Μg N2O Research Articles

NosZ II/nosZ I ratio regulates the N2O reduction rates in the eutrophic lake sediments

Nitrous oxide (N2O) is a more potent greenhouse gas with an atmospheric lifetime of 121 years, contributing significantly to climate change and stratospheric ozone depletion. Lakes are hotspots for N2O release due to the imbalance between N2O sources and sinks. N2O-reducing bacteria are the only biological means to mitigate N2O emission, yet their roles in lakes are not well studied. This study investigated the potential for N2O reduction, keystones of typical and atypical N2O-reducing bacterial communities, and their correlations with environmental factors in the sediments of Lake Taihu through microcosm experiments, high-throughput sequencing of the nosZ gene, and statistical modeling. The results showed that potential N2O reduction rates in sediments ranged from 13.71 to 76.95 μg N2O g−1 d−1, with lower rates in December compared to March and July. Correlation analysis indicated that the nosZ II/nosZ I ratio and the trophic lake index (TLI) were the primary factors influencing N2O reduction rates and N2O-reducing bacterial community structures. The genera Pseudogulbenkiania and Ardenticatena were identified as the most abundant typical and atypical N2O-reducing bacteria, respectively, and were also recognized as the keystone taxa. Quantitative real-time PCR (qPCR) results revealed that nosZ II was more abundant than nosZ I in the sediments. Partial least squares path modeling (PLS-PM) further demonstrated that atypical N2O-reducing bacteria had significant positive effects on N2O reduction process in the sediments (p < 0.05). Overall, this study highlights the crucial ecological roles of atypical N2O-reducing bacteria in the sediments of the eutrophic lake of Taihu, underscoring their potential in mitigating N2O emissions.

Methane and nitrous oxide emissions in the rice-shrimp rotation system of the Vietnamese Mekong Delta

Rice-shrimp rotation systems are one of the widespread farming practices in the Vietnamese Mekong Delta coastal areas. However, greenhouse gas (GHG) emissions in the system have remained unclear. This study aimed to examine methane (CH4) and nitrous oxide (N2O) emissions from the system, including (i) land-based versus high-density polyethylene-lined (HDPE) nursery ponds and (ii) conventional versus improved grow-out ponds inoculated with effective microorganisms (EM) bioproducts. The results showed that CH4 flux in land-based and HDPE-lined nursery ponds were 1.04 and 0.25 mgCH4 m−2 h−1, respectively, while the N2O flux was 8.37 and 6.62 μgN2O m−2 h−1, respectively. Global warming potential (GWP) from land-based nursery ponds (18.3 g CO2eq m−2) was approximately 3 folds higher than that of the HDPE-lined nursery pond (6.1 g CO2eq m−2). Similarly, the mean CH4 and N2O fluxes were 15.84 mg CH4 m−2 h−1 and 7.17 μg N2O m−2 h−1 for the conventional ponds, and 10.51 mg CH4 m−2 h−1 and 7.72 μg N2O m−2 h−1 for the improved grow-out ponds. Conventional practices (2388 g CO2eq m−2) had a higher 1.5-fold GWP compared to the improved grow-out pond (1635 g CO2eq m−2). The continuation of the land-based nursery pond and conventional aquacultural farming practices increase CH4 emission and GWP, while applying HDPE-lined nursery ponds combined with improved grow-out ponds could be a promising approach for reducing GHG emissions in rice-shrimp rotation systems. This study recommends further works in the rice-shrimp rotation systems, including (i) an examination of the effects of remaining rice stubbles in the platform on the availability of TOC levels and GHG emissions and (ii) ameliorating dissolved oxygen (DO) concentration on the effectiveness of GHG emission reduction.

