Eco-evolutionary strategies for relieving carbon limitation under salt stress differ across microbial clades.

With the continuous expansion of saline soils under climate change, understanding the eco-evolutionary tradeoff between the microbial mitigation of carbon limitation and the maintenance of functional traits in saline soils represents a significant knowledge gap in predicting future soil health and ecological function. Through shotgun metagenomic sequencing of coastal soils along a salinity gradient, we show contrasting eco-evolutionary directions of soil bacteria and archaea that manifest in changes to genome size and the functional potential of the soil microbiome. In salt environments with high carbon requirements, bacteria exhibit reduced genome sizes associated with a depletion of metabolic genes, while archaea display larger genomes and enrichment of salt-resistance, metabolic, and carbon-acquisition genes. This suggests that bacteria conserve energy through genome streamlining when facing salt stress, while archaea invest in carbon-acquisition pathways to broaden their resource usage. These findings suggest divergent directions in eco-evolutionary adaptations to soil saline stress amongst microbial clades and serve as a foundation for understanding the response of soil microbiomes to escalating climate change.

Urban green space area mitigates the accumulation of heavy metals in urban soils.

Despite that the heavy metals in urban soils pose a threat to public health, the critical factors that influence their concentrations in urban soils are not well understood. In this study, we conducted a survey of surface soil samples from urban green spaces in Shanghai, to analyze the concentrations of the key heavy metals. The results showed that Zn was the most abundant metal with an average concentration of 122.99 mg kg-1, followed by Pb (32.72 mg kg-1) and Cd (0.23 mg kg-1). All concentrations were found to be below the risk screening values defined by the National Environmental Quality Standards for soils of development land in China (GB36600-2018), indicating no current risk in Shanghai. However, there was a clear accumulation of heavy metals, as the mean concentrations were significantly higher than the background values. Furthermore, we explored the relationships between key heavy metals with population density, GDP and green space area. Both Spearman correlation and Random Forest analysis indicated that per capita green space area (pGSA) and population density were the most crucial factors influencing the status of heavy metals in urban soils, unlike edaphic factors e.g. SOM content in farmland soils. Specifically, there was a significantly positive linear correlation between heavy metal concentrations and population density, with correlation coefficients ranging from 0.3 to 0.4. However, the correlation with pGSA was found to be non-linear. The nonlinear regression analysis revealed threshold values between heavy metals concentrations and pGSA (e.g Zn 22.22 m2, Pb 24.92 m2, and Cd 25.92 m2), with a sharp reduction in heavy metal concentrations below the threshold and a slow reduction above the threshold. It suggests that an increase in per capita green space area can mitigate the accumulation of heavy metals caused by growing population density, but the effect is limited after the threshold. Our findings not only provide insights into the distribution patterns of heavy metals in the urban soils at the local scale, but also contribute to the urban greening at the global scale and offer guidance for city planning in the face of increasing population densities over the coming decades.

Innovative strategy for the conservation of a millennial mausoleum from biodeterioration through artificial light management.

Artificial lights can cause critical microbial biodeterioration of heritage monuments by promoting the outbreak of phototrophic microbiomes when they are used for touristic viewing. Here, with the ultimate aim of providing innovative solutions for the conservation and visiting of such monuments, we conducted a pioneering two-year in situ manipulative experiment to evaluate the impacts of different artificial light wavelengths (i.e., blue, green and red lights compared to white light) on the phototrophic microbiome of a millennial Chinese imperial mausoleum. Our results show that artificial light can shape the ecophysiological features of the phototrophic bacteriome in this monument and reduce its potential for further biodeterioration. In general, Cyanobacteria dominated (42.0% of the total relative abundance) the phototrophic bacteriome of this cultural relic; however, they were also very sensitive to the choice of artificial light. Compared to white light, monochromatic light, especially green light, reduced Cyanobacteria abundances (18.6%) by decreasing photosynthetic pigment abundances (42.9%); decreased the abundances of heterotrophic species belonging to Proteobacteria (4.5%) and the proportion of genes (6.1%) associated with carbon (i.e., carbon fixation), nitrogen (i.e., denitrification), and sulfur (i.e., dissimilatory sulfate reduction) cycling; and further decreased organic acid (10.1-14.1%) production of the phototrophic bacteriome, which is known to be involved in biodeterioration. Taken together, our findings constitute a major advancement in understanding how light wavelengths influence the phototrophic microbiome in cultural relics, and we found that artificial lights with certain wavelengths (e.g., green light) can help long-term conservation while allowing tourism activities.

