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We integrated chemical, enzymatic, isotopic and molecular approaches to investigate both straw decomposition and its priming effect (PE) on native soil organic carbon (SOC) decomposition in soils with 23 years of application of chemical fertilizer (NPK) and partial substitution of chemical fertilizer by organic manure (NPKM). We found that NPK and NPKM past application significantly increased decomposition of straw. The increases in straw decomposition were not correlated with the abundances of microbiome assimilating straw carbon, but were significantly correlated with abundances of total bacteria, fungi and activities of cellulose-degrading enzymes. In addition, application of NPK did not change straw-induced PE while application of NPKM markedly reduced PE. The variation of PE with different past fertilization was correlated with the abundance of residue-stimulated fungi. The unchanged PE with NPK application in the presence of enriched nutrients and reduced pH was probably due to residue-promoted growth of acid-tolerant SOC-decomposing taxa (unclassified bacteria families belong to Acidobacteria GP3, Gamaproteobacteria and WPS-2 and unclassified fungal families belong to Chaetothyriales and Agaricomycetes). Our research sheds light on the complex processes of carbon transformation in the soils undergoing different long-term nutrient management. • NPK and NPK-manure application increased straw decomposition. • NPK application did not change residue-induced priming effect. • NPK-manure application reduced residue-induced priming effect. • Straw decompositions were mainly related to cellulose depolymerizing ability. • Priming effects were mainly related to abundance of stimulated fungi. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of silicate fertilizer on denitrification and associated gene abundance in a paddy soil. A consecutive trial from 2013 to 2015 was conducted including the following treatments: control (CK), mineral fertilizer (NPK), NPK plus sodium metasilicate (NPK + MSF), and NPK plus slag-based silicate fertilizer (NPK + SSF). Real-time quantitative PCR (qPCR) was used to analyze the abundances of nirS, nirK, and nosZ genes. Potential NO emissions and ammonium and nitrate concentrations were related to the nirS and nirK gene abundance. Compared with the NPK treatments, the addition of a Si fertilizer decreased NO emission rates and denitrification potential by 32.4-66.6 and 22.0-59.2%, respectively, which were probably related to increased rice productivity, soil Fe availability, and soil N depletion. The abundances of nirS and nirK genes were decreased by 17.7-35.8% and 21.1-43.5% with addition of silicate fertilizers, respectively. Rates of total NO and NO from denitrification (DeNO) emission were positively correlated with the nirS and nirK gene abundance. Nitrate, exchangeable NH , and Fe concentrations were the main factors regulating the nirS and nirK gene abundance. Silicate fertilization during rice growth may serve as an effective approach to decreasing NO emissions. [ABSTRACT FROM AUTHOR]

The association between microbial communities and plant growth in long-term fertilization system has not been fully studied. In the present study, impacts of long-term fertilization have been determined on the size and activity of soil microbial communities and wheat performance in a red soil (Ultisol) collected from Qiyang Experimental Station, China. For this, different microbial communities originating from long-term fertilized pig manure (M), mineral fertilizer (NPK), pig manure plus mineral fertilizer (MNPK), and no fertilizer (CK) were used as inocula for the Ultisol tested. Changes in total bacterial and fungal community composition and structures using Ion Torrent sequencing were determined. The results show that the biomass of wheat was significantly higher in both sterilized soil inoculated with NPK (SNPK) and sterilized soil inoculated with MNPK (SMNPK) treatments than in other treatments ( P < 0.05). The activities of β-1,4- N-acetylglucosaminidase (NAG) and cellobiohydrolase (CBH) were significantly correlated with wheat biomass. Among the microbial communities, the largest Ascomycota phylum in soils was negatively correlated with β-1,4-glucosidase (βG) ( P < 0.05). The phylum Basidiomycota was negatively correlated with plant biomass (PB) and tillers per plant (TI) ( P < 0.05). Nonmetric multidimensional scaling analysis shows that fungal community was strongly correlated with long-term fertilization strategy, while the bacterial community was strongly correlated with β-1,4- N-acetylglucosaminidase activity. According to the Mantel test, the growth of wheat was affected by fungal community. Taken together, microbial composition and diversity in soils could be a good player in predicting soil fertility and consequently plant growth. [ABSTRACT FROM AUTHOR]

Temperature is an important factor governing the community traits of N 2 O-emission related functional guilds (mainly autotrophic ammonia oxidizers and heterotrophic denitrifiers) and their activities. However, there have been few attempts to explore the broad response patterns of these guilds to temperature changes across arable soils. For this, a temperature-controlled (15, 25 and 35 °C) microcosm experiment was conducted using three arable soils (Fujian, Gansu, and Jiangsu) in China under two different fertilizations (no fertilization control (CK) and inorganic fertilization (NPK)). In conjunction with the measurement of N 2 O emission, the community structure and abundance of ammonia oxidizing archaea (AOA) and bacteria (AOB), as well as nirS - and nirK -denitrifiers were assessed using T-RFLP and quantitative PCR, respectively. The analysis of community traits indicated a consistent response pattern of AOAs to temperature in terms of guild abundance, and a consistent effect of inorganic fertilization on the abundance of AOBs, but soil-dependent response patterns to fertilization and temperature were found for nirS - and nirK -denitrifiers in terms of abundance and community structure. The correlation analysis suggested that AOAs possibly assumed a role in N 2 O emission in all the tested soils, and nirS -denitrifiers probably participated in N 2 O emission in both the Fujian and Gansu soil, while a considerable amount of N 2 O emission in the Jiangsu soil might have been derived from heterotrophic nitrification. [ABSTRACT FROM AUTHOR]

Emissions of the greenhouse gas nitrous oxide (N 2 O) from soil are sensitive to many factors including temperature, nutrient status, pH and bulk-density. Interactions among these are complex, particularly in agricultural systems where fertilizer-addition has interactive influences across many soil properties. Under laboratory conditions, the temperature sensitivity of N 2 O emissions, as measured by Q 10 values (fractional change in rate with a 10 °C increase in temperature), was higher in soils receiving long-term fertilizer addition compared with control. Different fertilization regimes significantly influenced the emission pathways. Application of manure increased the proportion of potential N 2 O derived from denitrification although the incubation condition used in the present study might not be favorable for anaerobic denitrification. The abundance of archaeal amoA gene copies increased under all fertilizer treatments, but that of bacterial amoA only increased under mineral (NPK) fertilization. Meanwhile, abundance of nirS , nirK and nosZ only increased under OM and MNPK fertilization. T-RFLP analyses showed that both ammonia oxidizing and denitrifier community structures were altered by fertilization, but only the nirS community structure was sensitive to temperature change. Furthermore, a strong correlation was observed between nirS gene abundance and potential N 2 O emissions. Relationships between AOA, nirK gene abundances and potential N 2 O emission were significant but relatively weak. PLS path model revealed that besides direct effect, potential N 2 O emission was also indirectly influenced by temperature through mediation of NH 4 + concentration and nirS -type denitrifier. Our work suggests that warming-induced elevation of potential N 2 O emission could be strengthened by long-term application of fertilizers, especially organic manure, via shifting community abundance and structure of nirS -type denitrifier. [ABSTRACT FROM AUTHOR]

