and plant lignin in < 40-year forests. • P addition decreased muramic acid in the < 40-year forests. • Microbe and enzyme activity affect microbial residues and plant lignin retention. Soil microbial residues and plant-derived compounds are important components of the stable carbon (C) pool in forest soil. It is not well understood how microbial residues and plant lignin phenols respond to nutrient inputs in subtropical forests of different ages, especially in mature forest stands. Here, a 5-year nitrogen (N) and phosphorus (P) fertilization (addition) management experiment was conducted in two stages of subtropical forests (<40- and > 80-year). We found that the concentrations of amino sugars (i.e., microbial residues) and plant lignin phenols and their contributions to soil organic carbon (SOC) were significantly higher in the > 80-year forests than in the < 40-year forests. In the < 40-year forests, N addition increased amino sugars and lignin phenols and their contributions to SOC, whereas P addition decreased muramic acid (bacterial-derived) and its contribution to SOC. In the > 80-year forests, however, N and P addition had no significant effect on amino sugars and lignin phenols and their contributions to SOC. Overall, soil total amino sugars and lignin phenols could be directly and indirectly affected by forest age and N addition, and could be only indirectly impacted by P addition. Our results suggest that microbial residues and plant lignin phenols are sensitive to the nutrient additions in the young forests, which have a greater potential for the soil stable C sequestration in comparison with the mature forests. [ABSTRACT FROM AUTHOR]

The low utilization efficiency of nitrogen fertilizer in agricultural ecosystem has caused serious economic and environmental issues. Dicyandiamide (DCD) is a widely used nitrification inhibitor, which can inhibit nitrification via affecting ammonia oxidizing microorganisms with minimal influence on other soil microorganisms, thereby reducing the leaching of nitrate and emission of greenhouse gases. The factors influencing the efficiency of DCD in soil include soil temperature, pH, texture, organic matter, moisture, etc. Recently, the application of molecular methods in agricultural systems has shed new light on the microbial mechanism underlying nitrification inhibition by DCD. In this review, the enzymatic inhibition mechanism, the application effects and their influence factors of DCD were summarized, and the prospects of its application were discussed as well. [ABSTRACT FROM AUTHOR]

Archaea, as the third life form distinct from bacteria and eukaryota, widely distribute in various kinds of habitats, and play important roles in the biogeochemical cycles of carbon and nitrogen and in ecosystem functioning. As the biomarker of archaea, archaeal membrane lipids can be used to investigate the archaeal community composition and its responses to the environment. This paper introduced the structural characteristics of archaeal membrane lipids and the differences in the membrane lipids composition among different archaeal communities, and discussed the feasibility of using archeal membrane lipids in depicting archaeal community composition. The abundance of archaeal membrane lipids in the environment could be used to characterize the biomass of archaea, and the related results could complement and ascertain each other with the DNA-based biomolecular approaches on the accuracy, analysis efficiency, and cost. Based on the description of the difficulties and importance of using archaeal membrane lipids to analyze the composition and abundance of archaeal communities, and by linking to the environmental factors such as temperature and pH that affected the archaeal community composition, the relationships between archaea and their habitats were further expatiated, and the evolution process of archaeal communities and its application prospects in the studies of geochemistry and geological events were analyzed. [ABSTRACT FROM AUTHOR]

Eukaryota, bacteria and archaea are the three domains of life. As the third domain of life, archaea has been found not only in extreme environments such as high-temperature, high-saline, and extremely acid habitats, but also in moderate environments including ocean, lake and soil, which implies that archaea may contribute greatly to various ecosystems. By targeting the 16S rRNA gene with real-time PCR approaches, this paper studied the abundance of archaea, crenarchaea and bacteria from two agricultural soil profiles and two long-term fertilization stations Qiyang (QY) and Fengqiu (FQ). The 16S rRNA gene copy number of crenarchaea was 1-2 orders of magnitude lower than that of archaea, and the order of these three groups was crenarchaea < archaea < bacteria. The ratios of both archaea and crenarchaea to bacteria increased with soil depth. The abundance of archaea and crenarchaea had significantly different responses to different fertilization treatments. In QY station, the copy numbers of archaeal and bacterial 16S rRNA gene had significant positive correlations with soil pH (r=0.850, P<0.01 and r=0.676, P<0.05, respectively); in FQ station, all the 16S rRNA gene copy numbers of archaea, crenarchaea and bacteria had no significant correlations with soil pH, but significantly correlated with soil organic matter (r=0.783, P<0.05;r=0.827,P<0.05;r=0.767, P<0.05, respectively). To understand the distribution of archaea and crenarchaea in agricultural soil could provide important information to evaluate their ecological functions in soil ecosystem and element cycling. [ABSTRACT FROM AUTHOR]