Small water body significantly contributes to nitrous oxide emissions in China's aquaculture

Aquaculture systems are expected to act as potential hotspots for nitrous oxide (N2O) emissions, largely attributed to substantial nutrient loading from aquafeed applications. However, the specific patterns and contributions of N2O fluxes from these systems to the global emissions inventory are not well characterized due to limited data. This study investigates the patterns of N2O flux across 127 freshwater systems in China to elucidate the role of aquaculture ponds and lakes/reservoirs in landscape N2O emission. Our findings show that the average N2O flux from aquaculture ponds was 3.63 times higher (28.73 μg N2O m−2 h−1) than that from non-aquaculture ponds. Additionally, the average N2O flux from aquaculture lakes/reservoirs (15.65 μg N2O m−2 h−1) increased 3.05 times compared to non-aquaculture lakes/reservoirs. The transition from non-aquaculture to aquaculture practices has resulted in a net annual increase of 7589 ± 2409 Mg N2O emissions in China's freshwater systems from 2003 to 2022, equivalent to 20% of total N2O emissions from China's inland water. Particularly, the robust negative regression relationship between N2O emission intensity and water area suggests that small ponds are hotspots of N2O emissions, a result of both elevated nutrient concentrations and more vigorous biogeochemical cycles. This indicates that N2O emissions from smaller aquaculture ponds are larger per unit area compared to equivalent larger water bodies. Our findings highlight that N2O emissions from aquaculture systems can not be proxied by those from natural water bodies, especially small water bodies exhibiting significant but largely unquantified N2O emissions. In the context of the rapid global expansion of aquaculture, this underscores the critical need to integrate aquaculture into global assessments of inland water N2O emissions to advance towards a low-carbon future.

Substantial uptake of nitrous oxide (N2O) by shoots of mature European beech

Similar to soils, tree stems emit and consume nitrous oxide (N2O) from the atmosphere. Although tree leaves dominate tree surface area, they have been completely excluded from field N2O flux measurements and therefore their role in forest N2O exchange remains unknown. We explored the contribution of leaf fluxes to forest N2O exchange. We determined the N2O exchange of mature European beech (Fagus sylvatica) stems and shoots (i.e., terminal branches) and of adjacent forest floor, in a typical temperate upland forest in Germany. The beech stems, and particularly the shoots, acted as net N2O sinks (−0.254 ± 0.827 μg N2O m−2 stem area h−1 and −4.54 ± 1.53 μg N2O m−2 leaf area h−1, respectively), while the forest floor was a net source (2.41 ± 1.08 μg N2O m−2 soil area h−1). The unstudied tree shoots were identified as a significant contributor to the net ecosystem N2O exchange. Moreover, we revealed for the first time that tree leaves act as substantial N2O sinks. Although this is the first study of its kind, it is of global importance for the proper design of future flux studies in forest ecosystems worldwide. Our results demonstrate that excluding tree leaves from forest N2O flux measurements can lead to misinterpretation of tree and forest N2O exchange, and thus global forest greenhouse gas flux inventories.

Landfill intermediate cover soil microbiomes and their potential for mitigating greenhouse gas emissions revealed through metagenomics

Landfills are a major source of anthropogenic methane emissions and have been found to produce nitrous oxide, an even more potent greenhouse gas than methane. Intermediate cover soil (ICS) plays a key role in reducing methane emissions but may also result in nitrous oxide production. To assess the potential for microbial methane oxidation and nitrous oxide production, long sequencing reads were generated from ICS microbiome DNA and reads were functionally annotated for 24 samples across ICS at a large landfill in New York. Further, incubation experiments were performed to assess methane consumption and nitrous oxide production with varying amounts of ammonia supplemented. Methane was readily consumed by microbes in the composite ICS and all incubations with methane produced small amounts of nitrous oxide even when ammonia was not supplemented. Incubations without methane produced significantly less nitrous oxide than those incubated with methane. In incubations with methane added, the observed specific rate of methane consumption was 0.776 +/− 0.055 μg CH4 g dry weight (DW) soil−1 h−1 and the specific rate of nitrous oxide production was 3.64 × 10−5 +/− 1.30 × 10−5 μg N2O g DW soil−1 h−1. The methanotrophs Methylobacter and an unclassified genus within the family Methlyococcaceae were present in the original ICS samples and the incubation samples, and their abundance increased during incubations with methane. Genes encoding particulate methane monooxygenase/ ammonia monooxygenase (pMMO) were much more abundant than genes encoding soluble methane monooxygenase (sMMO) across the landfill ICS. Genes encoding proteins that convert hydroxylamine to nitrous oxide were not highly abundant in the ICS or incubation metagenomes. In total, these results suggest that although ammonia oxidation via methanotrophs may result in low levels of nitrous oxide production, ICS microbial communities have the potential to greatly reduce the overall global warming potential of landfill emissions.