Preferable inorganic fertilization over the last decades has led to fertility degradation of black soil in Northeast China. However, how fertilization regimes impact denitrification and its related bacterial community in this soil type is still unclear. Here, taking advantage of a suit of molecular ecological tools in combination of assaying the potential denitrification (DP), we explored the variation of activity, community structure, and abundance of nirS and nirK denitrifiers under four different fertilization regimes, namely no fertilization control (N0M0), organic pig manure (N0M1), inorganic fertilization (N1M0), and combination of inorganic fertilizer and pig manure (N1M1). The results indicated that organic fertilization increased DP, but inorganic fertilization had no impacts. The increase of DP was mirrored by the shift of nirS denitrifiers' community structure but not by that of nirK denitrifiers'. Furthermore, the change of DP coincided with the variation of abundances of both denitrifiers. Shifts of community structure and abundance of nirS and nirK denitrifiers were correlated with the change of soil pH, total nitrogen (TN), organic matter (OM), C:P, total phosphorus (TP), and available phosphorus (Olsen P). Our results suggest that the change of DP under these four fertilization regimes was closely related to the shift of denitrifying bacteria communities resulting from the variation of properties in the black soil tested. [ABSTRACT FROM AUTHOR]

The impacts of long-term application of inorganic and organic fertilizers on the activity, community composition, and abundance of denitrifying bacteria in an aquic soil of Northeast China were analyzed in this study. Denitrifying taxa were characterized for their nitrite reductase genes, nirS and nirK . The results showed that addition of inorganic fertilizer to soil decreased potential denitrification enzyme activity (DEA) by 41.1%, and this effect was mirrored by a reduction (39.0%) in the nirS -, but not nirK -denitrifiers' abundance. Addition of organic fertilizer increased DEA by 41.3% but had no impact on the abundance of either nirS - or nirK -denitrifiers. Inorganic fertilization strongly altered the community structure of nirK but only marginally impacted the community structure of nirS -denitrifiers; organic fertilizer had no influence on the community structures of these two guilds. DEA was significantly correlated with community structure of nirK -denitrifiers, but not with community structure of nirS -denitrifiers and abundances of both nirK - and nirS -denitrifiers. Moreover, community structure of nirK -denitrifiers was significantly correlated with pH, while nirS -denitrifiers were impacted by soil pH, total phosphorus (TP), and Olsen phosphorus (Olsen P) status. Our results suggest that different influences of inorganic and organic fertilization on DP are linked to a distinct structural change of nirS - and nirK -denitrifying bacterial communities in this aquic brown soil. [ABSTRACT FROM AUTHOR]

Abstract: It is unclear how inhibition of nitrous oxide (N2O) emissions by nitrification inhibitor (NI) is regulated through the ammonia oxidizing bacteria (AOB) or archaea (AOA) in arable soils. In this study, we investigated effects of 2-chloro-6-(trichloromethyl)-pyridine (Nitrapyrin, NP) on N2O emissions, and characterized the ammonia oxidizing microbial community in three arable soils typical of northern China. In alluvial, black, and paddy soils, average N2O emission rates were increased by addition of urea by 3.5, 0.7 and 2.1 pM N2O g−1 soil h−1, respectively, but were reduced by 2.9, 0.4 and 2.2 pM N2O g−1 soil h−1 when urea was applied with NP. The stimulation and suppression of N2O emission by urea and NP occurred alongside fluctuation in the growth of AOB in alluvial and paddy soils (P < 0.01). Weak stimulation and suppression of N2O emissions by urea and NP corresponded with weak effects on AOB abundances in the black soil. Changes in N2O emissions were not significantly correlated with AOA abundances in any of the three soils. The results showed that differential responses of N2O emission to urea and NP application in arable soils can be mainly explained by differences in growth of ammonia oxidizing bacteria. [Copyright &y& Elsevier]

Crop residue decomposition is a process largely mediated by soil microbes. This study aimed to investigate the dynamic of crop residue decomposition, change in fungal community composition and extracellular enzymatic activity in maize (Zea mays L.) residue via utilization of a two-year residue-bags study in north-central China. After the residue was buried in soil, the cumulative residue mass loss rate was 33%, 74%, and 85% after 2, 12, and 24 months, respectively. Total fungal abundance and the activities of beta (β)-glucosidase, β- d -cellobiosidase, and β-xylosidase were greater at the initial stage of decomposition and gradually decreased over time. However, the phenol oxidase activity presented an opposite pattern relative to the hydrolytic enzymes. The fungal community composition was similar in the residue during the initial (0) and 2 months after, with the phylum Ascomycota (classes Sordariomycetes and Dothideomycetes) dominating the community composition for the first two months but then decreased gradually over time. Phyla Basidiomycota , Cercozoa , and classes Eurotiomycetes and Tremellomycetes presented an increasing-decreasing trend during the decomposition process. The phylum Zygomycota (class Leotiomycetes) gradually increased over time and showed greater abundance at the later stage of decomposition; while the fungal community composition was similar in soil and residue samples for the 20–24 months. This study highlights the relevancy of fungal abundance for playing a critical role in residue decomposition, with the composition of this community changing from the dominance of copiotrophic populations in the early stage to oligotrophic populations in the later stage. • Residue decomposed rapidly in the first 2 months and gradually decreased over time. • Fungal abundance and hydrolytic enzymes changed synchronously with residue loss. • Phylum Ascomycota dominated fungal community at the early stage of decomposition. • Basidiomycota and Zygomycota dominated at the intermediate and later stages, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Nutrient inputs to soil can alter mineralization of organic matter and subsequently affect soil carbon levels. To understand how elemental interactions affect the biogeochemistry and storage of soil C, we examined soils receiving long-term applications of mineral fertilizer and manure-containing fertilizers. As cellulose is the dominant form of carbon entering arable soils, cellulolytic communities were monitored through enzymatic analysis, and characterization of the abundance (real-time PCR) and diversity (terminal restriction fragment length polymorphism, T-RFLP) of fungal cellobiohydrolases (cbhI) genes. The data showed that long-term mineral fertilization increased soil organic C and crop productivity, and reduced soil heterotrophic respiration and cellobiohydrolases (CBH) activity. Correspondingly, the diversity and community structure of cellulolytic fungi were substantially altered. The variation in cellulolytic fungi is mainly attributable to shifts in the proportion of Eurotiomycetes. In addition, CBH activity was significantly correlated with the diversity and community structure of cellulolytic fungi. These results suggest that enhanced C storage by mineral fertilizer addition occurs not only from extra organic carbon input, but may also be affected through the cellulose decomposing community in arable soil. [Copyright &y& Elsevier]