Water availability creates global thresholds in multidimensional soil biodiversity and functions.

Soils support an immense portion of Earth's biodiversity and maintain multiple ecosystem functions which are essential for human well-being. Environmental thresholds are known to govern global vegetation patterns, but it is still unknown whether they can be used to predict the distribution of soil organisms and functions across global biomes. Using a global field survey of 383 sites across contrasting climatic and vegetation conditions, here we showed that soil biodiversity and functions exhibited pervasive nonlinear patterns worldwide and are mainly governed by water availability (precipitation and potential evapotranspiration). Changes in water availability resulted in drastic shifts in soil biodiversity (bacteria, fungi, protists and invertebrates) and soil functions including plant-microbe interactions, plant productivity, soil biogeochemical cycles and soil carbon sequestration. Our findings highlight that crossing specific water availability thresholds can have critical consequences for the provision of essential ecosystem services needed to sustain our planet.

The impact of Ag nanoparticles on methane emission in two typical paddy soils.

Numerous applications of Ag nanoparticles (AgNPs) have increased the likelihood of their release and accumulation in agroecosystem. Thus far, few studies have evaluated the impacts of AgNPs to soil methane emissions and the microbial dynamics. In this study, microcosmic experiments were conducted to investigate the responses of methanogenic processes from two paddy soils (Cambisols and Ultisols) subjected to four AgNPs doses (0.1, 1, 10 and 50 mg/kg). The results showed that 0.1 and 1 mg/kg AgNPs had no significant effects on CH4 emissions, but 50 mg/kg AgNPs increased soil CH4 emissions in both paddy soils. The aggravation effect of AgNPs on CH4 emissions was more apparent in Ultisols compared to Cambisols paddy soils. Real-time PCR suggested that 50 mg/kg AgNPs significantly increased the ratio of methanogenic to bacterial gene for both paddy soils. Amplicon sequencing indicated that methanogenic community was clustered into a separate group after 50 mg/kg AgNPs exposure. Structural equation model illustrated that Methanosarcinales was both significantly responded to AgNPs in Cambisols and Ultisols soils; however, Methanocellales significantly responded to AgNPs only in Cambisols soils. Subsequently, uncontrolled use of AgNPs may account as an environmental risk due to the potentially increased soil CH4 emissions in paddy ecosystems.

Beyond the snapshot: identification of the timeless, enduring indicator microbiome informing soil fertility and crop production in alkaline soils.

