nosZ Gene Research Articles

Active bacteria driving N2O mitigation and dissimilatory nitrate reduction to ammonium in ammonia recovery bioreactors.

Shifting from ammonia removal to recovery is the current strategy in wastewater treatment management. We recently developed a microaerophilic activated sludge system for retaining ammonia whereas removing organic carbon with minimal N2O emissions. A comprehensive understanding of nitrogen metabolisms in the system is essential to optimize system performance. Here, we employed metagenomics and metatranscriptomics analyses to characterize the microbial community structure and activity during the transition from a microoxic to an oxic condition. A hybrid approach combining high-quality short reads and Nanopore long reads reconstructed 98 medium- to high-quality non-redundant metagenome-assembled genomes from the communities. The suppressed bacterial ammonia monooxygenase (amoA) expression was upregulated after shifting from a microoxic to an oxic condition. Seventy-three reconstructed metagenome-assembled genomes (>74% of the total) from 11 bacterial phyla harbored genes encoding proteins involved in nitrate respiration; 39 (~53%) carried N2O reductase (nosZ) genes with the predominance of clade II nosZ (31 metagenome-assembled genomes), and 24 (~33%) possessed nitrite reductase (ammonia-forming) genes (nrfA). Clade II nosZ and nrfA genes exhibited the highest and second-highest expressions among nitrogen metabolism genes, indicating robust N2O consumption and ammonification. Non-denitrifying clade II nosZ bacteria, Cloacibacterium spp., in the most abundant and active phylum Bacteroioda, were likely major N2O sinks. Elevated dissolved oxygen concentration inhibited clade II nosZ expression but not nrfA expression, potentially switching phenotypes from N2O reduction to ammonification. Collectively, the multi-omics analysis illuminated bacteria responsible for N2O reduction and ammonification in microoxic and oxic conditions, facilitating high-performance ammonia recovery.

Stutzerimonas stutzeri culture enhances microbial community structure and tomato seedling growth in saline soil.

Plant growth-promoting rhizobacteria (PGPR) improve microbial community structure, promote crop growth, and reduce greenhouse gas emissions in agricultural soils; however, the effects of PGPR fermentation on the growth and salt tolerance of tomato plants remain unclear. In this study, we aimed to investigate the effects of the PGPR Stutzerimonas stutzeri NRCB010 on the microbial communities, tomato growth, and nitrous oxide (N2O) emissions in saline soil by performing a greenhouse pot experiment. The experiment was conducted under two soil salt concentrations (0 and 3 g kg-1 NaCl) and three treatments (LSFJ broth, NRCB010 cells, and NRCB010 culture). Both salt stress and NRCB010 treatments significantly affected the physicochemical properties and microbial community structure of tomato rhizosphere soil. Treatment with 3 g kg-1 NaCl significantly reduced the shoot and root dry weights of the plants compared with those of the control plants. Application of NRCB010 cells as well as that of culture promoted the growth of tomato seedlings and alleviated salt stress. The copy number changes in the nosZⅠ gene on day 3 and amoA gene on day 25 demonstrated that NRCB010 cells significantly reduced soil N2O emissions when treated with 0 g kg-1 NaCl. Furthermore, soil physicochemical properties, plant biomass, and soil microbial diversity were correlated with each other. The results emphasize the enormous potential of S. stutzeri NRCB010 culture to resist abiotic stress, promote crop growth, and improve the rhizosphere soil microenvironment; however, its ability to decrease N2O emissions is constrained by soil salinity.

