Linking bacterial life strategies with the distribution pattern of antibiotic resistance genes in soil aggregates after straw addition.

Straw addition markedly affects the soil aggregates and microbial community structure. However, its influence on the profile of antibiotic resistance genes (ARGs), which are likely associated with changes in bacterial life strategies, remains unclear. To clarify this issue, a soil microcosm experiment was incubated under aerobic (WS) or anaerobic (AnWS) conditions after straw addition, and metagenomic sequencing was used to characterise ARGs and bacterial communities in soil aggregates. The results showed that straw addition shifted the bacterial life strategies from K- to r-strategists in all aggregates, and the aerobic and anaerobic conditions stimulated the growth of aerobic and anaerobic r-strategist bacteria, respectively. The WS decreased the relative abundances of dominant ARGs such as QnrS5, whereas the AnWS increased their abundance. After straw addition, the macroaggregates consistently exhibited a higher number of significantly altered bacteria and ARGs than the silt+clay fractions. Network analysis revealed that the WS increased the number of aerobic r-strategist bacterial nodes and fostered more interactions between r-and K-strategist bacteria, thus promoting ARGs prevalence, whereas AnWS exhibited an opposite trend. These findings provide a new perspective for understanding the fate of ARGs and their controlling factors in soil ecosystems after straw addition. ENVIRONMENTAL IMPLICATIONS: Straw soil amendment has been recommended to mitigate soil fertility degradation, improve soil structure, and ultimately increase crop yields. However, our findings highlight the importance of the elevated prevalence of ARGs associated with r-strategist bacteria in macroaggregates following the addition of organic matter, particularly fresh substrates. In addition, when assessing the environmental risk posed by ARGs in soil that receives crop straw, it is essential to account for the soil moisture content. This is because the species of r-strategist bacteria that thrive under aerobic and anaerobic conditions play a dominant role in the dissemination and accumulation of ARG.

Trojan horselike T6SS effector TepC mediates both interference competition and exploitative competition.

The type VI secretion system (T6SS) is a bacterial weapon capable of delivering antibacterial effectors to kill competing cells for interference competition, as well as secreting metal ion scavenging effectors to acquire essential micronutrients for exploitation competition. However, no T6SS effectors that can mediate both interference competition and exploitation competition have been reported. In this study, we identified a unique T6SS-1 effector in Yersinia pseudotuberculosis named TepC, which plays versatile roles in microbial communities. First, secreted TepC acts as a proteinaceous siderophore that binds to iron and mediates exploitative competition. Additionally, we discovered that TepC has DNase activity, which gives it both contact-dependent and contact-independent interference competition abilities. In conditions where iron is limited, the iron-loaded TepC is taken up by target cells expressing the outer membrane receptor TdsR. For kin cells encoding the cognate immunity protein TipC, TepC facilitates iron acquisition, and its toxic effects are neutralized. On the other hand, nonkin cells lacking TipC are enticed to uptake TepC and are killed by its DNase activity. Therefore, we have uncovered a T6SS effector, TepC, that functions like a "Trojan horse" by binding to iron ions to provide a valuable resource to kin cells, whereas punishing cheaters that do not produce public goods. This lure-to-kill mechanism, mediated by a bifunctional T6SS effector, may offer new insights into the molecular mechanisms that maintain stability in microbial communities.

Biochar leachate reduces primary nitrogen assimilation by inhibiting nitrogen fixation and microbial nitrate assimilation.

Biochar contains biotoxic aromatic compounds, and their influence on nitrogen-fixing cyanobacteria, the critical nitrogen fixer in paddy soil, has never been tested. Here, the physiological, metabolomic, and transcriptomic analyses of Nostoc sp. PCC7120 in response to biochar leachate were performed. The results suggested that biochar leachate inhibited the efficiency of photosynthesis, nitrogen fixation, and nitrate assimilation activities of nitrogen-fixing cyanobacteria. Biochar leachate containing aromatic compounds and odd- and long-chain saturated fatty acids impaired the membrane structure and antenna pigments, damaged the D1 protein of the oxygen evolution complex, and eventually decreased the electron transfer chain activity of photosystem II. Moreover, the nitrogen fixation and nitrate assimilation abilities of nitrogen-fixing cyanobacteria were inhibited by a decrease in photosynthetic productivity. A decrease in iron absorption was another factor limiting nitrogen fixation efficiency. Our study highlights that biochar with relatively high contents of dissolved organic matter poses a risk to primary nitrogen assimilation reduction and ecosystem nitrogen loss. Further evidence of the potential negative effects of biochar leachates on the fixation and assimilation capacity of nitrogen by soil microbes is needed to evaluate the impact of biochar on soil multifunctionality prior to large-scale application.