BACKGROUND: Microorganisms are known to be important drivers of biogeochemical cycling in soil and hence could act as a proxy informing on soil conditions in ecosystems. Identifying microbiomes indicative for soil fertility and crop production is important for the development of the next generation of sustainable agriculture. Earlier researches based on one-time sampling have revealed various indicator microbiomes for distinct agroecosystems and agricultural practices as well as their importance in supporting sustainable productivity. However, these microbiomes were based on a mere snapshot of a dynamic microbial community which is subject to significant changes over time. Currently true indicator microbiomes based on long-term, multi-annual monitoring are not available. RESULTS: Here, using samples from a continuous 20-year field study encompassing seven fertilization strategies, we identified the indicator microbiomes ecophysiologically informing on soil fertility and crop production in the main agricultural production base in China. Among a total of 29,184 phylotypes in 588 samples, we retrieved a streamlined consortium including 2% of phylotypes that were ubiquitously present in alkaline soils while contributing up to half of the whole community; many of them were associated with carbon and nutrient cycling. Furthermore, these phylotypes formed two opposite microbiomes. One indicator microbiome dominated by Bacillus asahii, characterized by specific functional traits related to organic matter decomposition, was mainly observed in organic farming and closely associated with higher soil fertility and crop production. The counter microbiome, characterized by known nitrifiers (e.g., Nitrosospira multiformis) as well as plant pathogens (e.g., Bacillus anthracis) was observed in nutrient-deficit chemical fertilizations. Both microbiomes are expected to be valuable indictors in informing crop yield and soil fertility, regulated by agricultural management. CONCLUSIONS: Our findings based on this more than 2-decade long field study demonstrate the exciting potential of employing microorganisms and maximizing their functions in future agroecosystems. Our results report a "most-wanted" or "most-unwanted" list of microbial phylotypes that are ready candidates to guide the development of sustainable agriculture in alkaline soils.

Organic fertilizer potentiates the transfer of typical antibiotic resistance gene among special bacterial species.

The propagation of antibiotic resistance genes (ARGs) in environments has evoked many attentions, however, how to identify their host pathogenic bacteria in situ remains a great challenge. Here we explored the bacterial host distribution and dissemination of a typical ARG, sul1 gene, in agricultural soils through the simultaneous detection of sul1 and its host 16S rRNA gene by emulsion paired isolation and concatenation PCR (epicPCR). Compared to chemical fertilizer, organic fertilizer (chicken manure) led to a higher prevalence of sul1 gene in the soil, and dominant bacterial hosts of sul1 gene were classified into Proteobacteria and Bacteroidetes phyla. Additionally, significant higher diversity of antibiotic resistance bacteria (ARB), higher rate of horizontal gene transfer (HGT), higher rate of mobile genetic elements (MGE) and higher proportion of pathogens were all observed in the treatment of organic fertilizer. This study alerts potential health risks of manure applications in agricultural soils.

Microbial Community Composition and Activity in Saline Soils of Coastal Agro-Ecosystems.

Soil salinity is a serious problem for agriculture in coastal regions. Nevertheless, the effects of soil salinity on microbial community composition and their metabolic activities are far from clear. To improve such understanding, we studied microbial diversity, community composition, and potential metabolic activity of agricultural soils covering non-, mild-, and severe-salinity. The results showed that salinity had no significant effect on bacterial richness; however, it was the major driver of a shift in bacterial community composition and it significantly reduced microbial activity. Abundant and diverse of microbial communities were detected in the severe-salinity soils with an enriched population of salt-tolerant species. Co-occurrence network analysis revealed stronger dependencies between species associated with severe salinity soils. Results of microcalorimetric technology indicated that, after glucose amendment, there was no significant difference in microbial potential activity among soils with the three salinity levels. Although the salt prolonged the lag time of microbial communities, the activated microorganisms had a higher growth rate. In conclusion, salinity shapes soil microbial community composition and reduces microbial activity. An addition of labile organic amendments can greatly alleviate salt restrictions on microbial activity, which provides new insight for enhancing microbial ecological functions in salt-affected soils.

Multikingdom interactions govern the microbiome in subterranean cultural heritage sites.

SignificanceThe conservation of historical relics against microbial biodeterioration is critical to preserving cultural heritages. One major challenge is our limited understanding of microorganisms' dispersal, colonization, and persistence on relics after excavation and opening to external environments. Here, we investigate the ecological and physiological profiles of the microbiome within and outside the Dahuting Han Dynasty Tomb with a 1,800-y history. Actinobacteria dominate the microbiome in this tomb. Via interkingdom signaling mutualism, springtails carry Actinobacteria as one possible source into the tomb from surrounding environments. Subsequently, Actinobacteria produce cellulases combined with antimicrobial substances, which helps them to colonize and thrive in the tomb via intrakingdom competition. Our findings unravel the ecology of the microbiomes colonizing historical relics and provide help for conservation practices.