Microbial recruitment and microbial ecological roles in soil nutrient cycling of Populus cathayana males and females

Soil nitrogen (N) availability influences plant production and soil nutrient cycling. However, how it influences sex-specific microbial community composition and rhizosphere nutrient cycling in dioecious plant species is poorly understood. We examined the rhizospheric bacterial and fungal community assemble and their influences on soil nutrient cycling under different N backgrounds in 30-year-old experimental stands and a soil microbial reshaping-controlled experiment. In comparison to male trees, female trees increased fungal community diversity, and the relative abundance of taxa related to nutrient availability; elevated phosphorus (P) mobilization by increasing acidic phosphatase activity and carboxylic acid release; and decreased the counts of denitrification nirS, nirK, and nosZ genes at high N supply. Males increased the nifH gene counts related to microbial N fixation at high N supply. Low N supply increased N fixation nifH gene counts in the rhizosphere of females. Males decreased bacterial and fungal diversity, increased enzymatic activities related to organic N and P mineralization, and elevated soil nitrate-nitrogen levels at low N supply. Our results indicate that sex-specific responses to N availability are associated with rhizospheric bacterial and fungal community composition and diversity and their effects on rhizospheric nutrient cycling, which may explain sex-specific resource utilization and niche differentiation.

Comprehensive effects of biochar-assisted nitrogen and phosphorus bioremediation on hydrocarbon removal and microecological improvement in petroleum-contaminated soil

Biochar is widely used in agricultural soils, but its effects with nitrogen and phosphorus amendments on petroleum-contaminated soil are unclear. This study investigated biochar-assisted biostimulation in a microcosm experiment, focusing on hydrocarbon degradation, nitrogen cycling, and soil properties. Compared to the biostimulation alone (BS), biochar combined biostimulation (BSC) significantly enhanced the abundances of petroleum hydrocarbon degraders including Lysobacter and Brevundimonas, which led to a 17% increase in total petroleum hydrocarbon (TPH) degradation, with 9% and 39% enhancements in saturated hydrocarbon degradation and aromatic hydrocarbon fraction degradation, respectively. Biochar also promoted ammonia and nitrous oxide oxidation by upregulating AOA, AOB, norB, and nosZ genes, while controlling nitrogen loss by downregulating nirK. Soil moisture, oxidation–reduction potential (ORP), dehydrogenase activity (SDHA), and microbial proliferation were significantly enhanced. Structural equation models (SEM) indicated synergistic interactions between nitrogen cycling and hydrocarbon degradation. Biochar enhances hydrocarbon degradation and nitrogen cycling, offering a promising soil remediation approach.

Enhancing biological nitrogen removal of slaughterhouse and meat processing wastewater in three-stage AO process by influent allocation: From lab-scale to full-scale investigation

Three-stage anoxic/aerobic (AO) process is promising for efficient nitrogen removal from high-strength wastewater. Herein, the effects of influent allocation modes (50/40/10 vs. 50/25/25) on nitrogen removal performance for treating slaughterhouse and meat processing wastewater (SMPW) were investigated from lab-scale to full-scale three-stage AO processes. Compared to 50/25/25 (94.1 %), the allocation mode of 50/40/10 achieved a higher nitrogen removal of 97.7 % and better adaptability to ammonia load. The second anoxic tank contributed the highest total nitrogen (TN) removal in the system with allocation mode of 50/40/10, while simultaneous nitrification–denitrification and aerobic denitrification in the thrid oxic tank effectively enhanced the TN removal efficiency. Microbial community analysis revealed that SMPW treatment systems tended to enrich lipolytic bacteria (Pseudomonas and Bacillus), cellulolytic bacteria (Christensenellaceae_R-7_group), proteolytic bacteria (Proteiniclasticum, Planococcus, and OLB8), and denitrifying glycogen accumulating bacteria (Candidatus_Competibacter). Meanwhile, the inherent nature of SMPW promoted an increase in the dissimilatory nitrate reduction to ammonium pathway, while the abundant and complex organic substances environment ensured efficient nitrogen removal. The influent allocation mode had no significant effect on nitrification process, but the 50/40/10 allocation mode obviously enriched the nitrous oxide reductase encoded by gene nosZ, which reduced carbon emission. The reliability of 50/40/10 was verified in a 35,000 m3/d full-scale SMPW treatment plant, with the effluent COD, TN, and ammonia nitrogen stabilized at 18 ± 5, 4.7 ± 1.8, and 0.9 ± 0.2 mg/L, respectively, after 48 days. This study provides a valuable reference for effective regulation of three-stage AO process in treating SMPW.

