Depth-temperature coupling shapes denitrifier community assembly and metabolic adaptation in drinking water reservoir sediments.

Denitrification regulates spatiotemporal pattern of N2O emission in an interconnected urban river-lake network

Impact of aged and virgin microplastics on sedimentary nitrogen cycling and microbial ecosystems in estuaries

Reclaimed water (RW) is widely used in agricultural systems; however, it affects soil properties and the surrounding environment, thus influencing soil nitrogen transformation and increasing N2O and NO emissions. Understanding the influencing mechanism of N2O production in RW-irrigated soil is very important for water resource utilization and environmental protection, but it is rarely studied. This study investigated the impact of three nitrogen ions (NH4+, NO3−, NO2−) on the nitrogen transformation process and non-biological processes affecting NO and N2O emissions from soil under multiyear RW-irrigated conditions. The results showed that RW effectively increased the abundance of nitrifying and denitrifying functional genes, leading to a significant increase (p < 0.05) in soil NO and N2O emissions under ammonium treatment. Furthermore, RW can reduce the cumulative NH3 emission by 19.11% compared to deionized water (DW). In nitrate treatment, RW can significantly increase (p < 0.05) the nitrate conversion rate by increasing the abundance of denitrifying genes, but not significantly enhance N2O and NO emissions. In NO2− oxidation, RW could increase the abundance of nitrifying genes (AOA-amoA, AOB-amoA), thereby promoting the progression of nitrifier denitrification and leading to a substantial increase (p < 0.05) in soil N2O production. In summary, RW irrigation primarily increases N2O emissions from soil by enhancing soil autotrophic nitrification and heterotrophic nitration. To effectively control soil N2O emissions under agricultural irrigation with RW, it is crucial to carefully manage soil nitrification and adjust the ratio of ammonium and nitrate in the soil.

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.

To determine the effect of three N-fertilisers on N2O emission and abundance of nitrification and denitrification genes in bulk and rhizosphere soil of tomato and common bean, two vegetable crops representative of main horticultural crops in South Spain. Four consecutive harvests of tomato and common bean fertilised with urea, ammonium or nitrate were carried out. The total abundance of bacteria, archaea, nitrifiers and denitrifiers was estimated by quantitative PCR. Soil physicochemical properties and N2O emission were also determined. Regardless of the plant species, the highest N2O emission was produced by the soil treated with urea, followed by ammonium and nitrate. Bacteria were more abundant than archaea in the bulk and rhizosphere soil. The abundance of the ammonia-oxidising archaea was greater than the ammonia-oxidising bacteria in the rhizosphere, but lower in the bulk soil. N-fertilisation increased the gene copy number of denitrifiers, which were more abundant in the bulk soil. N-fertilisation decreases N2O production due to increased abundance of the nosZ gene. The abundance of nitrification and denitrification genes in bulk and rhizosphere soils is dependent on the type of fertiliser. For both plant species, the ratio of the genes involved in production and reduction of N2O by bulk and rhizosphere was similar.

Manure‐based biochar is an effective amendment to increase both carbon sequestration and the fertility of degraded soils, whereas the responses of N2O emissions and microbial‐N cycling genes to its application and the underlying mechanisms are poorly understood. Here, four biochars were produced under two pyrolysis temperatures (300 and 700°C) and with two organic C extraction procedures (water and acetone extraction). The resulting biochars were either with relative enrichment or depletion in easily mineralizable carbon (EMC) compared with recalcitrant C. We added biochars, with urea and sodium nitrate, to a degraded red soil and incubated the amended soils at moisture levels of 60% and 130% field capacity. All the biochars decreased nitrification gene abundance, that is, amoA. Biochars with EMC had greater stimulatory effects on the abundance of denitrification genes (nirK, nirS, and nosZ) and N2O emission, regardless of moisture level and N form, compared with biochar without EMC. Biochar‐induced microbial activity, biochar aliphatics, and alkyl groups correlated positively with N2O emission and denitrification gene abundance. The water dissolved organic C of biochar facilitated the conversion of N2O to N2, whereas the acetone extractable C fraction postponed the completion of denitrification. In conclusion, the N2O emission and denitrification gene abundance increased with decreasing biochar aromaticity and increasing EMC content. Our study emphasizes that the EMC supply in manure‐based biochars also importantly mediates soil N2O emission and microbial N cycling genes, adding to current understanding of influencing factors such as biochar pH, porosity, N availability, and redox property.

Response of microbial nitrogen transformation processes to antibiotic stress in a drinking water reservoir

Silver nanoparticles and Fe(III) co-regulate microbial community and N2O emission in river sediments

The distinct phases of fresh-seawater mixing intricately regulate the nitrogen transformation processes in a high run-off estuary: Insight from multi-isotopes and microbial function analysis

Coffee intercropping reduces soil N2O and N2 emissions: Empirical test and meta-analysis.