The microbiology underpinning soil nitrogen cycling in northeast China remains poorly understood. These agricultural systems are typified by widely contrasting temperature, ranging from −40 to 38°C. In a long-term site in this region, the impacts of mineral and organic fertilizer amendments on potential nitrification rate (PNR) were determined. PNR was found to be suppressed by long-term mineral fertilizer treatment but enhanced by manure treatment. The abundance and structure of ammonia-oxidizing bacterial (AOB) and archaeal (AOA) communities were assessed using quantitative polymerase chain reaction and denaturing gradient gel electrophoresis techniques. The abundance of AOA was reduced by all fertilizer treatments, while the opposite response was measured for AOB, leading to a six- to 60-fold reduction in AOA/AOB ratio. The community structure of AOA exhibited little variation across fertilization treatments, whereas the structure of the AOB community was highly responsive. PNR was correlated with community structure of AOB rather than that of AOA. Variation in the community structure of AOB was linked to soil pH, total carbon, and nitrogen contents induced by different long-term fertilization regimes. The results suggest that manure amendment establishes conditions which select for an AOB community type which recovers mineral fertilizer-suppressed soil nitrification. [ABSTRACT FROM AUTHOR]

Abstract: Both plants and microbes influence soil nutrient cycling. However, the links between plants, microbes and nutrient cycling are poorly understood. In this study, we investigated how plant identity and interspecific competition influence soil nitrogen cycling and attempted to link plant identity and interspecific competition to community structures of bacterial and archaeal ammonia oxidizers based on terminal restriction fragment length polymorphism analysis (T-RFLP) of bacterial and archaeal ammonia monooxygenase (amoA) genes. Faba bean and maize monocultures and a faba bean/maize mixture were planted with two nitrogen levels (0 and 100mg Nkg−1 soil as urea). Soil mineral nitrogen, ammonia oxidizer function (potential nitrification activity, PNA) and community structures were measured 28 and 54 days after plant emergence. Faba bean and maize substantially differed in their influences on mineral nitrogen concentrations and PNA in rhizosphere soils. Soil mineral nitrogen and PNA in the rhizosphere soils of the faba bean/maize mixture were closer to those of the maize monoculture than to those of the faba bean monoculture. T-RFLP with restriction enzymes BsaJI and Hpy8I distinguished variations in bacterial and archaeal ammonia oxidizers community structure, respectively, and detected both between-cluster and within-cluster variations in bacterial ammonia oxidizers. T-RFLP data showed that nitrogen addition favored part of a Nitrosospira cluster 3b sequence type and suppressed part of a cluster Nitrosospira 3a sequence type of bacterial ammonia oxidizers, while it had no influence on the archaeal ammonia oxidizer community structure. Although multivariate analysis showed that the function and community structure of bacterial ammonia oxidizers were significantly correlated, plant species and interspecific competition did not significantly change the community structure of bacterial and archaeal ammonia oxidizers. These results indicate that plant species and interspecific competition regulate soil nitrogen cycling via a mechanism of other than alteration in the community structure of ammonia oxidizers as investigated by DNA based methods. [Copyright &y& Elsevier]

Abstract: Knowledge about carbon allocation below ground is necessary to understand soil ecosystem functioning and the global C cycle. It is common knowledge that different plant species coexist in natural and agricultural systems. By using a modified 13C pulse-chase approach, which enabled us to label individual plants in either mono- or mixed cultures, we investigated the effect of coexistence of different neighboring species on plant carbon partitioning. Maize and faba bean were used as our test plants and isotope pulse labeling was performed twice at 26 and 54d after emergence. The results showed that a higher proportion of photoassimilates was distributed below ground in maize than in faba bean, resulting in a greater ratio of root to shoot biomass for maize plants during the experiment. The carbon distribution to roots was slightly higher in mixed cultures at 26d than the counterpart monocultures. The distribution of the plant-assimilated 13C to soil dissolved organic carbon was also greater in mixed cultures at 26d relative to the monocultures. The most significant effect of the mixed culturing was a dramatic increase of 13C incorporation into the soil microbial biomass. These results indicated that the plant carbon allocation below ground was altered in the presence of a different neighboring species. The increase of plant diversity probably enhances the soil microbial activity and hence the turnover of the plant-derived carbon in soil. [Copyright &y& Elsevier]

[Display omitted] • High plant density significantly enhanced soil microbial abundance and diversity. • Microbial composition across N rates shared more similarity under high plant density. • High plant density increased AOA and significantly decreased nir S gene abundance. • Increased root biomass, and N uptake mitigated the negative effects of excessive N. To obtain high maize yield (Zea mays L.), nitrogen (N) fertilizer is widely used across the world and has greatly altered soil microbial communities and influenced soil health. Increasing plant density is an effective strategy for increasing maize yield, while variations in soil microbial communities in response to plant density under high N levels have not been well-studied. In Northeast China, maize was grown at low (LD, 67,500 plants ha−1) and high (HD, 90,000 plants ha−1) densities, combined with three N application rates of 0, 200, and 400 kg N ha−1yr−1(N0, N200 and N400). Based on a six-year field experiment, key soil microbial characteristics and physicochemical properties of top soils (0–20 cm), as well as yield and vegetative parameters were examined. Compared with that of LD, the maize grain yield of HD increased 10.8 % across N application rates from 2012 to 2017 (P < 0.05), while no significant differences between N200 and N400 were observed. HD significantly increased microbial biomass carbon (MBC), microbial biomass N (MBN), and bacterial and fungal diversity at N400 (P < 0.05). Dominant bacterial phyla across all samples were Proteobacteria , Acidobacteria , Actinobacteria and Thaumarchaeota , and fungal phyla were Ascomycota , Basidiomycota and Zygomycota. Species composition of HD shared more similarity between N200 and N400 than that of LD. HD significantly increased the abundance of Nitrososphaera and reduced the abundance of Pseudomonas and Sphingobium. From LD to HD, ammonia-oxidizing archaea (AOA) gene abundance increased while nir K gene abundance decreased at all N application rates, and ammonia oxidizing bacteria (AOB) and nir S gene abundances decreased at N0 and N400 but increased at N200 (P < 0.05). Shoot biomass and N uptake were positively correlated with MBC and MBN but negatively correlated with microbial community diversity. HD directly increased root biomass and N uptake, then reduced soil N contents (NH 4 +-N, NO 3 –-N, and TN) and thus positively regulated soil microbial communities. Relative differences of diversity indexes and functional gene abundances between N application rates of HD were significantly lower than those of LD. Overall, our findings indicate that higher plant density of maize could mitigate the adverse effects of N fertilizer overuse on soil microbial communities, thus reconciling maize productivity and black soil health in Northeast China. [ABSTRACT FROM AUTHOR]