Effectiveness of a novel composite filler to enhance phosphorus removal in constructed wetlands.

Improving the adsorption performance of wetland fillers is of great significance for enhancing pollutant removal in constructed wetlands. Currently, limited by complex preparation processes and high costs, large numbers of high adsorption fillers studied in lab are difficult to be applied in practical engineering. In this study, a newly low-cost and efficient phosphorus removal composite wetland filler (CFB) is prepared by using industrial and agriculture waste (steel slag and oyster shells) and natural ore (volcanic rock) as raw materials. The results show that phosphorus removal efficiency was largely enhanced by synergistic effects of steel slag, oyster shells, and volcanic rock, and it was mainly influenced by the proportion of each component of CFB. Based on the fitting of the classical isothermal equation, the adsorption capacity of CFB is 18.339 mg/g. The adsorption of phosphorus by CFB is endothermic and spontaneous, and there are heterogeneous surfaces and multi-layer adsorption processes, as well as pH value and temperature, are free from the influence on CFB phosphorus removal. During the practical wastewater application experiments, the phosphorus removal rate of the CFB-filled constructed wetland apparatus (CW-A) can reach 94.89% and is free from the influence on the removal of other pollutants (COD, TN, and NH3-N) by the system. Overall, the prepared CFB is of excellent decontamination effect, an extremely simple preparation process, low cost, and sound practical engineering application potential, providing new ideas and approaches for enhancing the phosphorus removal capacity and waste resource utilization of constructed wetland systems.

Age- and sex-stratified detection rates and associated factors of colorectal neoplasia in the Tianjin colorectal cancer screening program from 2012 to 2020.

PURPOSE: Colorectal cancer (CRC) screening has been implemented in Tianjin, China since 2012. The objective was to estimate the neoplasia detection rate in a high-risk population by age and sex and to investigate the potential factors associated with colorectal neoplasia. PATIENTS AND METHODS: This study is based on data of the Tianjin CRC screening program from 2012 to 2020. Residents with a positive high-risk factors questionnaire (HRFQ) or a positive faecal immunochemical test (FIT) were identified as high-risk participants and were subsequently recommended for a free colonoscopy. RESULTS: A total of 4,117,897 eligible participants aged 40-74 years completed both a HRFQ and FIT, and 217,164 (5.3%) of them were identified as high-risk participants. Positive rates of preliminary screening increased with age and were higher in females than in males. For 57,971 participants undertaking colonoscopy, the detection rates of nonadvanced adenoma, advanced adenoma and CRC were 37.8%, 5.7% and 1.6%, respectively. Detection rates of advanced neoplasia increased from the age of 50 and were higher in males. For nonadvanced neoplasia, a strong increase was observed in males from the age of 40 and in females from the age of 50. Male sex had a greater impact on individuals aged 40-49 than on older individuals. Several factors including current smoking, drinking, and higher body mass index (BMI) were significantly associated with the presence of neoplasia, whereas, these associations were mainly restricted to individuals aged above 50 but not those aged 40-49 years. CONCLUSIONS: These findings support that age-specific risk stratification and sex-specific initiating ages for CRC screening should be recommended to improve the accuracy and effectiveness of current screening strategy.

Reduced trace gas oxidizers as a response to organic carbon availability linked to oligotrophs in desert fertile islands.