Soil type and wetting intensity control the enhancement extent of N2O efflux in soil with drought and rewetting cycles

Climate change alters the intensity and frequency of drought and rewetting (D/W) events; however, the influence patterns of D/W on soil N2O efflux in the water-limited area were not fully understood. Therefore, the impacts of D/W cycles varying in different extent of rewetting and frequency to N2O efflux in two kinds of soil on the Loess Plateau were investigated. The incubation conditions consisted of 1) D/W treatments with four 7-day cycles from 10% water holding capacity (WHC) to 60%WHC or 90%WHC, 2) constant moisture of 60%WHC and 90%WHC. The pulse of N2O efflux rate under 10−60%WHC treatment was higher than that under 10−90%WHC treatment in calcic cambisols, while opposite trend was observed in earth-cumuli-orthic anthrosols. Meanwhile, the pulse of N2O efflux rate decreased as cycle number increased for different wetting intensities and soil types. The direct N2O efflux under 10−60%WHC and 10−90%WHC treatments were 5.49 and 1.89 μg N2O–N g−1 soil in calcic cambisols, with those being 1.92 and 10.85 μg N2O–N g−1 soil in earth-cumuli-orthic anthrosols, respectively. The N loss in earth-cumuli-orthic anthrosols was approximately 5.74 times greater than that in calcic cambisols under 10−90%WHC treatment, whereas the N loss under 10−60%WHC treatment was about 2.86 times greater in calcic cambisols than that in earth-cumuli-orthic anthrosols. This study suggested that extreme rainfall events can enhance the N2O efflux and N loss in agricultural soils on the Loess Plateau in terms of soil type and wetting intensity, which should not be ignored in the N fertilizer management.

CH4 and N2O fluxes during paddy rice crop development, post-harvest, and fallow

Paddy fields are major sources of greenhouse gases, mainly methane (CH4) and nitrous oxide (N2O). Defining the sampling times for determining the average diurnal emission rates is an important step in optimizing field measurement, avoiding the influence of possible peaks. With this purpose, diurnal gas measurements (CH4 and N2O) were taken using the static chamber method during five 24 h-periods (campaigns), every 2 h, at three rice crop development stages (R2, C1 campaign; R5, C2 campaign, and R8, C3 campaign), and in post-harvest (PH, C4 campaign) and in fallow (FP, C5 campaign) periods. The CH4 fluxes remained close to the average flux both at C1 (9.4 ± 1.0 mg CH4 m-2 h-1) and C2 (10.2 ± 1.4 mg CH4 m-2 h-1), allowing the gas sampling at any time of the day, except at 5:00 p.m. when a peak was observed at C1. As the CH4 fluxes for C3, C4, and C5 were close to zero, no average value was identified. The average N2O fluxes were low at C1 (1.0 ± 5.7 μg N2O m-2 h-1) and at C4 (6.7 ± 2.6 μg N2O m-2 h-1), increasing at C2 (26.9 ± 9.3 μg N2O m-2 h-1) and C3 (21.2 ± 7.2 μg N2O m-2 h-1) and reaching higher values during the C5 campaign (73.7 ± 33.3 μg N2O m-2 h-1). In general, considering the average flux values recorded in this study, the most appropriate times for sampling N2O during the C1, C2, C3, and C4 campaigns would be from 9 p.m. to 1 a.m. and also around 11:00 a.m. Average N2O flows in fallow would be more likely around 11:00 p.m. and 11 a.m.