There are many kinds of soil amendments that consist of different materials. The soil amendment is usually of benefit to plant health. However, the effects of the soil amendments on plant disease have rarely been compared and the involved mechanisms are largely unknown. In the present study, we investigated the influences of five contrasting soil amendments (i.e., potassium silicate (PS), calcium silicate (CS), biochar (BC), calcium silicate humic acid (SCHA), and bio-organic fertilizer (BOF)) on tomato bacterial wilt. In addition, we dissected the mechanism with high-throughput sequencing. The results showed that BC, SCHA, and BOF significantly reduced the incidence and delayed the disease, while BOF significantly reduced the incidence of bacterial wilt disease in the whole tomato growing period. In the early stage of the disease, BC, SCHA, and BOF significantly reduced the soil pH compared to CK. However, the contents of soil NH4+-N and NO3−-N were significantly increased. Some beneficial bacteria genera (Burkholderia, Mortierella, and Trichoderma) had a certain correlation with the incidence. Burkholderia and Mortierella were negatively associated with morbidity, but Trichoderma was positively associated with morbidity. Particularly, the Spearman correlation and the least partial squares path analysis indicated that Trichoderma was significantly positively correlated with the disease incidence, the soil physicochemical properties, and the numbers of soil pathogens (NSP) were significantly positively correlated with the number of root pathogens (NRP) and the physicochemical properties of plants were negatively correlated with the disease incidence. Moreover, BOF had better inhibitory effect on the occurrence of tomato bacterial wilt. Our results have implications for the better integrated management of tomato bacterial wilt. [ABSTRACT FROM AUTHOR]

Soil in high latitude and altitude cold regions contains over half of soil organic carbon (SOC) globally, so the decomposition of these SOCs under climate warming could release huge amounts of carbon dioxide to the atmosphere, amplifying climate warming. However, it is still unclear how the SOC storages will change when the ecosystem reaches the final and stable stage (i.e., the climax) under long-term warming. This is mainly because the turnover times of SOC in cold regions exceeds hundreds or even thousands of years, much longer than the periods of simulated warming experiments. Herein we used natural geothermal warming gradients in a Tibetan alpine grassland to determine SOC changes and underlying plant and microbial mechanisms at the potential climax. SOC concentrations were significantly decreased by 21.4%–30.6% under high-level soil warming (+4∼+6 °C), but remained unchanged under low-level soil warming (+2 °C). The losses of SOC were primarily from mineral-associated organic carbon, rather than unprotected particulate organic carbon. The shifts of microbial communities and associated decline of microbial carbon use efficiency, rather than plant-driven carbon fluxes, substantially contributed to the SOC changes. This observed SOC losses at the climax of alpine grassland by high-level warming provide strong empirical support for the positive soil carbon-climate feedback in cold regions, which could not be concluded from short-term experiments or only based on ecosystem carbon fluxes alone. The divergent responses of SOC to different degrees of warming suggest that models must account for these heterogeneous carbon dynamics for projecting future climate warming scenarios. • High-level rather than low-level warming led to soil carbon loss at the potential climax. • Soil carbon loss by warming was primarily from mineral-associated organic carbon. • The decrease of microbial carbon use efficiency contributed to soil carbon loss. [ABSTRACT FROM AUTHOR]

The main objectives of this study were to elucidate the roles of silicon (Si) in alleviating the effects of 2 mM zinc (high Zn) stress on photosynthesis and its related gene expression levels in leaves of rice (Oryza sativa L.) grown hydroponically with high-Zn stress. The results showed that photosynthetic parameters, including net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO2 concentration, chlorophyll concentration and the chlorophyll fluorescence, were decreased in rice exposed to high-Zn treatment. The leaf chloroplast structure was disordered under high-Zn stress, including uneven swelling, disintegrated and missing thylakoid membranes, and decreased starch granule size and number, which, however, were all counteracted by the addition of 1.5 mM Si. Furthermore, the expression levels of Os08g02630 (PsbY), Os05g48630 (PsaH), Os07g37030 (PetC), Os03g57120 (PetH), Os09g26810 and Os04g38410 decreased in Si-deprived plants under high-Zn stress. Nevertheless, the addition of 1.5 mM Si increased the expression levels of these genes in plants under high-Zn stress at 72 h, and the expression levels were higher in Si-treated plants than in Si-deprived plants. Therefore, we conclude that Si alleviates the Zn-induced damage to photosynthesis in rice. The decline of photosynthesis in Zn-stressed rice was attributed to stomatal limitation, and Si activated and regulated some photosynthesis-related genes in response to high-Zn stress, consequently increasing photosynthesis. [ABSTRACT FROM AUTHOR]

It is well documented that slag-based silicon fertilizers have beneficial effects on the growth and disease resistance of rice. However, their effects vary greatly with sources of slag and are closely related to availability of silicon (Si) in these materials. To date, few researches have been done to compare the differences in plant performance and disease resistance between different slag-based silicon fertilizers applied at the same rate of plant-available Si. In the present study both steel and iron slags were chosen to investigate their effects on rice growth and disease resistance under greenhouse conditions. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the effects of slags on ultrastructural changes in leaves of rice naturally infected by Bipolaris oryaze, the causal agent of brown spot. The results showed that both slag-based Si fertilizers tested significantly increased rice growth and yield, but decreased brown spot incidence, with steel slag showing a stronger effect than iron slag. The results of SEM analysis showed that application of slags led to more pronounced cell silicification in rice leaves, more silica cells, and more pronounced and larger papilla as well. The results of TEM analysis showed that mesophyll cells of slag-untreated rice leaf were disorganized, with colonization of the fungus (Bipolaris oryzae), including chloroplast degradation and cell wall alterations. The application of slag maintained mesophyll cells relatively intact and increased the thickness of silicon layer. It can be concluded that applying slag-based fertilizer to Si-deficient paddy soil is necessary for improving both rice productivity and brown spot resistance. The immobile silicon deposited in host cell walls and papillae sites is the first physical barrier for fungal penetration, while the soluble Si in the cytoplasm enhances physiological or induced resistance to fungal colonization. [ABSTRACT FROM AUTHOR]