Atmospheric trace gases, such as H2 and CO, are important energy sources for microbial growth and maintenance in various ecosystems, especially in arid deserts with little organic substrate. Nonetheless, the impact of soil organic C availability on microbial trace gas oxidation and the underlying mechanisms are unclear at the community level. This study investigated the energy and life-history strategies of soil microbiomes along an organic C gradient inside and out of Hedysarum scoparium islands dispersed in the Mu Us Desert, China. Metagenomic analysis showed that with increasing organic C availability from bare areas into "fertile islands", the abundance of trace gas oxidizers (TGOs) decreased, but that of trace gas nonoxidizers (TGNOs) increased. The variation in their abundance was more related to labile/soluble organic C levels than to stable/insoluble organic C levels. The consumption rates of H2 and CO confirmed that organic C addition, especially soluble organic C addition, inhibited microbial trace gas oxidation. Moreover, microorganisms with distinct energy-acquiring strategies showed different life-history traits. The TGOs had lower 16 S rRNA operon copy numbers, lower predicted maximum growth rates and higher proportions of labile C degradation genes, implying the prevalence of oligotrophs. In contrast, copiotrophs were prevalent in the TGNOs. These results revealed a mechanism for the microbial community to adapt to the highly heterogeneous distribution of C resources by adjusting the abundances of taxa with distinct energy and life-history strategies, which would further affect trace gas consumption and C turnover in desert ecosystems.

Soil organic carbon stability mediate soil phosphorus in greenhouse vegetable soil by shifting phoD-harboring bacterial communities and keystone taxa.

Addition of organic amendments, such as manure and straw, to arable fields as a partial substitute for mineral phosphorus (P), are a sustainable practice in high-efficiency agricultural production. Different organic inputs may induce varied soil organic carbon (OC) stability and phoD harboring microbes, subsequently regulate P behavior, but the underlying mechanisms are poorly understood. A 11-year field experiment examined P forms by 31P-nuclear magnetic resonance (NMR), OC chemical composition by 13C NMR, and biologically-based P availability methods, phoD bacterial communities, and their co-occurrence in soils amended with chemical P fertilizer (CF), chemical P partly substituted by organic amendments including pig manure (CM), a mixture of pig manure and corn straw (CMS), and corn straw (CS), with equal P input in all treatments. Organic amendments significantly increased soil labile Pi (CaCl2-P, citrate-P, 2.91-3.26 and 1.16-1.32 times higher than CF) and Po (enzyme-P, diesters, 4.08-7.47 and 1.71-2.14 times higher than CF) contents and phosphatase activities, while significantly decreased aromaticity (AI) and recalcitrance indexes (RI) of soil C, compared with CF. The keystone genera in manured soils (Alienimomas and Streptomyces) and straw-applied soils (Janthinobacterium and Caulobacter) were significantly correlated with soil enzyme-P, microbial biomass P (MBP), diesters, and citrate-P. Soil AI and RI were significantly correlated with the phoD keystone and soil P species. It suggested that the keystone was impacted by soil OC stability and play a role in regulating P redistribution in amended soils. This study highlights how manure and straw incorporation altered soil OC stability, shaped the phoD harboring community, and enhanced soil P biological processes promoted by the keystone taxa. The partial substitution of mineral P by mixture of manure and straw is effectively promote soil P availability and beneficial for environmental sustainability.

Crop residue return sustains global soil ecological stoichiometry balance.

Although soil ecological stoichiometry is constrained in natural ecosystems, its responses to anthropogenic perturbations are largely unknown. Inputs of inorganic fertilizer and crop residue are key cropland anthropogenic managements, with potential to alter their soil ecological stoichiometry. We conducted a global synthesis of 682 data pairs to quantify the responses of soil carbon (C), nitrogen (N), and phosphorus (P) and grain yields to combined inputs of crop residue plus inorganic fertilizer compared with only inorganic fertilizer application. Crop residue inputs enhance soil C (10.5%-12%), N (7.63%-9.2%), and P (2.62%-5.13%) contents, with an increase in C:N (2.51%-3.42%) and C:P (7.27%-8.00%) ratios, and grain yields (6.12%-8.64%), indicating that crop residue alleviated soil C limitation caused by inorganic fertilizer inputs alone and was able to sustain balanced stoichiometry. Moreover, the increase in soil C and C:N(P) ratio reached saturation in ~13-16 years after crop residue return, while grain yield increase trend discontinued. Furthermore, we identified that the increased C, N, and P contents and C:N(P) ratios were regulated by the initial pH and C content, and the increase in grain yield was not only related to soil properties, but also negatively related to the amount of inorganic N fertilizer input to a greater extent. Given that crop residual improvement varies with soil properties and N input levels, we propose a predictive model to preliminary evaluate the potential for crop residual improvement. Particularly, we suggest that part of the global budget should be used to subsidize crop residue input management strategies, achieving to a win-win situation for agricultural production, ecological protection, and climate change mitigation.

