Intermittent irrigation changes production,oxidation, and emission of CH4 in paddy fields determined with stable carbon isotope technique

Intermittent irrigation is an important option for mitigating CH₄ emissions from paddy fields. In order to better understand its controlling processes in CH₄ emission, CH₄ fluxes, CH₄ production and oxidation potentials in paddy soils, and ¹³C-isotopic signatures of CH₄ were observed in field and incubation experiments. The relative contribution of acetate to total CH₄ production (f_ac) and fraction of CH₄ oxidized (f_ox) in the field was also calculated using the isotopic data. At the beginning of the rice season, the theoretical ratio of acetate fermentation: H₂/CO₂ reduction = 2:1 was reached, however, in the late season H₂/CO₂-dependent methanogenesis became dominant. Compared to continuous flooding, intermittent irrigation significantly reduced CH₄ production potential and slightly decreased f_ac-value, indicating methanogens, particularly acetate-utilizing methanogens, were inhibited. CH₄ oxidation was very important, especially in paddy fields under intermittent irrigation where 19–83% of the produced CH₄ was oxidized. Intermittent irrigation enhanced CH₄ oxidation potential slightly and raised f_ox-value significantly relative to continuous flooding. Intermittent irrigation significantly decreased CH₄ flux creating a more positive δ¹³C-value of emitted CH₄ by 12–22‰. A significant negative correlation was found between CH₄ fluxes and values of δ¹³CH₄ suggesting that the less the CH₄ oxidation, the higher the CH₄ emission, and the lower the δ¹³C-value of emitted CH₄. Collectively, the findings show that intermittent irrigation reduced the seasonal CH₄ production potential by 45% but increased the fraction of CH₄ oxidized by 45–63%, thus decreasing the seasonal CH₄ emission from the paddy fields by 71%, relative to continuous flooding.     

稻虾共作对秸秆还田后稻田温室气体排放的影响

稻虾共作模式是稻田种养复合模式的重要组成部分,其主要特点是稻草全量还田、非稻季持续淹水和周年养殖克氏原螯虾。目前对稻虾共作模式稻田温室气体排放的影响尚不清楚。本研究以江汉平原冬泡无稻草还田为对照,设置冬泡+稻草还田和冬泡+稻草还田+养虾处理,探讨稻草还田及稻虾共作对稻田系统CH_4、N_2O和CO_2排放的影响,为准确评估稻田温室气体排放提供数据支撑和理论支持。结果表明,在大田监测期间,冬泡+稻草还田处理CH_4累积排放量比冬泡无稻草还田处理显著增加(P0.05),2015年和2016年增幅分别为27.23%和60.08%;冬泡+稻草还田+养虾处理CH_4累积排放量比冬泡+稻草还田显著降低(P0.05),2015年和2016年降幅分别为29.02%和41.19%。冬泡+稻草还田处理CO_2累积排放比冬泡无稻草还田处理显著提高;与冬泡无稻草还田处理相比较,冬泡+稻草还田处理和冬泡+稻草还田+养虾处理对N_2O累积排放无显著影响。从温室效应角度看,冬泡+稻草还田处理温室效应比冬泡无稻草还田处理大幅度增加,而冬泡+稻草还田基础上进行养虾则可大幅度降低CH_4排放,从而降低因秸秆还田带来的温室效应增强。所有处理水稻产量无显著差异,与冬泡+稻草还田处理相比,冬泡+稻草还田+养虾可显著降低温室气体排放强度。和冬泡无稻草还田处理相比,冬泡+稻草还田和冬泡+稻草还田+养虾对土壤可溶性有机碳(DOC)、乙酸和NH_4~+-N并无显著影响。冬泡+稻草还田+养虾可极显著提高单位面积收益。     

水稻油菜轮作稻田甲烷排放及其总量估算

利用静态箱/气相色谱法对川中丘陵区水稻油菜轮作稻田进行水稻全生长季CH4排放观测。结果表明,稻田CH4排放有明显的季节变化,呈“前低后高”的变化趋势,CH4排放峰出现在水稻抽穗扬花期;测定期内稻田CH4平均排放通量为6.20mg/m2.h。对影响稻田CH4排放的因素分析发现,淹水条件下水稻移栽到抽穗初期,水稻植株生长是影响稻田CH4排放的关键因素;水稻抽穗期到成熟期,温度是影响稻田CH4排放的关键因素。水稻油菜轮作稻田在水稻生长季中CH排放总量为173.96kg/hm2。     

