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Purpose: To clarify the geographical distribution pattern of asymbiotic nitrogen activity and diazotrophic community in paddy soils, and to understand the primary environmental driving factors driving asymbiotic nitrogen fixation rate (ANFR) and community diversity. Materials and methods: The ANFR and the environmental driving factors of diazotrophic community diversity were investigated in 76 paddy soils across 6 major rice-growing regions in China by 15N2 labeling and nifH gene high-throughput sequencing. Results and discussions: Among all the sample sites, the northeast region had relatively higher ANFR (p < 0.05) compared to other regions. There was no significant correlation between soil ANFR and nifH abundance. The ANFR was significantly affected by Mo, total N and total P, while C:N ratio, exchangeable Ca and pH had a significant influence on nifH abundance. Proteobacteria, Thermodesulfobacteriota and Cyanobacteria dominated within the diazotrophic community across the paddy soils. Furthermore, 50.7% of the variance in community compositions could be attributed to different environmental variables. These multifactorial drivers, including Ca, C:N ratio, Mg, Na, Mn, N:P ratio, Mo and pH, significantly influence formation of specific diazotrophic microbial groups. Conclusions: (1) No significant correlation between the rate of asymbiotic nitrogen fixation in paddy soil and the abundance of the nifH gene. (2) The ANFR was significantly positively correlated with the molybdenum, phosphorus, potassium, nitrogen and organic carbon contents. (3) The abundance of the nifH gene was primarily correlated with Ca content and the soil C:N ratio. (4) Distinct diazotrophic communities are influenced by different environmental drivers. (5) Alphaproteobacteria and Spirochaetota are more abundant in soils with high elevated nitrogen and molybdenum content, indicating their significant contributions to nitrogen fixation in paddy soil. [ABSTRACT FROM AUTHOR]

The soil environment plays an important role in urban ecosystems. To study the heavy metal contamination of soil in Beilun District, Ningbo, we collected soil samples from 60 points in urban and peri-urban areas of Beilun District and analyzed the spatiotemporal variation and sources of heavy metal pollution in various land-use types. The results shown that the heavy metal contents in 2015 and 2022 were higher than the background soil values of Ningbo city, and there was an accumulation of heavy metals over these 7 years. The contents of heavy metals in green belts and woodland in 2022 were higher than those in 2015, while there was no significant change in agricultural land. The heavy metal contents in both years were mainly in the order green belts > agricultural land > woodland. The spatiotemporal distribution of heavy metal content showed that heavy metal pollution in Beilun District was concentrated in five industrial areas, and there was a trend toward the disappearance of highly polluted points. But the single-factor pollution index, pollution load index (PLI), and geoaccumulation index (Igeo) indicated that there was no significant heavy metal pollution in Beilun District, and individual elements at specific points showed slight pollution. The source analysis results showed that the main source of Hg is chemical, As is mainly derived from agricultural, Cr, Ni and Cu are mainly derived from natural, the main sources of Zn and Cd are electroplating and machinery activities, and the main source of Pb is traffic. These results specify a reference for future investigation on urban soil heavy metals, and the source apportionment results provide a scientific foundation for subsequent soil heavy metal pollution treatment. [ABSTRACT FROM AUTHOR]

Chemoautotrophic canonical ammonia oxidizers (ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB)) and complete ammonia oxidizers (comammox Nitrospira) are accountable for ammonia oxidation, which is a fundamental process of nitrification in terrestrial ecosystems. However, the relationship between autotrophic nitrification and the active nitrifying populations during 15N-urea incubation has not been totally clarified. The 15N-labeled DNA stable isotope probing (DNA-SIP) technique was utilized in order to study the response from the soil nitrification process and the active nitrifying populations, in both acidic and neutral paddy soils, to the application of urea. The presence of C2H2 almost completely inhibited NO3−-N production, indicating that autotrophic ammonia oxidation was dominant in both paddy soils. 15N-DNA-SIP technology could effectively distinguish active nitrifying populations in both soils. The active ammonia oxidation groups in both soils were significantly different, AOA (NS (Nitrososphaerales)-Alpha, NS-Gamma, NS-Beta, NS-Delta, NS-Zeta and NT (Ca. Nitrosotaleales)-Alpha), and AOB (Nitrosospira) were functionally active in the acidic paddy soil, whereas comammox Nitrospira clade A and Nitrosospira AOB were functionally active in the neutral paddy soil. This study highlights the effective discriminative effect of 15N-DNA-SIP and niche differentiation of nitrifying populations in these paddy soils. Key points: • 15N-DNA-SIP technology could effectively distinguish active ammonia oxidizers. • Comammox Nitrospira clade A plays a lesser role than canonical ammonia oxidizers. • The active groups in the acidic and neutral paddy soils were significantly different. [ABSTRACT FROM AUTHOR]