Aims: Phytohormones are a group of signal compounds that regulate plant growth, development, health and plant-soil interactions. We aimed to investigate the distribution and controlling factors of a diverse set of phytohormones found in the plant-soil continuum. Methods: Twenty phytohormones belonging to seven categories were studied in maize roots, rhizosphere and bulk soil with ultra-high-performance liquid chromatography–tandem mass spectrometry. In addition, the microbiomes shaped by gamma-sterilization and reinoculation were analyzed using high throughput sequencing. Results: We found three major distribution patterns of the 17 phytohormones detected along the root-soil continuum. In the first of these, the phytohormones were predominant in roots, followed by rhizosphere and then by bulk soil. In the second pattern, concentrations of the phytohormones were smallest in the rhizosphere. While, in the third pattern, concentrations of the phytohormones were greatest in the rhizosphere. The concentrations of the phytohormones were closely related to those of root phytohormone or roots biomass as well as relative abundances of wide range of microbial taxa. Conclusions: The results indicated that the distribution patterns of six categories of phytohormones in the root-soil continuum are driven by a balance between the production and uptake by the roots and the production, utilization and degradation by the soil microbiome in a phytohormone-specific manner. [ABSTRACT FROM AUTHOR]

Biochar amendment can reduce CH 4 emissions from paddy soils. However, little is known about how the soil microbial communities associated with paddy soil CH 4 emissions respond to biochar aging after biochar amendment. In this study, we examined the effects of biochar on CH 4 emissions, soil properties, and abundance/community composition of methanogens and methanotrophs in a double rice cropping system from 2012 to 2016. Straw-derived biochar was applied once in 2012 at 24 and 48 t ha−1. Biochar application decreased the annual CH 4 emissions by 20–51%. Biochar increased the abundances of both methanogens and methanotrophs, with a larger increase of methanotrophs than methanogens in the first year, mainly caused by the increases in soil dissolved organic carbon, NH 4 +-N, and porosity. Biochar suppressed the abundance of methanogens and had little effect on the methanotrophs in the following three years, probably due to the increased soil porosity. Eventually, the ratios of abundance of methanogens to methanotrophs decreased by 11–31% in each of the four years and were positively correlated to CH 4 emissions. Biochar addition increased the relative abundances of Methanocella and Methanospirillum and reduced those of Methanoregula and Methanosaeta for methanogens, while it increased the proportion of the basophilic methanotrophs Methylomicrobium and decreased that of Methylocaldum in the growing season 2014. Our results demonstrate that biochar aging greatly alters the responses of abundances and community compositions of soil methanogens and methanotrophs to biochar addition. The reduction of CH 4 emissions owing to biochar in the long run was probably mainly due to the lesser suppression of abundance and activity of methanotrophs compared with methanogens. • Biochar decreased paddy CH 4 emissions across four years. • Biochar significantly reduced methanogen:methanotroph ratios in four years. • Fresh biochar with nutrients stimulated methanotrophs and methanogens in year one. • Aged biochar suppressed methanogen growth in years 2–4 due to increased soil porosity. • Biochar reduced the acetoclastic methanogen abundances at tillering and ripening. [ABSTRACT FROM AUTHOR]

The mechanism by which temperature sensitivity (TS) of soil N 2 O emissions is increased by agricultural management with application of nitrogen fertilizer (AMN) is unclear. We hypothesized that a higher TS of N 2 O emission induced by AMN is the result of the faster growth of specific microorganisms in response to faster nitrogen (N) mineralization at higher temperatures. To test this hypothesis, we used reciprocal transplants to separate the contributions of abiotic and microbial components to the TS of N 2 O emissions in an arable soil receiving organic and inorganic fertilizers and its neighboring natural grassland soil treated with two levels of N. N 2 O sources were separated with acetylene, and the abundances of N 2 O-producing microbes were assessed by quantifying the copy numbers of the associated functional genes. Compared with natural soil, only changes in abiotic properties increased the Q 10 (the factor by which the rate increases with a 10 °C rise in temperature) by 105.7%, while changes in both abiotic and the microbiome increased the Q 10 by 225.2%. Higher TS of N 2 O emission in the arable soil induced by a microbiome shift was associated with faster N mineralization, increased proportion of nitrification-N 2 O emission, and faster growth of ammonia-oxidizing bacteria at higher temperatures. Addition of ammonium nitrate further enhanced the TS of N 2 O emissions, the proportion of nitrification-N 2 O emission, and the increased extent of the growth of ammonia-oxidizing bacteria in the soil with AMN compared to the natural grassland soil. Substrate-driven growth of ammonia-oxidizing bacteria with higher substrate preference contributes significantly to the higher TS of N 2 O emission caused by AMN. [ABSTRACT FROM AUTHOR]

Belowground biodiversity is essential for soil functioning, but the effect of belowground biodiversity loss on food safety is unknown. We investigated the loss of soil microbial diversity on insecticides accumulation in Brassica. We manipulated soil biodiversity using the dilution-to-extinction approach in a Brassica-soil-insecticide system, monitored microbial communities via high-throughput sequencing, and identified potential functional microbes. Compared with unsterilized soil, the richness of functional bacteria was reduced by 14.1%, 36.2%, 51.6% and 73.2%, respectively, in the corresponding sterilized soil inoculated with 1-, 10 −2 -, 10 −4 - and 10 −6 -fold diluted soil suspension. The acetamiprid and imidacloprid concentrations increased significantly in Brassica tissues grown in sterilized soil inoculated with 10 −6 -fold diluted suspension. A bacterial group predominated in functional microbes of soils inoculated with 1-, 10 −2 - or 10 −4 -fold diluted suspension, but the relative abundance declined in soil inoculated with a 10 −6 -fold diluted suspension. Our findings revealed that undesirable impacts by the loss of soil biodiversity at an intermediate level on the accumulation of soil contaminant in plants could be alleviated by microbial functional redundancy through disproportionally complementary growth of specific functional microbial taxa, but severe loss of soil biodiversity would threaten food safety. [ABSTRACT FROM AUTHOR]