Abstract: Soil acidification can result in the release of heavy metals stabilized by soil components into soil solution, and therefore it causes ecological risk. The kinetics of Cd desorption from two Chinese soils (ultisol and oxisol) distributed in the acid rain sensitive areas of southern China, were studied using a flow-stirred method under simulated acid rain conditions. Cd desorption was well described by the first-order kinetic equation. Percentages of Cd desorbed were 80–99% in ultisol and 25–28% in oxisol, respectively. Cd desorption, regarded as a heterogeneous diffusion in soils, could be also fitted by the Elovich equation. The desorption process could be divided into a fast reaction and a slow reaction, which were corresponded to the exchangeable and the specific sorbed Cd, respectively. The obtained results are essential to understand the process of heavy metal release under acid deposition conditions and to evaluate the ecological risk of acid deposition in those acid rain sensitive areas of China. [Copyright &y& Elsevier]

Biogenic Mn oxides exert important controls on trace metal cycling in aquatic and soil environments. A Mn-oxidizing bacterium Bacillus sp. WH4 was isolated from Fe¿Mn nodules of an agrudalf in central China. The biogenic Mn oxides formed by mediation of this Mn oxidizing microorganism were identified as short-ranged and nano-sized Mn oxides. Cd adsorption isotherms, pH effect on adsorption and kinetics were investigated in comparison with an abiotic Mn oxide todorokite. Maximum adsorption of Cd to the biogenic Mn oxides and todorokite was 2.04 and 0.69mmol g¿1 sorbent, respectively. Thus, the biogenic Mn oxides were more effective Cd adsorbents than the abiotic Mn oxide in the aquatic environment. The findings could improve our knowledge of biogenic Mn oxides formation in the environment and their important roles in the biogeochemical cycles of heavy metals. [Copyright &y& Elsevier]

Copper (Cu) is massively used as feed additives in intensive farms, and the discharge and utilization of livestock wastes may cause certain environmental problems. In this paper, a cultivated black soil in Northeast China was sampled, and added with pig manures that contained different concentration of Cu to simulate the vegetable soil under different years of pig manure fertilization. With this soil, a pot experiment was conducted to study the effects of soil Cu accumulation via the application of the pig manures on the aboveground biomass and its Cu concentration of pakchoi (Brassica chinensis L.), soil microbial biomass carbon, and soil enzymes (dehydrogenase, urease, and acid phosphatase) activities. The results showed that pig manure application increased the aboveground biomass of pakchoi significantly, but had no significant effects on the aboveground biomass Cu concentration. Under the application of pig manure, soil dehydrogenase and urease activities increased in a definite period of time, but their activities as well as soil acid phosphatase activity were depressed gradually with the increase of soil Cu concentration. When the soil total Cu concentration reached 301.3 mg·kg-1, the aboveground biomass of pakchoi, soil microbial biomass carbon, and the activities of dehydrogenase, urease, and acid phosphatase were greatly reducd. The aboveground biomass Cu concentration of pakchoi had significant positive correlations with the concentration of soil total and water soluble Cu (P<0.01), while the aboveground biomass was negatively correlated with soil total Cu concentration (P<0.05). It was suggested that the threshold value of Cu in black soil under vegetable cultivation should be less than 301.3 mg·kg-1. [ABSTRACT FROM AUTHOR]