Soybean–maize intercropping system can improve the utilization rate of farmland and the sustainability of crop production systems. However, there is a significant gap in understanding the interaction mechanisms between soil carbon (C), nitrogen (N), and phosphorus (P) cycling functional genes, rhizosphere microorganisms, and nutrient availability. To reveal the key microorganisms associated with soil nutrient utilization and C, N, and P cycling function in the soybean–maize intercropping system, we investigated the changes in soil properties, microbial community structure, and abundance of functional genes for C, N, and P cycling under soybean–maize intercropping and monocropping at different fertility stages in a pot experiment. We found that there was no significant difference in the rhizosphere microbial community between soybean–maize intercropping and monocropping at the seeding stage. As the reproductive period progressed, differences in microbial community structure between intercropping and monocropping gradually became significant, manifesting the advantages of intercropping. During the intercropping process of soybean and maize, the relative abundance of beneficial bacteria in soil rhizosphere significantly increased, particularly Streptomycetaceae and Pseudomonadaceae. Moreover, the abundances of C, N, and P cycling functional genes, such as abfA, mnp, rbcL, pmoA (C cycling), nifH, nirS-3, nosZ-2, amoB (N cycling), phoD, and ppx (P cycling), also increased significantly. Redundancy analysis and correlation analysis showed that Streptomycetaceae and Pseudomonadaceae were significantly correlated with soil properties and C, N, and P cycling functional genes. In brief, soybean and maize intercropping can change the structure of microbial community and promote the proliferation of beneficial bacteria in the soil rhizosphere. The accumulation of these beneficial bacteria increased the abundance of C, N, and P cycling functional genes in soil and enhanced the ability of plants to fully utilize environmental nutrients and promoted growth. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) can affect phosphorus (P) cycling in paddy fields by changing soil properties and microbial community function, but their impact on soil P availability remains unclear. A laboratory incubation experiment was applied to explore the effect of different MPs on the soil available P content. Amendment with nonbiodegradable MPs significantly (p < 0.05) reduced soil P availability, whereas the available P content decreased with increasing biodegradable MP content from 0.1 to 1.0% (except in the 1.0% poly(lactic acid) treatment). The presence of MPs inhibited soil alkaline phosphatase activity and reduced the copy numbers of microbial functional genes involved in organic P mineralization (phoD and phoX) and inorganic phosphate solubilization (ppk and pqqC). There were positive linear relationships of the soil available P content with phosphatase activity and the phoX and pqqC genes. Partial least squares path modeling indicated that nonbiodegradable MPs indirectly reduced the soil available P content by controlling the abundance of microbial functional genes involved in organic P mineralization, whereas amendment with biodegradable MPs did not significantly affect soil P availability directly or indirectly. Our results provide evidence that MPs have the potential to reduce the available P substrate in soils, and management practices should be established to improve P availability in MP-polluted paddy fields. [ABSTRACT FROM AUTHOR]

Pesticides are environmental contaminants of great interest because of their toxicity, persistence in the environment and bio-accumulative nature. However, there is a scarcity of literature concerning human exposure to pesticides through the consumption of contaminated drinking water. This study investigates the levels of multiple pesticides in drinking water and their subsequent carcinogenic and non-carcinogenic risk in five selected districts (Peshawar basin) of Khyber Pakhtunkhwa-Pakistan, to understand the exact scenario of pesticide toxicity in the sources of drinking water. The water samples were extracted by liquid–liquid extraction and analyzed using gas chromatography mass spectrometry (GCMS). Results obtained indicated that the detected concentrations of ∑21 pesticides ranged between 0 and 883.7 µg L−1 in the study area. The highest concentration was detected for methiocarb (mean 5.30 µg L−1), followed by acetamiprid (0.90 µg L−1), while the lowest was observed for cyhalothrin (0.01 µg L−1). The highest concentration of EU Watch List of Contaminants of Emerging Concern (methiocarb and acetamiprid) in the study area is alarming. Most of the pesticide residues recorded in the water samples exceeded the maximum residue limits except for dieldrin and cyhalothrin. Whereas, the residues of aldicarb, carbofuran deg, carbofuran, atrazine, alpha endosulfan, beta endosulfan, cypermethrin-1, difenoconazol-I and difenoconazol-II were not observed in any of the collected samples. The incremental lifetime cancer risk of endocrine disruptors such as dieldrin, o,p′ DDT, o,p′ DDD, and p,p′ DDE was > 10–6, posing potentially serious carcinogenic risk to the local inhabitants. Whereas, the non-carcinogenic risk through pesticide exposure was negligible, suggesting no/little risk to the inhabitants from these chemicals in drinking water. Regular monitoring is needed to evaluate pesticide concentrations not only in drinking water sources but also in soil and food crops as they pose serious eco-toxicological risks. [ABSTRACT FROM AUTHOR]