Green manure rotation is commonly used to increase soil fertility and improve crop yield. However, the effects of this management practice on the underground microbial ecosystem and the indirect impact on the aboveground crop growth have not been systematically analysed. In this study, we investigated the rice rhizosphere and bulk soil microbial community in a 31-year-old field experimental site treated with different green manures and rice rotations using both 16S rDNA high-throughput sequencing and quantitative PCR approaches. Four treatments have been setup in this experimental site since 1982, including a rice-rice-winter fallow treatment as a control and three green manure rotation treatments: rice-rice-Chinese milk vetch, rice-rice-rape and rice-rice-ryegrass. The qPCR results showed that the bacterial abundances in the rice rhizosphere of the green manure rotation treatments were all significantly higher than in the winter fallow (p < 0.05), but no significant differences were found among those three green manure rotation treatments. Moreover, α-diversity analysis revealed that green manure rotations decreased the microbial diversity (Shannon and Simpson indexes) and richness (Chao value) in the rice rhizosphere. Permutational Multivariate Analysis of Variance based on β-diversity revealed the microbial community was significantly switched in rice rhizosphere after long-term green manure rotation (p < 0.01). Additionally, the soil and plant characteristics contributed almost equally to the rhizosphere bacterial community based on a partial CCA-based variation partitioning analysis. At the genus level, the well-known plant-growth-promoting rhizobacteria Acinetobacter (31%–41%) and Pseudomonas (14%–28%) were the preponderant groups in green manure rotation treatments but accounted for only 4.4% and 2.5% in the winter fallow treatment. Overall, long-term rice-rice-green manure rotation shaped the microbial community in the rice rhizosphere; in particular, some beneficial bacteria, Acinetobacter and Pseudomonas , accumulated in the rhizosphere of green manure treatments. [ABSTRACT FROM AUTHOR]

To evaluate long-term effect of biochar application on yield-scaled greenhouse gas emissions (YSGE) in a paddy rice cropping system, a 4-year field experiment by static chamber - gas chromatograph method was conducted in South China. Principal component analysis and terminal restriction fragment length polymorphism (T-RFLP) and real-time qPCR was used to unravel the microbial mechanisms of biochar addition. Six treatments were included: control (CK), application of 5 t ha − 1 biochar (BC1), application of 10 t ha − 1 biochar (BC2), application of 10 t ha − 1 biochar (BC3), rice straw return at 2400 kg ha − 1 (RS) and inoculated rice straw return at 2400 kg ha − 1 (RI). The results indicated that biochar amendment significantly decreased methane (CH 4 ) and gross greenhouse gas (GHG) emissions. This may primarily be ascribed to the stimulated biodiversity and abundance of methanotrophic microbes, increased soil pH and improved aeration by reducing bulk density after biochar incorporation. Compared with CK, RS and RI, 26.18%, 70.02%, 66.47% of CH 4 flux and 26.14%, 70.16%, 66.46% of gross GHG emissions were reduced by biochar (mean of three biochar treatments), respectively. Furthermore, biochar significantly increased harvest index of double rice production ( p < 0.05). In comparison with CK, RS and RI, 29.14%, 68.04%, 62.28% of YSGE was reduced by biochar, respectively, and the highest biochar addition rate (20 t ha − 1 ) contributed most to the mitigation of GHG emissions (36.24% decrease compared to CK) and improvement of rice yield (7.65% increase compared to CK). Results of our study suggested that long-term application of biochar should be the potential way to mitigate GHGs emissions and simultaneously improve rice productivity in the paddy rice system. [ABSTRACT FROM AUTHOR]

This study used an artificial enrichment microbial consortium to examine the effects of different substrate conditions on microbial diversity, composition, and function (e.g., zinc leaching efficiency) through adding pyrite (SP group), chalcopyrite (SC group), or both (SPC group) in sphalerite bioleaching systems. 16S rRNA gene sequencing analysis showed that microbial community structures and compositions dramatically changed with additions of pyrite or chalcopyrite during the sphalerite bioleaching process. Shannon diversity index showed a significantly increase in the SP (1.460), SC (1.476), and SPC (1.341) groups compared with control (sphalerite group, 0.624) on day 30, meanwhile, zinc leaching efficiencies were enhanced by about 13.4, 2.9, and 13.2 %, respectively. Also, additions of pyrite or chalcopyrite could increase electric potential (ORP) and the concentrations of Fe and H, which were the main factors shaping microbial community structures by Mantel test analysis. Linear regression analysis showed that ORP, Fe concentration, and pH were significantly correlated to zinc leaching efficiency and microbial diversity. In addition, we found that leaching efficiency showed a positive and significant relationship with microbial diversity. In conclusion, our results showed that the complicated substrates could significantly enhance microbial diversity and activity of function. [ABSTRACT FROM AUTHOR]

Background and aims: We investigated the effects of silicon (Si) on chlorophyll concentration, photosynthesis, leaf chloroplast ultrastructure, and expression of genes involved in photosynthesis to elucidate the mechanisms through which Si mediated alleviation of manganese (Mn) toxicity in rice ( Oryza sativa L.). Methods: Rice seedlings were grown hydroponically with normal Mn (6.7 μM) or high Mn (2 mM) concentrations, both with (1.5 mM) and without Si supplementation. Leaf chloroplast ultrastructure was observed by scanning and transmission electron microscopy. Differentially expressed genes relating to photosynthesis were identified by high-throughput sequencing, and their relative expression levels were evaluated by real-time quantitative PCR. Results: Chlorophyll and carotenoid concentrations and net photosynthesis decreased with chloroplast degradation under high Mn stress. High Mn concentrations may have inhibited photosynthesis through several mechanisms, including suppressing chlorophyll and ATP synthesis, decreasing light-harvesting processes, impairing photosystem I (PSI) stability and structure, and slowing activity of phosphoribulokinase. Si enhanced Mn tolerance efficiently by increasing chlorophyll concentration, light-use efficiency, and ATP concentration as well as by stabilizing the structure of PSI and promoting CO assimilation. Conclusions: Our findings suggest active involvement of Si in Mn detoxification, ranging from physiological responses to gene expression. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an essential element for plant growth and development. N levels in soil may also impact plant disease occurrence. However, the physiological and microbial mechanisms between N levels in soil and plant disease occurrence are not quite clear at present. In this study, we examined the impact of seven urea levels (0 to 800 mg kg−1 soil) on the physiology of tomato (Lycopersicon esculentum) and fungal disease occurrence. Our results showed that the disease incidence and index caused by a tomato early blight pathogen (Alternaria alternata) increased with increasing N levels. The disease index and percentage of disease incidence were positively correlated with N content, indole-3-acetic acid (IAA) and salicylic acid (SA) in plants, but negatively correlated with fungal community diversity. In addition to pathogens (A. alternata) that cause known early blight, 39 other fungal taxa were also identified as plant pathogens in tomato roots, leaves, and soil, the dominant putative pathogens included Ceratobasidiaceae sp., Fusarium oxysporum , Macrophomina phaseolina , Nectriaceae sp., Podosphaera fusca and Trichoderma viride. N levels affected the distribution and dynamics of the fungal pathogen community, such as the abundance of Fusarium oxysporum increased by 33% on roots from days 25 to 35. Our results demonstrated that plants undergo complex disease risk from different pathogens under different N levels, highlighting a need for proper N management, and integration of nutrient management as a disease control approach for sustainable agricultural production. [Display omitted] • The disease incidence and index of tomato early blight increased with increasing nitrogen levels. • Disease occurrence was positively correlated with plant N nutrition. • Disease occurrence was negatively correlated with connectance and average degree of fungal co-occurrence network. • 39 fungal taxa were identified as potential plant pathogens in tomato-soil system. • The pathogens abundance varied with pathogen types, time, and plant tissue under different nitrogen levels. [ABSTRACT FROM AUTHOR]

