Search Results (74)

The emission of nitrogen oxides (N₂O) in rivers is an important source of potent greenhouse gases. However, the mechanism at the interface between rivers and riverbanks remains unclear. This study quantified N₂O emissions from natural and artificial riparian zones across seasons and explored the microbial mechanisms affecting N₂O production and consumption in an intensive agricultural river network in China. Significant seasonal variability in N₂O emission rates was observed (p < 0.05), with mean values of 0.56 ± 0.09 mmol·m⁻²·h⁻¹ in autumn and 1.13 ± 0.32 mmol·m⁻²·h⁻¹ in spring. In spring, emissions from natural riparian zones (1.38 ± 0.28 mmol·m⁻²·h⁻¹) were significantly higher than those from artificial riparian zones (0.89 ± 0.05 mmol·m⁻²·h⁻¹). All wind-based models significantly overestimated N₂O emissions (p < 0.05) due to inflated IPCC emission factors (EF_5r), exceeding measured values by 1.76–3.09 times. Dissolved organic carbon and nitrite nitrogen were identified as key environmental drivers of N₂O emissions. Nitrogen fixation and ammonification accounted for 82.3% of N₂O production. Network analysis revealed a dominant microbial niche containing nitrifiers, sulfate-reducing bacteria, and carbohydrate-degrading taxa. Partial least squares path modeling indicated that riparian zone type altered DOC and NO₂⁻ availability, regulated nifH and ureC gene abundances, and enhanced N₂O production. These findings underscore the importance of riparian-zone-specific microbial regulation of riverine N₂O emissions and demonstrate the necessity of refining EF_5r estimates for agricultural river networks. Full article

Copper (Cu) pollution poses environmental and health risks. Owing to its adaptability and potential for water purification, Nymphoides peltata (N. peltata) is being considered for use in the remediation of Cu pollution. However, the feasibility of using N. peltata for the remediation of Cu-polluted water bodies has not yet been assessed. Here, the physiological response of N. peltata to Cu stress was determined. N. peltata samples were exposed to varying Cu concentrations (0.2, 0.4, 0.6 and 0.8 mg∙L⁻¹), and the activities of glutamine synthetase (GS), nitrate reductase (NR), nitrite reductase (NiR), ribulose-1,5-diphosphate carboxylase (Rubisco), and glycolate oxidase (GO) were measured together with the concentrations of photosynthetic pigments. The results revealed that under Cu stress, NR and GS activities significantly decreased, while NiR activity significantly increased. Exposure to 0.2 mg∙L⁻¹ Cu promoted chlorophyll synthesis and enhanced Rubisco and GO activities; in contrast, exposure to Cu concentrations above 0.4 mg∙L⁻¹ significantly inhibited the aforementioned parameters. These findings indicate that Cu stress, regardless of concentration, significantly affects nitrogen metabolism in N. peltata by decelerating nitrate reduction and impairing the ammonification process. Meanwhile, only high Cu concentrations significantly affected photosynthesis. N. peltata can survive low Cu stress by regulating its photosynthetic enzymes. Therefore, N. peltata has potential for the ecological restoration of water bodies polluted with low Cu concentrations. Full article

Nitrogen (N) is the most widely used nutrient in agriculture in the form of urea, yet it is one of the least efficient in terms of application due to losses through volatilization and leaching. The combination of urea with micronutrient sources, especially in the form of nanoparticles, is a promising technology for reducing these losses. Two greenhouse experiments were conducted with the objective of evaluating the influence of coating urea with zinc oxide nanoparticles (NPZnO) and iron oxide nanoparticles (NPFe₂O₃), associated with elemental sulfur (S°), on the leaching of mineral nitrogen and the production of dry mass and accumulation of N in young corn plants. The coating (0.26% w/w) of urea with elemental sulfur (S°) and NPZnO and NPFe₂O₃ reduced N losses through leaching (−21.3%) and delayed the nitrification process of N in the soil (−71.8%). This coating increased the efficiency of nitrogen fertilization in young corn plants, boosting the production of dry mass in leaves (+39.4%), stems (+68.8%), and roots (+61.6%), as well as the absorption of N in the above-ground biomass (+64.1%), compared to conventional urea. The use of urea coated with NPZnO and NPFe₂O₃ associated with S° is an environmentally sound solution for supplying N and micronutrients such as Fe and Zn in a more efficient and sustainable manner, especially in sandy soils with low organic matter content, which are common in the semi-arid region of Brazil. Full article

