Relationships between ammonia oxidizers and N2O and CH4 fluxes in agricultural fields with different soil types

Nitrous oxide (N₂O) is a greenhouse gas that contributes to the destruction of stratospheric ozone, and agricultural soil is an important source of N₂O. Aerobic soils are sinks for atmospheric methane (CH₄), a greenhouse gas. Ammonia monooxygenase (AMO) can oxidize CH₄, but CH₄ is mostly oxidized by methane monooxygenase (MMO), and CH₄ oxidation by AMO is generally negligible in the soil. We monitored the N₂O and CH₄ fluxes after urea application in fields containing different soils using an automated sampling system to determine the effects of environmental and microbial factors on the N₂O and CH₄ fluxes. The soil types were Low-humic Andosol (Gleyic Haplic Andosol), yellow soil (Gleyic Haplic Alisol) and gray lowland soil (Entric Fluvisol). Cumulative N₂O emissions from the yellow soil were higher than those from other soil types, although the difference was not significant. The CH₄ uptake level by Andosol was one order of magnitude higher than that by other soils. There were significant relationships between the ammonia oxidation potential, AOB and AOA amoA copy numbers, and the CH₄ uptake. In contrast, the gene copy numbers of methane-oxidizing bacteria (MOB) pmoA were below the detection limit. Our results suggested that the AMOs of AOB and AOA may have more important roles than those previously considered during CH₄ oxidation in agricultural soils treated with N fertilizers.     

Effects of option mitigating ammonia volatilization on CH4 and N2O emissions from a paddy field fertilized with anaerobically digested cattle slurry

A lysimeter experiment was carried out to evaluate the effects of the NH₃ volatilization mitigation by adding anaerobically digested cattle slurry (ADCS) alone, with wood vinegar (WV) or with a higher level of floodwater (HFW), on emissions of CH₄ and N₂O from a paddy soil planted with fodder rice. We have carried out the following treatments: (1) chemical fertilizer, (2) ADCS, (3) ADCS + WV, and (4) ADCS + HFW; the height of floodwater was 10 cm in the latter treatment, and it was 3 to 4 cm in the other treatments just before fertilizer applications. Nitrogen fertilizer rate added to soil in each treatment was 30 g NH₄⁺–N m⁻² (split in one basal and two top-dressing additions). Ammonia volatilization in the ADCS treatment was 2.7 g NH₃–N m⁻² throughout the growing season, and it was significantly reduced by 79% and 55% in the ADCS + WV and ADCS + HFW treatments, respectively. The total amount of CH₄ emitted in the ADCS treatment in the growing season was not significantly enhanced by the mitigation of NH₃ volatilization either by adding wood vinegar or by increasing the height of the floodwater. Negligible N₂O emissions were observed in all treatments during the growing period.     

Inoculation with N2-generating denitrifier strains mitigates N2O emission from agricultural soil fertilized with poultry manure

Pelleted poultry manure is recommended for use with agricultural soil as a replacement for chemical fertilizers; however, application of the manure stimulates nitrous oxide (N₂O) emission from the soil through denitrification. To mitigate the N₂O emission caused by application of pelleted poultry manure, soil microcosms were set up; each microcosm was inoculated with one of the following N₂-generating denitrifier strains previously been isolated from paddy soil: Azoarcus, Dyella, Dechloromonas, Niastella, and Burkholderia. When pelleted poultry manure was incubated on its own, N₂O was produced by denitrification. In contrast, N₂O emission was significantly lowered when the manure was inoculated with most of the N₂-generating strains. In soil microcosms, N₂O was emitted during incubation after application of the pelleted manure, while N₂O flux was significantly lowered when the soil was inoculated with Azoarcus sp. KS11B, Niastella sp. KS31B, or Burkholderia sp. TSO47-3 on the 12th day of incubation. In addition, when pelleted manure was inoculated with the strains prior to application in the soil microcosms, the level of N₂O emission was significantly lowered to ca. 40–60 % that from the non-inoculated control. Our study provides the prototype of a technique that uses microbial technology to mitigate N₂O emission from agricultural soil fertilized with pelleted poultry manure.     

