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Integrating inorganic fertilizers (NPK) with organic materials have been common practices for sustainable agriculture production in low-productivity paddy soil. A 4-year field experiment was conducted to investigate the effects of the annual application of inorganic fertilizer in contrast with the combined application of organic manures and NPK on rice grain yield and the soil chemical properties. Six treatments, including control (no fertilizer), NPK alone, NPK plus spent mushroom compost at 1.5 Mg ha −1 (NPK + MC), NPK plus green manure at 3.6 Mg ha −1 (NPK + GM), NPK plus cattle manure at 4.7 Mg ha −1 (NPK + CM), and NPK plus rice straw at 3.0 Mg ha −1 (NPK + RS)—were applied in this study. The results indicated that the rice grain yields for 2014 under the NPK + CM and NPK + RS treatments were 11.4% and 9.3% higher, respectively, compared with the NPK alone treatment. No significant differences in rice yield were observed between the plots using NPK and NPK + MC or NPK + GM treatments. The application of CM to the soil surface led to significantly higher soil pH (0.16–0.29 units), cation exchange capacity (CEC) (17.4%–21.9%), and lower exchangeable acidity and Al 3+ concentrations at soil depths of 0–20 cm, compared with the NPK alone treatment. However, no significant differences in pH or concentrations of base cations in the soil were observed in the 0–10 cm soil layer after the application of NPK alone or NPK plus the other three organic amendments. Additionally, the application of NPK + CM at 4.7 Mg ha −1  y −1 showed the highest available P concentration at 0–10 cm depth. Overall, the rice grain yield, soil pH, and available P were effectively improved by NPK in combination with CM at 4.7 Mg ha −1 . [ABSTRACT FROM AUTHOR]

Pig manure has been utilized as a good feedstock to produce biochar. However, the pig manure-derived biochar from intensive pig cultivation contains high levels of total and bioavailable heavy metals. In this study, the co-pyrolysis of pig manure with other biomass (e.g. rice straw) at 300–700 °C was investigated to solve the above-mentioned topic. The ammonium acetate (CH 3 COONH 4 ), Tessier sequential extraction procedure and hydrogen peroxide were adopted to evaluate the bioavailability, chemical speciation, and potential risk of Cu and Zn in the biochars. Results showed that the addition of rice straw significantly reduced the concentrations of total, exchangeable and carbonate-associated Cu and Zn in the biochars compared to the single pig manure biochars. Co-pyrolysis of pig manure with rice straw at a mass ratio of 1:3 and at 600 °C could be most effective to reduce the concentrations of CH 3 COONH 4 -extractable and potential released Cu and Zn in the biochars. In conclusion, the co-pyrolysis process is a feasible management for the safe disposal of metal-polluted pig manure in an attempt to reduce the bioavailability and potential risk of heavy metals at relatively high pyrolysis temperatures. [ABSTRACT FROM AUTHOR]

The aim was to investigate the influence of pentachlorophenol (PCP) on the soil microbial communities and the coupled mechanism between PCP reductive dechlorination and soil redox under anaerobic condition. Accordingly, a slurry incubation experiment was carried out in which bacterial and archaeal communities were detected by MiSeq amplicon sequencing. The original microbial community balance was gradually disrupted and new microbial structure was reconstructed subsequently through self-regulation and acclimation during PCP transformation, coupling with the changes of soil biogeochemical redox dynamics. The phylum Bacteroidetes predominated during the earlier PCP dechlorination period and then was progressively replaced by Proteobacteria and Firmicutes groups when PCP was mostly transformed into 2,3,4,5-TeCP and 3,4,5-TCP. Heatmap and hierarchical cluster analysis revealed the Clostridium -like, Geobacter -like and Dehalococcoides -like organisms enriched concurrently during PCP reductive dechlorination processes. The relative abundance changes of the redox-active microorganisms, together with their relevance to the corresponding biogeochemical redox processes, showed that PCP dechlorination, Fe(III) and SO 4 2 − reduction, as well as methanogenesis were coupled terminal electron accepting processes. The combined analysis of the microbial function, the affinity for substrates (H 2 and acetate) and the sensitivity for PCP toxicity by microorganisms might explain why electron transport chain has changed in soil biogeochemical redox process. Our study offers a comprehensive description of the impact of PCP on the soil microbial community structures, which could be very useful for understanding the regulation of soil nutrient and energy transfer during biogeochemical cycling processes in soils with significant inputs of exogenous pollutants. [ABSTRACT FROM AUTHOR]

The intensive and unregulated application of feed additives to commercial pig foods has resulted in high levels of Cu and Zn in pig manure. The aim of this study was to assess the impacts of composting and pyrolysis processes on the bioavailability and chemical speciation of Cu and Zn in pig manure products by single and sequential extractions, and to compare metal bioavailability in composts and biochar-amended soils in incubation experiments. Composting and pyrolysis processes can convert exchangeable and carbonate-bound Cu and Zn to organic matter and residual fractions, and significantly reduce the potential availability of metals in composts and biochars. The DTPA-Cu and Zn concentrations in soils amended with biochar BC700 were lower than in composts and soils amended with biochar BC400. It is suggested that 700 °C is the preferred pyrolysis temperature for the conversion of pig manure contaminated with heavy metals to biochar, in order to minimize environmental pollution. [ABSTRACT FROM AUTHOR]

A large number of soils, worldwide, are acid (normally pH < 5.5) and suffering from on-going soil acidification. Acid soils or soils undergoing acidification generally have low fertility and low crop productivity. Biochars have been reported to be of potential value in agriculture for improving soil properties and in reducing the hazards caused by soil acidification and in naturally acidic soils. However, the ameliorant effects of biochars on acid soils and the mechanisms involved have not previously been critically reviewed. Here we summarize the phenomena, and mechanisms involved in the improvement of soil acidity by biochars, the alleviation of aluminum toxicity, the enhancement of nutrient availability, and changes in nitrification by collating data in the literature. In addition, the agronomic effectiveness and environmental concerns in the incorporation of biochar and other soil additives (i.e. lime, industrial by-products, organic wastes and plant residues) to acid soils are systemically compared. We conclude that biochar is a potentially effective amendment to reverse or to prevent acidification in acid soils. Finally, perspectives for further research in terms of soil acidification are presented to address some issues that are still poorly understood and/or highly controversial. [ABSTRACT FROM AUTHOR]