Nitrogen (N) mineralization is a complex microbial-driven process that controls the supply of N for plants and microbes. The relative contribution of different microbial N-cycling species/genes to the variation in N mineralization rate (NMR) across contrasting forest biomes was unclear. Here, we investigate the linkages between soil metagenomes and N mineralization rates across 10 contrasting forest biomes (covering temperate, subtropical, and tropical forests) along a 3425 km north–south forest in China. We found that the NMR was higher in subtropical forests, and the variation in NMR can be explained by climate and soil environments, particularly for soil substrate NH₄⁺. Similar to NMR, microbial N-cycling genes/species were also higher in subtropical forests, suggesting that the higher microbial N-cycling traits in warm regions may drive higher NMR. We also quantified the contribution of microbial N-cycling gene pathways to NMR across forest biomes and found that the microbial N-denitrification pathway (genes like norZ, narG, nirK, and norB) and nitrification pathway (genes like nxr) explained more variation in NMR than other pathways, such as N ammonification. Collectively, our work demonstrates the importance of microbial N-cycling traits to explain soil N mineralization rates across forest biomes and suggests that this information can be used to help improve the management of the N cycle in forests across biomes. Full article

Excessive application of nitrogen (N) fertilizer increases the risk of soil NO₃⁻-N leaching in fluvial soil, threatening soil and groundwater quality and safety. Enhancing soil carbon (C) by returning straw to the field can efficiently improve soil quality. The process of increasing C/N by straw returning to regulate soil nitrogen transformation and mitigate NO₃⁻-N leaching, and the ecological threshold of straw application rate in fluvial soil need to be further explored. This study aims to research a series of soil C/N ratio treatments (including no straw, CK; C/N of 15, 20, 25, 30, 35 and 40), which were set up by adding straw at different application rates, and to investigate the underlying process of increasing C/N ratio by incorporating straw to mitigate NO₃⁻-N leaching. As the soil C/N ratio increased, the total soil nitrogen showed a fluctuating increase with the highest value in S40 treatment (increased by 358 mg kg⁻¹), while the NO₃⁻-N leaching amount reached the lowest value at the C/N ratio of 20, with an average reduction of 45% (decreased by 29.3 mg kg⁻¹). Increasing soil C/N ratio significantly increased soil microbial biomass, cellulase, urease and N-acetyl-β-D-glucosaminidase activities while it decreased the net N mineralization rate, ammonification rate and nitrification rate. Principal component analysis showed that the NO₃⁻-N leaching was positively correlated with the ammonification rate, nitrification rate and net N mineralization rate, and negatively correlated with the abundances of bacteria, fungi and nitrogen-fixing genes (nifH) (p < 0.01). Structural equation model analysis showed that straw-regulated C/N, dissolved organic N and soil fungi were the most important factors affecting NO₃⁻-N leaching, followed by the ammonification rate. Overall, increasing soil C/N by adding straw could enhance soil microbial biomass (especially fungi) and enzyme activities to promote soil N storage and reduce net N mineralization, ammonification and nitrification to decrease NO₃⁻-N leaching. Full article

Nitrogen in all of its forms sustains Earth. In every known terrestrial and aquatic habitat, nitrogen controls microbial activity, plant productivity, trophic dynamics, and animal and human growth. This review has tried to show how nitrogen cycling is influenced by both terrestrial and marine ecosystems in addition to by changes spurred on by the climate. The availability, transformation, and final fate of nitrogen throughout the various ecosystems are influenced by these interconnected biochemical and biophysical processes, which are fueled by microbial communities. Predicting and reducing human impacts on the changing ecosystem requires an understanding of these complex interconnections. Anthropogenic and climatic changes alter the structure and function of soil microbial communities, as well as the main metabolic processes of the nitrogen cycle, such as nitrification, denitrification, nitrogen fixation, and ammonification. The mechanisms by which anthropogenic stress alters nitrogen cycling processes, the effects on ecosystem function, and possible mitigation techniques for a balanced nitrogen cycle are all discussed in this review. Full article