Increase in soil carbon sequestration using rice husk charcoal without stimulating CH4 and N2O emissions in an Andosol paddy field in Japan

Abstract

Biochar application has been recognized as an effective option for promoting carbon (C) sequestration, but it may also affect the production and consumption of methane (CH₄) and nitrous oxide (N₂O) in soil. A 1-year field experiment was conducted to investigate the effects of rice husk charcoal application on rice (Oryza sativa L.) productivity and the balance of greenhouse gas exchanges in an Andosol paddy field. The experiment compared the treatments of rice husk charcoal applied at 10, 20 and 40 Mg ha^?1 (RC10, RC20 and RC40, respectively), rice husk applied at 20 Mg ha^?1 (RH20), and the control (CONT). Rice straw and grain yields did not significantly differ among the treatments. The seasonal cumulative CH₄ emissions were 38–47% higher from RC10, RC20 and RC40 than from the CONT. However, the increases were not in proportion to the application rates of rice husk charcoal, and their values did not significantly differ from the CONT. On the contrary, the RH20 treatment significantly increased the cumulative CH₄ emission by 227% compared to the CONT. The N₂O emissions during the measurement were not affected by the treatments. As a result, the combined global warming potential (GWP) of CH₄ and N₂O emissions was significantly higher in RH20 than in the other treatments. There was a positive linear correlation between C storage in the top 10 cm of soil and the application rate of rice husk charcoal. The increases in soil C contents compared to the CONT corresponded to 98–149% of the C amounts added as rice husk charcoal and 41% of the C added as rice husk. Carbon dioxide (CO₂) fluxes in the off season were not significantly different among RC10, RC20, RC40 and CONT, indicating that C added as rice husk charcoal remained in the soil during the fallow period. The CO₂ equivalent balance between soil C sequestration and the combined GWP indicates that the rice husk charcoal treatments stored more C in soil than the CONT, whereas the RH20 emitted more C than the CONT. These results suggest that rice husk charcoal application will contribute to mitigating global warming without sacrificing rice yields.     

Potential fluxes of N2O and CH4 from soils of three forest types in Eastern Canada

We conducted laboratory incubation experiments to elucidate the influence of forest type and topographic position on emission and/or consumption potentials of nitrous oxide (N₂O) and methane (CH₄) from soils of three forest types in Eastern Canada. Soil samples collected from deciduous, black spruce and white pine forests were incubated under a control, an NH₄NO₃ amendment and an elevated headspace CH₄ concentration at 70% water-filled pore space (WFPS), except the poorly drained wetland soils which were incubated at 100% WFPS. Deciduous and boreal forest soils exhibited greater potential of N₂O and CH₄ fluxes than did white pine forest soils. Mineral N addition resulted in significant increases in N₂O emissions from wetland forest soils compared to the unamended soils, whereas well-drained soils exhibited no significant increase in N₂O emissions in-response to mineral N additions. Soils in deciduous, boreal and white pine forests consumed CH₄ when incubated under an elevated headspace CH₄ concentration, except the poorly drained soils in the deciduous forest, which emitted CH₄. CH₄ consumption rates in deciduous and boreal forest soils were twice the amount consumed by the white pine forest soils. The results suggest that an episodic increase in reactive N input in these forests is not likely to increase N₂O emissions, except from the poorly drained wetland soils; however, long-term in situ N fertilization studies are required to validate the observed results. Moreover, wetland soils in the deciduous forest are net sources of CH₄ unlike the well-drained soils, which are net sinks of atmospheric CH₄. Because wetland soils can produce a substantial amount of CH₄ and N₂O, the contribution of these wetlands to the total trace gas fluxes need to be accounted for when modeling fluxes from forest soils in Eastern Canada.     