The changes to soil properties due to biochar addition may affect both the direction and magnitude of priming effects. However, the mechanisms involved in biochar induced priming effects still remain largely unknown due to the limitation of methods to separate more than two carbon (C) sources (e.g. soil, biochar, substrate). We combined 14 C labeling with 13 C natural abundance to separate the total CO 2 from i) native soil organic C (SOC, C 3 signature), ii) added glucose ( 14 C labelled) and iii) biochar (C 4 signature). The primed soil CO 2 emissions following a large addition of glucose (1000 mg glucose kg −1 soil) to one Chinese and one German Luvisol soil were much larger (140% and 53% respectively) in a soil recently amended with maize derived biochar (pyrolyzed at 400 °C), compared to non amended soil. Glucose addition at a lower rate (100 mg C kg −1 soil) produced no significant differences in priming effects of native soil organic matter between the biochar amended and non-amended soils. Glucose also caused priming of biochar decomposition, with an additional C 4 biochar loss of between 270 μg CO 2 -C g −1 and 540 μg CO 2 -C g −1 depending on soils and glucose concentrations. Approaches using two stable isotopes ( 13 C and 12 C) have previously been limited to partitioning two sources (biochar C and soil organic C). Here, for the first time, 14 C labeling was combined with 13 C natural abundance to partition three C sources in a biochar amended soil. By partitioning soil CO 2 emissions derived from SOC, added biochar and glucose decomposition, this study provides a better understanding of the priming effects following addition of substrates to biochar amended soil, to approximate to the true complexity of biochar enriched soils. [ABSTRACT FROM AUTHOR]

In agroecosystems, soil bacterial and fungal communities are crucial for soil and plant health because of their diverse metabolic functions. However, little is known about the effect of long term paddy management on microbial communities. This study was conducted to assess the responses of the soil bacterial and fungal communities to cultivation history along a paddy soil chronosequence by using phospholipid fatty acid (PLFA) profiling and Illumina HiSeq sequencing. Soil samples were collected from the paddy fields (50, 100, 300, 1000, and 2000 years of paddy use; P50-P2000-), the adjacent arable chronosequence (50, 100 and 300 years of land use; NP50-NP300) and mudflat (estuarine sediment, representing the parent material for paddy and arable soil reclamation). The results showed that soil microbial biomass PLFAs increased significantly with increasing soil organic C which accumulated more under paddy than arable management. Bacterial taxonomic groups assigned to Proteobacteria and Acidobacteria changed relatively in the transition from tidal wetland to agricultural land. The relative abundances of dominant bacterial phyla in paddy soil orderly changes with cultivation time. The dominant fungal phyla in all samples were Ascomycota, Chytridiomycota, Basidiomycota, Glomeromycota and Zygomycota , representing 18.50%, 18.46%, 10.02%, 7.34%, and 7.19%, respectively. The succession of fungal community structure was mainly associated with changes in Ascomycota . Correlation analysis showed that higher soil total carbon and nitrogen related to long-term cultivation were associated with lower Proteobacteria and Ascomycota , but higher Verrucomicrobia . Furthermore, different land use type differed significantly in their fungal composition, but likely had similar effects on the succession of bacterial composition, mainly the Proteobacteria and Acidobacteria . Our results indicate that orderly succession of soil bacterial and fungal communities occurred along the long-term development of paddy soil, which in turn was associated with changes in soil physicochemical properties over time. [ABSTRACT FROM AUTHOR]

Biodiesel Co-Product (BCP) is a complex organic material formed during the transesterification of lipids. We investigated the effect of BCP on the extracellular microbial matrix or ‘extracellular polymeric substance’ (EPS) in soil which is suspected to be a highly influential fraction of soil organic matter (SOM). It was hypothesised that more N would be transferred to EPS in soil given BCP compared to soil given glycerol. An arable soil was amended with BCP produced from either 1) waste vegetable oils or 2) pure oilseed rape oil, and compared with soil amended with 99% pure glycerol; all were provided with 15 N labelled KNO 3 . We compared transfer of microbially assimilated 15 N into the extracellular amino acid pool, and measured concomitant production of exopolysaccharide. Following incubation, the 15 N enrichment of total hydrolysable amino acids (THAAs) indicated that intracellular anabolic products had incorporated the labelled N primarily as glutamine and glutamate. A greater proportion of the amino acids in EPS were found to contain 15 N than those in the THAA pool, indicating that the increase in EPS was comprised of bioproducts synthesised de novo. Moreover, BCP had increased the EPS production efficiency of the soil microbial community (μg EPS per unit ATP) up to approximately double that of glycerol, and caused transfer of 21% more 15 N from soil solution into EPS-amino acids. Given the suspected value of EPS in agricultural soils, the use of BCP to stimulate exudation is an interesting tool to consider in the theme of delivering sustainable intensification. [ABSTRACT FROM AUTHOR]

Most studies of the effects of manure amendment on the occurrence of antibiotics and antibiotic resistance genes (ARGs) in soil employ the investigation of grab samples or short-term laboratory studies. However, the effects of long-term manure applications on antibiotics, ARGs and their vertical distribution in paddy soil in field experiments are lacking. We assessed the concentrations of antibiotics, ARGs and their vertical distribution in paddy soil receiving long-term manure applications in four field experiments. High concentrations of tetracyclines were detected in most manured soils, while sulfonamides were not detectable. Long-term manure amendments generally increased the antibiotic concentrations and ARGs abundances in the paddy soil over decades. However, in some sites such significant trends of ARGs could not be observed. The abundance of ARGs was statistically correlated with antibiotics and soil properties including pH and soil organic matter (SOM), indicating their importance in the selection of resistance genes. Tetracyclines could be detected in soil at different depths and the concentrations of tetracyclines and abundance of ARGs generally decreased with increasing soil depths. [ABSTRACT FROM AUTHOR]