Fungal diversity dominates the response of multifunctionality to the conversion of pure plantations into two-aged mixed plantations.

Plantation forests are essential in driving global biogeochemical cycling and mitigating climate change. Biodiversity and environmental factors can shape multiple forest ecosystem functions simultaneously (i.e., multifunctionality). However, their effect on multifunctionality when pure plantations are converted into two-aged plantations remains underexplored. Therefore, we assessed above- and below-ground biodiversity and environmental factors and 11 ecosystem functions in different plantation types in subtropical China. The two-aged mixed plantations exhibited higher multifunctionality than did a pure plantation, primarily due to soil fungal diversity and secondarily due to tree diversity, based on the coefficient of variation for tree diameter at breast height (CVD) and community-weighted specific leaf area (CWMSLA). Further analysis revealed saprotrophy as the key soil fungal trophic mode in maintaining multifunctionality. Moreover, structural equation modeling confirmed that soil environmental factors, namely the soil water content and pH, had no direct association with multifunctionality, but were indirectly related to multifunctionality via elevated CVD and CWMSLA, respectively. Our results indicate that the tree and soil fungal diversity, as well as soil environmental factors, resulting from the conversion of pure plantations to two-aged mixed plantations, can enhance multifunctionality, and provide a better comprehensive understanding of the driving mechanisms of multifunctionality, leading to the sustainable management of subtropical plantation forest ecosystems.

Assessing the effectiveness of the intervention measures of COVID-19 in China based on dynamical method.

Normalized interventions were implemented in different cities in China to contain the outbreak of COVID-19 before December 2022. However, the differences in the intensity and timeliness of the implementations lead to differences in final size of the infections. Taking the outbreak of COVID-19 in three representative cities Xi'an, Zhengzhou and Yuzhou in January 2022, as examples, we develop a compartmental model to describe the spread of novel coronavirus and implementation of interventions to assess concretely the effectiveness of Chinese interventions and explore their impact on epidemic patterns. After applying reported human confirmed cases to verify the rationality of the model, we apply the model to speculate transmission trend and length of concealed period at the initial spread phase of the epidemic (they are estimated as 10.5, 7.8, 8.2 days, respectively), to estimate the range of basic reproduction number (2.9, 0.7, 1.6), and to define two indexes (transmission rate v t and controlled rate v c ) to evaluate the overall effect of the interventions. It is shown that for Zhengzhou, v c is always more than v t with regular interventions, and Xi'an take 8 days to achieve v c  > v t twice as long as Yuzhou, which can interpret the fact that the epidemic situation in Xi'an was more severe. By carrying out parameter values, it is concluded that in the early stage, strengthening the precision of close contact tracking and frequency of large-scale nucleic acid testing of non-quarantined population are the most effective on controlling the outbreaks and reducing final size. And, if the close contact tracking strategy is sufficiently implemented, at the late stage large-scale nucleic acid testing of non-quarantined population is not essential.

A risk scoring system for advanced colorectal neoplasia in high-risk participants to improve current colorectal cancer screening in Tianjin, China.

BACKGROUND: Given the limited effectiveness of the current Chinese colorectal cancer (CRC) screening procedure, adherence to colonoscopy remains low. We aim to develop and validate a scoring system based on individuals who were identified as having a high risk in initial CRC screening to achieve more efficient risk stratification and improve adherence to colonoscopy. METHODS: A total of 29,504 screening participants with positive High-Risk Factor Questionnaire (HRFQ) or faecal immunochemical test (FIT) who underwent colonoscopy in Tianjin from 2012-2020 were enrolled in this study. Binary regression analysis was used to evaluate the association between risk factors and advanced colorectal neoplasia. Internal validation was also used to assess the performance of the scoring system. RESULTS: Male sex, older age (age ≥ 50 years), high body mass index (BMI ≥ 28 kg/m2), current or past smoking and weekly alcohol intake were identified as risk factors for advanced colorectal neoplasm. The odds ratios (ORs) for significant variables were applied to construct the risk score ranging from 0-11: LR, low risk (score 0-3); MR, moderate risk (score 4-6); and HR, high risk (score 7-11). Compared with subjects with LR, those with MR and HR had ORs of 2.47 (95% confidence interval, 2.09-2.93) and 4.59 (95% confidence interval, 3.86-5.44), respectively. The scoring model showed an outstanding discriminatory capacity with a c-statistic of 0.64 (95% confidence interval, 0.63-0.65). CONCLUSIONS: Our results showed that the established scoring system could identify very high-risk populations with colorectal neoplasia. Combining this risk score with current Chinese screening methods may improve the effectiveness of CRC screening and adherence to colonoscopy.