Sewage sludge application stimulated soil N2O emissions with a low heavy metal pollution risk in Eucalyptus plantations

Sewage sludge (SS) has been extensively used as an alternative fertilizer in forest plantations, which are beneficial in supplying timbers and mitigating climate change. However, whether the extra nitrogen (N) applied by SS would enhance the soil nitrous oxide (N2O) emission, an important greenhouse gas, in forest plantations have not been well understood. The objective of this study is to evaluate the ecological effects of SS application on soils, by investigating the soil N2O emission and the toxicity of the potentially toxic elements (PTEs) in soil. A field fertilization experiment was conducted in Eucalyptus plantations with four fertilization rates (0 kg m−2, 1.5 kg m−2, 3.0 kg m−2, and 4.5 kg m−2). The soil N2O emissions were monitored at a soil depth of 0–10 cm using static chamber method, soil chemical properties, and PTEs were determined at soil depths of 0–10 cm, 10–20 cm, and 20–40 cm. The average soil N2O emission rate was 8.1 μg N2O–N h−1 m−2 in plots without SS application (control). The application of SS significantly increased the soil N2O emissions by 7–10 times as to control. The increased N2O emissions were positively related to the soil total phosphorus and nitrogen and negatively correlated with copper and zinc, which increased with the SS application. However, the potential ecological risk index (Ei) and the comprehensive potential ecological risk index (RI) of PTEs were lower than 40 and 150 respectively, which indicating a low toxicity of PTEs to soil health. After seven months of SS application, the priming effects of SS on soil N2O emissions gradually diminished. These findings suggest that the application of SS may increase N2O emissions at the initial stages of application (<7 months) and may have a low PTEs pollution risk, even at a high SS addition rate (4.5 kg m−2).

Growth response to nitrate enrichment helps facilitate success of an alien Potamogeton in New Zealand streams

Motivated by stream ecosystem degradation by eutrophication, we mimicked slow flowing lowland stream conditions with a novel experimental setup to further our understanding of aquatic plant responses to increases in nitrate and light. We conducted a mesocosm growth experiment of two species from the genus Potamogeton: P. crispus (alien) and P. ochreatus (native), grown at four nitrate and four light levels. We hypothesised that (i) internal nutrient status of the plants would scale with water column nutrient concentration, and that (ii) plant performance would reflect the nutrient status of the plant. Furthermore, we hypothesised that (iii) a low irradiance level would negate the effects of an increased nitrate level. In relation to (ii) we hypothesised that (iv) the traits of the alien species would enable it to outperform the native species where both the availability of light and nutrient resources was high. Internal tissue N content was broadly similar in the two higher (>250 μg NO3− L−1) and the two lower nutrient treatments (<20 μg NO3− L−1) in both species and plants were therefore collapsed into high and low N-groups. High-N individuals had higher growth rates than low-N ones regardless of species or light treatment and plants had reduced growth rates at the lowest light treatment, however this response was less evident for P. crispus. The highest growth rate was found at the high-N individuals of P. crispus at the highest light treatment, and correspondingly, in this treatment this species exhibited an increase in branching degree and lateral spread from the low-N plants. As P. crispus spreads by fragmentation, our results show it to be a highly effective competitor in anthropogenically impacted areas compared to its native counterpart. Our study exemplifies how light can influence eutrophication responses of plants and how both need to be accounted for in management decisions.

Effect of Post-harvesting with Different Photoperiods under Artificial Light Sources on Nitrate and Vitamin C Contents in Hydroponic Green Oak Lettuce

Green oak lettuce (Lactuca sativa L.) is a popular vegetable for consumers, but it is concerned about nitrate contamination that may harm human health. However, light can affect nitrate reduction and contribute to the accumulation of vitamin C in vegetables. Therefore, this study focused on the effects of post-harvesting with different photoperiods under artificial light sources on vitamin C and nitrate content in hydroponic green oak lettuce. Green oak lettuces were grown in the NFT system, harvested, and post-harvested under Bulb-LED (Experiment I), Bar-LED (Experiment II), and fluorescent lamp (FL) (Experiment III) for 6, 12, and 24 h photoperiods and replaced the nutrient solution with tap water. The nitrate content was significantly reduced after post-harvesting for 12 h photoperiods under FL (9,012 µg NO3- -N/g dry weight) followed by Bulb-LED (13,985 µg NO3- -N/g dry weight) and 24 h photoperiods for Bar-LED (10,727 µg NO3- -N/g dry weight). Vitamin C content was highest after post-harvesting for 24 h photoperiods under Bar-LED (45.47 µg/ml), followed by Bulb-LED (44.73 µg/ml) and FL (35.40 µg/ml). Post-harvesting with artificial light sources for 12 to 24 h photoperiods can improve hydroponic green oak lettuce quality.