A greenhouse study was conducted to investigate the effects of inorganic (phosphate rock, single superphosphate and calcium magnesium phosphate) and organic amendments (peat, straw manure and pig manure) on the uptake of lead (Pb) and trace elements by Chinese Cabbage ( Brassica chinensis ) grown in an acidic red soil. The application of all organic amendments increased the soil pH while inorganic amendments such as single superphosphate did not. Both inorganic and organic amendments decreased the availability and uptake of Pb while the organic amendments were superior to the inorganic (phosphate) amendments in reducing the availability of the more labile (soluble and exchangeable Pb) forms of soil Pb. More Pb was taken up by roots than shoots with all soil amendments. Among the organic amendments, straw manure and pig manure caused the largest decrease in Pb availability at 456.5 and 457.3 mg kg −1 , respectively, when a high level of 30 g organic amendments kg −1 was applied. The organic amendments greatly increased the fraction D targeted to Fe–Mn oxides bound Pb, and decreased the fraction A (water-soluble), B (exchangeable), and C (carbonate-bound), thereby decreasing the solubility and mobility of Pb in soil. The organic amendments also significantly improved the concentrations of Fe, Mn, Cu and Zn in the soil and shoots (except Fe in shoots and/or roots), which are essential for plant nutrition. The organic amendments of straw and pig manure lowered the availability and uptake of Pb but not that of other trace metals. Thus, these amendments have the potential to remediate Pb-contaminated soils in situ . [ABSTRACT FROM AUTHOR]

Soil adenosine 50-triphosphate (ATP) is an excellent indicator of soil microbial biomass in moist aerobic soils, having an extracellular half life of less than 1 h. It is measured by the firefly luciferin-luciferase system. Jenkinson and Oades (1979) proposed a method to measure ATP in aerobic soils, with a reagent of Na2HPO4, trichloroacetic acid (TCA) and paraquat, (TCA reagent). Their method has been superseded by an alternative where paraquat is replaced by imidazole, termed the TIP reagent. Both methods give the same results. We found a constant biomass ATP concentration of 7.9 ± 2.24 mmol ATP g-1 biomass C in aerobic soils irrespective of substrate addition and a much lower, and highly variable concentration of 2.83 ± 0.82 in anaerobic soils. Possible reasons are discussed. [ABSTRACT FROM AUTHOR]

• Low-N soil had higher RPEs and relative primed N than high-N ones. • The RPEs and relative primed N were higher in high-Fe than low-Fe oxides soil. • Biotic process was reflected in increased microbial biomass and enzyme activity. • The abiotic process was responsible for C exchanged between root-C and Fe-SOC. • Biotic–abiotic mechanisms regulated soil C and N mineralization in the rhizosphere. The effect of living roots on the co-mineralization of soil organic carbon (SOC) and nitrogen (SON) and driving mechanisms of the rhizosphere priming effect (RPE) remains unclear. Moreover, it is still poorly understood whether the abiotic mechanisms, whereby roots accelerate soil organic matter (SOM) loss by destabilizing organo-mineral associations, are involved. Biotic and abiotic processes involved in the RPE and gross N mineralization (GNM) were investigated using three paddy soils (C 3) under maize (C 4 plant) cultivation. The soils had high and low total N (1.79 and 3.3 g kg−1 soil) as well as iron- (Fe-) (hydr-) oxide (1.1 and 2.2 g kg−1 soil) contents, which gave the following combinations: high-Fe/low-N, low-Fe/low-N, and low-Fe/high-N. The RPEs and GNM were measured using a 13C-natural abundance approach and 15N-pool dilution technique, respectively, on day 86 of maize cultivation. Living roots enhanced native SOC mineralization by 70.4–204% and GNM by 118–382%. As expected, biotic mechanisms contributed to RPEs ('microbial activation' and 'microbial N-mining') that was supported by the increase of soil microbial biomass C and extracellular enzyme activities in presence of plant, and the lower C/N ratio of primed SOM than the original SOM in unplanted soils. Higher RPEs and relative primed N mineralization via stronger 'microbial N-mining' were found in low-Fe/low-N vs low-Fe/high-N soils. In contrast to expectations, the RPEs and relative primed N mineralization were greater in high-Fe/low-N versus low-Fe oxide soils. The strongest decrease in SOM-derived Fe-bound C and increase in root-derived Fe-bound C were observed in the high-Fe soil, because root exudates liberated more C from Fe-bound SOM and co-precipitated with Fe oxides. This shows that the abiotic process was involved in RPEs whereby root exudates promoted soil C loss by releasing it from Fe-organic complexes. Thus, this study demonstrated that coupled biotic-abiotic processes could regulate RPEs. [ABSTRACT FROM AUTHOR]

Contaminations by heavy metals in the environment always exist as a mixture of both metal and metalloid. Thus, it is a challenge to simultaneously remove both components due to their adverse chemical behaviors. Herein, effective cadmium (Cd) and arsenic (As) removal in aqueous solution was achieved by use of a novel composite, which was synthesized by Bacillus sp. K1 loaded onto Fe 3 O 4 biochar (MBB). The combination with Bacillus sp. K1 provided new biosorption sites such as amine and hydroxyl groups in the composite surface, which significantly increasing the removal capability of Cd(II) by 230% when compared with the raw magnetic biochar. Both competition and synergy effects were found in binary system. Adsorption of As(III) extended active sites for capturing Cd(II), which appeared on the surface of the MBB as type B ternary surface complexes. The maximum adsorption capacity of Cd(II) and As(III) reached 25.04 and 4.58 mg g−1 in a binary system, respectively. In summary, this environmentally friendly composite is promising for simultaneous Cd(II) and As(III) remediation. Unlabelled Image • Cd(II) removal capacity of the composite was 230% higher than raw biochar. • -NH 2 and -OH of Bacillus sp. K1 enhanced the removal capability of Cd(II). • Competition and synergy effects were found in Cd(II) and As(III) adsorption by MBB. • Type B ternary surface complexes existed in adsorption process of Cd(II) and As(III). [ABSTRACT FROM AUTHOR]