Organic and Inorganic Amendments Shape Bacterial Indicator Communities That Can, In Turn, Promote Rice Yield.

The dynamic patterns of the belowground microbial communities and their corresponding metabolic functions, when exposed to various environmental disturbances, are important for the understanding and development of sustainable agricultural systems. In this study, a two-year field experiment with soils subjected to: chemical fertilization (F), mushroom residues (MR), combined application of chemical fertilizers and mushroom residues (MRF), and no-fertilization (CK) was conducted to evaluate the effect of fertilization on the soil bacterial taxonomic and functional compositions as well as on the rice yield. The highest rice yield was obtained under MRF. Soil microbial properties (microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), urease, invertase, acid phosphatase, and soil dehydrogenase activities) reflected the rice yield better than soil chemical characteristics (soil organic matter (SOM), total N (TN), total K (TK), available P (AP), available K (AK), and pH). Although the dominant bacterial phyla were not significantly different among fertilizations, 10 bacterial indicator taxa that mainly belonged to Actinobacteria (Nocardioides, Marmoricola, Tetrasphaera, and unclassified Intrasporangiaceae) with functions of xenobiotic biodegradation and metabolism and amino acid and nucleotide metabolism were found to strongly respond to MRF. Random Forest (RF) modeling further revealed that these 10 bacterial indicator taxa act as drivers for soil dehydrogenase, acid phosphatase, pH, TK, and C/N cycling, which directly and/or indirectly determine the rice yield. Our study demonstrated the explicit links between bacterial indicator communities, community function, soil nutrient cycling, and crop yield under organic and inorganic amendments, and highlighted the advantages of the combined chemical and organic fertilization in agroecosystems.

Temperature thresholds drive the global distribution of soil fungal decomposers.

Unraveling the biogeographic pattern of soil fungal decomposers along temperature gradients-in smooth linearity or an abrupt jump-can help us connect the global carbon cycle to global warming. Through a standardized global field survey, we identify the existence of temperature thresholds that control the global distribution of soil fungal decomposers, leading to abrupt reductions in their proportion (i.e., the relative abundance in the fungal community) immediately after crossing particular air and soil temperature thresholds. For example, small increases over the mean annual temperature threshold of ~9°C result in abrupt reductions in their proportion, paralleling a similar temperature threshold for soil carbon content. We further find that the proportion of soil fungal decomposers is more sensitive to temperature increases under arid conditions. Given the positive correlation between the global distributions of fungal decomposers and soil heterotrophic respiration, the reported temperature-driven abrupt reductions in fungal decomposers could further suppress their driven soil decomposition processes and reduce carbon fluxes from soils to the atmosphere with implications for climate change feedback. This work not only advances the current knowledge on the global distribution of soil fungal decomposers, but also highlights that small changes in temperature around certain thresholds can lead to potential unexpected consequences in global carbon cycling under projected climate change.

Organic matter- and temperature-driven deterministic assembly processes govern bacterial community composition and functionality during manure composting.

Although many studies have shown that microbial communities play important roles in organic waste composting due to the involvement of specific microbial taxa with metabolic functions, the underlying ecological processes of community assembly and governing factors remain elusive. Thus, a chicken manure composting experiment as a model system of microbially mediated organic waste composting was conducted. Ecological null modeling and metabolic functional prediction combined with electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were used to quantify assembly processes governing bacterial community composition and functions during composting. The results showed the predominant role of deterministic assembly processes in shifting community compositions both across and within composting stages. Stochastic assembly processes also concomitantly influenced microbial community compositions. Changes in the organic matter (OM) content and its chemical properties and temperature governed bacterial community assembly processes throughout the stages by selecting specific bacterial taxa such as Cardiobacteriales, Bacteroidales, and Lachnospiraceae on day 1, Firmicutes on days 6, 25 and 37, and Sphingobacteriales, Thermoactinomycetaceae, Actinobacteria, and Novibacillus on day 45. These taxa ultimately influenced community functions such as environmental information processing, carbohydrate and amino acid metabolism, cellular processes, and genetic information processes involved in composting. Taken together, this study indicates that deterministic assembly processes governed by OM content and quality as well as temperature influenced microbial community turnover and determined community functions during composting. These results are important for better understanding and predicting microbial-driven composting and for ultimately manipulating microorganisms for environmentally-friendly composting outcomes.