Interactions Between Bacterivorous Nematodes and Bacteria Reduce N2O Emissions.

Trophic interactions in micro-food webs, such as those between nematodes and their bacterial prey, affect nitrogen cycling in soils, potentially changing nitrous oxide (N2O) production and consumption. However, how nematode-mediated changes in soil bacterial community composition affect soil N2O emissions is largely unknown. Here, microcosm experiments are performed with the bacterial feeding nematode Protorhabditis to explore the potential of nematodes in regulating microbial communities and thereby soil N2O emissions. Removal of nematodes by defaunation resulted in increased N2O emissions, with the removal of Protorhabditis contributing most to this increase. Further, inoculation with Protorhabditis altered bacterial community composition and increased the relative abundance of Bacillus, and the abundance of the nosZ gene in soil. In vitro experiments indicated that Protorhabditis reinforce the reduction in N2O emissions by Bacillus due to suppressing competitors and producing bacteria growth stimulating substances such as betaine. The results indicate that interactions between nematodes and bacteria modify N2O emissions providing the perspective for the mitigation of greenhouse gas emissions via manipulating trophic interactions in soil.

Nitrogen and Water Additions Affect N2O Dynamics in Temperate Steppe by Regulating Soil Matrix and Microbial Abundance

Elucidating the effects of nitrogen and water addition on N2O dynamics is critical, as N2O is a key driver of climate change (including nitrogen deposition and shifting precipitation patterns) and stratospheric ozone depletion. The temperate steppe is a notable natural source of this potent greenhouse gas. This study uses field observations and soil sampling to investigate the seasonal pattern of N2O emissions in the temperate steppe of Inner Mongolia and the mechanism by which nitrogen and water additions, as two different types of factors, alter this seasonal pattern. It explores the regulatory roles of environmental factors, soil physicochemical properties, microbial community structure, and abundance of functional genes in influencing N2O emissions. These results indicate that the effects of nitrogen and water addition on N2O emission mechanisms vary throughout the growing season. Nitrogen application consistently increase N2O emissions. In contrast, water addition suppresses N2O emissions during the early growing season but promotes emissions during the peak and late growing seasons. In the early growing season, nitrogen addition primarily increased the dissolved organic nitrogen (DON) levels, which provided a matrix for nitrification and promoted N2O emissions. Meanwhile, water addition increased soil moisture, enhancing the abundance of the nosZ (nitrous oxide reductase) gene while reducing nitrate nitrogen (NO3−-N) levels, as well as AOA (ammonia-oxidizing archaea) amoA and AOB (ammonia-oxidizing bacteria) amoA gene expression, thereby lowering N2O emissions. During the peak growing season, nitrogen’s role in adjusting pH and ammonium nitrogen (NH4+-N), along with amplifying AOB amoA, spiked N2O emissions. Water addition affects the balance between nitrification and denitrification by altering aerobic and anaerobic soil conditions, ultimately increasing N2O emissions by inhibiting nosZ. As the growing season waned and precipitation decreased, temperature also became a driver of N2O emissions. Structural equation modeling reveals that the impacts of nitrogen and water on N2O flux variations through nitrification and denitrification are more significant during the peak growing season. This research uncovers innovative insights into how nitrogen and water additions differently impact N2O dynamics across various stages of the growing season in the temperate steppe, providing a scientific basis for predicting and managing N2O emissions within these ecosystems.

Nano-Selenium Elevating Leaf Quality and Growth Via Microbial-Regulating Nitrogen Availability Under Ammonium and Nitrate Spraying in Tea Plants.