Background and aims: This study aimed to investigate the roles of silicon (Si) in ameliorating manganese (Mn) toxicity in two rice ( Oryza sativa L.) cultivars: i.e. cv. Xinxiangyou 640 (XXY), a Mn-sensitive cultivar and cv. Zhuliangyou 99 (ZLY), a Mn-tolerant cultivar. Methods: Plants were cultured in nutrient solution containing normal Mn (6.7 μM) or high Mn (2.0 mM), both with or without Si supply at 1.5 mM Si. Results: Plant growth was severely inhibited by high Mn in cv. XXY, but was enhanced by Si supply. In cv. XXY, Si-enhanced tolerance resulted from a restriction of Mn transport, whereas in cv. ZLY Mn uptake was depressed. In cv. XXY, high Mn significantly increased superoxide dismutase (SOD), catalase and ascorbate peroxidase activities but decreased non-protein thiols and glutathione concentrations, leading to accumulation of HO and malondialdehyde. The addition of Si significantly counteracted high Mn-elevated malondialdehyde and HO concentrations and enhanced plant growth. In cv. ZLY, high Mn considerably raised SOD activities and glutathione concentrations, thus leading to relatively low oxidative damage. Conclusions: Si-enhanced Mn tolerance was attributed mainly to restricted Mn transport in cv. XXY but to depressed Mn uptake in cv. ZLY. Silicon mainly influenced non-enzymatic antioxidants in these two rice cultivars under high Mn stress. [ABSTRACT FROM AUTHOR]

The objective of this study is to elucidate the roles of silicon (Si) in enhancing tolerance to excess zinc (Zn) in two contrasting rice ( Oryza sativa L.) cultivars: i.e. cv. TY-167 (Zn-resistant) and cv. FYY-326 (Zn-sensitive). Root morphology, antioxidant defense reactions and lipid peroxidation, and histochemical staining were examined in rice plants grown in the nutrient solutions with normal (0.15 μM) and high (2 mM) Zn supply, without or with 1.5 mM Si. Significant inhibitory effects of high Zn treatment on plant growth were observed. Total root length (TRL), total root surface area (TRSA) and total root tip amount (TRTA) of both cultivars were decreased significantly in plants treated with high Zn, whereas these root parameters were significantly increased when Zn-stressed plants were supplied with 1.5 mM Si. Supply of Si also significantly decreased Zn concentration in shoots of both cultivars, indicating lower root-to-shoot translocation of Zn. Moreover, superoxide dismutase (SOD), catalase (CAT), and asorbate peroxidase (APX) activities were increased, whereas malondialdehyde (MDA) and hydrogen peroxide (HO) concentrations were decreased in Si-supplied plants of both Zn-sensitive and Zn-resistant rice cultivars exposed to Zn stress. These alleviative effects of Si, further confirmed by the histochemical staining methods, were more prominent in the Zn-resistant cultivar than in the Zn-sensitive one. Taken together, all these results suggest that Si-mediated alleviation of Zn toxicity is mainly attributed to Si-mediated antioxidant defense capacity and membrane integrity. The possible role of Si in reduction of root-to-shoot translocation of Zn can also be considered. [ABSTRACT FROM AUTHOR]

Abstract: A series of hydroponics experiments were performed to investigate roles of silicon (Si) in enhancing cadmium (Cd) tolerance in two pakchoi (Brassica chinensis L.) cultivars: i.e. cv. Shanghaiqing, a Cd-sensitive cultivar, and cv. Hangyoudong, a Cd-tolerant cultivar. Plants were grown under 0.5 and 5mg Cd L−1 Cd stress without or with 1.5mM Si. Plant growth of the Cd-tolerant cultivar was stimulated at the lower Cd level, but was decreased at the higher Cd level when plants were treated with Cd for one week. However, Plant growth was severely inhibited at both Cd levels as stress duration lasted for up to three weeks. Plant growth of the Cd-sensitive cultivar was severely inhibited at both Cd levels irrespective of Cd stress duration. Addition of Si increased shoot and root biomass of both cultivars at both Cd levels and decreased Cd uptake and root-to-shoot transport. Superoxide dismutase, catalase and ascorbate peroxidase activities decreased, but malondialdehyde and H2O2 concentrations increased at the higher Cd level, which were counteracted by Si added. Ascorbic acid, glutathione and non-protein thiols concentrations increased at the higher Cd level, which were further intensified by addition of Si. The effects of Si and Cd on the antioxidant enzyme activity were further verified by isoenzyme analysis. Silicon was more effective in enhancing Cd tolerance in the Cd-tolerant cultivar than in the Cd-sensitive cultivar. It can be concluded that Si-enhanced Cd tolerance in B. chinensis is attributed mainly to Si-suppressed Cd uptake and root-to-shoot Cd transport and Si-enhanced antioxidant defense activity. [Copyright &y& Elsevier]