Methane emissions from paddy fields in Bali Island,Indonesia

Abstract

Methane emission rates from plots with and without fertilizer and rice straw application, and growth of two rice varieties (an improved variety, IR74 or IR64, and a local variety, Krueng Aceh) in two Indonesian paddy fields (Inceptisol and Alfisol soils of volcanic ash origin) were measured every week throughout the growth period in the first and the second cropping seasons, 1994. The CH₄ emission rates from the fields were similar between the two varieties. The effect of chemical fertilizer on the increase of the emissions was observed only in the Tabanan paddy field for the plots treated with rice straw. Application of rice straw increased the CH₄ emission rates. The mean rates of CH₄ emission were 1.37-2.13 mg CH₄?C m^?2 h^?1 for the plots without rice straw and 2.14–3.62 mg CH₄?C m^?2 h^?1 for the plots with rice straw application in the Alfisol plots, and 2.32–3.32 mg CH₄ -C m-2 h-1 for the plots without rice straw and 4.18–6.35 mg CH₄?C m^?2 h^?1 for the plots with rice straw application in the Inceptisol plots, respectively. Total amounts of CH₄ emitted during the growth period were 3.9–6.8 and 2.6–3.3 g CH₄?C m^?2 for the Alfisol plots and 6.9–10.7 and 4.2–5.8 g CH₄?C m^?2 for the Inceptisol plots with and without rice straw application, respectively. These findings suggested that CH₄ emission from tropical paddy fields with soils of volcanic ash origin is low.     

Nitrous oxide emission from wetland rice soil as affected by the application of controlled-availability fertilizers and mid-season aeration

 N₂O emission from a wetland rice soil as affected by the application of three controlled-availability fertilizers (CAFs) and urea was investigated through a pot experiment. N₂O fluxes from the N fertilized paddy soil averaged 44.8–69.3 μg N m^–2 h^–1 during the rice growing season, accounting for 0.28–0.51% of the applied N. The emission primarily occurred during the mid-season aeration (MSA) and the subsequent re-flooding period. Fluxes were highly correlated with the NO₃ ^– and N₂O concentrations in the soil water. As there were relatively large amounts of NH₄ ⁺-N present in the soil of the CAF treatments at the beginning of MSA, leading to large amounts of NO₃ ^–-N during the MSA and the subsequent re-flooding period, the tested CAFs were not effective in reducing N₂O emission from this paddy soil. The potential of applied CAFs to reduce N₂O emissions from paddy soil is discussed. Received: 25 May 1999     

Controlled irrigation and drainage of a rice paddy field reduced global warming potential of its gas emissions

The effect of controlled drainage on methane (CH₄) and nitrous oxide (N₂O) emissions from a paddy field under controlled irrigation (CI) was investigated by controlling the sub-surface drainage percolation rate with a lysimeter. CI technology is one of the major water-saving irrigation methods for rice growing in China. Water percolation rates were adjusted to three values (2, 5, and 8 mm d^?1) in the study. On the one hand, the CH₄ emission flux and total CH₄ emission from paddy fields under CI decreased with the increase of percolation rates. Total CH₄ emissions during the growth stage of rice were 1.83, 1.16, and 1.05 g m^?2 in the 2, 5, and 8 mm d^?1 plots, respectively. On the other hand, the N₂O emission flux and total N₂O emissions from paddy fields under CI increased with the increase of percolation rates. Total N₂O emissions during the growth stage of rice were 0.304, 0.367, and 0.480 g m^?2 in the 2, 5, and 8 mm d^?1 plots, respectively. The seasonal carbon dioxide (CO₂) equivalent of CH₄ and N₂O emissions from paddy fields under CI was lowest in the 2 mm d^?1 plot (1364 kg CO₂ ha^?1). This value was 1.4% and 19.4% lower compared with that in the 5 and 8 mm d^?1 plots, respectively. The joint application of CI and controlled drainage may be an effective mitigation strategy for reducing the carbon dioxide equivalents of CH₄ and N₂O emissions from paddy fields.     