Nano-selenium fertilizers can promote plant growth and nitrogen availability. However, little information is available on the effects of nano-selenium on tea leaf quality, soil nutrient availability and associated microbe-driven mechanisms. This study examined the effects of nano-selenium on the tea leaf quality and soil nitrogen cycling in 20-year-old tea plantations when the leaves were sprayed with ammonium or nitrate. Leaf selenium and amino acid contents increased ninefold and 9%, respectively, with nano-selenium in "Zhongcha108" and "Longjing43." Rhizosphere bacterial and fungal community compositions were more sensitive to selenium and nitrogen applications in "Longjing43" than in "Zhongcha108." "Zhongcha108" enriched more taxa related to microbial growth, while more taxa related to cellular maintenance and nutrient acquisition enriched in "Longjing43." Nano-selenium application decreased the copy number of AOA and AOB genes, and nosZ and nirK genes by 59%, 53%, 37% and 46% under ammonium, and by 77%, 43%, 38% and 65%, respectively, under nitrate spraying, in "Longjing43." However, the expression of these genes increased by nano-selenium in "Zhongcha108" with ammonium spraying. It is concluded that a nano-selenium application increases tea leaf quality, and this effect on nitrogen cycling and ecological functioning largely depends on the tea cultivar-specific bacterial and fungal composition and function.

Assessing biochar's impact on greenhouse gas emissions, microbial biomass, and enzyme activities in agricultural soils through meta-analysis and machine learning.

The role of biochar in reducing greenhouse gas (GHG) emissions and improving soil health is a topic of extensive research, yet its effects remain debated. Conflicting evidence exists regarding biochar's impact on soil microbial-mediated emissions with respect to different GHGs. This study systematically examines these divergent perspectives, aiming to investigate biochar's influence on GHG emissions and soil health in agricultural soils. The meta-analysis includes 2594 paired observations from 157 studies conducted between 2000 and 2024. It was found that biochar increased the presence of amoA and nosZ genes by 39.4% and 41.7%, respectively, while reducing the abundance of the nirS gene by 17.8%. This led to a 13.1% decrease in N2O emissions. Nitrous emissions were positively associated with mean annual temperature and biochar's pyrolysis temperature and dosage while inversely related to soil pH, nitrogen fertilisation rate, and biochar pH and carbon content. Biochar also regulated enzyme activity related to the nutrient cycle and increased microbial biomass carbon, nitrogen, and phosphorus by 16.6%, 23.9%, and 50.2%, respectively, leading to changes in microbial community diversity. These changes contributed to a reduction in CO2 and CH4 emissions, particularly when biochar and nitrogen fertiliser were applied at doses below 21.4tha-1 and 242.5kgha-1, as predicted by machine learning models. This study offers an overview of the positive impact of biochar amendments on soil GHG emissions mitigation. The key predictive factors identified could help optimise biochar production and targeted amendments, potentially improving soil health and achieving carbon neutrality in agroecosystems.

Diversified crop rotations exert a profound influence on the nosZI denitrifier community.

Agricultural soils are a significant contributor to global nitrous oxide (N2O) emissions, which is primarily driven by microbial nitrification and denitrification processes. Diversifying crop rotations can enhance soil nitrogen (N) utilization and influence N-cycling microbes, particularly the denitrifiers. Here, we evaluated the abundance, diversity, and community structure of soil denitrifiers by analyzing the denitrification genes (nirS, nirK, and nosZI) with a 14-year experiment of continuous and rotated crop systems. Compared to continuous cotton (C), crop rotations altered abundance of the nirS, nirK, and nosZI genes, but the responses varied among different rotation patterns (p<0.05). Diversified crop rotations decreased Shannon index of the nirS and nirK gene communities, while increased that of the nosZI gene communities. Diversified crop rotations greatly changed community structure of the nirS, nirK and nosZI gene communities (p<0.05). Among the responsive operational taxonomic units (OTUs), 2.62%, 2.52%, and 4.31% of the nirS, nirK, and nosZI genes were involved in the responses, respectively. Notably, a significant increase in OTUs belonged to N-fixing groups (i.e., Herbaspirillum and Rhodanobacter), while a decrease in OTUs affiliated to Achromobacter and Bosea was observed in diversified crop rotations. Furthermore, soil pH and C/N ratio correlated significantly with the nirS gene community structure (p<0.05), SOC and C/N ratio correlated with the nirK gene community (p<0.05), and soil pH, TN, NO3--N, and C/N ratio correlated with the nosZI gene community (p<0.05), respectively. In conclusion, our study demonstrates that long-term diversified crop rotations significantly altered the microbial communities related to denitrification, especially the nosZI gene community. These findings highlight the importance of diversified crop rotations in fostering soil denitrifiers communities that contribute to N₂O reduction, potentially supporting sustainable agricultural practices by reducing greenhouse gas emissions. However, future studies should be focus on both the nosZI and nosZII clades communities to offer a more complete picture of microbial contributions to soil N-cycling and N2O emission reduction.