耕作措施对双季稻田CH4与N2O排放的影响

随着全球气温的不断升高,温室气体减排成为研究的热点。该文旨在研究不同耕作措施下双季稻田CH4及N2O排放特征及其消长关系,为稻田温室气体减排及土壤固碳潜力评价提供依据。试验在湖南省宁乡县进行,通过静态箱法测定翻耕秸秆还田（CT）、旋耕秸秆还田（RT）、免耕秸秆还田（NT）的稻田CH4及N2O排放。结果表明：CH4排放主要来自于晚稻田,翻耕、旋耕和免耕晚稻田CH4排放分别占研究时段CH4排放的69%,67%,73%;各处理冬闲季CH4排放均不到研究时段排放量1%,冬闲CH4排放量为RT＞CT＞NT,差异显著;N2O排放时间变异性较大,早稻稻田N2O排放量为RT＞NT＞CT,晚稻稻田N2O排放量为NT＞RT＞CT,冬闲期各处理稻田N2O均为负排放;从研究时段排放量分析,翻耕秸秆还田有利于减少N2O排放,免耕秸秆还田有利于减少CH4排放;CH4与N2O排放呈显著负相关,冬闲季稻田CH4与N2O排放相关性不显著。总之,NT减少了CH4排放,虽N2O排放略有增加,但CH4与N2O引发的综合温室效应有所减弱。     

不同施肥方式对农田土壤CO2和N2O排放的影响

采用静态箱/气相色谱法研究不同施肥方式以及环境因子对农田土壤CO2和N2O排放通量的影响,结果表明,不同施肥方式对农田土壤CO2排放的季节模式无明显影响,但是影响了N2O排放的季节模式。不同施肥方式对土壤CO2排放通量影响不明显,主要影响土壤N2O排放,整个小麦、玉米生长季,分两次施肥的F2与分四次施肥的F1相比,土壤N2O排放量增加,化肥配合有机肥施用(MF)的土壤N2O通量大于单纯的化肥处理,秸秆还田降低了土壤N2O的排放。相关分析结果表明,土壤CO2排放与大气温度、地表温度、土壤温度和土壤水分均呈显著正相关关系(P<0.01)。由于肥料施用的影响,土壤N2O排放和土壤温度、水分的相关分析并不显著。土壤N2O排放受土壤硝态氮和铵态氮变化的影响。     

Nutrient fluxes in runoff on reseeded blanket bog, limed and fertilized with urea, phosphorus and potassium

Abstract. Studies have been made of the effects of 15 g N/m² as urea in two dressings during April and June on annual nutrient fluxes in runoff from reseeded blanket bog also receiving annually 6 g P/m² as granular superphosphate and 6 kg K/m² as potassium chloride. Urea applications increased significantly ( P < 0.05) the mean annual ammonium-N flux from 17 mg/m² for the P + K plots to 245 mg/m² for the N + P + K plots. Annual fluxes of total P, K and Ca were also increased ( P < 0.05) by the addition of urea. This was attributed to the effects of increased acidity around grass roots following N uptake as ammonium-N. In contrast, nitrate-N was removed from rainwater throughout the year and concentrations in runoff were at the limit of detection (< 0.01 mg/1) on many occasions. Concentrations of organic-N in runoff exceeded those of ammonium-N, but were not significantly changed by fertilization.     

Groundwater level controls CO2, N2O and CH4 fluxes of three different hydromorphic soil types of a temperate forest ecosystem