Saponins From Platycodon grandiflorum Reduces Cisplatin-Induced Intestinal Toxicity in Mice through Endoplasmic Reticulum Stress-Activated Apoptosis.

Saponins from the roots of Platycodon grandiflorum, an edible medicinal plant, have shown a wide range of beneficial effects on various biological processes. In this study, an animal model was established by a single intraperitoneal injection of cisplatin (20[Formula: see text]mg/kg) for evaluating the protective effects of saponins from the roots of P. grandiflorum (PGS, 15[Formula: see text]mg/kg and 30[Formula: see text]mg/kg) in mice. The results indicated that PGS treatment for 10 days restored the destroyed intestinal mucosal oxidative system, and the loosened junctions of small intestinal villi was significantly improved. In addition, a significant mitigation of apoptotic effects deteriorated by cisplatin exposure in small intestinal villi was observed by immunohischemical staining. Also, western blot showed that PGS could effectively prevent endoplasmic reticulum (ER) stress-induced apoptosis caused by cisplatin in mice by restoring the activity of PERK (an ER kinase)-eIF2[Formula: see text]-ATF4 signal transduction pathway. Furthermore, molecular docking results of main saponins in PGS suggested a better binding ability with target proteins. In summary, the present work revealed the underlying protective mechanisms of PGS on intestinal injury induced by cisplatin in mice.

Application of Manure Rather Than Plant-Origin Organic Fertilizers Alters the Fungal Community in Continuous Cropping Tobacco Soil.

Continuous cropping leads to the development of serious fungal diseases in tobacco plants and depleted yield of tobacco (Nicotiana tabacum), which can be mitigated by organic fertilization. Yet, we know little about how organic fertilizers affect the fungal community of continuous cropping tobacco soil. In this study, we investigated the soil fungal community after 11 years of tobacco planting with chemical fertilization (CF) or chemical fertilization combined with organic fertilizers obtained from plant or animal origin, including oil cake (CFO), straw (CFS), and farmyard fertilizer (CFM). The predominant phyla of Ascomycota (70%) and Mortierellomycota (15%) were identified in all the treatments. A significantly higher proportion of Pyrenochaetopsis and lower relative abundance of Sordariomycetes were observed in the CFM group compared to the controls. Compared to CF and non-fertilized control (CK), CFO and CFS led to higher species richness (P < 0.05), while CFM led to a less uniform fungal community, indicated by lower Shannon and higher Simpson diversity indices (P < 0.05). Pearson's correlation and redundancy analysis suggested that fertilizations primarily influenced the fungal community by altering the soil nutrient conditions, among which soil organic carbon and total phosphorus significantly correlated with the fungal diversity and community composition (P < 0.05). Notably, FUNGuild annotation suggested that while other treatments showed no significant effect on the fungal trophic modes, CFM strongly increased the abundance of saprotrophic fungi by more than 30% (P < 0.05), thus preventing the prevalence of potential pathotypes and symbionts. The results suggest that the type of organic fertilizers is essential to the long-term effects of organic application on the fungal community, and the animal-origin manure seems to be a better choice than plant-origin materials in continuous cropping tobacco fields.

Flooding and straw returning regulates the partitioning of soil phosphorus fractions and phoD-harboring bacterial community in paddy soils.