The triggering response has attracted much research interest. However, the main C source of triggered CO 2 –C and the dynamics of soil microbial biomass C (biomass C) and adenosine 5′-triphosphate (ATP) concentrations during the triggering response still remain largely unknown. We labeled the soil microbial biomass of three soil layers (0–10 cm, 10–30 cm and 30–60 cm) of a forest soil with dried aboveground maize (22 atom%, 2.5 mg g−1 soil) and glucose (22 atom%, 2.5 mg g−1 soil) to determine the contribution of the four potential C sources involved in the triggering response: 13C-labeled maize and glucose, biomass C, soil organic carbon (SOC), and triggering glucose. After 56 days of soil pre-incubation, the 13C abundances of biomass C and SOC were 5.27–6.71 and 1.94–2.82 atom%, respectively. Addition of 10 μg glucose-C g−1 soil caused a strong and rapid triggering response resulting in 2.3–6 times more triggered CO 2 –C evolved than was contained in the triggering glucose, which increased with soil depth. The atom% 13C–CO 2 values of model calculations were closest to measured values when assumed to derive completely from biomass C. Biomass C did not significantly change at day 1 but significantly decreased by 7.1–27.6% at day 5. ATP concentrations (nmol ATP g−1 soil) increased from 6.2-10.8% by day 1 to 9.2- 28% by day 5 (p < 0.05). Soil biomass C and ATP contents reached values similar to those of the control after 10 days. These results indicate that the CO 2 –C from the triggering response mainly derived from mineralization of biomass C during the early triggering stage and from mineralization of residual substrates thereafter. Biomass ATP concentrations (μmol ATP g−1 biomass C) remained constant during the later stages. We conclude that the triggering response is mainly due to the rapid activation of soil microorganisms through mineralization of biomass C. Microorganisms that adopt this survival strategy, may have a rapid reaction in the utilization of fresh substrates. • Pre-incubation with 13C enriched substrates labeled biomass C and SOC. • Biomass indexes showed dynamic changes during the triggering response. • In the early stage triggered C was derived from mineralization of biomass C. • Extra CO 2 –C evolved increased with soil depth. [ABSTRACT FROM AUTHOR]

• Following CHCl 3 fumigation, SOC mineralization is little affected. • With increasing fresh soil inoculation, SOC mineralization rate is little affected. • Microbes recover proportionally to inoculation rates. • DOC cumulates in fumigated soil. • DOC generation, rather than microbes, is crucial in SOC mineralization. The Regulatory Gate Hypothesis proposes that the rate of soil organic C mineralization is largely controlled by abiotic processes rather than biological ones. To further test this hypothesis, a repeatedly fumigated soil was inoculated with increasing weights of the initial fresh soil (0, 2, 10 and 25%) and then incubated for 30 days. The CO 2 -C evolved, soil microbial biomass C and adenosine 5′-triphosphate were measured at days 1, 5, and 30. The fresh soil was incubated as a control. Our aim was to further test the Regulatory Gate hypothesis that the rate of mineralization of stabilized soil organic matter is not regulated by the size, activity or community structure of the microbial biomass. Cumulative CO 2 evolved changed little, irrespective of weight of inoculum, in the inoculated soils during the incubation. Soil respiration rates of inoculated soils (21 µg CO 2 -C g−1 soil) were significantly higher than those of non-inoculated-fumigated soil (18 µg CO 2 -C g−1 soil) and fresh soil (18.5 µg CO 2 -C g−1 soil) at the beginning of the incubation (day 0–1). However, they were not significantly different (6.5 µg CO 2 -C g−1 soil in inoculated soils) from those in non-inoculated-fumigated and fresh soil (5.5 and 7.1 µg CO 2 -C g−1 soil respectively) at the end of the incubation. Soil adenosine 5′-triphosphate (ATP) proportionally increased in the inoculated soils, but remained much lower (0.49–0.78 nmol g−1 soil) than that in fresh soil (2.28 nmol g−1 soil) until the end of the incubation. The recoveries of the microbial communities and diversity in the inoculated soils were proportional to the inoculation rates. Proteobacteria, mainly Gammaproteobacteria, had the highest recovery in inoculated soils after incubation, and Nitrospira the lowest. We conclude that soil organic matter mineralization is not regulated by the size or composition of the soil microbial population, but mainly depends on the conversion of non-bioavailable SOC to bioavailable substrate C. The precise processes involved now require further research to improve our understanding of the mechanisms driving the mineralization of soil organic matter. [ABSTRACT FROM AUTHOR]

• Biochar addition inhibited the reductive dechlorination of PCP in flooded soil. • Soil Fe(III)/SO 4 2− reduction and methanogenesis were improved simultaneously. • Complex chemical-microbial coupled mechanisms regulated the biochar effect. • Biochar might act as the electron mediator and regulate functional selection of the core microbial groups. • The addition of biochar might not be an effective remediation strategy for PCP dechlorination in flooded soil. Biochar has received increasing attention for its multifunctional applications as a soil amendment. The dual effect of biochar on reductive organic pollutants and soil biogeochemical processes under anaerobic environments in parallel has yet to be fully explored. In this study, anaerobic batch experiments were conducted to examine the effect of biochar on both reductive transformation of pentachlorophenol (PCP) and soil redox processes in flooded soil. Compared to biochar-free controls, the reductive dechlorination of PCP was significantly inhibited following biochar addition, with the inhibition degree increased with increasing amount of biochar. Dissimilatory iron and sulfate reduction, as well as the production of methane, were significantly enhanced following biochar addition. The bacterial and archaeal communities showed a functional selection responded to the addition of biochar and PCP, with the core functional groups at the genus level including Dethiobacter , Clostridium , Geosporobacter , Desulfuromonas , Desulfatitalea , and Methanosarcina. These findings indicated that biochar could affect soil microbial redox processes and may act as an electron mediator altering electron distribution from PCP dechlorination to the predominant soil reduction processes, and increase understanding regarding biochar's comprehensive effects on the remediation of natural flooded soil polluted by chlorinated organic pollutants that can be degraded reductively. [ABSTRACT FROM AUTHOR]

• The environmental fingerprints of the soil Fe-Mn nodules were established. • Synchrotron-based microprobes were applied for interpretation of fingerprints. • The porosity of the nodules indicates the change rate of the soil redox potential. • The elemental and structural information reveal soil nodules' formation history. • The paleoclimate can be retrieved from the fingerprints of the soil nodules. Ferromanganese nodules are important pedogenic indicators in soil. They are usually characterized by clearly expressed ring structures. Although these features are believed to be significant environmental fingerprints, the reasons for their formation still await interpretation. Here, we interpreted these fingerprints by the synergistic use of noninvasive synchrotron-radiation based techniques and advanced analytical methods. The results revealed that the soil nodules were formed due to the filling of the pore networks of the soil matrix that was mediated by both abiotic and biotic factors during alternative soil wetting-drying cycles. The ring structures are therefore the memories of the soil redox history. The variations in elemental compositions of the ring structures indicates the soil moisture conditions at the time of formation. Their porosity reflects the rate of change in soil redox potential and the soil redox potential is mainly affected by precipitation. [ABSTRACT FROM AUTHOR]