Suppressing methane emission and global warming potential from rice fields through intermittent drainage and green biomass amendment

Winter cover crops are recommended to improve soil quality and carbon sequestration, although their use as green manure can significantly increase methane (CH₄) emission from paddy soils. Soil management practices can be used to reduce CH₄ emission from paddy soils, but intermittent drainage is regarded as a key practice to reduce CH₄ emission and global warming potential (GWP). However, significantly greater emissions of carbon dioxide (CO₂) and nitrous oxide (N₂O) are expected when large amounts of cover crop biomass are incorporated into soils. In this study, we investigated the effects of midseason drainage on CH₄ emission and GWP following incorporation of 0, 3, 6 and 12 Mg/ha of cover crop biomass. Methane, CO₂ and N₂O emission rates significantly (P < 0.05) increased with higher rates of cover crop biomass incorporation under both irrigation conditions. However, intermittent drainage effectively reduced seasonal CH₄ fluxes by ca. 42–46% and GWP by 17–31% compared to continuous flooding. Moreover, there were no significant differences in rice yield between the two water management practices with similar biomass incorporation rates. In conclusion, intermittent drainage and incorporation of 3 Mg/ha of green biomass could be a good management option to reduce GWP.     

土壤质地、温度和Eh对稻田甲烷排放的影响

本文报道在田间条件下,土南地,温度和Ｅｈ影响稻田ＣＨ４排放通量的研究结果。中国科学院封丘生态试验站的小区试验表明,在当地常规水分管理即间歇灌溉条件下,供试小区和妥田的ＣＨ４平均排放通量仅为０．１６－１．８６ｍ ｇＣＨ４／ｍ＾２ｈ。     

Characteristics of greenhouse gas emissions from rice paddy fields in South Korea under climate change scenario RCP-8.5 using the DNDC model

Understanding the greenhouse gas(GHG)emission from rice paddy fields is essential to come up with appropriate countermeasure in response to global warming.However,GHG emissions from paddy fields in South Korea are not well characterized.The objectives of this study were to estimate the carbon dioxide(CO₂)and methane(CH₄)emissions from rice paddy fields in South Korea,under the Representative Concentration Pathway 8.5(RCP-8.5)climate change scenario using the DNDC(i.e.,DeNitrification-DeComposition)model at 1-km²resolution.The performance of the model was verified with field data collected using a closed chamber,which supports the application of the model to South Korea.Both the model predictions and field measurements showed that most(>95%)GHG emissions occur in the cropping period,between April and October.As a baseline(assuming no climate change),the national sums of the CO₂and CH₄emissions for the 2020 s and 2090 s were estimated to be 5.8×10⁶and 6.0×10⁶t CO₂-equivalents(CO₂-eq)year^-1for CO₂and 6.4×10⁶and 6.6×10⁶t CO₂-eq year^-1for CH₄,respectively,indicating no significant changes over 80 years.Under RCP-8.5,in the 2090 s,CH₄emissions were predicted to increase by 10.7×10⁶and 14.9×10⁶t CO₂-eq year^-1,for a 10-or 30-cm tillage depth,respectively.However,the CO₂emissions gradually decreased with rising temperatures,due to reduced root respiration.Deep tillage increased the emissions of both GHGs,with a more pronounced effect for CH₄than CO₂.Intermittent drainage in the middle of the cropping season can attenuate the CH₄emissions from paddy fields.The findings of this work will aid in developing nationwide policies on agricultural land management in the face of climate change.     

Incorporation of rice straw mitigates CH4 and N2O emissions in water saving paddy fields of Central Vietnam

This study evaluated the effects of rice straw and water regimes on CH₄ and N₂O emissions from paddy fields for two rice growing seasons (summer 2014 and spring 2015). Water regimes included alternating wet–dry irrigation (AWD) maintained at three levels (–5 cm, – 10 cm and –15 cm) in comparison to continuous flooding irrigation (CF). Rice straw (5 t ha^–1) was incorporated into the top soil (0 – 15 cm), distributed and burned in situ. Results showed that using burned in situ rice straw was found to reduce seasonal cumulative CH₄ emission (24–34% in summer; 18–28% in spring), N₂O emission (21–32% in summer; 22–29% in spring) and lower rice yield (8–9%) than rice straw incorporation into top soil. AWD methods reduced the amount of CH₄ production (22.6–41.5%) and increased N₂O emission (25–26%) without any decrease in rice yield. Rice straw incorporation into the top soil with AWD had higher water productivity (23–37%) than rice straw when burned in situ with CF. The results conclude that AWD and rice straw management can be employed as mitigation strategy for CH₄ and N₂O emissions from paddy fields in Central Vietnam.     