[Effects of salinity on soil bacterial diversity and assembly processes in coastal soils.] / ç›åº¦å¯¹æ»¨æµ·åœŸå£¤ç»†èŒå¤šæ ·æ€§å’Œç¾¤è½æž„å»ºè¿‡ç¨‹çš„å½±å“.

Coastal saline soil is an important reserve resource of agricultural land. Soil microorganisms play a key role in soil nutrient cycling. However, it is still far from clear about the effects of salinity on soil microbial community. We examined the effects of salinity on soil bacterial abundance, diversity, and community assembly, by collecting soil samples in coastal areas with three salinity levels (non-, mild-, and severe-salinity). Our results showed that the activity of dehydrogenase and the abundance of bacteria significantly decreased in the severe-saline soils, while the diversity of bacteria remained unchanged, compared with non- and mild-saline soils. Bacterial communities were clustered by salinity. Null model was used to infer bacterial community assembly processes. Salinity was the main driving factor for bacterial community assembly. Deterministic process driven by salinity played a leading role in controlling bacterial community composition in coastal saline soil. These findings suggested that coastal saline soils contain abundant microbes within the salinity range, and have a biological basis for soil improvement. Due to the high deterministic process of microbial community assembly, it would be difficult for alien species to colonize coastal saline soils. Salt-tolerant and indigenous strains are recommended when using microbial technology to reclaim coastal saline soils.

Important ecophysiological roles of non-dominant Actinobacteria in plant residue decomposition, especially in less fertile soils.

BACKGROUND: Microbial-driven decomposition of plant residues is integral to carbon sequestration in terrestrial ecosystems. Actinobacteria, one of the most widely distributed bacterial phyla in soils, are known for their ability to degrade plant residues in vitro. However, their in situ importance and specific activity across contrasting ecological environments are not known. Here, we conducted three field experiments with buried straw in combination with microcosm experiments with 13C-straw in paddy soils under different soil fertility levels to reveal the ecophysiological roles of Actinobacteria in plant residue decomposition. RESULTS: While accounting for only 4.6% of the total bacterial abundance, the Actinobacteria encoded 16% of total abundance of carbohydrate-active enzymes (CAZymes). The taxonomic and functional compositions of the Actinobacteria were, surprisingly, relatively stable during straw decomposition. Slopes of linear regression models between straw chemical composition and Actinobacterial traits were flatter than those for other taxonomic groups at both local and regional scales due to holding genes encoding for full set of CAZymes, nitrogenases, and antibiotic synthetases. Ecological co-occurrence network and 13C-based metagenomic analyses both indicated that their importance for straw degradation increased in less fertile soils, as both links between Actinobacteria and other community members and relative abundances of their functional genes increased with decreasing soil fertility. CONCLUSIONS: This study provided DNA-based evidence that non-dominant Actinobacteria plays a key ecophysiological role in plant residue decomposition as their members possess high proportions of CAZymes and as a group maintain a relatively stable presence during plant residue decomposition both in terms of taxonomic composition and functional roles. Their importance for decomposition was more pronounced in less fertile soils where their possession functional genes and interspecies interactions stood out more. Our work provides new ecophysiological angles for the understanding of the importance of Actinobacteria in global carbon cycling. Video abstract.