Both soil pH and substrate quality exert a critical influence on the decomposition of organic substrates and the production of microbial biomass. However, it is elusive the interactive effects of soil pH and substrate quality on the microbial assembly, and subsequently the dynamics of organic substrates. We applied two substrates (maize flour and maize straw) with different substrate qualities to soils of different pHs (from 4.63 to 6.32), sampled from a field trial previously unamended, or amended with wheat biochar (10 t ha−1) or organic fertilizer (10 t ha−1 composted pig manure). The natural abundance 13C technique was used to determine the net mineralization rate of added C4 maize materials and the assimilation of substrates into microbial biomass C (MBC) during 60 days incubation. At the early stage, soil pH and substrate quality both positively regulated substrate mineralization, while the level of soil C saturation dominated the biomass synthesis efficiency (BSE) compared with soil pH and substrate quality. Soil pH had contradictory relationships with mineralization and BSE at the final stage of mineralization, implying high pH was tightly associated with higher C use efficiency (CUE). Overall, the bacterial community assembly was determined by the interactive effect of soil pH and substrate quality, while soil pH was the key driver to shape fungal community structure, diversity, and composition. Soil pH had a consistent effect on microbial utilization, which, however, were only affected by substrate quality in the early stage. Image 1 • Status of soil C saturation had greater effect on BSE than pH and substrate quality at the early stage. • Higher pH induced higher C use efficiency (CUE). • Soil pH had a continuous effect on microbial mineralization and utilization. • Bacterial community assembly was interactively affected by pH and substrate quality. • Soil pH was the key driver to shape fungal community structure, diversity, and composition. [ABSTRACT FROM AUTHOR]

Organochlorine pesticides have been extensively used for many years to prevent insect diseases of rice (Oryza sativa L.), but little is known about their residual impacts on the underground micro-ecology in anaerobic environment. In this glasshouse study, we characterized the lindane effects on the assembly of root-associated microbiomes of commonly used indica, japonica and hybrid rice cultivars, and their feedback in turn, in modifying lindane anaerobic dissipation during 60 days' rice production. The results showed that rice growth inhibited the anaerobic dissipation of lindane, but was not affected apparently by lindane at initial spiked concentration of 4.62 and 18.54 mg kg−1 soil. Suppressed removal of lindane in rice planted treatments as compared with that in unplanted control was likely due to inhibited reductive dechlorination induced by a comprehensive effect of radial O 2 secretion of rice root and co-occurring Fe(III) reduction that consumed electron competitively in rice rhizosphere. However, the hybrid cultivar exhibited a less suppression than the conventional cultivars in high polluted soils. Bacteria was more sensitively responded to lindane pollution than fungal taxa, and Actinobacteria, Chloroflexi, Verrucomicrobia and Proteobacteria were the main different phyla between hybrid and conventional cultivars, with a more stable community structure exhibited in the hybrid rice under lindane stress. Our study highlights the assembly and variation of root-associated microbiomes in responses of lindane pollution, and suggests that hybrid rice cultivar might be most competent for cultivation in paddy fields polluted by lindane and other organochlorine pesticides, especially in the area with high residual levels. • Rice growth inhibited the dissipation of lindane with hybrid cultivar having a less suppression than conventional cultivars. • Lindane and cultivar significantly affected the assembly of rice root-associated bacterial and fungal microbiomes. • The endosphere and rhizosphere compartments showed the greatest divergence. • A more stable community structure exhibited in the hybrid rice cultivar under lindane stress. • Hybrid rice might be the most competent cultivar for paddy fields polluted by organochlorine pesticides such as lindane. [ABSTRACT FROM AUTHOR]

The relationship between metallic micronutrients and soil microorganisms, and thereby soil functioning, has been little explored. Here, we investigate the relationship between metallic micronutrients (Fe, Mn, Cu, Zn, Mo and Ni) and the abundance, diversity and function of soil microbiomes. In a survey across 180 sites in China, covering a wide range of soil conditions the structure and function of the soil microbiome are highly correlated with metallic micronutrients, especially Fe, followed by Mn, Cu and Zn. These results are robust to controlling for soil pH, which is often reported as the most important predictor of the soil microbiome. An incubation experiment with Fe and Zn additions for five different soil types also shows that increased micronutrient concentration affects microbial community composition and functional genes. In addition, structural equation models indicate that micronutrients positively contribute to the ecosystem productivity, both directly (micronutrient availability to plants) and, to a lesser extent, indirectly (via affecting the microbiome). Our findings highlight the importance of micronutrients in explaining soil microbiome structure and ecosystem functioning., (© 2023. The Author(s).)

Microorganisms play an important role in soil phosphorus (P) cycling and regulation of P availability in agroecosystems. However, the responses of the functional and ecological traits of P-transformation microorganisms to long-term nutrient inputs are largely unknown. This study used metagenomics to investigate changes in the relative abundance of microbial P-transformation genes at four long-term experimental sites that received various inputs of N and P nutrients (up to 39 years). Long-term P input increased microbial P immobilization by decreasing the relative abundance of the P-starvation response gene (phoR) and increasing that of the low-affinity inorganic phosphate transporter gene (pit). This contrasts with previous findings that low-P conditions facilitate P immobilization in culturable microorganisms in short-term studies. In comparison, long-term nitrogen (N) input significantly decreased soil pH, and consequently decreased the relative abundances of total microbial P-solubilizing genes and the abundances of Actinobacteria, Gammaproteobacteria, and Alphaproteobacteria containing genes coding for alkaline phosphatase, and weakened the connection of relevant key genes. This challenges the concept that microbial P-solubilization capacity is mainly regulated by N:P stoichiometry. It is concluded that long-term N inputs decreased microbial P-solubilizing and mineralizing capacity while P inputs favored microbial immobilization via altering the microbial functional profiles, providing a novel insight into the regulation of P cycling in sustainable agroecosystems from a microbial perspective.