Effect of the number of tillages in fallow season and fertilizer type on greenhouse gas emission from a rice (Oryza sativa L.) paddy field in Ehime,southwestern Japan

Agricultural fields, including rice (Oryza sativa L.) paddy fields, constitute one of the major sources of atmospheric methane (CH₄) and nitrous oxide (N₂O). Organic matter application, such as straw and organic fertilizer, enhances CH₄ emission from paddy fields. In addition, rice straw management after harvest regulates CH₄ emissions in the growing season. The interaction of tillage times and organic fertilizer application on CH₄ and N₂O emissions is largely unknown. Therefore, we studied the effects of fallow-season tillage times and fertilizer types on CH₄ and N₂O emissions in paddy fields in Ehime, southwestern Japan. From November 2011 to October 2013, four treatments, two (autumn and spring) or one (spring) in the first year, or two (autumn and spring) or three (autumn, winter, and spring) in the second year times of tillage with chemical or organic fertilizer application, were established. Gas fluxes were measured by the closed-chamber method. Increasing the number of tillage times from one to two decreased succeeding CH₄ emission and the emission factor for CH₄ (EF_CH4) in the rice-growing season, suggesting that the substrate for CH₄ production was reduced by autumn and spring tillage in the fallow season. Higher EF_CH4 [1.8–2.0 kg carbon (C) ha^?1 d^?1] was observed when more straw was applied (6.9–7.2 Mg ha^?1) in the second year. Organic fertilizer application induced higher CH₄ emission just after the application as basal and supplemental fertilizers, especially at a lower straw application rate. This indicated that EF_CH4 in the organically managed fields should be determined individually. Organic fertilizer application with two tillage times induced N₂O efflux during the rice-growing season in the second year, but N₂O emissions were not affected by winter tillage. Although paddy fields can act as an N₂O sink because of reduced soil conditions when straw application was high, application of organic C and nitrogen as fertilizer can enhance N₂O production by the denitrification process during the growing season, especially in the ripening stage when soil anaerobic conditions became moderate. These results suggest that negative emission factors for N₂O (EF_N2O) can be applied, and EF_N2O of organic fertilizer should be considered during the estimation of N₂O emission in the paddy field.     

Effect of the herbicide butachlor on methane emission and ebullition flux from a direct-seeded flooded rice field

 Application of a commercial formulation of the herbicide butachlor (N-butoxymethyl-2-chloro-2′,6′-diethyl acetanilide) at 1 kg a.i. ha^–1 to an alluvial soil planted with direct-seeded flooded rice (cv. Annada), significantly inhibited both crop-mediated emission and ebullition fluxes of methane (CH₄). Over a cropping period of 110 days, the crop-mediated cumulative emission flux of CH₄ was lowered by ∼20% in butachlor-treated field plots compared with that of an untreated control. Concurrently, ebollition flux of CH₄ was also retarded in butachlor-treated field plots by about 81% compared with that of control plots. Significant relationships existed between CH₄ emission and redox potential (E _h) and Fe²⁺ content of the flooded soil. Application of butachlor retarded a drop in soil redox potential as well as accumulation of Fe²⁺ in treated field plots. Methanogenic bacterial population, counted at the maturity stage of the crop, was also low in butachlor-treated plots, indicating both direct and indirect inhibitory effects of butachlor on methanogenic bacterial populations and their activity. Results indicate that butachlor, even at field-application level, can effectively abate CH₄ emission and ebollition from flooded soils planted to rice whilst maintaining grain yield. Received: 15 March 2000     

The influence of land use and pesticides on methane oxidation in some Belgian soils

 In a first experiment, the effect of land use on the uptake rate of atmospheric CH₄ was studied in laboratory incubations of intact soil cores. A soil under deciduous forest showed the highest CH₄ oxidation. Its overall CH₄ uptake during the measuring period (202 days) was 1.03 kg CH₄ ha^–1. Natural grassland showed the second highest CH₄ oxidizing capacity (0.71 kg CH₄ ha^–1). The overall amount of CH₄ uptake by fertilized pasture was 0.33 kg CH₄ ha^–1. CH₄ oxidation in arable soils with different fertilizer treatments varied between 0.34 and 0.37 kg CH₄ ha^–1. Undisturbed soils had a higher CH₄ uptake capacity than agricultural soils. The moisture content of the soil was found to be an important parameter explaining temporal variations of CH₄ oxidation. Different methods of fertilization which had been commenced 10 years previously were not yet reflected in the total CH₄ uptake rate of the arable soil. In a second experiment, a number of frequently used pesticides were screened for their possible effect on CH₄ oxidation. In a sandy arable soil lenacil, mikado and oxadixyl caused significantly reduced CH₄ oxidation compared to the control. Under the same conditions, but in a clayey arable soil, mikado, atrazine and dimethenamid caused a reduction of the CH₄ uptake. In a landfill cover soil, with a 100-fold higher CH₄ oxidation rate, no inhibition of CH₄ oxidation was observed, not even when the application rate of pesticides was tenfold higher than usual. Received: 1 December 1998     