Hydromorphic soils should exhibit higher climate change feedback potentials than well aerated soils since soil organic matter (SOM) losses in them are predicted to be much larger than those of well aerated soils. To evaluate a combined feedback relationship between groundwater level (GWL) and total greenhouse gas (GHG) emission, a greenhouse microcosm experiment was performed by exposing three hydromorphic forest soil types that differed in carbon content to three water levels (?40, ?20 and ?5 cm) while plants were excluded. Net GHG fluxes were measured continuously. GHG concentrations plus oxygen were measured in soil air and soil water at different depths. In this study, soil type hardly affected GHG emissions but GWL did. CO₂ emissions peaked at GWL of ?40 cm and declined on average to 65 and 33% during GWL at ?20 and ?5 cm, respectively. CH₄ emissions showed the opposite pattern having the highest emission rates at GWL of ?5 cm and compared to that on average only ?3 and ?8% during GWL at ?20 and ?40 cm, respectively. The highest mean N₂O emissions were detected at the intermediate GWL of ?20 cm, whereas it is reduced on average to 18% for GWL at ?40 cm and at ?5 cm. The highest greenhouse gas emissions (in CO₂ equivalents) were calculated for GWL at ?20 cm. During GWL at ?40 cm, CO₂ equivalent fluxes were only insignificantly lower. CO₂ equivalent fluxes reduced explicitly in mean to 35% with GWL at ?5 cm. The outcome emphasizes that anaerobic SOM decomposition apparently produces a lower warming potential than aerobic SOM decomposition. Undoubtedly, hydromorphic soils have to be considered for climate–carbon feedback scenarios.     

The Maturity and CH4, N2O,NH3 Emissions from Vermicomposting with Agricultural Waste

This study investigated the maturity and gaseous emissions from vermicomposing with agricultural waste. A vermicomposting treatment (inoculated Eisenia fetida) was conducted over a 50-day period, taking tomato stems as the processing object and using cow dung as the nutrient substrate. A thermophilic composting treatment without earthworm inoculation was operated as a control treatment. During the experiment, maturity indexes such as temperature, pH, C/N ratio, and germination index (GI) were determined and continuous measurements of earthworm biomass and CH₄, N₂O, and NH₃ emissions were carried out. The results showed that the temperature during vermicomposting was suitable for earthworm survival, and the earthworm biomass increased from 10.0 to 63.1 kg m^?3. Vermicomposting took less time on average to reach the compost maturity standard (GI 80%), and reached a higher GI (132%) in the compost product compared with the thermophilic composting treatment. Moreover, the decrease of the C/N ratio in vermicompost indicated stabilization of the waste. The activities of earthworms played a positive role in reducing gaseous emissions in vermicompost, resulting in less emissions of NH₃ (12.3% NH₃-N of initial nitrogen) and total greenhouse gases (8.1 kg CO₂-eq/t DM) than those from thermophilic compost (24.9% NH₃-N of initial nitrogen, 22.8 kg CO₂-eq/t DM). Therefore, it can be concluded that vermicomposting can shorten the period required to reach compost maturity, can obtain better maturity compost, and at the same time reduce gaseous emissions. As an added advantage, the earthworms after processing could have commercial uses.     

Influence of forest disturbance on CO2, CH4 and N2O fluxes from larch forest soil in the permafrost taiga region of eastern Siberia

Abstract

To evaluate the effect of increasing forest disturbances on greenhouse gas budgets in a taiga forest in eastern Siberia, CO₂, CH₄ and N₂O fluxes from the soils were measured during the growing season in intact, burnt and clear-felled larch forests (4–5 years after the disturbance). Soil temperature and moisture were higher at the two disturbed sites than at the forest site. A 64–72% decrease in the Q ₁₀ value of soil CO₂ flux from the disturbed sites compared with the forest site (5.92) suggested a reduction in root respiration and a dominance of organic matter decomposition at the disturbed sites. However, the cumulative CO₂ emissions (May–August) were not significantly different among the sites (2.81–2.90 Mg C ha^?1 per 3 months). This might be because decreased larch root respiration was compensated for by increased organic matter decomposition resulting from an increase in the temperature and root respiration of invading vegetation at the disturbed sites. The CH₄ uptake (kg C ha^?1 per 4 months [May–September]) at the burnt site was significantly higher (–0.15) than the uptake at the forest (–0.045) and clear-felled sites (0.0027). Although there were no significant differences among the sites, N₂O emission (kg N ha^?1 per 4 months) was slightly lower at the burnt site (0.013) and higher at the clear-felled site (0.068) than at the forest site (0.038). This different influence of burning and tree felling on CH₄ and N₂O fluxes might result from changes in the physical and chemical properties of the soil with respect to forest fire.     