To investigate whether elevated CO2 (eCO2) changes the influence of nanoparticles (NPs) on soil microbial communities and the mechanisms, various nano-ZnO (0, 100, 300, and 500 mg·kg−1) and CO2 concentrations (400 and 800 µmol·mol−1) were applied to tomato plants (Solanum lycopersicum L.) in growth chambers. Plant growth, soil biochemical properties, and rhizosphere soil microbial community composition were analyzed. In 500 mg·kg−1 nano-ZnO-treated soils, root Zn content was 58% higher, while total dry weight (TDW) was 39.8% lower under eCO2 than under atmospheric CO2 (aCO2). Compared with the control, the interaction of eCO2 and 300 mg·kg−1 nano-ZnO decreased and increased bacterial and fungal alpha diversities, respectively, which was caused by the direct effect of nano-ZnO (r = − 1.47, p < 0.01). Specifically, the bacterial OTUs decreased from 2691 to 2494, while fungal OTUs increased from 266 to 307, when 800–300 was compared with 400–0 treatment. eCO2 enhanced the influence of nano-ZnO on bacterial community structure, while only eCO2 significantly shaped fungal composition. In detail, nano-ZnO explained 32.4% of the bacterial variations, while the interaction of CO2 and nano-ZnO explained 47.9%. Betaproteobacteria, which are involved in C, N, and S cycling, and r-strategists, such as Alpha- and Gammaproteobacteria and Bacteroidetes, significantly decreased under 300 mg·kg−1 nano-ZnO, confirming reduced root secretions. In contrast, Alpha- and Gammaproteobacteria, Bacteroidetes, Chloroflexi, and Acidobacteria were enriched in 300 mg·kg−1 nano-ZnO under eCO2, suggesting greater adaptation to both nano-ZnO and eCO2. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States 2 (PICRUSt2) analysis demonstrated that bacterial functionality was unchanged under short-term nano-ZnO and eCO2 exposure. In conclusion, nano-ZnO significantly affected microbial diversities and the bacterial composition, and eCO2 intensified the damage of nano-ZnO, while the bacterial functionality was not changed in this study. [ABSTRACT FROM AUTHOR]

Polyethylene glycol (PEG) is widely used as phase change materials (PCMs). However, the leakage and low thermal conductivity issues restrict its practical application. Herein, a series of novel MWCNTs/HPC/PEG PCMs (named as PCMMHP) have been synthesized by hydroxypropyl cellulose grafting onto PEG for the first time and doping multi-walled carbon nanotubes (MWCNTs). The results indicate that the PCMMHP exhibit excellent shape stability and without leakage keeping warm for an hour at 353.2 K. The melting and freezing enthalpy of the PCMM1HP7 is 134.7 J g−1 and 131.2 J g−1, respectively; and corresponding melting point and crystallization temperature are about 324.9 K and 308.8 K, respectively. The PCMMHP show a good reversible thermal stability after 100 heating/cooling cycles. In addition, adding 4 mass% MWCNTs, the PCMM4HP7 possess a higher thermal conductivity of 0.6019 W m−1 K−1, which is 2.1 times that of the PCMHP without MWCNTs (0.2895 W m−1 K−1) and 1.9 times that of pure PEG (0.3228 W m−1 K−1). In a word, the fabricated PCMMHP is a kind of shape-stabilized PCM and has good latent ability. It will have a broad potential application in thermal energy storage applications. [ABSTRACT FROM AUTHOR]

Sorghum has a great capacity to release biological nitrification inhibitors (BNIs), but the inhibitory effect on nitrification and ammonia oxidizer populations under planted soil conditions is unclear. A pot experiment with three nitrogen (N) application rates (0, 50, and 200 mg N kg−1) was set up to detect the influence of sorghum growth on soil nitrification and investigate the function of blocking the activity of ammonia oxidizers. A 15N-labeled experiment was also conducted to detect the N form absorbed by sorghum. Sorghum root exudates were collected at 30 days after transplanting to hydroponic culture and added into cultured soil to determine the shifts in the populations of nitrifiers. The 15N labeling experiment showed that the uptake rate by sorghum of ammonium N fertilizer was 24% and that of nitrate N fertilizer was 9%, indicating that sorghum was an ammonium using plant. Compared with unplanted soil, sorghum planting had a significant inhibitory effect on the nitrification process even at the high-N fertilizer rates. Autotrophic nitrification was the prevailing process, and sorghum root exudation inhibited this process as much as dicyandiamide (DCD, 10 mg kg−1). Root exudates had a significant inhibitory effect on ammonia-oxidizing bacteria (AOB) but had no effect on ammonia-oxidizing archaea (AOA). [ABSTRACT FROM AUTHOR]