There are global concerns about heavy metal (HM) contamination in soils, which in turn has produced an increased demand for soil remediation. Biochar has been widely documented to effectively immobilize metals in contaminated soils and has received increasing attention for use in soil remediation. Here, we review recent progresses in understanding metal-biochar interactions in soils, potential risks associated with biochar amendment, and application of biochar in soil remediation in China. These recent studies indicate that: (1) the remediation effect depends on the characteristics of both biochar and soil and their interactions; (2) biochar applications could decrease the mobility/bioavailability of HMs in soils and HM accumulation in plants; and (3) despite its advantages, biochar applications could pose ecological and health risks, e.g., by releasing toxic substances into soils or by inhalation of biochar dust. Research gaps still exist in the development of practical methods for preparing and applying different biochars that target specific HMs. In the future, the long term effects and security of biochar applications on soil remediation, soil organisms and plant growth need to be considered., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Mobile colloids such as nanoparticles (NPs) are often considered to affect the fate and transport of various contaminants by serving as carriers. Many studies have focused on the effect of engineered NPs on contaminant transport. To date, very little information is available on the co-transport of natural soil NPs with typical organic contaminants. This study investigated the co-transport of phenanthrene (PHE) and pentachlorophenol (PCP) by three soil NPs through saturated sand columns. Soil NPs with high organic matter and particle concentration were the most effective in transporting PHE through columns. In addition, soil NPs significantly increased the transport of low-level PHE (0.2 mg L -1 ) but there was no obvious increase at 1.0 mg L -1 PHE. This is attributed to a higher ratio of NP-associated PHE to total PHE at a low-level than at a high-level during transport. In contrast to PHE, the chemical speciation of PCP determined its mobility, which was highly dependent on solution pH. At pH 6.5, anionic PCP became dominant and soluble in the effluent. This could account for the negligible effect of soil NPs on PCP mobility. At pH 4.0, however, neutral molecular PCP dominated and, as expected, decreased mobility of PCP occurred. Soil NPs considerably enhanced the transport of neutral PCP in NP-associated forms compared to controls, due to the high hydrophobicity and sorption affinity of PCP to NPs. The mobility of soil NPs was little affected by PHE and PCP under tested conditions. This study indicated that highly mobile soil NPs may be effective carriers for organic contaminants and give a new direction to polluted site remediation by using a natural material, e.g., soil., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Hematite nanoparticles (NPs) exist naturally and ubiquitously in soil, and they are always associated with soil organic matter by forming organic-inorganic complexes. In this work, hematite NPs coated with peat humic acid (HA peat ) and soil humic acid (HA soil ) were chosen as sorbents for hydrophobic organic contaminants (HOCs) to simulate the sorption processes in soil. Ionizable pentachlorophenol (PCP) and non-ionizable phenanthrene (PHE) were selected as representative HOCs. Compared with sorption isotherms of uncoated hematite NPs, the coating of HA onto the surface of hematite NPs substantially increased its sorption affinity for PCP and PHE by about 1-2 orders of magnitude, and the increasing degree was positively correlated to the HA content. These phenomena emphasized the dominant role of HA in the sorption process. The reduced polarity and the introduction of functional groups contributed to the enhanced sorption of HOCs on HA-coated hematite NPs. Furthermore, HA peat -hematite NPs showed higher sorption affinity for both PCP and PHE than HA soil -hematite NPs, which was mainly due to the lower polarity and higher hydrophobicity of HA peat -hematite NPs. The sorption of PCP and PHE on HA-coated hematite NPs was inhibited obviously with increasing pH values and the pH effect on PCP sorption was more significant than that of PHE, due to the deprotonation of functional groups within adsorbed HA, the loose structure of adsorbed HA and the dissociation of PCP. Our findings elucidated the mechanisms involved in HOCs sorption processes by HA-hematite NPs and provided a theoretical basis for environmental remediation with natural NPs (e.g., hematite NPs)., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

A three-year field test was conducted in an area surrounding past mining activity (mining area) to investigate the value of a novel comprehensive remediation strategy for Cd and Pb contamination, which included screening of low accumulated vegetable cultivars that take up Cd and Pb less than normal cultivars, in situ soil remediation using different soil amendments, and health risk assessment that evaluates the possibility of safe consumption for the vegetables. Results showed that cultivar Huoqing 91-5C of which vegetable was selected as a low accumulator of Cd and Pb in a soil contaminated with 0.5 mg kg -1 and 8180 mg kg -1 total Cd and Pb concentrations, respectively. Addition of 20 t ha -1 of biochar with 2 t ha -1 of calcium superphosphate in 10 cm depth could decrease available Cd and Pb by 70% and 85% after 1 year, respectively. Following treatments, hazard quotients for adults and children were below 1, indicating that the vegetables grown were safe for human consumption. The total cost of remediation was $3885 ha -1 , so the cost of the remediation of the combination of Cd and Pb was economic in this mining area., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