Evaluation of Microbe-Driven Soil Organic Matter Quantity and Quality by Thermodynamic Theory.

Microbial communities, coupled with substrate quality and availability, regulate the stock (formation versus mineralization) of soil organic matter (SOM) in terrestrial ecosystems. However, our understanding of how soil microbes interact with contrasting substrates influencing SOM quantity and quality is still very superficial. Here, we used thermodynamic theory principles and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) to evaluate the linkages between dissolved organic matter (DOM [organic substrates in soil that are readily available]), thermodynamic quality, and microbial communities. We investigated soils from subtropical paddy ecosystems across a 1,000-km gradient and comprising contrasting levels of SOM content and nutrient availability. Our region-scale study suggested that soils with a larger abundance of readily accessible resources (i.e., lower Gibbs free energy) supported higher levels of microbial diversity and higher SOM content. We further advocated a novel phylotype-level microbial classification based on their associations with OM quantities and qualities and identified two contrasting clusters of bacterial taxa: phylotypes that are highly positively correlated with thermodynamically favorable DOM and larger SOM content versus those which are associated with less-favorable DOM and lower SOM content. Both groups are expected to play critical roles in regulating SOM contents in the soil. By identifying the associations between microbial phylotypes of different life strategies and OM qualities and quantities, our study indicates that thermodynamic theory can act as a proxy for the relationship between OM and soil microbial communities and should be considered in models of soil organic matter preservation.IMPORTANCE Microbial communities are known to be important drivers of organic matter (OM) accumulation in terrestrial ecosystems. However, despite the importance of these soil microbes and processes, the mechanisms behind these microbial-SOM associations remain poorly understood. Here, we used the principles of thermodynamic theory and novel Fourier transform ion cyclotron resonance mass spectrometry techniques to investigate the links between microbial communities and dissolved OM (DOM) thermodynamic quality in soils across a 1,000-km gradient and comprising contrasting nutrient and C contents. Our region-scale study provided evidence that soils with a larger amount of readily accessible resources (i.e., lower Gibbs free energy) supported higher levels of microbial diversity and larger SOM content. Moreover, we created a novel phylotype-level microbial classification based on the associations between microbial taxa and DOM quantities and qualities. We found two contrasting clusters of bacterial taxa based on their level of association with thermodynamically favorable DOM and SOM content. Our study advances our knowledge on the important links between microbial communities and SOM. Moreover, by identifying the associations between microbial phylotypes of different life strategies and OM qualities and quantities, our study indicates that thermodynamic theory can act as a proxy for the relationship between OM and soil microbial communities. Together, our findings support that the association between microbial species taxa and substrate thermodynamic quality constituted an important complement explanation for soil organic matter preservation.

Balanced stochastic versus deterministic assembly processes benefit diverse yet uneven ecosystem functions in representative agroecosystems.

Ecological assembly processes, by influencing community composition, determine ecosystem functions of microbiomes. However, debate remains on how stochastic versus deterministic assembly processes influence ecosystem functions such as carbon and nutrient cycling. Towards a better understanding, we investigated three types of agroecosystems (the upland, paddy, and flooded) that represent a gradient of stochastic versus deterministic assembly processes. Carbon and nutrient cycling multifunctionality, characterized by nine enzymes associated with soil carbon, nitrogen, phosphorous and sulfur cycling, was evaluated and then associated with microbial assembly processes and co-occurrence patterns of vital ecological groups. Our results suggest that strong deterministic processes favour microorganisms with convergent functions (as in the upland agroecosystem), while stochasticity-dominated processes lead to divergent functions (as in the flooded agroecosystem). To benefit agroecosystems services, we speculate that it is critical for a system to maintain balance between its stochastic and deterministic assembly processes (as in the paddy agroecosystem). By doing so, the system can preserve a diverse array of functional traits and also allow for particular traits to flourish. To further confirm this speculation, it is necessary to develop a systematic knowledge beyond merely characterizing general patterns towards the associations among community assembly, composition, and ecosystem functions.