Distinct response of nitrogen metabolism to exogenous cadmium (Cd) in river sediments with and without Cd contamination history.

The role of metal resistance on nitrogen metabolism function and community resilience against Cd is important for elucidating the evolutionary dynamics of key ecological functions in river ecosystems. In this study, the response of nitrogen transforming function to Cd exposure in river sediments from the Yangtze River Basin with varying levels of heavy metal contamination history (Cd-contaminated and Cd-free sediments) was compared to understand how Cd influenced nitrogen metabolism under varying metal resistance conditions. The results showed that chronic and persistent Cd pollution of sediments caused an elevation of transport efflux metal resistance genes (MRGs) and a reduction in the uptake MRGs, leading to a stronger tolerance to Cd for Cd-contaminated sediment than Cd-free ones. Specifically, denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) respectively responded to Cd through different mechanisms. Exogenous Cd (5-100 mg kg-1) influenced denitrification rates (-70 %-100 % deviation to control group) by regulating key genera (Thiobacillus, Magnetospirillum, Sideroxydans etc.) and gene clusters for denitrification. Both adaptive nature of anammox bacteria and co-regulation of key genera (Candidatus_Scalindua, Candidatus_Jettenia, Planctomyces etc.) and gene hzsA were drivers of differential responses in sediments from various contamination history. Environmental factors rather than contamination history, key genera or genes were probably critical ones determining Cd-resistance in DNRA, being more tolerant to Cd in sediments with higher TOC and NH4+. Stimulation of N2O reduction process (genera Gemmatimonas and Gemmatirosa and genes nosZ) in Cd-contaminated sediments by exogenous Cd lowered N2O emission risk, whereas the reverse was true for Cd-free sediments. These results enrich our understanding about the linkages among MRGs and nitrogen reduction functions in river.

Extreme soil salinity reduces N and P metabolism and related microbial network complexity and community immigration rate.

Soil microbiomes are well known to suffer from the effects of rising salinity. There are, however, no current understandings regarding its specific effects on microbial metabolic functions associated with nitrogen (N) and phosphorus (P) cycling, particularly in the Yellow River Delta (YRD), one of the largest estuaries in the world. This research examined soil microbiomes at 50 sites in the YRD region to analyze their co-occurrence networks and their relationship with N (nitrification, denitrification, dissimilatory, assimilatory, fixation, and mineralization) and P (solubilization, mineralization, transportation, and regulation) metabolism processes. Our findings indicate a notable reduction in soil multifunctionality as salinity levels increase, with Halofilum-ochraceum playing a significant role in nitrification, whereas Bacteroidetes-SB0662-bin-6 helps solubilize inorganic P in highly saline areas. High soil salinity negatively affected the amoA gene involved in nitrification and increased the nosZ gene involved in denitrification in extreme salinity soil with 8.2g/kg salt content. Extreme salinity significantly reduced the expression of genes involved in inorganic P solubilization, such as ppa and ppx. Additionally, the alkaline P gene phoD exhibited significant decreases in extremely saline soils, thereby impeding the mineralization of organic P. The neutral community models indicated that microbial community immigration rate showed a linear negative relationship with soil EC in the six N and four P processes. Salinization, however, displayed a nonlinear pattern with clearly defined thresholds on the community of microbes involved in N and P cycling. Reduced microbial diversity and interactions are causing a decline in soil multifunctionality, and the soil multifunctionality and network edges jointly limited the microbial community immigration rate involved in N and P cycling. It is crucial to preserve soil microbial functions to support nutrient cycling and predict the ecological effects of soil salinization.