Water Management Influencing Methane and Nitrous Oxide Emissions from Rice Field in Relation to Soil Redox and Microbial Community

Abstract

Methane (CH₄) and nitrous oxide (N₂O) emissions from an irrigated rice field under continuous flooding and intermittent irrigation water management practices in northern China were measured in situ by the static chamber technique during May to October in 2000. The intermittent irrigation reduced total growing‐season CH₄ emission by 24.22% but increased N₂O emission by 23.72%, when compared with the continuous flooding. Soil Eh and four related bacterial groups were also measured to clarify their effects on gaseous emissions. Three ranges of soil redox potential were related to gas emissions: below ?100 mV with vigorous CH₄ emission, above +100 mV with significant N₂O emission, and +100 to ?100 mV with little CH₄ and N₂O emissions. Intermittently draining the field increased soil oxidation, with a decrease in CH₄ emission and an increase in N₂O emission. In general the mid‐season drainage slightly increased the populations of methanotrophs, nitrifiers, and denitrifiers but decreased that of methanogens.     

Greenhouse gas emissions in response to straw incorporation,water management and their interaction in a paddy field in subtropical central China

A field experiment was conducted to study the effects of combination of straw incorporation and water management on fluxes of CH₄, N₂O and soil heterotrophic respiration (Rh) in a paddy field in subtropical central China by using a static opaque chamber/gas chromatography method. Four treatments were set up: two rice straw incorporation rates at 0 (S1) and 6 (S2) t ha^?1 combined with two water managements of intermittent irrigation (W1, with mid-season drainage) and continuous flooding (W2, without mid-season drainage). The cumulative seasonal CH₄ emissions for the treatments of S1W2, S2W1 and S2W2 increased significantly by 1.84, 5.47 and 6.63 times, respectively, while seasonal N₂O emissions decreased by 0.67, 0.29 and 1.21 times, respectively, as compared to S1W1 treatment. The significant increase in the cumulative Rh for the treatments S1W1, S2W1 and S2W2 were 0.54, 1.35 and 0.52 times, respectively, in comparison with S1W2. On a seasonal basis, both the CO₂-equivalents (CO₂e) and yield-scaled CO₂e (GHGI) of CH₄ and N₂O emissions increased with straw incorporation and continuous flooding, following the order: S2W2>S2W1>S1W2>S1W1. Thus, the practices of in season straw incorporation should be discouraged, while mid-season drainage is recommended in paddy rice production from a point view of reducing greenhouse gas emissions.     

Different response of silicate fertilizer having electron acceptors on methane emission in rice paddy soil under green manuring

Cultivation of green manure plants during the fallow season in rice paddy soil has been strongly recommended to improve soil properties. However, green manuring may impact greenhouse gas emission, methane (hereafter, CH₄) in particular, under the flooded rice cultivation and thus, application of chemical amendments being electron acceptors can be an effective mitigation strategy to reduce CH₄ emissions in irrigated rice (Oryza sativa L.) field amended with green manure. To investigate the effect of iron (Fe) slag silicate fertilizer (hereafter, silicate fertilizer), which was effective in reducing CH₄ emission and increasing rice productivity, in green manure-amended paddy soil, the aboveground biomass of Chinese milk vetch (hereafter, vetch) was added at rates of 0, 10, 20, and 40 Mg (fresh weight) ha⁻¹ before the application of silicate fertilizer, which was added at rates of 0 and 2.3 Mg ha⁻¹. Silicate fertilization reduced the seasonal CH₄ flux by ca. 14.5% and increased rice yield by ca. 15.7% in the control (no vetch application) treatment. However, CH₄ production was increased by silicate fertilization in vetch-treated soil particularly at the initial rice growing stage, which was probably due to the enhanced decomposition of added organic matters by the silicate liming effect. In conclusion, silicate fertilization is not effective in reducing CH₄ production in green manure-amended rice paddy soils and its use should be properly controlled.     