Flooding and straw returning are effective agricultural practices in promoting phosphorus (P) availability in paddy soils. However, little is known about the effects of these practices and their interaction on the soil P pools and functional microbes responsible for soil P mobilization. Our 4-year paddy field experiment aimed to analyze the responses of soil P fractions and phoD-harboring bacterial communities in a double-rice cropping system to intermittent flooding (IF) and continuous flooding (CF), in plots with (+ S) and without (-S) straw return. Compared to IF, CF significantly increased soil citrate-P and marginally decreased the HCl-P fractions, suggesting that the stable inorganic P pools are transferred to labile inorganic P at lower redox potentials. Compared to the -S treatments, + S treatments significantly increased the labile organic fractions (enzyme-P). Correspondingly, a decreased soil total organic P concentration was observed in + S treatment. Additionally, + S treatment significantly increased the activity of acid phosphomonoesterase and alkaline phosphomonoesterase and the abundance of phoD-harboring bacteria. These results indicated that straw promoted organic P minimization to release orthophosphate. The diversity of the phoD-harboring bacteria and complexity of the co-occurrence network decreased under the CF + S treatment; however, all keystone species of the phoD-harboring bacteria were retained in this oxygen-deficient environment. This study highlights that irrigation regimes mediate the processes of inorganic P mobilization, while straw returns regulate the processes of organic P mineralization. Additionally, flooding could be a more effective agricultural practice than straw returning to promote soil P availability in paddy soils. KEY POINTS: •Soil P pools and phoD-harboring bacteria communities were assessed. •Straw return mainly affects the mineralization of organic P. •Continuous flooding mainly affects the mobilization of inorganic P.

Endoplasmic Reticulum Stress-Activated PERK-eIF2α-ATF4 Signaling Pathway is Involved in the Ameliorative Effects of Ginseng Polysaccharides against Cisplatin-Induced Nephrotoxicity in Mice.

Although previous studies have reported that saponins (ginsenosides, the major active and most representative ingredients in Panax ginseng C.A. Meyer) exerted a good ameliorative effect on cisplatin (CP)-induced acute kidney injury in animal models, little attention has been paid to a large number of polysaccharides isolated and purified from ginseng. This work aimed to investigate the protective effect and the possible molecular mechanism of ginseng polysaccharide (WGP) on CP-induced kidney toxicology in mice. The results from biomarker analysis including serum creatinine (CRE) and blood urea nitrogen (BUN) confirmed the protective effect of WGP at 200 and 400 mg/kg on CP-induced renal-toxicology. We found that WGP reduces the apoptosis of kidney cells by inhibiting endoplasmic reticulum (ER) stress caused by CP, which is manifested by increased phosphorylation of PERK. In addition, the apoptosis-associated with caspase 3 activation in renal cells induced by CP was inhibited after administration of WGP, and the phosphorylation levels of PI3K and AKT were also reduced significantly. We also demonstrated that after exposure to CP, the unfolded protein response signaling pathway PERK-eIF2α-ATF4 axis was significantly activated, manifested by increased phosphorylation of eIF2α and increased expression of ATF4 and CHOP. Interestingly, the WGP administration improves this situation. Furthermore, the supplement of WGP inhibited the overexpression of nuclear factor-kappa B p65 (NF-κB p65) and tumor necrosis factor-α (TNF-α) caused by CP exposure. In short, for the first time, our findings indicated that WGP could effectively prevent CP-induced ER stress, inflammation, and apoptosis in renal cells, in part, by regulating the PI3K/AKT and PERK-eIF2α-ATF4 signaling pathways.

T4-like Phages Reveal the Potential Role of Viruses in Soil Organic Matter Mineralization.

Viruses are the most abundant biological entities in the world, but their ecological functions in soil are virtually unknown. We hypothesized that greater abundance of T4-like phages will increase bacterial death and thereby suppress soil organic carbon (SOC) mineralization. A range of phage and bacterial abundances were established in sterilized soil by reinoculation with 10-3 and 10-6 dilutions of suspensions of unsterilized soil. The total and viable 16S rRNA gene abundance (a universal marker for bacteria) was measured by qPCR to determine bacterial abundance, with propidium monoazide (PMA) preapplication to eliminate DNA from non-viable cells. Abundance of the g23 marker gene was used to quantify T4-like phages. A close negative correlation between g23 abundance and viable 16S rRNA gene abundance was observed. High abundance of g23 led to lower viable ratios for bacteria, which suggested that phages drove microbial necromass production. The CO2 efflux from soil increased with bacterial abundance but decreased with higher abundance of T4-like phages. Elimination of extracellular DNA by PMA strengthened the relationship between CO2 efflux and bacterial abundance, suggesting that SOC mineralization by bacteria is strongly reduced by the T4-like phages. A random forest model revealed that abundance of T4-like phages and the abundance ratio of T4-like phages to bacteria are better predictors of SOC mineralization (measured as CO2 efflux) than bacterial abundance. Our study provides experimental evidence of phages' role in organic matter turnover in soil: they can retard SOC decomposition but accelerate bacterial turnover.