Several Mn oxide minerals commonly occurring in soils were synthesized by modified or optimized methods. The morphologies, structures, compositions and surface properties of the synthesized Mn oxide minerals were characterized. Adsorption and redox reactions of heavy metals on these minerals in relation to the mineral structures and surface properties were also investigated. The synthesized birnessite, todorokite, cryptomelane, and hausmannite were single-phased minerals and had the typical morphologies from analyses of XRD and TEM/ED. The PZCs of the synthesized birnessite, todorokite and cryptomelane were 1. 75, 3. 50 and 2. 10, respectively. The magnitude order of their surface variable negative charge was: birnessite≥cryptomelane>todorokite. The hausmannite had a much higher PZC than others with the least surface variable negative charge. Birnessite exhibited the largest adsorption capacity on heavy metals Pb2+, Cu2+, Co2+, Cd2+ and Zn2+, while hausmannite the smallest one. Birnessite, cryptomelane and todorokite showed the greatest adsorption capacity on Pb2+ among the tested heavy metals. Hydration tendency (pK 1) of the heavy metals and the surface variable charge of the Mn minerals had significant impacts on the adsorption. The ability in Cr(III) oxidation and concomitant release of Mn2+ varied greatly depending on the structure, composition, surface properties and crystallinity of the minerals. The maximum amounts of Cr(III) oxidized by the Mn oxide minerals in order were (mmol/kg): birnessite (1330. 0)>cryptomelane (422. 6)>todorokite (59. 7)>hausmannite (36. 6). [Copyright &y& Elsevier]

Microbiota in urban green spaces underpin ecosystem services that are essential to environmental health and human wellbeing. However, the factors shaping the microbial communities in urban green spaces, especially those associated with turf grass phyllosphere, remain poorly understood. The lack of this knowledge greatly limits our ability to assess ecological, social and recreational benefits of urban green spaces in the context of global urbanization. In this study, we used amplicon sequencing to characterize soil and grass phyllosphere bacterial communities in 40 urban green spaces and three minimally disturbed national parks in Victoria, Australia. The results indicated that urbanization might have shown different impacts on soil and grass phyllosphere microbial communities. The bacterial diversity in soil but not in grass phyllosphere was significantly higher in urban green spaces than in national parks. Principal coordinate analysis revealed significant differences in the overall patterns of bacterial community composition between urban green spaces and national parks for both soil and grass phyllosphere. Industrial development, as represented by the number of industries in the region, was identified as a key driver shaping the bacterial community profiles in urban green spaces. Variation partitioning analysis suggested that industrial factors together with their interaction with other factors explained 20% and 28% of the variances in soil and grass phyllosphere bacterial communities, respectively. The findings highlight the importance of industrial development in driving the spatial patterns of urban microbiomes, and have important implication for the management of microbiomes in urban green spaces. Image 1 • Urbanization might differently impact soil and grass phyllosphere microbial communities in urban green spaces. • Industrial development was a key driver shaping the bacterial community profiles in urban green spaces. • The impact of urbanization on the bacterial communities might derive from increased environmental pollution. [ABSTRACT FROM AUTHOR]

Plant microbiome, as the second genome of plant, and the interface between human and environmental microbiome, represents a potential pathway of human exposure to environmental pathogens and resistomes. However, the impact of host identity on the profile of resistomes in plant phyllosphere is unclear and this knowledge is vital for establishing a framework to evaluate the dissemination of antibiotic resistance via the plant microbiome. Here, we explored the phyllosphere microbiome and resistomes in 12 selected plant species. By using High-throughput quantitative PCR, we identified a total of 172 unique resistance genes in plant phyllosphere microbiome, which was significantly divergent from the profile of resistomes in associated soils (Adonis, P < 0.01). Host identity had a significant effect on the plant resistome, which was mainly attributed to the dissimilarity of phyllosphere bacterial phylogeny across different plants. We identified a core set of plant resistomes shared in more than 80% of samples, which accounted for more than 64% of total resistance genes. These plant core resistomes conferred resistance to antibiotics that are commonly administered to humans and animals. Our findings extend our knowledge regarding the resistomes in plant phyllosphere microbiome and highlight the role of host identity in shaping the plant associated antibiotic resistance genes. Image 1 • Plant phyllosphere microbiome is an important reservoir of ARGs. • Host identities significantly affect the profile of plant resistomes. • A core plant associated resistomes was identified. Main finding : Plant phyllosphere microbiome is an important reservoir of ARGs and host identity had a significant effect on the plant associated resistome. [ABSTRACT FROM AUTHOR]