Deepened snow in combination with summer warming increases growing season nitrous oxide emissions in dry tundra, but not in wet tundra

Impacts of increased winter snowfall and warmer summer air temperatures on nitrous oxide (N2O) dynamics in arctic tundra are uncertain. Here we evaluate surface N2O dynamics in both wet and dry tundra in West Greenland, subjected to field manipulations with deepened winter snow and summer warming. The potential denitrification activity (PDA) and potential net N2O production (N2Onet) were measured to assess denitrification and N2O consumption potential. The surface N2O fluxes averaged 0.49 ± 0.42 and 2.6 ± 0.84 μg N2O–N m−2 h−1, and total emissions were 212 ± 151 and 114 ± 63 g N2O–N scaled to the entire study area of 0.15 km2, at the dry and wet tundra, respectively. The experimental summer warming, and in combination with deepened snow, significantly increased N2O emissions at the dry tundra, but not at the wet tundra. The deepened snow increased winter soil temperatures and growing season soil N availability (DON, NH4+-N or NO3−-N), but no main effect of deepened snow on N2O fluxes was found at either tundra ecosystem. The mean PDA was 5- and 121-fold higher than the N2Onet at the dry and wet tundra, respectively, suggesting that N2O might be reduced and emitted as dinitrogen (N2). Overall, this study reveals modest but evident surface N2O fluxes from tundra ecosystems in Western Greenland, and suggests that projected increases in winter precipitation and summer air temperatures may increase N2O emissions, particularly at the dry tundra dominating in this region.

Biochar and hematite amendments suppress emission of CH4 and NO2 in constructed wetlands

Constructed wetlands (CWs) are considered a widely used cost-effective technology for pollutant removal. However, greenhouse gas emissions are a non-negligible problem in CWs. In this study, four laboratory-scale CWs were established to evaluate the effects of gravel (CWB), hematite (CWFe), biochar (CWC), and hematite + biochar (CWFe-C) as substrates on pollutants removal, greenhouse gas emissions, and associated microbial characteristics. The results showed that the biochar-amended CWs (CWC and CWFe-C) enhanced the removal efficiency of pollutants, with 92.53 % and 93.66 % of COD and 65.73 % and 64.41 % of TN removal, respectively. Both single and combined inputs of biochar and hematite significantly reduced CH4 and N2O fluxes, with the lowest average of CH4 flux obtained in CWC (5.99 ± 0.78 mg CH4 m−2 h−1) and the least N2O flux in CWFe-C (287.57 ± 44.84 μg N2O m−2 h−1). The substantial reduction of global warming potentials (GWP) was obtained in the applications of CWC (80.25 %) and CWFe-C (79.5 %) in biochar-amended CWs. The presence of biochar and hematite mitigated CH4 and N2O emissions by modifying microbial communities with higher ratios of pmoA/mcrA and nosZ genes abundances, as well as increasing the abundance of denitrifying bacteria (Dechloromona, Thauera and Azospira). This study demonstrated that biochar and the combined use of biochar and hematite could be the potential candidates as functional substrates for the efficient removal of pollutants and simultaneously reducing GWP emissions in the constructed wetlands.