Root-associated microorganisms play an important role in plant nutrition and productivity. However, our understanding of how a plant-microbiome system responds to pre-planting soil management remains limited. Here, continuous labeling with 13CO2 gas combined with stable isotope probing (SIP) was applied to explore bacterial utilization of plant-derived carbon (C) in the tomato rhizosphere as affected by biochar amendment or reductive soil disinfestation (RSD). Our results showed that RSD treatment strongly shaped the soil bacterial community composition, while biochar soil amendment had little impact on the community in the rhizosphere of tomato. We observed that the bacterial community in the RSD treatment, which actively utilized plant-derived C, belonged to various phyla (i.e., Proteobacteria, Cyanobacteria, Verrucomicrobia, and Acidobacteria), while the genus Streptomyces (phylum Actinobacteria) was the main bacterial taxa that actively utilized plant-derived C in the biochar and control treatments. This study provides evidence that biochar application or RSD pre-planting soil management practices induced distinct bacterial utilization of plant-derived C, which may in turn regulate plant productivity in agricultural systems. Key points: • Genus Streptomyces was the main bacterial group utilizing plant-derived carbon in both control and biochar treatments. • Reductive soil disinfestation altered bacterial utilization of plant-derived carbon. • Biochar did not alter the composition of the bacterial communities but had more labeled bacterial taxa utilizing plant-derived carbon. [ABSTRACT FROM AUTHOR]

The most severe outcome of the widespread interspecific competition that occurs between invasive organisms and their local congeners is species displacement. The western flower thrips, Frankliniella occidentalis (Pergande), which originated from western North America, has invaded much of the agricultural world since the 1970s, and in so doing, has become a dominant thrips species in many of the areas it has invaded. Its invasion success and the extent of its distribution in the regions it has invaded can be largely attributed to its superiority in interspecific competition. In some instances, however, F. occidentalis has been less successful in its invasion attempts and has not become dominant in its new environment. Thrips species displacements often arise from interactions of different mechanisms that are mediated by numerous biotic and abiotic factors. In this review, we summarize competitive interaction events that have been documented between F. occidentalis and several species of other locally present thrips, their interaction mechanisms and mediating factors. This review will help to better understand displacement events of thrips species in some areas and to develop management strategies for thrips species with high invasion potential. [ABSTRACT FROM AUTHOR]

Purpose: The success of phytoremediation relies on beneficial plant-microbe interactions. However, the changes of soil microbiota, during the phytoremediation of ion-adsorption rare earth element (REE) mine tailings, are far from understood. The present study was conducted to reveal the co-occurrence patterns and key regulating factors of bacterial communities in ion-adsorption REE mine tailings with phytoremediation. Materials and methods: A field experiment was conducted on an ion-adsorption REE mine tailing to test three phytoremediation strategies: (i) phytostabilization with grasses, (ii) phytostabilization with economic crops, and (iii) phytoextraction with REE hyperaccumulators. The bacterial community diversity, co-occurrence patterns, and the key regulating environmental factors in bulk and rhizospheric soils after 16 months of reclamation were studied by 16S Illumina high-throughput sequencing. Results and discussion: The soils of plots with REEs-hyperaccumulators had significantly higher α-diversity than those planted with non-accumulators. After phytoremediation, the diversity and relative abundances of bacteria assisting in nutrient acquisition pronouncedly increased in the bulk soil of the reclaimed plots. Some plant growth–promoting bacteria (PGPB), e.g., Rhodanobacter, Streptomyces, and Bacillus, were enriched in the rhizospheric soil samples. Meanwhile, soil nutrient (total carbon and total nitrogen) concentration and REE availability were the most significant factors shaping the bacterial communities. Furthermore, special bacterial consortia of Bacilli took up the positions of the keystone species. Conclusions: The results revealed the co-occurrence patterns and key regulating factors of bacterial communities in ion-adsorption REE mine tailings, which will provide more crucial information for the optimization of the reclamation of REE tailings. [ABSTRACT FROM AUTHOR]