Synergistic effects of heterogeneous mature compost and aeration rate on humification and nitrogen fixing during kitchen waste composting.

Sludge mature compost (SMC) is notable for its high production, easy accessibility, and stable supply. This study investigated the impact of the SMC addition and different aeration rates on the humification and nitrogen fixing process during kitchen waste composting. The results demonstrated that addition of SMC prolonged the thermophilic phase, as a comparison, increased aeration shortened this phase. The addition of SMC and increased aeration enhanced humus formation and nitrogen retention. SMC introduced more amide and polysaccharide compounds into the compost, promoting the Maillard humification pathway. Additionally, both SMC and high aeration inhibited denitrification: the SMC reduced the abundance of the nirK gene, while high aeration decreased the abundance of nosZ gene. Network analysis revealed that higher aeration enhanced fungal interactions but diminished bacterial interactions. Conversely, SMC addition bolstered both bacterial and fungal interactions. The final compost product with SMC addition showed a 11.56%-44.19% reduction in antibiotic resistance gene content compared with the control group, and heavy metal contents remained within safe application limits. The combination of high SMC addition and high aeration achieved optimal humification and nitrogen retention, underscoring its potential as a promising solution for kitchen waste composting.

Organic materials return suppressed soil N2O emissions by changing the composition instead of abundance of denitrifying microbial community

Organic materials returned to the field have a significant effect on N2O emissions from agricultural fields, but the knowledge about the relationship between soil denitrifying microorganisms and N2O emissions is limited. Hence, we delved deeper into the significance of denitrifying microorganisms in N2O emissions by examining the soil N2O emissions, gene copy numbers, and community structures of denitrifying microorganisms during the wheat harvest season, three years after the partial substitution of chemical nitrogen fertilizers with various organic materials, including straw, pig manure, and biogas residues. The results showed that compared with chemical fertilizer, straw return did not change N2O emission, and pig manure and biogas residue, especially pig manure return, significantly reduced N2O emission (62 % and 45 %). Organic materials return did not change the gene copy number of denitrifying microorganisms, but had a significant effect on the community structure. The relative abundance of genera in the three organic materials treatments differed significantly from the chemical fertilizer treatment. The pig manure treatment had marker genera in the nosZ gene. Among the nirK, nirS, and nosZ genes, Sinorhizobium, norank_p_environment_samples, and unclassified_k_norank_d_bacteria, respectively, had the greatest effect on N2O emissions. The results of the RDA and the minimum depth method indicated that K, pH, and SOC were the key environmental factors influencing the structural changes of nirK, nirS and nosZ communities. Overall, organic materials, especially pig manure, effectively suppressed N2O emissions by changing the relative abundance and community structure of the dominant genera of denitrifying microorganisms.

Freshwater snails (Bellamya aeruginosa) bioturbation to enhance nitrogen removal and associated mechanism in constructed wetlands

In this study, total nitrogen (TN) removal efficiency of Pontederia cordata and Myriophyllum elatinoides in surface flow constructed wetlands (SFCWs) with Bellamya aeruginosa were 6.43% and 3.54% higher, respectively, than those in non-B. aeruginosa SFCWs. Further, bioturbation could promote N uptake by plants and release from sediment. In summer and autumn, potential nitrification rate was significantly higher in SFCWs with snails than that in SFCWs without snails. In each season, potential denitrification rate was significantly higher in SFCWs with snails than that in SFCWs without snails. Additionally, ammonia oxidizing archaea, narG, nirS, nirK and nosZ gene abundances were significantly higher in SFCWs with snails than those in SFCWs without snails. Structural equation model analysis revealed a strong positive correlation between nitrifiers and denitrifiers in SFCWs with snails, suggesting that bioturbation enhanced N removal by increasing synergistic effect of nitrifying and denitrifying bacteria.