Tidal restoration to reduce greenhouse gas emissions from freshwater impounded coastal wetlands

Freshwater impounded wetlands are created by artificially restricting coastal wetlands connection to tides. The decrease in salinity and altered hydrology can significantly increase greenhouse gas (GHG) emissions, specifically methane (CH4). Restoration of freshwater impounded wetlands through tidal reintroduction can potentially reduce GHG emissions; however, studies in tropical regions are scare. This study investigates the potential for tidal restoration of impounded freshwater coastal wetlands by comparing their GHG emissions with tidally connected mangrove and saltmarshes in the Burdekin catchment in Queensland, Australia. We found that freshwater impounded wetlands had significantly higher CH4 emissions (3,633 ± 812 μg CH4 m−2 hour−1) than mangroves (27 ± 8 μg CH4 m−2 hour−1) and saltmarsh (13 ± 8 μg CH4 m−2 hour−1). Soil redox, moisture, carbon, nitrogen, and bulk density were all significantly correlated to methane emissions. Conversely, freshwater impounded wetlands had significantly lower nitrous oxide (N2O) emissions (−0.72 ± 0.18 μg N2O m−2 hour−1) than mangroves and saltmarsh (0.35 ± 0.29 and 1.32 ± 0.52 μg N2O m−2 hour−1 respectively). Nevertheless, when converting to CO2 equivalents (CO2‐eq), freshwater impounded wetlands emitted 91 ± 20 g CO2‐eq m−2 hour−1, compared to the much lower 0.8 ± 0.2 and 0.7 ± 0.2 g CO2‐eq m−2 hour−1 emission rates for mangroves and saltmarsh. In conclusion, restoration of freshwater impounded wetlands through tidal restoration is likely to result in reduced GHG emissions.

How do biochar size fractions and organic fertilizers interactively influence nitrous oxide emission from a tropical vertisol?

AbstractBackgroundNitrous oxide (N2O) emission from agriculture is increasing alarmingly due to intensive application of inorganic and organic fertilizers. Recently, biochar has been identified as a promising additive to improve agriculture by enhancing soil function and mitigate greenhouse gas emission. However, it is unclear how biochar of different size fractions influences N2O emission from agricultural soil.AimsThe current experiment aims to understand how the size of biochar (BC) and organic fertilizers interactively influence N2O emission from a tropical vertisol.MethodsBC was prepared using pigeon pea (Cajanus cajan) stalks and further processed to obtain two size fractions (&lt;0.25 mm or 0.25–2.00 mm). Organic fertilizers (vermicompost [VC], poultry manure [PM], or farmyard manure [FYM]) and BC were added to soil to evaluate N2O emission potential. BC was added to soil at 10% (w/w), whereas the organic fertilizers were added at 80 kg N ha–1. Emission of CO2 and the abundance of 16S rRNA and amoA gene copies were estimated after incubation period. The interactive effect of BC size fractions and organic fertilizers were statistically evaluated.ResultsBoth BC and organic fertilizers stimulated N2O emission in soil. BC of larger size stimulated N2O emission (µg N2O produced g–1 soil day–1) more than smaller size. Of the three organic fertilizers, PM resulted highest N2O (0.380) emission followed by FYM (0.240) and VC (0.210). BC (0.25 mm) + PM produced least N2O. Abundance of heterotrophic bacterial 16S rRNA gene copies and ammonia‐oxidizing bacterial (AOB) amoA gene copies were highest in PM + BC and lowest in control. Significant relation (p &lt; 0.0001) existed among N2O emission, CO2 emission, and microbial abundance.ConclusionsBC of small size fraction along with organic fertilizers can be an effective strategy to mitigate N2O emission from tropical vertisol.

Prairie wetlands as sources or sinks of nitrous oxide: Effects of land use and hydrology