Purpose: Due to the inevitable interaction between bacteria and soil minerals, whether bacteria could exert the excepted functions in the soil is yet to be confirmed and how minerals affect biosorption potential is needed to be investigated. The purposes of this study were to explore the adsorption behavior and mechanism of metal-resistant bacteria attaching to typical red soil minerals under different conditions and to discuss whether biosorption potential would be altered after the addition of functional bacteria to soil. Materials and methods: Here, we tested equilibrium adsorption along with zeta potential analysis, scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and desorption to investigate the adsorption of two metal-resistant bacteria (Gram-negative Enterobacter sp. EG16 and Gram-positive Bacillus subtilis DBM) onto typical red soil minerals including goethite, kaolinite, and gibbsite under different environmental factors. Results and discussion: We found that the minerals adsorbed more EG16 cells than DBM, and the adsorption capacities followed the sequence of goethite > kaolinite > gibbsite. Both the surfaces of bacteria and mineral were pH-dependent in our tested pH range (4.0–7.0), and the maximum adsorption was at pH 4.0. Increasing ionic strength resulted in less adsorption of bacteria onto goethite, whereas bacterial adsorption onto kaolinite was the opposite. These observations elucidated that electrostatic interaction was the dominant contributor. The adsorption conformed to the Langmuir and pseudo-second-order kinetic model implying chemical adsorption, and the result of FTIR also supported that. Desorption experiment has suggested the significant contribution of electrostatic force and the minor dominator of functional groups for bacteria–mineral combination. Conclusions: The results of this study indicated that electrostatic interaction was the dominant contributor to bacteria–mineral combination and functional groups coordination contributed less than 10%. This finding suggested most adhered bacteria could still provide active sites for heavy metal biosorption. Thus, although 50–90% of added functional bacteria has adhered to minerals, the bacteria–mineral combination had a limited impact on biosorption. [ABSTRACT FROM AUTHOR]

Purpose: The landfill soil microbes related to nutrient cycling, such as carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling, are changed by continuous waste decomposition. Monitoring the changes that occur in CNPS functional genes in different types of landfill cover soils as a whole is vital to our understanding of microbial function in element cycling. Materials and methods: The high-throughput quantitative polymerase chain reaction–based chip (HT-Q-PCR) method was used to explore differences in the abundance of 71 CNPS functional genes in cover soils (0–20 cm, 20–40 cm, and 40–60 cm) from two types of landfills (sanitary and non-sanitary) and to examine the soil pH and the concentrations of C, N, P, S, and 6 heavy metals. Results and discussion: The absolute abundances of CNPS functional genes varied greatly, with the highest gene abundance reaching 5.28 × 109 copies per gram of soil, and 11% (8/71) of the genes not detected. Among the detected genes, there was a much higher functional gene abundance in the sanitary landfill than in the non-sanitary landfill cover soils, and the difference in gene abundance became more significant with increasing sampling depth. In addition to landfill type and sampling depth, the soil pH, soil dissolved organic carbon (DOC), available N (AN), and available S (AS) correlated significantly to functional gene abundance. Conversely, soil heavy metals, such as Cu, Cd, Cr, Zn, and Ni, had no effects on functional gene abundance, which might be due to their low contents. Conclusions: Our results suggest that sanitary landfill increases soil CNPS gene abundance compared to that of non-sanitary landfill. The findings provide suggestions for landfill treatment and ecological protection, especially regarding vegetation restoration. [ABSTRACT FROM AUTHOR]

Purpose: Biological nitrogen fixation (BNF) plays an important role in nitrogen cycling by transferring atmospheric dinitrogen to the soil. BNF is performed by symbiotic and asymbiotic nitrogen-fixing microorganisms. However, the abundance, activity, and community structure of diazotrophs under different nitrogen fertilizer application rates and how root exudates influence diazotrophs remain unclear. Materials and methods: 15N-N2 and 13C-CO2 labeling, DNA-based stable isotope probing (SIP), and molecular biological techniques were used in this study. The abundance, activity, and structure of symbiotic and asymbiotic diazotrophs under different nitrogen fertilizer applications in paddy soil were investigated. Results and discussion: We found that the nitrogen fixation capacity in milk vetch (Astragalus sinicus L.) and nifH gene abundance in the root nodules were significantly higher in the low-nitrogen treatment than in the control (zero) and high-nitrogen treatments. Nitrogen-fixing bacteria were abundant in the soils with a high biodiversity. Soil nifH gene sequences were dominated by α-, β-, and δ-proteobacteria, as well as by Cyanobacteria. The relative abundance of α-proteobacteria was lower, and the relative abundance of Cyanobacteria was higher under high nitrogen. Incubation of soil with 13CO2 and subsequent DNA-SIP analysis demonstrated that OTU65 from α-proteobacteria was relatively more abundant in heavy fractions of the 13C-labeled soils than that in the unlabeled soils, indicating that α-proteobacteria may prefer rhizodeposition carbon to other organic carbon. However, OTU24 and OTU73 from δ-proteobacteria had relatively high abundances in light fractions both in the 13C-labeled and unlabeled samples, indicating that δ-proteobacteria may prefer other soil organic carbon to rhizodeposition carbon. Conclusions: The results suggested that soil N availability and rhizodeposition strongly modified the microbial communities of nitrogen-fixing bacteria. Moderate nitrogen application increased the symbiotic biological N fixing activity in the Astragalus sinicus L. rhizosphere. The BNF activity in the legume-rhizobia system is regulated by the exchange of organic C and N nutrient between the host plant and N-fixing bacteria. [ABSTRACT FROM AUTHOR]