N2O and CH4 fluxes from a volcanic grassland soil in Nasu,Japan: Comparison between manure plus fertilizer plot and fertilizer-only plot

Abstract

We examined the effects of manure + fertilizer application and fertilizer-only application on nitrous oxide (N₂O) and methane (CH₄) fluxes from a volcanic grassland soil in Nasu, Japan. In the manure + fertilizer applied plot (manure plot), the sum of N mineralized from the manure and N applied as ammonium sulfate was adjusted to 210 kg N ha^?1 year^?1. In the fertilizer-only applied plot (fertilizer plot), 210 kg N ha^?1 year^?1 was applied as ammonium sulfate. The manure was applied to the manure plot in November and the fertilizer was applied to both plots in March, May, July and September. From November 2004 to November 2006, we regularly measured N₂O and CH₄ fluxes using closed chambers. Annual N₂O emissions from the manure and fertilizer plots ranged from 7.0 to 11.0 and from 4.7 to 9.1 kg N ha^?1, respectively. Annual N₂O emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). This difference could be attributed to N₂O emissions following manure application. N₂O fluxes were correlated with soil temperature (R = 0.70, P < 0.001), NH⁺ ₄ concentration in the soil (R = 0.67, P < 0.001), soil pH (R = –0.46, P < 0.001) and NO^? ₃ concentration in the soil (R = 0.40, P < 0.001). When included in the multiple regression model (R = 0.72, P < 0.001), however, the following variables were significant: NH⁺ ₄ concentration in the soil (β = 0.52, P < 0.001), soil temperature (β = 0.36, P < 0.001) and soil moisture content (β = 0.26, P < 0.001). Annual CH₄ emissions from the manure and fertilizer plots ranged from –0.74 to –0.16 and from –0.84 to –0.52 kg C ha^?1, respectively. No significant difference was observed in annual CH₄ emissions between the plots. During the third grass-growing period from July to September, however, cumulative CH₄ emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). CH₄ fluxes were correlated with NH⁺ ₄ concentration in the soil (R = 0.21, P < 0.05) and soil moisture content (R = 0.20, P < 0.05). When included in the multiple regression model (R = 0.29, P < 0.05), both NH⁺ ₄ concentration in the soil (β = 0.20, P < 0.05) and soil moisture content (β = 0.20, P < 0.05) were significant.     

耕作方式和稻草还田对双季稻田CH_4和N_2O排放的影响

稻田温室气体(甲烷和氧化亚氮)排放强度受多种田间管理的影响,以往对各种措施间的交互效应研究较少。为此,该研究利用改进的静态箱-气相色谱法进行了连续4个生长季的湖南典型双季稻田温室气体排放强度观测,旨在分析耕作和稻草还田2种措施的交互效应并探寻多措施联合减缓温室气体排放强度的途径。试验设4个处理:翻耕(CWS,conventional tillage without straw residue)、免耕(NWS,no till without straw residue)、免耕高茬还田(HN,no till with high stubble straw residue)和翻耕高茬还田(HC,conventional tillage with high stubble straw residue)。结果表明,耕作和稻草还田2种措施对稻田甲烷排放有显著的交互效应(P0.05),但对氧化亚氮交互效应不显著。2种措施对稻田温室气体排放强度的影响有明显的季节和年际变异。多生长季平均而言,各处理甲烷排放顺序为HCHNCWSNWS(HC显著高于HN,HN和CWS差异不显著),水稻产量顺序为CWSHNHCNWS(HN和CWS差异不显著),而温室气体排放强度(greenhouse gas intensity)顺序为HCCWSHNNWS(HN显著低于HC和CWS,P0.05)。可见,"免耕高茬还田"模式能抵消翻耕处理的高温室气体排放,并能比NWS处理提高水稻产量,显著减缓双季稻田温室气体排放强度。在保护性耕作和农田碳库提升的需求下,该模式应被予以高度重视。该研究可为中国双季稻主产区温室气体排放强度减缓措施的选择提供科学支撑。     