Straw return amplifies the stimulated impact of night-warming on N2O emissions from wheat fields in a rice-wheat rotation system

ContextThe rise in winter and spring nighttime temperatures is a hallmark of global climate change, and warming has been proven to stimulate N2O emissions from wheat fields. However, it remains elusive whether this increasing effect is influenced by straw return, a practice considered globally as a future climate-smart agricultural strategy. Objectives or methodsA 3-year field experiment (2020−2023) was conducted with two straw treatments (S0: straw removal; S1: straw return) and two warming treatments (W0: no-warming; W1: night-warming) to quantify the effects of straw return and night-warming on N2O emissions from wheat fields in a rice-wheat rotation system. ResultsStraw return (S1) boosted post-jointing N2O production, whereas night-warming (W1) stimulated N2O emissions before the booting stage. Notably, the interaction between straw return and night-warming significantly affected seasonal cumulative N2O emissions, with W1 causing an 11.1 % increase under S0 and a more substantial 18.1 % increase observed under S1. Moreover, both S1 and W1 increased N2O warming potential, yield-scaled, and biomass-scaled N2O emissions. Compared to S0W0, soil dissolved organic C and inorganic N content increased in S1W1, while pH declined. Both S1 and W1 enhanced soil nitrification enzyme activity, nitrate reductase activity, and nitrite reductase activity in comparison to their respective controls. Additionally, S1W1 increased N2O production and inhibited N2O reduction by upregulating AOB-amoA and nirS gene abundances and downregulating nosZ gene expression, as evidenced by the elevated (nirS+nirK)/nosZ ratio. Random forest analysis identified that denitrification enzyme activity was the most important factor influencing N2O emissions. Conclusions or implicationsOur findings suggest that rice straw return may amplify the increasing effect of night-warming on N2O emissions from wheat fields. From an environmental protection perspective, straw return under the context of future warming will lead to an increased risk of N2O emissions, which may further exacerbate climate warming.

Rape straw-driven mitigation of greenhouse gas emissions and key bacterial communities during the treatment of pig farm manure in the ectopic fermentation system

Rice chaff, sawdust, and rape straw are commonly used as padding materials in the ectopic fermentation system. However, the characteristics of greenhouse gas emissions the ectopic fermentation system using rice chaff, sawdust, as well as the effects of rape straw on these emissions, remain unclear. This study investigated the effects of different proportions of rape straw (0, 10%, 25%, and 50%) on greenhouse gas emission characteristics in this system. The experimental results indicated that the treatment group containing rice chaff, sawdust, and more than 25% rape straw significantly increased fermentation temperature, prolonged the thermophilic phase, enhanced the maturity of fermentation products, and altered microbial community structures compared to the control group with only rice chaff and sawdust. Redundancy analysis revealed that replacing rice chaff and sawdust with 50% rape straw significantly decreased the relative abundance of methanogens (e.g., Methanospirillum and Methanobacterium) and denitrifying species (e.g., Denitrificimonas caeni and Aliarcobacter butzleri), resulting in reductions in cumulative emissions of CH4 and N2O by up to 44.6% and 84.9%, respectively, compared to the treatment group with rice chaff and sawdust alone. The absolute abundance of the nosZ gene was positively correlated with N2O emissions. Therefore, rape straw has been demonstrated to be an effective padding material that reduces CH4 and N2O emissions while enhancing the maturity of fermentation products in the ectopic fermentation system.