Purpose: Microbial nitrification plays an important role in nitrogen cycling in ecosystems. Nitrification is performed by ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) including complete ammonia oxidizers. However, the relative importance of nitrifiers in autotrophic nitrification in relation to soil pH is still unclear.Materials and methods: Combining DNA-based stable isotope probing (SIP) and molecular biological techniques, we investigated the abundance, structure, and activity of AOA, AOB, and NOB along a pH-gradient (3.97-7.04) in a vegetable cropped soil.Results and discussion: We found that AOA abundance outnumbered AOB abundance and had a significantly negative relationship with soil pH. The abundances of NOB Nitrospira 16S rRNA, nxrB gene, and Nitrobacter nxrA gene were affected by soil pH. Incubation of soil with 13CO2 and DNA-SIP analysis demonstrated that significant 13CO2 assimilation by AOA rather than by AOB occurred in the acidic soils, whereas the labeled 13C level of AOA was much less in the neutral soil than in the acidic soils. There was no evidence of 13CO2 assimilation by NOB except for Nitrobacter with NxrB gene at pH 3.97. Phylogenetic analysis of AOA amoA gene in the 13C- and 12C-labeled treatments showed that the active AOA mainly belonged to Nitrososphaera in the acidic soils.Conclusions: These results suggested that the main performer of nitrification was AOA in the acidic soils, but both AOA and AOB participated in nitrification in the neutral soil with low nitrification activity. NOB Nitrospira and Nitrobacter did not grow in the soils with pH 4.82-7.04 and other populations of NOB were probably involved in nitrite oxidation in the vegetable cropped soil. [ABSTRACT FROM AUTHOR]

Laboratory and greenhouse experiments were carried out to investigate the chemical, physical, and microbial properties of seawater-neutralized bauxite residues and the effects of additional leaching (1 pore volume of deionized water versus an additional 6 pore volumes) and amendment with gypsum (5%) and/or cattle manure (6%) on its properties and on the growth of Rhodes grass (Chloris gayana). Additional leaching resulted in a decrease in EC, exchangeable Na, SAR, and ESP. For unamended control treatments, additional leaching induced a rise in pHSE from 8.5 to 9.6 and pH1:5 from 9.1 to 10.1 due to dissolution of residual alkalinity. Addition of gypsum arrested this pH increase resulting in a final pHSE of 7.5 and pH1:5 of 8.8. In control treatments, additional leaching resulted in a pronounced decrease in Rhodes grass yields. However, in gypsum and cattle manure-amended treatments, it led to substantial yield increases and decreases in tissue Al and Na concentrations and increased K/Na ratios. Upon drying for the first time, bauxite residue was shown to contract and form a solid massive structure. The aggregates formed from crushing this material were water stable (as measured by wet sieving). Additions of cattle manure or gypsum to residue aggregates did not affect pore size distribution. Addition of cattle manure increased organic C and microbial biomass C content and basal respiration rate while additional leaching increased basal respiration and metabolic quotient. It was concluded that a combination of drying and crushing the residue, amending it with gypsum and organic manure followed by extensive leaching results in the formation of a medium that supports plant growth. [ABSTRACT FROM AUTHOR]

We quantified deviations in regional forest biomass from simple extrapolation of plot data by the biomass expansion factor method (BEF) versus estimates obtained from a local biomass model, based on large-scale empirical field inventory sampling data. The sources and relative contributions of deviations between the two models were analyzed by the boosted regression trees method. Relative to the local model, BEF overestimated accumulative biomass by 22.12%. The predominant sources of the total deviation (70.94%) were stand-structure variables. Stand age and diameter at breast height are the major factors. Compared with biotic variables, abiotic variables had a smaller overall contribution (29.06%), with elevation and soil depth being the most important among the examined abiotic factors. Large deviations in regional forest biomass and carbon stock estimates are likely to be obtained with BEF relative to estimates based on local data. To minimize deviations, stand age and elevation should be included in regional forest-biomass estimation. [ABSTRACT FROM AUTHOR]

Purpose: Nitrogen fixation by free-living diazotrophs from the atmosphere is an important pathway for nitrogen input into the soil. However, there is little information regarding soil diazotrophic community composition and diversity under long-term fertilization in rice paddy ecosystems.Materials and methods: Using the 15N2-tracing method and nifH gene as a molecular marker, we investigated the abundance, structure, and activity of soil diazotrophic community in soil at a 30-year-old filed experimental site treated with four different fertilizer management practices: control (non-fertilization), chemical NPK fertilizers, NPK plus rice straw (NPK+RS), or NPK plus chicken manure (NPK+OM).Results and discussion: Among all the treatments, the NPK+OM treatment significantly improved the soil nutritional status. Fertilization increased both bacteria and nifH gene abundances, with the highest values (p < 0.05) found in the NPK+OM treatment. The potential nitrogen fixation rate ranged from 14.6 to 118 μg kg−1 day−1, and the highest rates (p < 0.05) were also observed in the NPK+OM treatment. Long-term chemical NPK fertilization decreased the diversity of diazotrophic community, whereas NPK+RS and NPK+OM treatments maintained the diversity of diazotrophic community. Long-term fertilization changed diazotrophic community as compared to non-fertilization, but there were no significant differences among fertilized treatments. Most nifH sequences were closely linked to Alphaproteobacteria, which was dominated by the genera Bradyrhizobium. Relatively higher Cyanobacteria abundances were observed in the unfertilized soil as compared with fertilized soil.Conclusions: Our results suggest that long-term fertilization increased the abundance of diazotrophs and changed their community structure, and combined use of chicken manure and chemical NPK fertilizers can significantly improve the activity of diazotrophic community. [ABSTRACT FROM AUTHOR]