National and global greenhouse gas (GHG) budgets are continually being refined as data become available. Primary sources of the potent GHG nitrous oxide (N2O) include agricultural soil management and burning of fossil fuels, but comprehensive N2O budgets also incorporate less prominent factors such as wetlands. Freshwater wetland GHG flux estimates, however, have high uncertainty, and wetlands have been identified as both sources and sinks. Here, we analyzed a regional database of >26,000 N2O chamber flux measurements sampled across >150 wetlands from the Prairie Pothole Region (PPR) in the Great Plains of North America. Our goal was to identify important land use and hydrologic drivers of N2O flux to help reduce uncertainty in N2O models, and to incorporate these drivers into an upscaled estimate of wetland N2O emissions from the U.S. portion of the PPR. Within individual wetlands, exposed soils with no standing water, such as along wetland edges, were hotspots that accounted for greater than 90% of wetland N2O emissions. In contrast wet (i.e., ponded) areas had minimal or negative N2O flux. N2O flux from wetlands nested within croplands (16.3–17.3 μg N2O m−2 hr−1) was, in some instances, nearly double that from wetlands within grasslands (9.2–14.4 μg N2O m−2 h−1). We estimated that seasonal N2O flux from PPR wetlands equated to roughly 0.2% (1.04 Tg CO2 equivalents) of the U.S. N2O budget (c. 2019). Overall, even though PPR wetlands are a small net source of N2O to the atmosphere, their emissions are negligible relative to agricultural soil management. Policy and management to restore wetland hydrology and surrounding uplands from cropland to grasslands can reduce landscape N2O fluxes. Future activities focused on wetland N2O flux would benefit from inclusion of adjacent land use and hydrologic factors, as well as from incorporation of temporally dynamic ponded wetland areas.

Nitrous oxide production and nitrogen transformations in a soil amended with biosolids

The application of organic amendments to agricultural soils enables the recycling of nutrients, further reducing the inputs of synthetic fertilizers for crop production. However, the production of N2O emissions is a concern that arises from such a practice. A 35 d incubation experiment was conducted with soils receiving three contrasting types of biosolids — mesophilic anaerobic digested (BM), composted (BC), and alkaline-stabilized (BA) — at four water-filled pore spaces (WFPS): 28%, 40%, 52%, and 64%. A zero-N-addition control was also evaluated. Across all the three types of biosolids, N2O production increased with soil moisture content, with BM and BC producing the overall highest N2O fluxes. The most intense pulses of N2O production were exhibited by BC at the beginning of the incubation. The highest cumulative N2O production was found with 64% WFPS and from BC- (409 μg N2O–N·kg−1 soil) or BM-amended soils (390 μgN2O–N·kg−1 soil), which produced more than four and two times the emissions from the control and BA-amended soils at 64% WFPS, respectively. We also found the highest nitrification rates in the BM- and BC-amended soils. The total N2O production was exponentially associated with the NO3−–N concentration present at the end of the experiment (R2 = 0.83). Changes in the concentration of the soil available N indicated the occurrence of mineralization, nitrification, and denitrification over the incubation. These results provided insight into the interacting responses of N2O production to soil moisture contents, biosolids treatment stabilization and properties, and soil N availability.

Nitrous oxide surface fluxes in a low Arctic heath: Effects of experimental warming along a natural snowmelt gradient

Climate change is profound in the Arctic where increased snowfall during winter and warmer growing season temperatures may accelerate soil nitrogen (N) turnover and increase inorganic N availability. Nitrous oxide (N2O) is a potent greenhouse gas formed by soil microbes and in the Arctic, the production is seen as limited mainly by low inorganic N availability. Hence, it can be hypothesized that climate change in the Arctic may increase total N2O emissions, yet this topic remains understudied. We investigated the combined effects of variable snow depths and experimental warming on soil N cycling in a factorial field study established along a natural snowmelt gradient in a low Arctic heath ecosystem. The study assessed N2O surface fluxes, gross N mineralization and nitrification rates, potential denitrification activity, and the pools of soil microbial, soil organic and soil inorganic N, carbon (C) and phosphorus (P) during two growing seasons. The net fluxes of N2O averaged 1.7 μg N2O–N m−2 h−1 (range −3.6 to 10.5 μg N2O–N m−2 h−1), and generally increased from ambient (1 m) to moderate (2–3 m) snow depths. At the greatest snow depth (4 m) where snowmelt was profoundly later, N2O fluxes decreased, likely caused by combined negative effects of low summer temperatures and high soil moisture. Positive correlations between N2O and nitrate (NO3−) and dissolved organic N (DON) suggested that the availability of N was the main controlling variable along the snowmelt gradient. The maximum N2O fluxes were observed in the second half of August associated with high NO3− concentrations. The effect of growing season experimental warming on N2O surface flux varied along the snowmelt gradient and with time. Generally, the experimental warming stimulated N2O fluxes under conditions with increased concentrations of inorganic N. In contrast, warming reduced N2O fluxes when inorganic N was low. Experimental warming had no clear effects on soil inorganic N. The study suggests that if increased winter precipitation leads to a deeper snow cover and a later snowmelt, total emissions of N2O from low Arctic heath ecosystems may be enhanced in the future and, dependent on dissolved N availability, summer warming may stimulate or reduce total emissions.