Evaluation of soil properties and bulk δ15N to assess decadal changes in floodplain denitrification following restoration

Stream and floodplain restoration is a popular billion‐dollar industry in the United States, with many restorations being conducted to satisfy water pollution regulations and nutrient reduction goals. The long‐term efficacy of these restorations is, however, not well studied, and key soil metrics that can be used for performance assessments have not been developed. We evaluated a chronosequence of 12 restoration sites spanning an age range of 0–22 years to assess changes in denitrification rates and associated soil parameters. Restored versus unrestored reaches were compared for denitrification rate and functional gene nosZ, bulk soil δ15N, soil organic carbon (SOC), soil organic matter (SOM), bulk density, and soil moisture. Denitrification, SOM, SOC, and soil moisture were all found to increase with site age at restored sites, with the largest increase for the 10–22 age category. Bulk density decreased with time, with a significant decrease in restored floodplain soils. Bulk soil δ15N was highest immediately after restoration, decreased with restoration age, and was not positively correlated with denitrification. This may reduce its potential as a proxy for denitrification. Overall, this study reveals that selected soil metrics (SOC, SOM, soil moisture, and bulk density) could serve as a valuable proxy for denitrification and could help assess the denitrification effectiveness of floodplain restorations at the decadal time scales. Ideally, the soil metrics should be combined with other short‐term assessment measures, such as those for stream and groundwaters, for a robust performance assessment of restored floodplains.

Biochar amendment affects the microbial genetic profile of the soil, its community structure and phospholipid fatty acid contents

Biochar (BC) amendment has been proposed as a promising strategy for mitigating greenhouse gas (GHG) emissions, specifically carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Conducting a meta-analysis to evaluate the impact of biochar on microbial genetic profile, community structure, and phospholipid fatty acid (PLFA) contents can aid in identifying key microbial groups involved in GHG production and consumption, and assessing the overall effectiveness of biochar in reducing GHG emissions. The present meta-analysis revealed that the addition of biochar resulted in a 22 % and 41 % reduction in pmoA and mcrA genes of methanogenic microorganisms, respectively. The mcrA/pmoA ratio significantly increased by 81 %. Gene abundances exhibited a positive response to biochar amendment, with increases observed in nifH, nirK, nirS, nosZ, and nosZ (nirS + nirK) genes by 13 %, 32 %, 37 %, 42 %, and 79 %, respectively. Moreover, biochar amendment influenced the microbial community structure accordingly. The concentration of PLFAs increased in response to BC treatment in the following order: A-bacteria (+49 %) < Fungi (+30 %) < Gram-pb (+21 %) < G-bacteria (+17 %) < Gram-nb (+11 %). These findings indicate that biochar amendment shapes the microbial community structure, further emphasizing its significance in enhancing soil fertility.

Dose Effect of Drinking Water Nitrate on Health, Feed Intake, Rumen Fermentation and Microbiota, and Nitrogen Excretion in Holstein Heifers for a Sustainable Water Use

The present study aimed to evaluate the potential hazardous effects of NO3− concentration in drinking water on health, feed intake, rumen fermentation and microbiota, and nitrogen excretion of Holstein heifers fed a high-concentrate diet for a sustainable water use. Twenty-four Holstein heifers were individually allocated and assigned to one of four treatments with increasing drinking water NO3− concentration: CTR, without NO3−; LOW, with 44 mg NO3−/L; MOD, with 110 mg NO3−/L; and HIGH, with 220 mg NO3−/L. The entire study lasted 168 days. Fortnightly water NO3− concentration and daily feed and water intake were recorded. Blood parameters, rumen pH, volatile fatty acids, NO3− and NO2− concentration, microbiota, and apparent total tract digestibility were determined at the beginning and at the end of the study. Most of the analyzed parameters were similar among treatments. Denitrifying bacteria population, estimated as nosZ gene copies, were greater in HIGH animals than in CTR animals at the end of the study. In conclusion, drinking water NO3− concentration up to 220 mg/L has no detrimental effect on health, feed intake, rumen fermentation, nor N excretion in dairy beef cattle for periods up to 168 days; moreover, denitrifying bacteria population increased, which are related with the neutralization of the greenhouse gas N2O.