Paddy soil experiences repeated anaerobic and aerobic changes during rice growth, the dramatic dynamics of soil water status accompanied by changes in redox condition and O availability. However, the effect of rapid water status change on soil microbial biomass and community composition is not well explored. Here, we present a comprehensive study focusing on the short-term water status change in 13 Chinese paddy soils. In order to gain a reliable way to determine soil microbial biomass carbon (MBC) in flooded or water-saturated soils, we also evaluated two different procedures (nitrogen bubbled and 100 °C water bath) to remove chloroform in extracts during the fumigation process. Compared to non-flooded paddy soils, the flooded paddy soils tended to have a lower microbial biomass, and this was much clearer using adenosine 5′-triphosphate (ATP) and phospholipid fatty acid (PLFA) analysis compared to biomass measured by the fumigation method. Fungal biomass, which was indicated by both ergosterol and the PLFA 18:2ω6,9c, also decreased after short-term flooding. Changes in soil microbial community composition (determined by PLFA biomarkers) were observed after short-term flooding, but the extent varied between soils. This study indicates that the dynamics of short-term water status altered the soil microbial biomass (ATP, MBC, and total PLFA) and community composition. Finally, our results suggested that liquid fumigation combined with the nitrogen-bubbled method is the best choice for analyzing MBC concentrations in water-saturated soils. [ABSTRACT FROM AUTHOR]

Purpose: Organic matter amendment is usually used to improve soil physicochemical properties and to sequester carbon for counteracting climate change. There is no doubt that such amendment will change microbial activity and soil nitrogen transformation processes. However, the effects of straw and biochar amendment on anammox and denitrification activity and on community structure in paddy soil are unclear. Materials and methods: We conducted a 30-day pot experiment using rice straw and rice straw biochar to deepen our understanding about the activity, microbial abundance, and community structure associated with soil nitrogen cycling during rice growth. Results and discussion: Regarding activity, anammox contributed 3.1-8.1% of N production and denitrification contributed 91.9-96.9% of N production; straw amendment resulted in the highest denitrification rate (38.9 nmol N g h), while biochar amendment resulted in the highest anammox rate (1.60 nmol N g h). Both straw and biochar amendments significantly increased the hzsB and nosZ gene abundance ( p < 0.05). Straw amendment showed the highest nosZ gene abundance, while biochar amendment showed the highest hzsB gene abundance. Phylogenetic analysis of the anammox bacteria 16S rRNA genes indicated that Candidatus Brocadia and Kuenenia were the dominant genera detected in all treatments. Conclusions: Straw and biochar amendments have different influences on anaerobic ammonia oxidation and denitrification within paddy soil. Our results suggested that the changes in denitrification and anammox rates in the biochar and straw treatments were mainly linked to functional gene abundance rather than microbial community structure and that denitrification played the more major role in N production in paddy soil. [ABSTRACT FROM AUTHOR]

Yellow clay paddy soil (Oxisols) is a typical soil with low productivity in southern China. Nitrification inhibitors and slow release fertilizers have been used to improve nitrogen fertilizer utilization and reduce environmental impaction of the paddy soil. However, their effects on ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in paddy soil have rarely been investigated. In the present work, we compared the influences of several slow release fertilizers and nitrification inhibitors on the community structure and activities of the ammonia oxidizers in yellow clay soil. The abundances and community compositions of AOA and AOB were determined with qPCR, terminal restriction fragment length polymorphism (T-RFLP), and clone library approaches. Our results indicated that the potential nitrification rate (PNR) of the soil was significantly related to the abundances of both AOA and AOB. Nitrogen fertilizer application stimulated the growth of AOA and AOB, and the combinations of nitrapyrin with urea (NPU) and urea-formaldehyde (UF) inhibited the growth of AOA and AOB, respectively. Compared with other treatments, the applications of NPU and UF also led to significant shifts in the community compositions of AOA and AOB, respectively. NPU showed an inhibitory effect on AOA T-RF 166 bp that belonged to Nitrosotalea. UF had a negative effect on AOB T-RF 62 bp that was assigned to Nitrosospira. These results suggested that NPU inhibited PNR and increased nitrogen use efficiency (NUE) by inhibiting the growth of AOA and altering AOA community. UF showed no effect on NUE but decreased AOB abundance and shifted AOB community. [ABSTRACT FROM AUTHOR]