An anaerobic incubation was launched with varying nitrate (1, 5, 10 and 20 mM exogenous NaNO 3 ) and molybdate (20 mM Na 2 MoO 4 , a sulfate-reducing inhibitor) additions to investigate the characteristics of PCP dechlorination, as well as the reduction of natural co-occurring electron acceptors, including NO 3 - , Fe(III) and SO 4 2- , and the responses of microbial community structures under a unique reductive mangrove soil. Regardless of exogenous addition, nitrate was rapidly eliminated in the first 12 days. The reduction process of Fe(III) was inhibited, while that of SO 4 2- reduction depended on addition concentration as compared to the control. PCP was mainly degraded from orth-position, forming the only intermediate 2,3,4,5-TeCP by anaerobic microbes, with the highest PCP removal rate of average 21.9% achieved in 1 and 5 mM NaNO 3 as well as 20 mM Na 2 MoO 4 treatments and the lowest of 7.5% in 20 mM NaNO 3 treatment. The effects of nitrate on PCP dechlorination depended on addition concentration, while molybdate promoted PCP attenuation significantly. Analyses of the Illumina sequencing data and the relative abundance of dominant microorganisms indicated that the core functional groups regulated PCP removal at genera level likely included Bacillus, Pesudomonas, Dethiobacter, Desulfoporosinus and Desulfovbrio in the nitrate treatments; while that was likely Sedimentibacter and Geosporobacter&#95;Thermotalea in the molybdate treatment. Nitrate supplement but not over supplement, or addition of molybdate are suggested as alternative strategies for better remediation in the nitrate-deficient and sulfur-accumulated soil ecosystem contaminated by PCP, through regulating the growth of core functional groups and thereby coordinating the interaction between dechlorination and its coupled soil redox processes due to shifts of more available electrons to dechlorination. Our results broadened the knowledge regarding microbial PCP degradation and their interactions with natural soil redox processes under anaerobic soil ecosystems., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Heavy metal pollution can decrease the soil microbial biomass and significantly alter microbial community structure. In this study, a long-term field experiment (5 years) and short-term laboratory experiment (40 d) were employed to evaluate the effects of heavy metals (Cd, Cu, Zn), and their combinations at different concentrations, on the soil microbial biomass and the bacterial community. The ranges of heavy metal concentration in the long-term and short-term experiments were similar, with concentration ranges of Cd, Cu and Zn of about 0.3-1.5, 100-500, and 150-300 mg kg -1 , respectively. Microbial biomass decreased with increasing soil heavy metal concentrations in both the long-term and short-term experiments. The interaction between soil physicochemical factors (pH, TN, TC) and heavy metals (Cd, Cu, Zn) played a major role in change in the bacterial community in long-term polluted soil. In the laboratory experiment, although each heavy metal had an adverse effect on the microbial biomass and community structure, Cu appeared to have a greater role in the changes compared to Cd and Zn. However, the synergistic effects of the heavy metals were greater than those of the single metals and the synergistic effect between Cu and Cd was greater than that of Cu and Zn., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Soil ecological functions are largely determined by the activities of soil microorganisms, which, in turn, are regulated by relevant interactions between genes and their corresponding pathways. Therefore, the genetic network can theoretically elucidate the functional organization that supports complex microbial community functions, although this has not been previously attempted. We generated a genetic correlation network based on 5421 genes derived from metagenomes of forest soils, identifying 7191 positive and 123 negative correlation relationships. This network consisted of 27 clusters enriched with sets of genes within specific functions, represented with corresponding cluster hubs. The clusters revealed a hierarchical architecture, reflecting the functional organization in the soil metagenomes. Positive correlations mapped functional associations, whereas negative correlations often mapped regulatory processes. The potential functions of uncharacterized genes were predicted based on the functions of located clusters. The global genetic correlation network highlights the functional organization in soil metagenomes and provides a resource for predicting gene functions. We anticipate that the genetic correlation network may be exploited to comprehensively decipher soil microbial community functions.

Microplastics have a great potential to sorb organic pollutants from the adjacent environment. In this study, the sorption of tetracycline, a polar and ionizable antibiotic, on three types of microplastics (polyethylene (PE), polypropylene (PP) and polystyrene (PS)) were investigated in batch sorption experiments. The sorption isotherms were well fitted by the Langmuir model, indicating that not only hydrophobic interactions but also other interactions (e.g. electrostatic interactions) played important roles in the sorption process. PS had the maximum sorption capacity, following the order PS > PP > PE, which can be attributed to polar interactions and π-π interactions. The sorption of tetracycline on microplastics was significantly influenced by pH, with sorption capacity increasing gradually, peaking at pH 6.0 and then decreasing, likely due to the influence of tetracycline speciation with the change of pH. Fulvic acid was selected as representative dissolved organic matter (DOM) to examine the effect on sorption. The increasing concentration of fulvic acid inhibited the sorption of tetracycline on three microplastics, decreasing them by more than 90% at the fulvic acid concentration of 20 mg/L, which implied a greater affinity of tetracycline to fulvic acid than to microplastics. Increasing salinity from 0.05 to 3.5% had negligible effects on the sorption of tetracycline on the three microplastics. Our results highlight the importance of pH and DOM on the sorption of tetracycline on microplastics, and suggest the relatively minor role of microplastics in the fate and transport of tetracycline in the aquatic environment in the presence of DOM., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Microplastics and sulfamethoxazole coexist ubiquitously in the marine environment, and microplastics tend to sorb organic pollutants from the surrounding environment. Here, the sorption kinetics and isotherms of sulfamethoxazole on polyethylene (PE) microplastics closely fitted a pseudo-second-order model (R 2  = 0.98) and linear model (R 2  = 0.99), respectively, indicating that the sorption process was partition-dominant interaction. The main binding mechanism was possibly the van der Waals interaction for hydrophilic sulfamethoxazole onto hydrophobic PE microplastics. The effects of pH, dissolved organic matter and salinity on sorption behavior were also studied. The sorption behavior of sulfamethoxazole on PE microplastics was not significantly influenced by pH and salinity, probably because the electrostatic repulsion played a minor role. In addition, the negligible effect of dissolved organic matter was attributed to the greater affinity of sulfamethoxazole to PE microplastics than to dissolved organic matter. Our results demonstrated that PE microplastics may serve as a carrier for sulfamethoxazole in the aquatic environment., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The incorporation of various types of crop straw to agricultural soils has long been practiced to improve soil fertility. However, the effects of crop straw on the fate of organo-chlorine pesticides in flooded paddy soils are not well understood. The dechlorination of pentachlorophenol (PCP) in four vertical profiles (0-10, 10-20, 20-30, 30-50 mm depth) of two flooded paddy soils, a Plinthudult (Soil 1) and a Tropudult (Soil 2) was investigated following the application of four crop straws (rice, wheat, rape and Chinese milk vetch) to them. In all treatments, PCP dechlorination decreased with increasing soil depth. In the crop straw treatments, PCP was almost completely dechlorinated within 60 days, and rapidly transformed to 2,3,4,5-tetrachlorophenol, and further to 3,4,5-trichlorophenol. Further dechlorination of 3,4,5-trichlorophenol also occurred in all treatments except for the rape straw. It is possible that the NH 4 + and NO 3 - derived from the straw are responsible for the inhibition of the 3,4,5-trichlorophenol dechlorination. The reduction of Fe (III) and SO 4 2- increased following application of the crop straws. The RDA analysis indicated that the Fe (III) reducing bacteria might be involved in the ortho-dechlorination, while SO 4 2- reducing bacteria were involved in para- and meta-dechlorination of PCP. The complete detoxification of PCP depended upon both the crop straw type and soil properties., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The natural forest ecosystem in Eastern China, from tropical forest to boreal forest, has declined due to cropland development during the last 300 years, yet little is known about the historical biogeographic patterns and driving processes for the major domains of microorganisms along this continental-scale natural vegetation gradient. We predicted the biogeographic patterns of soil archaeal, bacterial, and fungal communities across 110 natural forest sites along a transect across four vegetation zones in Eastern China. The distance decay relationships demonstrated the distinct biogeographic patterns of archaeal, bacterial, and fungal communities. While historical processes mainly influenced bacterial community variations, spatially autocorrelated environmental variables mainly influenced the fungal community. Archaea did not display a distance decay pattern along the vegetation gradient. Bacterial community diversity and structure were correlated with the ratio of acid oxalate-soluble Fe to free Fe oxides (Feo/Fed ratio). Fungal community diversity and structure were influenced by dissolved organic carbon (DOC) and free aluminum (Ald), respectively. The role of these environmental variables was confirmed by the correlations between dominant operational taxonomic units (OTUs) and edaphic variables. However, most of the dominant OTUs were not correlated with the major driving variables for the entire communities. These results demonstrate that soil archaea, bacteria, and fungi have different biogeographic patterns and driving processes along this continental-scale natural vegetation gradient, implying different community assembly mechanisms and ecological functions for archaea, bacteria, and fungi in soil ecosystems. IMPORTANCE Understanding biogeographic patterns is a precursor to improving our knowledge of the function of microbiomes and to predicting ecosystem responses to environmental change. Using natural forest soil samples from 110 locations, this study is one of the largest attempts to comprehensively understand the different patterns of soil archaeal, bacterial, and fungal biogeography at the continental scale in eastern China. These patterns in natural forest sites could ascertain reliable soil microbial biogeographic patterns by eliminating anthropogenic influences. This information provides guidelines for monitoring the belowground ecosystem's decline and restoration. Meanwhile, the deviations in the soil microbial communities from corresponding natural forest states indicate the extent of degradation of the soil ecosystem. Moreover, given the association between vegetation type and the microbial community, this information could be used to predict the long-term response of the underground ecosystem to the vegetation distribution caused by global climate change.