Food waste (FW) management remains a critical challenge within the circular economy framework. This study examines low-temperature pretreatment (LT-PT) of food waste and its effects on physicochemical transformations and microbial community dynamics. Artificial food waste (AFW) was subjected to LT-PT at 60 °C for 24 h, 48 h, and 72 h to assess changes in organic matter solubilization, nitrogen and phosphorus transformations, microbial composition, and biomethane potential. The results show that LT-PT promotes volatile fatty acid (VFA) accumulation, ammonification, and organic matter solubilization, thereby enhancing substrate biodegradability. The largest VFA increase was observed for acetate, whose concentration increased by approximately 0.55 g/L between 0 h and 72 h of LT-PT. Metagenomic analysis revealed a pronounced shift in microbial communities, with fermentative bacteria (Leuconostocaceae) increasing to 53.08% after 24 h of LT-PT, while Cyanobacteria decreased from 81.31% at 0 h to 19.48% at 48 h. Biochemical methane potential (BMP) tests demonstrated that longer LT-PT durations improved methane yield, with the highest production (1170 NmL CH₄) recorded after 72 h of pretreatment. Kinetic modeling using first-order and modified Gompertz equations confirmed that LT-PT enhances methane production efficiency by accelerating substrate hydrolysis. These findings indicate that LT-PT is a promising strategy for optimizing food waste valorization via anaerobic digestion, supporting sustainable waste management and renewable energy generation. Full article

Soil nitrogen (N) is critical for crop yield. Although previous studies have shown that straw return enhances soil mineral N availability, the response of soil aggregate microbes to straw return and its impact on soil mineral N availability remains unclear. We conducted a 13-year experiment to explore how soil N mineralization potential, fungi, and bacteria within soil aggregates responded to straw return. Our findings indicated that straw return significantly increased mineral N concentrations in soil macroaggregates, with no statistically significant effect observed on microaggregate composition. We observed increased microbial community α-diversity, enhanced co-occurrence network stability, and an increase in functional groups associated with N (nitrate respiration, denitrification, nitrite denitrification) and carbon (saprotrophs, saprotroph–symbiotrophs, patho-saprotrophs) cycling within the aggregates. Additionally, microorganisms in macroaggregates were influenced by total N, while those in microaggregates were affected by soil total organic carbon and C–N ratio. A sensitivity network analysis identified specific microorganisms responding to straw return. Within macroaggregates, microbial community shifts explained 42.88% of mineral N variation, with bacterial and fungal β-diversity contributing 27.82% and 12.58%, respectively. Moreover, straw return upregulated N-cycling genes (N ammonification: sub, ureC, and chiA; nitrification: amoA-AOB; denitrification: nirK, nirS, nosZ, norB, and narG; and N fixation: nifH) in macroaggregates. Partial least squares path modeling revealed that N availability in macroaggregates was mainly driven by ammonification, with bacterial β-diversity explaining 23.22% and fungal β-diversity 15.16% of the variation. Our study reveals that macroaggregates, which play a crucial role in soil N supply, are highly sensitive to tillage practices. This finding provides a practical approach to reducing reliance on synthetic N fertilizers by promoting microbial-mediated N cycling, while sustaining high crop yields in intensive agricultural systems. Full article

The proximity of ecologically valuable areas to industrial zones indicates a strong need for monitoring their condition. Soil assessment involves both molecular techniques for studying microbial biodiversity, such as PCR, sequencing, and metagenomics, as well as parameters of biochemical and enzymatic activity of soil microorganisms. The authors studied the activity of microorganisms responsible for the nitrogen cycle to compare the condition of soils under different uses (wastelands and arable fields) located in the ecologically valuable areas of the Polesie National Park (PNP, protected area) and its surroundings. Additionally, they assessed the suitability of gangue for reclamation and its effectiveness depending on treatment duration (2 and 10 years). In most of the activities analyzed, their levels were lower in the park. A higher intensity of ammonification and nitrification was observed in the soil sampled from the field in the park; however, a reduced N₂O emission was also recorded after incubation in the lab of soil samples collected in the autumn, which may indicate that nitrogen loss from the soil does not occur in this particular habitat, which requires further, long-term and cyclical field trials. These observations confirm the potential protective role of the park in relation to soils and atmosphere in the context of the nitrogen cycle. The activities under study in the reclaimed soils were in both cases lower than in soils from the fields. The current results prove that this method of reclamation is not entirely effective; however, long-term reclamation yielded better results. The present study provided valuable information on the effectiveness of the protective role of the PNP in relation to soils and air. Additionally, these results may be helpful in making decisions regarding the use of waste, such as gangue, for reclamation. Full article