Purpose: Soil microorganisms are important in the cycling of plant nutrients. Soil microbial biomass, community structure, and activity are mainly affected by carbon substrate and nutrient availability. The objective was to test if both the overall soil microbial community structure and the community-utilizing plant-derived carbon entering the soil as rhizodeposition were affected by soil carbon (C) and nitrogen (N) availability. Materials and methods: A C-CO steady-state labeling experiment was conducted in a ryegrass system. Four soil treatments were established: control, amendment with carboxymethyl cellulose (CMC), amendment with ammonium nitrate (NF), combined CMC and NF. Soil phospholipid fatty acid (PLFA) and C labeling PLFA were extracted and detected by isotope ratio mass spectrometer. Results and discussion: The combined CMC and NF treatment with appropriate C/N ratio (20) significantly enhanced soil microbial biomass C and N, but resulted in lower soil inorganic N concentrations. There was no significant difference in soil PLFA profile pattern between different treatments. In contrast, most of the C was distributed into PLFAs 18:2ω6,9c, 18:1ω7c, and 18:1ω9c, indicative of fungi and gram-negative bacteria. The inorganic-only treatment was distinct in C PLFA pattern from the other treatments in the first period of labeling. Factor loadings of individual PLFAs confirmed that gram-positive bacteria had relatively greater plant-derived C contents in the inorganic-only treatment, but fungi were more enriched in the other treatments. Conclusions: Amendments with CMC can improve N transformation processes, and the ryegrass rhizodeposition carbon flux into the soil microbial community is strongly modified by soil N availability. [ABSTRACT FROM AUTHOR]

Rice straw application and flooding are common practices in rice production, both of which can induce changes in the microbial community. This study used soil microcosms to investigate the impact of water status (saturated and nonsaturated) and straw application (10 g kg soil) on soil microbial composition (phospholipid fatty acid analysis) and activity (MicroResp method). Straw application significantly increased total PLFA amount and individual PLFA components independent of soil moisture level. The amount of soil fungal PLFA was less than Gram-negative, Gram-positive, and actinomycete PLFA, except the drained treatment with rice straw application, which had higher fungal PLFA than actinomycete PLFA at the initial incubation stage. Straw amendment and waterlogging had different effects on microbial community structure and substrate-induced pattern. PLFA profiles were primarily influenced by straw application, whereas soil water status had the greater influence on microbial respiration. Of the variation in PLFA and respiration data, straw accounted for 30.1 and 16.7 %, while soil water status explained 7.5 and 29.1 %, respectively. Our results suggest that (1) the size of microbial communities in paddy soil is more limited by carbon substrate availability rather than by the anaerobic conditions due to waterlogging and (2) that soil water status is more important as a control of fungal growth and microbial community activity. [ABSTRACT FROM AUTHOR]

Purpose: Nitrous oxide (NO) is produced naturally in soils through microbial processes of nitrification and denitrification. In recent years, the long-term application of nitrogen-heavy fertilizers has led to the acidification of tea orchard soils with high NO emission. The present research aimed at finding out which process (nitrification or denitrification) dominates in NO production, whether certain fertilizer managements could reduce NO emission, and the effects of fertilizer management on the abundance of functional genes. Materials and methods: Two nitrification inhibitors, 3, 4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD), combined with different N fertilizers (ammonium sulfate and potassium nitrate) were applied to highly acidic tea orchard soil in an aerobic incubation experiment. Both amoA and nosZ gene abundances from different treatments were determined by quantitative PCR. An anaerobic nitrate effect test was carried out using CH inhibition method. Results and discussion: The application of nitrate fertilizers significantly ( P < 0.05) enhanced total NO emission. A linear regression analysis between total NO emission and average nitrate contents indicated that denitrification is the dominant source of NO in this tea orchard soil. In the anaerobic incubation, no significant difference of NO emission was observed between KNO and no KNO treatments before 96 h. Quantitative PCR revealed lower copy numbers of nosZ in nitrate-associated fertilizer-treated soils than the soils from other treatments. Compared with the control, ammonium fertilizers with DCD or DMPP significantly ( P < 0.05) inhibited nitrate production as well as NO. Conclusions: These results showed that denitrification is the dominant source of NO in this highly acidic soil. Nitrate addition could significantly inhibit the abundance of nitrous oxide reductase, therefore causing high NO emission. The application of ammonium fertilizers with DCD or DMPP could significantly reduce NO emission, possibly due to the effective inhibition of nitrate production. [ABSTRACT FROM AUTHOR]