Soil microbiota play a critical role in soil biogeochemical processes and have a profound effect on soil functions. Recent studies have revealed microbial co-occurrence patterns in soil microbial communities, yet the geographic pattern of topological features in soil microbial co-occurrence networks at the continental scale are largely unknown. Here, we investigated the shifts of topological features in co-occurrence networks inferred from soil microbiota along a continental scale in eastern China. Integrating archaeal, bacterial and fungal community datasets, we inferred a meta-community co-occurrence network and analyzed node-level and network-level topological shifts associated with five climatic regions. Both node-level and network-level topological features revealed geographic patterns wherein microorganisms in the northern regions had closer relationships but had a lower interaction influence than those in the southern regions. We further identified topological differences associated with taxonomic groups and demonstrated that co-occurrence patterns were random for archaea and non-random for bacteria and fungi. Given that microbial interactions may contribute to soil functions more than species diversity, this geographic shift of topological features provides new insight into studying microbial biogeographic patterns, their organization and impacts on soil-associated function.

Previous investigations observed that when soil was fumigated with ethanol-free CHCl3 for 24 h and then incubated under appropriate conditions, after the initial flush of CO2 was over, soil organic carbon (SOC) mineralization continued at the same rate as in the non-fumigated soil. This indicates that, following fumigation, the much diminished microbial population still retained the same ability to mineralize SOC as the much larger non-fumigated population. We hypothesize that although fumigation drastically alters the soil bacterial community abundance, composition, and diversity, it has little influence on the bacterial C-metabolic functions. Here, we conducted a 30-day incubation experiment involving a grassland soil and an arable soil with and without CHCl3 fumigation. At days 0, 7, and 30 of the incubation, the bacterial abundances were determined by quantitative PCR, and the bacterial community composition and diversity were assessed via the 16S rRNA gene amplicon sequencing. PICRUSt was used to predict the metagenome functional content from the sequence data. Fumigation considerably changed the composition and decreased the abundance and diversity of bacterial community at the end of incubation. At day 30, Firmicutes (mainly Bacilli) accounted for 70.9 and 94.6 % of the total sequences in the fumigated grassland and arable soil communities, respectively. The two fumigated soil communities exhibited large compositional and structural differences during incubation. The families Paenibacillaceae, Bacillaceae, and Symbiobacteriaceae dominated the bacterial community in the grassland soil, and Alicyclobacillaceae in the arable soil. Fumigation had little influence on the predicted abundances of KEGG orthologs (KOs) assigned to the metabolism of the main acid esters, saccharides, amino acids, and lipids in the grassland soil community. The saccharide-metabolizing KO abundances were decreased, but the acid ester- and fatty acid-metabolizing KO abundances were elevated by fumigation in the arable soil community. Our study suggests functional redundancy regarding the bacterial genetic potential associated with SOC mineralization.

Natural soil montmorillonite and kaolinite nanoparticles (NPs) were tested as efficient sorbents for organic contaminant (OC) removal through mimicking their natural environmental dispersive states. Sorption of both mineral NPs decreased with increasing pH with ionizable pentachlorophenol (PCP), but increased with pH with non-ionizable phenanthrene (PHE), within the pH range of 4-10. In contrast, sorption decreased consistently for both PCP and PHE, as a function of increasing ion concentration (0.001-0.1 mol L(-1)). Sorption differences were likely caused by the electrolytic conditions dependent upon surface chemistry of OCs and mineral NPs. The results confirmed that the highly dispersive soil mineral NPs would prevail over both engineered NPs and their regular μm-sized colloids for OC removal, due to their ecological advantages and higher sorption properties. This finding provided a realistic assessment of the environmental function of soil natural minerals in water once they are released from soil into OC polluted aqueous systems., (Copyright © 2015 Elsevier Ltd. All rights reserved.)