Impact of climate change on soil nitric oxide and nitrous oxide emissions from typical land uses in Scotland

Soil emissions of NO and N2O from typical land uses across Lowland and Highland Scotland were simulated under climate change conditions, during a short-term laboratory study. All locations investigated were significant sources of N2O (range: 157–277 µg N2O–N m−2 h−1) and low-to-moderate sources of NO emissions (range: 0.4–30.5 µg NO–N m−2 h−1), with a general tendency to decrease with altitude and increase with fertiliser and atmospheric N inputs. Simulated climate warming and extreme events (drought, intensive rainfall) increased soil NO pulses and N2O emissions from both natural and managed ecosystems in the following order: natural Highlands < natural Lowlands < grazed grasslands < natural moorland receiving high NH3 deposition rates. Largest NO emission rates were observed from natural moorlands exposed to high NH3 deposition rates. Although soil NO emissions were much smaller (6–660 times) than those of N2O, their impact on air quality is likely to increase as combustion sources of NO x are declining as a result of successful mitigation. This study provides evidence of high N emission rates from natural ecosystems and calls for urgent action to improve existing national and intergovernmental inventories for NO and N2O, which at present do not fully account for emissions from natural soils receiving no direct anthropogenic N inputs.

Effects of simulated acid rain on soil N2O emission from typical forest in subtropical sou-thern China.

Based on a long-term simulated acid rain experiment, soil N2O emission fluxes were measured using static chambers and the gas chromatography method in a coniferous and broadleaved mixed forest and a monsoon evergreen broadleaved forest in southern China. During the five-year observation periods (2014-2018), soil N2O emission fluxes in the two forests showed obvious seasonal variation. The soil N2O emission fluxes in wet season were significantly higher than that in dry season, with a large annual variation. Due to the decreases of precipitation, soil N2O emission fluxes of the two forests in 2017 and 2018 were generally low. Soil N2O emission flux was positively correlated with soil temperature and soil moisture. In the monsoon evergreen broadleaved forest, soil N2O emission flux in the control plot was 12.6 μg N2O·m-2·h-1. Soil N2O emission fluxes under the pH 3.5 and pH 3.0 treatments increased by 42.9% and 61.1%, respectively. Soil N2O emission was significantly increased under simulated acid rain in the monsoon evergreen broadleaved forest. Acid rain promoted soil N2O emission in the coniferous and broadleaved mixed forest, but without significant difference among the treatments. Under the scenario of increasing acid rain, soil N2O emission fluxes in typical subtropical southern China forests would increase, and the magnitude of such increase was different among forest types.

Diversity and structure of soil bacterial community in intertidal zone of Daliao River estuary, Northeast China

Soil samples from the intertidal zone of Daliao River, Northeast China, were collected in three seasons (autumn, L1; winter, L2; and spring, L3) to evaluate the diversity and structure of bacterial community using high-throughput sequencing. Soil physicochemical characteristics varied greatly with seasons, and the potential nitrification rates were detected in the range of 1.04–2.71 μg NO3−-N·g−1 dry soil·h−1 with the highest rate in spring (L3). Soil bacterial communities also differed seasonally, and nitrogen nutrients were the important variables affecting the bacterial communities as demonstrated by distance-based redundancy analysis and Mantel tests. Proteobacteria was the predominant phylum in soils showing a descending trend from L1 to L3. Woeseia and Ignatzschineria, both affiliating with Gammaproteobacteria, were the two most dominant genera, but they exerted different seasonal variations. The predicted functional profiles revealed 6 major nitrogen cycling processes, and the functional genes in relation to denitrification process were dominant in intertidal soils.