Nitrous oxide (N2O) is a powerful greenhouse gas and also the remaining threat to the ozone layer. N2O emission is mainly from cropland accounting for 82% of the global N2O increase, which is of great concern for policymakers making strategies for mitigating N2O emissions. One of such strategies is agroforestry systems which integrate trees into cropland and are considered as environmentally-friendly ecosystems, in particular in greenhouse gas mitigation (e.g. N2O emissions). The net balance of N2O flux is constrained by gross N2O emissions and uptake. However, we are still struggling to fully understand the complexity of gross N2O emissions and uptake due to its spatial- and temporal variation. No systematic comparison of gross N2O fluxes was conducted between cropland agroforestry and monoculture. Besides, N2O produced and consumed are not only in topsoil but also in subsoil and there is lacking information about how gross N2O emissions and uptake vary at depths in different types of agroforestry systems. The first study aimed to assess the impact of land-use change on gross N2O emissions and uptake and their associated controls between cropland agroforestry and monoculture. The study was conducted at three sites in Germany, of which two sites had paired cropland agroforestry and monoculture on a loam Calcaric Phaeozem soil and a clay Vertic Cambisol soil, and one site was a cropland monoculture on a sandy Arenosol soil. Gross N2O emissions and uptake were monthly measured by using the 15N2O pool dilution technique over two growing seasons (2018 - 2019). Our results showed that soil gross N2O emissions from the area-weighted tree and crop rows in the agroforestry did not differ from monoculture. Nonetheless, the unfertilized tree rows showed the lowest gross N2O emissions. Although tree rows only occupied 20% in the agroforestry, annual gross N2O emissions in the top 5-cm soil decreased by 6% to 36% in the agroforestry compared to monoculture. Gross N2O emissions were influenced by soil mineral N, available C, and moisture content rather than by denitrification gene abundance. Soil gross N2O uptake was highest in the tree row and decreased with distance into crop rows. The agroforestry tree row increased annual gross N2O uptake in the top 5-cm soil by 27% to 42% compared to monoculture. In the tree row, soil gross N2O uptake correlated with nirK gene abundance which, in turn, was correlated with nosZ clade II that was related to low mineral N-to-available C ratios. The second study aimed to compare gross N2O emissions and uptake between riparian tree buffer and tree row of alley cropping system, and between depths (0 – 5 vs. 40 – 60 cm), and to elucidate their associated abiotic and biotic controls. This study was conducted at two contrasting agroforestry systems in Germany: riparian tree buffer and tree row of the alley cropping system. We quantified gross N2O emissions and uptake using the 15N2O pool dilution technique in early spring (April), spring (June), summer (August), and fall (October). Our results showed that riparian tree buffer had higher gross N2O emissions and uptake in topsoil (0 – 5 cm) than the tree row of alley cropping but such differences were not observed in subsoil (40 – 60 cm). Although gross N2O emissions and uptake did not differ between the two depths in each agroforestry system, we observed a hot moment, i.e. early spring, for gross N2O emissions in topsoil of riparian tree buffer, with a large source of N2O observed. Gross N2O emissions were mainly controlled by mineral N, biodegradable organic carbon, and water-filled pore space rather than microbial population size between the two agroforestry systems and depths. Gross N2O uptake in topsoil was driven by available carbon and nirK gene abundance across agroforestry systems. But subsoil showed a sink of N2O due to low mineral N. Gross N2O uptake in subsoil was affected by soil temperature in each agroforestry system, indicating positive feedback of global warming. Overall, this research provides new insights into mitigation of N2O emissions from soil to atmosphere after conversion of cropland monoculture to agroforestry and also provides field-based rates of gross N2O fluxes at depths in contrasting agroforestry systems. Our research provides the first year-round quantification of gross N2O emission and uptake using 15N2O pool dilution for cropland agroforestry and monoculture, with key implications for support on greenhouse gas regulation function for policy implementation of agroforestry. Our findings emphasize that adjusting the tree and crop areal coverages of agroforestry can further optimize the benefits of agroforestry in reducing emissions and increasing uptake of N2O in soils. As discussed in the synthesis chapter, future studies should increase the measurement frequency of gross N2O fluxes at depths to capture hot moments and spots, especially in the riparian tree buffer, and further better constrain the contribution of subsoil to the ecosystem N loss although this area is relatively small.