• 13C highly enriched residue decomposition with NH 4 + and NO 3 − were investigated. • The contribution of bacterial and archaeal taxa in assimilating residue-C was quantified with qSIP. • Effects of N form on the decomposition of maize residue didn't differ at early stage in arable soil. • Contributions of most active phyla (e.g. Proteobacteria) did not differ with the two N at phylum level. • Thaumarchaeota (genus Nitrososphaera) assimilated more residue-C under ammonium enrichment. The decomposition of crop residues represents the largest organic carbon (C) input into agricultural ecosystems, and plays an important role in soil C sequestration and soil fertility. However, how different forms of mineral nitrogen (N) influence the decomposition of these residues, or their associated active microbes, is poorly understood. In this study, we investigated the impacts of ammonium ((NH 4) 2 SO 4) and nitrate (KNO 3) on the early stages (14 days) of decomposition of highly enriched 13C-labeled (13C atom% = 77.0%) maize residues. Further, we characterized the contributions of various bacterial and archaeal taxa using quantitative stable isotope probing (qSIP). To our surprise, we found that the majority of measured parameters including 13C soil respiration, total 13C microbial assimilation in soil DNA, as well as the diversity and structure of these microbial communities, were not significantly different between these two N forms during our 2-week incubation. Slight differences were observed however, in the activity of straw-metabolizing microbes. The qSIP revealed variability in 13C assimilation (excess atom fraction, EAF) among different microbial taxa at the operational taxonomic unit (OTU) level, with Proteobacteria , Bacteroidetes , and Verrucomicrobia being the most intensively 13C-labeled phyla, suggesting their potentially dominant roles in residue decomposition. However, only the 13C EAF of Thaumarchaeota (genus Nitrososphaera) was significantly higher in the ammonium treatment than in the nitrate treatment. The Nitrososphaera might indirectly participate in the decomposition of residues by fixing CO 2 or by directly incorporate 13C from organic matter. These results reveal a quantitative overview of the contribution of bacteria and archaea to residue decomposition. Further, we document that the similar effect of nitrate and ammonium on residue decomposition at the early stages is likely due to the unchanged activity of predominant bacterial taxa with the two N forms. [ABSTRACT FROM AUTHOR]

• Straw biochar increased the abundances of paddy soil bacteria and fungi 3–4 years after amendment. • Biochar amendment decreased soil bacteria/fungi ratios. • Biochar improved soil bacterial composition to favor TOC accumulation. • Biochar improved soil fungal composition to favor plant growth and TOC degradation. • Biochar reduced fungal abundances of plant pathogen in paddy soil. The effects of biochar application on soil microbial communities and functional characteristics and their correlations with soil fertility properties were explored in a double rice cropping system three to four years after a single biochar amendment. Three treatments including a control, a low (24 t ha−1), and a high (48 t ha−1) application rate of straw-derived biochar were constructed. Biochar amendment significantly increased the abundance of bacteria and fungi by up to 102 % and 178 %, respectively, which might be probably caused by the increases in soil total organic carbon (TOC), total nitrogen, and rice biomass as compared with the control. However, the abundance of archaea was only slightly elevated after biochar amendments. Bacteria/fungi ratios were significantly decreased by up to 61.4 % in the biochar treatments, probably because fungi were the dominant decomposers of increased recalcitrant carbon from biochar and rice biomass. Biochar stimulated the relative abundance of Acidobacteria, which favours soil organic carbon accumulation. Biochar increased the relative abundances of Mortierella and Westerdykella , which are more beneficial to plant growth and TOC degradation. Furthermore, potential phytopathogens of Athelia and Penicillium were decreased with biochar amendment. The results demonstrate that biochar application should be sustained as an effective measure for improving the microbial characteristics of paddy field by ameliorating its soil properties. [ABSTRACT FROM AUTHOR]

Bacterial community and soil enzymatic activity depend on soil and management conditions. Fertilization is an important approach to maintain and enhance enzyme activities and microbial community diversity. Although the effects of fertilizer application on soil microbial community and related parameters are explored, the effects on the soil microbiome associated with those of wheat plant organs, including those associated with roots and spikelets, are not well-known. Therefore, in this study, by using a sequencing approach, we assessed the effects of inorganic fertilizers, manure, and biochar on soil enzyme activities, bacterial community diversity and structure in the bulk soil, rhizosphere, roots, and spikelet of wheat (Triticumaestivum L.). For this, different treatment biochar (BC), manure (OM), low mineral fertilizer (HL), high mineral fertilizer (HF), and no fertilizer (FO) were used for the enzyme activities and bacterial community structure diversity tested. The result showed that organic amendment application increased total nitrogen, soil available phosphorus, and potassium compared to inorganic fertilizer and control, especially in the rhizosphere. Enzyme activities were generally higher in the rhizosphere than in the bulk soil and organic amendments increased activities of acid phosphatase (AcP), β-1,4-N-acetyl-glucosaminidase (NAG), and phenol oxydase (PhOx). Compared with soil and rhizosphere, bacterial diversity was lower in wheat roots and evenlower in the spikelet. From the bulk soil, rhizosphere to roots, the fertilization regimes maintained bacterial diversity, while organic amendment increased bacterial diversity in the spikelet. Fertilization regimes significantly influenced the relative abundances of 74 genera across 12 phyla in the four compartments. Interestingly, the relative abundance of Proteobacteria (Citrobacter, Pantoea, Pseudomonas, and unclassified Enterobacteriaceae) in the spikelet was decreased by increasing inorganic fertilizer and further by manure and biochar, whereas those of Actinobacteria (Microbacterium and an unclassified Microbacteriaceae) and Bacteroidetes (Hymenobacter and Chitinophagaceae) were increased. The results suggest that potential bacterial functions of both roots and above-ground parts of wheat would be changed by different organic amendment regimes (manure and biochar). [ABSTRACT FROM AUTHOR]

Response of biological communities to environmental stresses is a critical issue in ecology, but how microbial communities shift across heavy metal gradients remain unclear. To explore the microbial response to heavy metal contamination (e.g., Cr, Mn, Zn), the composition, structure and functional potential of sedimentary microbial community were investigated by sequencing of 16S rRNA gene amplicons and a functional gene microarray. Analysis of 16S rRNA sequences revealed that the composition and structure of sedimentary microbial communities changed significantly across a gradient of heavy metal contamination, and the relative abundances were higher for Firmicutes, Chloroflexi and Crenarchaeota, but lower for Proteobacteria and Actinobacteria in highly contaminated samples. Also, molecular ecological network analysis of sequencing data indicated that their possible interactions might be enhanced in highly contaminated communities. Correspondently, key functional genes involved in metal homeostasis (e.g., chrR, metC, merB), carbon metabolism, and organic remediation showed a higher abundance in highly contaminated samples, indicating that bacterial communities in contaminated areas may modulate their energy consumption and organic remediation ability. This study indicated that the sedimentary indigenous microbial community may shift the composition and structure as well as function priority and interaction network to increase their adaptability and/or resistance to environmental contamination. [ABSTRACT FROM AUTHOR]