Applicability of the soil gradient method for estimating soil–atmosphere CO2, CH4, and N2O fluxes for steppe soils in Inner Mongolia

For evaluating the applicability of the soil gradient method as a substitute for CO₂‐, CH₄‐, and N₂O‐flux measurements in steppe, we carried out chamber measurements and determined soil gas concentration at an ungrazed (UG99) and a grazed (WG) site in Inner Mongolia, China. The agreement of the concentration‐based flux estimates with measured chamber‐based fluxes varied largely depending on the respective GHG in the sequence CO₂ > CH₄ >> N₂O. A calibration of the gas‐transport parameter used to calculate fluxes based on soil gas concentrations improved the results considerably for CO₂ and CH₄. After calibration, the average deviation from the chamber‐based annual cumulative flux for both sites was 11.5%, 10.5%, and 59% for CO₂, CH₄, and N₂O. The gradient method did not constitute an adequate stand‐alone substitute for greenhouse‐gas flux estimation since a calibration using chamber‐based measurements was necessary and vigorous production processes were confined to the uppermost, almost water‐saturated soil layer.     

N2O and CH4 emission from soil amended with steam‐activated biochar

Steam‐activation increased CH₄ emission of stover biochar but decreased it for wood biochar by 14%^–70%. Biochar generally increased CH₄ emission but reduced N₂O emission by 10%–41%. Emission of N₂O was 17% lower for maize‐stover biochar compared to Eucalyptus‐wood biochar, and 3% lower for 350°C compared to 550°C pyrolysis temperature. Emission of CH₄ was 21% higher for activated stover biochar compared to Eucalyptus‐wood biochar and 10% lower for 350°C compared to 550°C pyrolysis temperature. No difference in net CO₂ equivalent was observed among biochar grades.     

CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska

Abstract

Forest fires can change the greenhouse gase (GHG) flux of borea forest soils. We measured carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes with different burn histories in black spruce (Picea mariana) stands in interior Alaska. The control forest (CF) burned in 1920; partially burned (PB) in 1999; and severely burned (SB1 and SB2) in 2004. The thickness of the organic layer was 22 ± 6 cm at CF, 28 ± 10 cm at PB, 12 ± 6 cm at SB1 and 4 ± 2 cm at SB2. The mean soil temperature during CO₂ flux measurement was 8.9 ± 3.1, 6.4 ± 2.1, 5.9 ± 3.4 and 5.0 ± 2.4°C at SB2, SB1, PB and CF, respectively, and differed significantly among the sites (P < 0.01). The mean CO₂ flux was highest at PB (128 ± 85 mg CO₂-C m^?2 h^?1) and lowest at SB1 (47 ± 19 mg CO₂-C m^?2 h^?1) (P < 0.01), and within each site it was positively correlated with soil temperature (P < 0.01). The CO₂ flux at SB2 was lower than that at CF when the soil temperature was high. We attributed the low CO₂ flux at SB1 and SB2 to low root respiration and organic matter decomposition rates due to the 2004 fire. The CH₄ uptake rate was highest at SB1 [–91 ± 21 μg CH₄-C m^?2 h^?1] (P < 0.01) and positively correlated with soil temperature (P < 0.01) but not soil moisture. The CH₄ uptake rate increased with increasing soil temperature because methanotroph activity increased. The N₂O flux was highest [3.6 ± 4.7 μg N₂O-N m^?2 h^?1] at PB (P < 0.01). Our findings suggest that the soil temperature and moisture are important factors of GHG dynamics in forest soils with different fire history.     