Soil nitrogen fate determines nitrogen availability for crops and their environmental impact, which is regulated by nitrogen transformation processes that are mediated through soil properties (e.g., pH) and environmental factors (e.g., hydrothermal conditions). Incubation experiments were conducted on soils with different pH levels (covering acidic to calcareous ranges) to study the effects of soil pH and hydrothermal conditions on nitrogen transformation and N₂O emissions. The results showed that the net ammonification rate was negatively correlated with soil pH, whereas the net nitrification rate, net nitrogen mineralization rate, and N₂O emission rate showed positive correlations. Structural equation modeling (SEM) indicated that soil pH and hydrothermal conditions exerted primary influences on soil net nitrogen transformation rates, consequently affecting N₂O emissions. Soil pH and hydrothermal conditions had 83% and 93% effects, respectively, on net nitrogen transformation rates, while they had 77% effects on N₂O emissions. Consequently, soil pH and hydrothermal conditions might be the key drivers influencing soil nitrogen transformation and N₂O emissions. Specifically, in subtropical regions characterized by high temperatures and abundant summer rainfall, regulating soil moisture could mitigate NO₃⁻-N accumulation and N₂O emissions, providing a targeted strategy for sustainable nitrogen management. Full article

Anaerobic ammonium oxidation (anammox) technologies have attracted substantial interest due to their advantages over traditional biological nitrogen removal processes, including high efficiency and low energy demand. Currently, multiple side-stream applications of the anammox coupling process have been developed, including one-stage, two-stage, and three-stage systems such as completely autotrophic nitrogen removal over nitrite, denitrifying ammonium oxidation, simultaneous nitrogen and phosphorus removal, partial denitrification-anammox, and partial nitrification and integrated fermentation denitritation. The one-stage system includes completely autotrophic nitrogen removal over nitrite, oxygen-limited autotrophic nitrification/denitrification, aerobic de-ammonification, single-stage nitrogen removal using anammox, and partial nitritation. Two-stage systems, such as the single reactor system for high-activity ammonium removal over nitrite, integrated fixed-film activated sludge, and simultaneous nitrogen and phosphorus removal, have also been developed. Three-stage systems comprise partial nitrification anammox, partial denitrification anammox, simultaneous ammonium oxidation denitrification, and partial nitrification and integrated fermentation denitritation. The performance of these systems is highly dependent on interactions between functional microbial communities, physiochemical parameters, and environmental factors. Mainstream applications are not well developed and require further research and development. Mainstream applications demand a high carbon/nitrogen ratio to maintain levels of nitrite-oxidizing bacteria, high concentrations of ammonium and nitrite in wastewater, and retention of anammox bacteria biomass. To summarize various aspects of the anammox processes, this review provides information regarding the microbial diversity of different genera of anammox bacteria and the engineering aspects of various side streams and mainstream anammox processes for wastewater treatment. Additionally, this review offers detailed insights into the challenges related to anammox technology and delivers solutions for future sustainable research. Full article

Soil fertilization with fertilizers derived from renewable sources is a topic of great interest in terms of the sustainable management of organic waste. To optimize the management of nitrogen supplied to the soil with digestates, it is necessary to deepen knowledge on the process of mineralization of organic nitrogen over time. In this research, a laboratory incubation system was utilized to study the impact of various digestate sources on nitrogen mineralization processes in soils and nitrogen mineralization kinetics. Six types of digestates of different origins and composition were administered to soil and the soil samples were placed under controlled conditions. The release of N was determined by measuring ammonium-N and nitrate-N concentrations in leachates during a 12-week period of incubation. The nonlinear regression technique was used to fit the cumulative leaching of total N to the Stanford and Smith first-order kinetic model during the incubation period. The results showed that the differences between digestates, nitrogen and organic carbon concentration, and C/N ratio influenced both ammonification and nitrification processes in the soil and the nitrogen mineralization kinetics. The processing of the statistical data highlighted that the potentially mineralizable nitrogen (MPN) followed first-order kinetics. Full article