[Characteristics of Paddy Soil Organic Carbon Mineralization and Influencing Factors Under Different Water Conditions and Microbial Biomass Levels].

Paddy soil often undergoes frequent dry-wet alternation. The change in water status not only affects the physical and chemical properties of the soil, but also changes the structure and diversity of the soil microbial communities, which in turn determines the rate of soil organic carbon mineralization. However, the effects of different water conditions and soil microbial biomass levels on the process of soil organic carbon mineralization and its mechanisms are still unclear. Therefore, this study took typical subtropical paddy soil as the research object, applied a laboratory incubation experiment with two water treatments of dry-wet and continuous flooding, and reduced the soil microbial biomass through chloroform fumigation, thereby obtaining high and low soil microbial biomass carbon contents, to elucidate the influencing mechanisms of microbial biomass and water conditions on organic carbon mineralization in paddy soil. The results showed that during the first 30 d of incubation, the dry-wet treatment was in a non-flooded stage and its cumulative CO2 emissions were significantly lower than those of the continuous flooded treatment. After 30 d, the dry-wet treatment entered the flooded stage. The difference in the cumulative CO2 emissions of the soils with a high microbial biomass carbon content between the dry-wet and continuous flooding treatments gradually decreased, and there was no significant difference on day 78. In the soil with a low microbial biomass carbon content, the cumulative CO2 emissions of the dry-wet treatment on day 78 was still significantly lower than that of the continuous flooded treatment. The soils with a low microbial biomass carbon content showed a faster CO2 emission rate at the beginning of the incubation period (first 20 d), which was 1.1-6.1 times greater than that of the high microbial biomass carbon soils owing to their high soil dissolved organic carbon (DOC) content, and the CO2 emission rate then gradually decreased until it was below that of the soil with a high microbial biomass carbon content. The soil organic carbon mineralization rate became stable later in the incubation period (days 45-78). The stable mineralization rate of the high microbial biomass carbon soil was 20%-30% higher than that of the low microbial biomass carbon soil. The multiple regression analysis results showed that the decrease in the soil DOC content (ΔDOC) and the increase in the Fe2+ content (ΔFe2+) significantly affected the change in cumulative CO2 emissions (ΔCO2) under continuous flooding conditions, but had no effect on ΔCO2 during the flooding stage of the dry-wet treatment. The correlation analysis showed that the daily CO2 emission rate of soils with high microbial biomass carbon was significantly positively correlated with glucosidase activity under dry-wet treatment and significantly negatively correlated with acetylglucosaminidase (NAG) and peroxidase activities under continuous flooding treatment. In the low microbial biomass carbon soils, the daily CO2 emission rate of the continuous flooding treatment was negatively correlated with the NAG activity, but showed no correlation with enzyme activities under dry-wet management. In summary, the cumulative CO2 emissions of dry-wet treatment were lower than those of continuous flooding treatment, and the difference was significant in soils with low microbial biomass carbon. The size of the soil microbial biomass determined the level of the stable soil organic carbon mineralization rate. The amount of soluble organic carbon and iron reduction affected the soil CO2 emissions under continuous flooding conditions, and the soil water conditions affected the daily CO2 emission rate and its key influencing enzymes. This study provides data and theoretical support for the carbon cycle and carbon sequestration potential in paddy soil.

Aerobic degradation of 4-fluoroaniline and 2,4-difluoroaniline: performance and microbial community in response to the inocula.

In this study, a distinct inoculum was investigated as an isolated variable within sequencing batch reactors via a comparison of the 4-fluoroaniline (4-FA) or 2,4-difluoroaniline (2,4-DFA) removal amounts. The inocula were derived from a treatment plant for treating pharmaceutical wastewater plus a small amount of municipal sewage (PMS), a treatment plant for treating fluoridated hydrocarbon wastewater (FHS), and a treatment plant for treating the comprehensive wastewater in an industrial park (CIS). There were slight differences among the degradation patterns of the 4-FA for the three inocula, whether during the enrichment period or the high concentration shock period. In contrast, it was observed that the degradation efficiency of 2,4-DFA initially varied with the inocula. The FHS-derived inoculum was determined to be optimal, exhibiting the earliest degradation reaction only after an acclimation of 7 days had the highest degradation rate constant of 0.519 h-1, and had the fastest recovery time of three weeks after high concentration shock. Additionally, compared with the PMS-derived inoculum, the CIS-derived inoculum exhibited an earlier degradation reaction within three weeks, and a higher microbial diversity, but a lower shock resistance and degradation rate constant of 0.257 h-1. High-throughput sequencing demonstrated that each final consortium was different in composition, and the microbial consortia developed well on the inoculum and substrate. In comparison of the similarity among the three 2,4-DFA enrichment cultures, the higher similarity (63.9-70.0%) among three final consortia enriching with 4-FA was observed. The results indicated that the inoculum played an important role in the degradation of FAs and the microbial bacterial communities of final consortia, and the effect extent might well depend on the fluorinated level of FAs.