Effects of nitrogen and sulfur deposition on CH4 and N2O fluxes in high-altitude peatland soil under different water tables in the Tibetan Plateau

Abstract

The effects of nitrogen (N) and sulfur (S) deposition on methane (CH₄) and nitrous oxide (N₂O) emissions under low (10 cm below soil surface) and high (at soil surface) water tables were investigated in the laboratory. Undisturbed soil columns from the alpine peatland of the Tibetan Plateau were analyzed. CH₄ emission was higher and N₂O emission was lower at the high water table than those at the low water table regardless of nutrient application. Addition of N (NH₄NO₃ (ammonium nitrate), 5 g N m^?2) decreased CH₄ emission up to 57% and 50% at low and high water tables, respectively, but correspondingly increased N₂O emission by 2.5 and 10.4 times. Addition of S (Na₂SO₄ (sodium sulfate), 2.5 g S m^?2) decreased CH₄ and N₂O emission by 64% and 79% at the low water table, respectively, but had a slightly positive effect at the high water table. These results indicated that the responses of CH₄ and N₂O emissions to the S deposition depend on the water table condition in the high-altitude peatland.     

稻田CH4和N2O综合排放对控制灌溉的响应

为了揭示水稻控制灌溉对稻田CH4和N2O综合排放的影响,该文采用静态暗箱-气相色谱法对控制灌溉稻田CH4和N2O排放进行原位观测,分析稻田CH4和N2O综合排放对控制灌溉水分调控的动态响应。结果表明,控制灌溉稻田CH4排放通量多低于常规灌溉稻田,且主要集中在水稻分蘖前期,峰值出现在土壤脱水后第1～2d,排放总量较常规灌溉稻田减少81.2%～82.8%;N2O排放通量多高于常规灌溉稻田,峰值出现在肥后且土壤脱水后3～4d,排放总量较常规灌溉稻田增加了121.8%～144.3%。控制灌溉稻田CH4和N2O的综合全球增温潜势较常规灌溉稻田显著减少(p<0.05),减少幅度为15.0%～34.8%。控制灌溉显著降低了稻田CH4和N2O的综合温室效应。     

Aeration effects on CO2, N2O,and CH4 emission and leachate composition of a forest soil

The availability of O₂ is one of the most important factors controlling the chemical and biological reactions in soils. In this study, the effects of different aeration conditions on the dynamics of the emission of trace gases (CO₂, N₂O, CH₄) and the leachate composition (NO₃^‐, DOC, Mn, Fe) were determined. The experiment was conducted with naturally structured soil columns (silty clay, Vertisol) from a well aerated forest site. The soil monoliths were incubated in a microcosm system at different O₂ concentrations (0, 0.001, 0.005, 0.01, 0.05, and 0.205 m³ m^‐3 in the air flow through the headspace of the microcosms) for 85 days. Reduced O₂ availability resulted in a decreased CO₂ release but in increased N₂O emission rates. The greatest cumulative N₂O emissions (= 1.6 g N₂O‐N m^‐2) were observed at intermediate O₂ concentrations (0.005 and 0.01 m³ m^‐3) when both nitrification and denitrification occurred simultaneously in the soil. Cumulative N₂O emissions were smallest (= 0.05 g N₂O‐N m^‐2) for the aeration with ambient air (O₂ concentration: 0.205 m³ m^‐3), although nitrate availability was greatest in this treatment. The emission of CH₄ and leaching of Mn and Fe were restricted to the soil columns incubated under completely anoxic conditions. The sequence of the reduction processes under completely anoxic conditions complied with the thermodynamic theory: soil nitrate was reduced first, followed by the reduction of Mn(IV) and Fe(III) and finally CO₂ was reduced to CH₄. The re‐aeration of the soil columns after 85 days of anoxic incubation terminated the production of CH₄ and dissolved Fe and Mn in the soil but strongly increased the emission rates of CO₂ and N₂O and the leaching of NO₃^‐ probably because of the accumulation of DOC and NH₄⁺ during the previous anoxic period.