This study examines nitrogen transformation mechanisms and compost quality in mesophilic aerobic composting of wheat straw, utilizing cow manure as a co-substrate to promote sustainable agricultural waste management. Two composting systems were established: group A (control) and group B (10% cow manure addition by wet weight). The addition of cow manure accelerated early organic matter decomposition and increased total nitrogen retention in group B. Nitrogen losses occurred primarily via ammonia volatilization during the initial and final composting stages, while functional gene analysis revealed enhanced ammonification and nitrification in both systems. Microbial community analysis showed that cow manure addition promoted nitrogen-fixing bacteria in the early phase and fungi associated with complex organic degradation in later stages. These findings underscore the potential of cow manure to enhance compost maturity, improve nitrogen efficiency, and support the development of sustainable composting practices that contribute to resource conservation. Full article

Arbuscular mycorrhizal fungi (AMF) can preferentially absorb the released ammonium (NH₄⁺) over nitrate (NO₃⁻) during litter decomposition. However, the impact of AMF’s absorption of NH₄⁺ on litter nitrogen (N) decomposition is still unclear. In this study, we investigated the effects of AMF uptake for NH₄⁺ on litter N metabolic characteristics by enriching NH₄⁺ via AMF suppression and nitrification inhibition in a subtropical Cinnamomum camphora forest. The results showed that AMF suppression and nitrification inhibition significantly decelerated litter decomposition in the early stage due to the repression of NH₄⁺ in extracellular enzyme activity. In the late stage, when soil NH₄⁺ content was low, in contrast, they promoted litter decomposition by increasing the extracellular enzyme activities. Nitrification inhibition mainly promoted the utilization of plant-derived N by promoting the degradation of the amide I, amide II, and III bands by increasing protease activity, and it promoted ammonification by increasing urease activities, whereas it reduced the utilization of microbial-derived N by decreasing chitinase activity. On the contrary, AMF suppression, which significantly reduced the ammonification rate and increased the nitrification rate, only facilitated the degradation of the amide II band. Moreover, it intensified the microbial-derived N decomposition by increasing chitinase activity. The degradation of the amide I and II bands still relied on the priming effects of AMF on soil saprotrophs. This was likely driven by AMF-mediated phosphorus (P) mineralization. Nutrient acquiring, especially P by phosphatase, were the main factors in predicting litter decomposition and protein degradation. Thus, AMF could relieve the end-product repression of locally enriched NH₄⁺ in extracellular enzyme activity and promote early-stage litter decomposition. However, the promotive effects of AMF on litter protein degradation and NH₄⁺ release rely on P mineralization. Our results demonstrated that AMF could alleviate the N limitation for net primary production via accelerating litter N decomposition and reducing N loss. Moreover, they could restrict the decomposition of recalcitrant components by competing with saprotrophs for nutrients. Both pathways will contribute to C sequestration in forest ecosystems, which advances our understanding of AMF’s contribution to nutrient cycling and ecosystem processes in subtropical forests. Full article

The Asian dung beetle (Catharsius molossus L.; Coleoptera: Scarabeidae) has been shown to positively affect soil bacterial diversity and the agronomic features of crop plants. In this study, we used bioinformatic tools to investigate the differences in bacterial functional phenotypes and ecological functions between control soil, cow dung-amended soil (CD), and cow dung-amended soil composted by dung beetles (DB). The soil bacterial metagenomes were sequenced and analyzed with the bioinformatic packages BugBase, PICRUSt2, Tax4Fun, and FAPROTAX to evaluate the effects of dung beetle-mediated composting on bacterial functions such as human and plant pathogenicity, trophic strategies, and soil nutrient transformation. BugBase proved useful for the determination of differences in major functional phenotypes, whereas FAPROTAX was effective at identifying differences in bacterial ecological functions between the treatments. Both tools suggested a relative decrease in human pathogens in the DB soil. This was corroborated by the pairwise comparison of abundances in bacterial species, which showed a significant reduction in the abundance of the broad-host-range pathogen Pseudomonas aeruginosa in the DB soil. In addition, FAPROTAX suggested a decrease in plant pathogens and an increase in chitinolytic bacteria, meaning that the DB treatment might be beneficial to the plant-growth-promoting bacteria involved in biological control. Finally, FAPROTAX revealed an array of ecological functions related to trophic strategies and macro- and micronutrient metabolism. According to these results, the activity of C. molossus beetles enhanced methanotrophy, ammonification, nitrification, sulfate reduction, and manganese oxidation, whereas iron respiration was decreased in the DB-treated soil. Our results represent a collection of general insights into the effects of C. molossus beetles on soil bacterial functions, which also reflect on the nutrient composition of dung beetle-composted soil. Full article