Diazotrophic Community Variation Underlies Differences in Nitrogen Fixation Potential in Paddy Soils Across a Climatic Gradient in China.

Biological nitrogen (N2) fixation as a source of new N input into the soil by free-living diazotrophs is important for achieving sustainable rice agriculture. However, the dominant environmental drivers or factors influencing N2 fixation and the functional significance of the diazotroph community structure in paddy soil across a climatic gradient are not yet well understood. Thus, we characterized the diazotroph community and identified the ecological predictors of N2 fixation potential in four different climate zones (mid-temperate, warm-temperate, subtropical, and tropical paddy soils) in eastern China. Comprehensive nifH gene sequencing, functional activity detection, and correlation analysis with environmental factors were estimated. The potential nitrogenase activity (PNA) was highest in warm-temperate regions, where it was 6.2-, 2.9-, and 2.2-fold greater than in the tropical, subtropical, and mid-temperate regions, respectively; nifH gene abundance was significantly higher in warm-temperate and subtropical zones than in the tropical or mid-temperate zones. Diazotroph diversity was significantly higher in the tropical climate zone and significantly lower in the mid-temperate zone. Non-metric multidimensional scaling and canonical correlation analysis indicated that paddy soil diazotroph populations differed significantly among the four climate zones, mainly owing to differences in climate and soil pH. Structural equation models and automatic linear models revealed that climate and nutrients indirectly affected PNA by affecting soil pH and diazotroph community, respectively, while diazotroph community, C/P, and nifH gene abundance directly affected PNA. And C/P ratio, pH, and the diazotroph community structure were the main predictors of PNA in paddy soils. Collectively, the differences in diazotroph community structure have ecological significance, with important implications for the prediction of soil N2-fixing functions under climate change scenarios.

[Response of Extracellular Enzyme Activities to Substrate Availability in Paddy Soil with Long-term Fertilizer Management].

The availability of carbon (C), nitrogen (N), and other substrates in soil determines the growth and metabolism of microorganisms and affects the activity of extracellular enzymes. To study the activities of ß-1,4-glucosidase (BG) and ß-1,4-N-acetylglucosaminidase (NAG) in response to C and N availability, samples that underwent four treatments-non-fertilization (CK), chemical fertilizer (NPK), combination of organic manure and chemical fertilizer (OM), and mixture of straw and chemical fertilizer (ST)-were collected from long-term fertilization paddy soil and incubated for 0, 4, 8, and 12 months to obtain soil with different C and N availability gradients. The results showed that the dissolved organic carbon(DOC) content of OM and ST treatment samples was 2-3 times higher than that of CK and NPK treatment samples. With the increase of DOC and ammonium (NH4+-N) contents, the activities of BG and NAG and the contents of microbial biomass C (MBC) and N (MBN) showed no increase during incubation within each treatment. Fertilization treatments, incubation time, and their interaction are crucial factors varying the contents of DOC, NH4+-N, MBC, and MBN among different fertilization treatments (P<0.01). There was a positive correlation between MBC/MBN and DOC/NH4+-N of OM treatment (P<0.05) and a negative relationship between ln(BG)/ln(NAG) and DOC/NH4+-N of ST treatment (P<0.01), indicating that the availability of substrates played a key role in the potential activity of extracellular enzymes in paddy soil, and the carbon-nitrogen ratio of microbial biomass was controlled by the C/N stoichiometry of substrates in soil. The results have a certain guiding significance for further study on the variation of extracellular enzyme activity in paddy soil, regulating the balance of carbon and nitrogen, and improving the fertility of paddy soil.