Disclosing the ecological implications of heavy metal disturbance on the microbial N-transformation process in the ocean tidal flushing urban estuary

牲畜排泄物返还被认为是对草地的一种天然的施肥措施，也是草地养分归还的一种重要途径，对于维持土壤肥力和植被生产力具有十分重要的生态学意义。论述了放牧牲畜粪便和尿液自身降解及其氮素变化、粪尿返还对草地土壤氮转化和氧化亚氮（N₂O）排放的作用机制及影响效应，指出排泄物氮输入使粪尿斑块成为草地土壤氮转化和N₂O排放的活跃点，且不同排泄物类型、土壤理化特性和气候条件等使土壤氮素矿化、固持、硝化及反硝化等关键过程具有复杂性和差异性，进而导致不同类型草地生态系统N₂O排放对牲畜排泄物返还的响应不尽相同。建议未来在全球气候变化背景下，应加强草地牲畜排泄物-植被-土壤体系氮素生物地球化学循环过程的系统研究，进一步加深天然草地关键氮素转化过程和N₂O排放的微生物作用机制方面的认识，从而有助于为优化放牧牲畜排泄物的管理模式、制定科学合理的草地土壤养分调控策略和维持草地生态系统可持续发展提供科学有效的理论指导。;Livestock excreta deposition is considered as a natural fertilization measure in grassland and also an important pathway for the return of grassland nutrients, which may generate greatly ecological significance for the maintenance of soil fertility and vegetation productivity. In this study, we systematically elaborated the variation of nitrogen embedded within grazing livestock dung and urine patches during its natural decomposition, so as to investigate the possible functional mechanisms and influential effects of livestock dung and urine application on soil nitrogen transformation process and nitrous oxide (N₂O) emission. Results showed that livestock excreta nitrogen input made the grassland area covered by dung and urine to become an active point for soil nitrogen transformation and N₂O emission. Generally speaking, the degradation rate of livestock dung was slow and its nitrogen release usually lasts for a long time, which may generate a series of effects on the soil nitrogen transformation and N₂O emission in the natural grassland. On the contrary, livestock urine deposition would rapidly increase soil mineralized nitrogen content in a short period of time, thus may generate a certain of priming effect on nitrogen dynamic and its form transformation in soil profiles, which probably deeply change the soil available nitrogen contents and the microenvironment that related to N₂O emission. It is worth noting that the differences in dung and urine patch shape, physicochemical properties, degradation and nitrogen release characteristics would inevitably alter the soil redox condition, nitrogen content and its form features of grassland soil profiles in different degrees, which may cause the complicated temporal-spatial response of soil nitrogen migration and transformation processes and the microbial functional mechanism differences in N₂O generation and emission. In addition, the differences in excreta types, soil physicochemical properties, and climatic conditions would complicatedly influence the major processes of soil nitrogen mineralization, immobilization, nitrification and denitrification, and therefore resulted in differential response of N₂O emission in different grassland ecosystems. Scientific suggestions were put forward that more attentions should be paid to strengthening the systematic research on the nitrogen biogeochemical cycling in the faecal-vegetation-soil system of grassland under the background of climate change, in order to deeply improve the theoretical understanding of major nitrogen transformation process and microbial mechanism of N₂O production and emission in the natural grassland. The results would provide scientific and theoretical guidance for optimizing livestock excreta management models, and formulating reasonable regulation strategies of grassland soil nutrients, so as to maintain the sustainable development of grassland ecosystems.

Dual drivers of riverine nitrogen transformation: Microbial-plankton community assembly and environmental interactions.

Nitrous oxide (N2O) from nitrogen fertilizers applied to sugarcane has high environmental impact on ethanol production. This study aimed to determine the main microbial processes responsible for the N2O emissions from soil fertilized with different N sources, to identify options to mitigate N2O emissions, and to determine the impacts of the N sources on the soil microbiome. In a field experiment, nitrogen was applied as calcium nitrate, urea, urea with dicyandiamide or 3,4 dimethylpyrazone phosphate nitrification inhibitors (NIs), and urea coated with polymer and sulfur (PSCU). Urea caused the highest N2O emissions (1.7% of N applied) and PSCU did not reduce cumulative N2O emissions compared to urea. NIs reduced N2O emissions (95%) compared to urea and had emissions comparable to those of the control (no N). Similarly, calcium nitrate resulted in very low N2O emissions. Interestingly, N2O emissions were significantly correlated only with bacterial amoA, but not with denitrification gene (nirK, nirS, nosZ) abundances, suggesting that ammonia-oxidizing bacteria, via the nitrification pathway, were the main contributors to N2O emissions. Moreover, the treatments had little effect on microbial composition or diversity. We suggest nitrate-based fertilizers or the addition of NIs in NH4+-N based fertilizers as viable options for reducing N2O emissions in tropical soils and lessening the environmental impact of biofuel produced from sugarcane.