Long-Term Stochasticity Combines With Short-Term Variability in Assembly Processes to Underlie Rice Paddy Sustainability.

Revealing temporal patterns of community assembly processes is important for understanding how microorganisms underlie the sustainability of agroecosystem. The ancient terraced rice paddies at Longji provide an ideal platform to study temporal dynamics of agroecosystem sustainability due to their chronosequential records of soil physicochemistry and well-archived microbial information along 630-year rice cultivation. We used statistical null models to evaluate microbial assembly processes along the soil chronosequences of Longji rice paddies through time. Stochastic and deterministic assembly processes jointly governed microbial community composition within successional eras (less than 250 years), and within-era determinism was mainly driven by soil fertility and redox conditions alone or in combination. Conversely, across successional eras (i.e., over 300 years), stochasticity linearly increased with increasing duration between eras and was eventually predominant for the whole 630 years. We suggest that the impact of stochasticity vs. determinism on assembly is timescale-dependent, and we propose that the importance of stochastic assembly of microbial community at longer timescales is due to the gradual changes in soil properties under long-term rice cultivation, which in turn contribute to the sustainability of paddy ecosystem by maintaining a diverse community of microorganisms with multi-functional traits. In total, our results indicate that knowledge on the timescales at which assembly processes govern microbial community composition is key to understanding the ecological mechanisms generating agroecosystem sustainability.

A beneficial role of arbuscular mycorrhizal fungi in influencing the effects of silver nanoparticles on plant-microbe systems in a soil matrix.

Silver nanoparticles (AgNPs) are considered to be emerging contaminant for plant-soil systems. AM arbuscular mycorrhizal (AM) fungi can alleviate the negative effects of a variety of pollutants on their hosts, but its potential roles in influencing the toxicity of AgNPs and the underlying mechanisms are still an open question. This study investigated the responses of maize (Zea mays L.) inoculated with or without AM fungi and soil microorganisms to different concentrations of AgNPs (0, 0.025, 0.25, and 2.5 mg kg-1). The inoculation of AM fungi helps to alleviate the AgNP-induced phytotoxicity. Compared to the non-AM fungal inoculated treatments, AM fungal inoculation significantly increased the mycorrhizal colonization, biomass and phosphorus (P) acquisitions of maize, with an upregulation of P transporter gene expression under AgNP treatments. AM fungal inoculation decreased Ag content in plant shoots and roots, downregulated expression levels of genes involved in Ag transport and gene encoding a metallothionein involved in metal homeostasis. The beneficial role of AM fungi extended to soil microbes. Compared to the non-AM fungal inoculated treatments, AM fungal inoculation decreased the toxicity of AgNPs to soil microbial activities and bacterial abundance. AM fungal inoculation increased the bacterial diversity and induced changes in the soil bacterial community composition. Altogether, the present study revealed that AM fungal symbiosis can play beneficial roles in mediating the negative effects exposed by AgNPs on plants probably through changing the expressions of potential Ag transporters and cooperating with soil bacterial community.

Characteristics and Complete Genome Analysis of Bacillus asahii OM18, a Bacterium in Relation to Soil Fertility in Alkaline Soils Under Long-Term Organic Manure Amendment.

Bacillus asahii strain OM18, a bacterium in relation to soil fertility, was isolated from alkaline soils under long-term organic manure application in the North China Plain. B. asahii species play a pivotal role in the promotion of both crop yield and soil fertility via accelerating carbon and phosphorus cycling. However, little is known about the characteristics of B. asahii and its underlying molecular mechanism involved in soil nutrient cycling as well as its potential in promoting crop growth. To this end, we report the characteristics and complete genome analysis of strain OM18, which is relevant to promoting plant growth in phosphorus-deficient alkaline soils. Our results provide a glimpse into the metabolic function of B. asahii OM18.