间隙灌溉和控释肥施用对稻田土壤产甲烷微生物的影响

间隙灌溉和控释肥施用影响稻田CH_4的产生和排放,然而其微生物机理尚不清楚。本研究通过采集稻季田间原位试验新鲜土样,采用核酸定量技术(qPCR)和末端限制性片段长度多态性(T-RFLP)技术,研究间隙灌溉和控释肥施用对稻田土壤产甲烷微生物群落丰度和结构的影响。结果表明,稻季CH_4排放量与古菌、产甲烷菌(mcr A基因)和甲烷氧化菌(pmo A基因)数量均呈极显著正相关关系(P0.01),而与细菌数量无显著相关性。间隙灌溉显著影响产甲烷菌和甲烷氧化菌数量的季节变化,其中烤田抑制产甲烷菌生长,而对甲烷氧化菌数量没有显著影响。与尿素相比,施用控释肥增加了稻田土壤细菌、古菌和产甲烷菌数量,降低了甲烷氧化菌数量。土壤古菌群落的优势T-RFs片段为184bp和391bp,其中184bp片段的相对丰度随着间隙灌溉的进行由45%~55%降低到23%~30%;而391bp片段则相反,其相对丰度由12%~18%增加到23%~26%。典型相关性分析(CCA)表明间隙灌溉显著影响土壤古菌群落结构(P0.001),而控释肥施用对土壤古菌群落结构没有明显影响。     

Abundance and community composition of methanotrophs in a Chinese paddy soil under long-term fertilization practices

Background, aim, and scope  As the second most important greenhouse gas, methane (CH₄) is produced from many sources such as paddy fields. Methane-oxidizing bacteria (methanotrophs) consume CH₄ in paddy soil and, therefore, reduce CH₄ emission to the atmosphere. In order to estimate the contribution of paddy fields as a source of CH₄, it is important to monitor the effects of fertilizer applications on the shifts of soil methanotrophs, which are targets in strategies to combat global climate change. In this study, real-time polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE) based on 16S rRNA and pmoA genes, respectively, were used to analyze the soil methanotrophic abundance and community diversity under four fertilization treatments: urea (N), urea and potassium chloride (NK), urea, superphosphate, and potassium chloride (NPK), and urea, superphosphate, potassium chloride, and crop residues (NPK+C), compared to an untreated control (CON). The objective of this study was to examine whether soil methanotrophs responded to the long-term, different fertilizer regimes by using a combination of quantitative and qualitative molecular approaches. Materials and methods  Soil samples were collected from the Taoyuan Experimental Station of Agro-ecosystem Observation at Changde (28°55′ N, 111°26′ E), central Hunan Province of China, in July 2006. Soil DNAs were extracted from the samples, then the 16S rRNA genes were quantified by real-time PCR and the pmoA genes were amplified via general PCR followed by DGGE, cloning, sequencing, and phylogenetic analysis. The community diversity indices were assessed through the DGGE profile. Results  Except for NPK, other treatments of N, NK, and NPK+C showed significantly higher copy numbers of type I methanotrophs (7.0–9.6 × 10⁷) than CON (5.1 × 10⁷). The copy numbers of type II methanotrophs were significantly higher in NPK+C (2.8 × 10⁸) and NK (2.5 × 10⁸) treatments than in CON (1.4 × 10⁸). Moreover, the ratio of type II to type I methanotrophic copy numbers ranged from 1.88 to 3.32, indicating that the type II methanotrophs dominated in all treatments. Cluster analyses based on the DGGE profile showed that the methanotrophic community in NPK+C might respond more sensitively to the environmental variation. Phylogenetic analysis showed that 81% of the obtained pmoA sequences were classified as type I methanotrophs. Furthermore, the type I-affiliated sequences were related to Methylobacter, Methylomicrobium, Methylomonas, and some uncultured methanotrophic clones, and those type II-like sequences were affiliated with Methylocystis and Methylosinus genera. Discussion  There was an inhibitory effect on the methanotrophic abundance in the N and a stimulating effect in the NK and NPK+C treatments, respectively. During the rice-growing season, the type II methanotrophs might be more profited from such a coexistence of low O₂ and high CH₄ concentration environment than the type I methanotrophs. However, type I methanotrophs seemed to be more frequently detected. The relatively complex diversity pattern in the NPK+C treatment might result from the strong CH₄ production. Conclusions  Long-term fertilization regimes can both affect the abundance and the composition of the type I and type II methanotrophs. The inhibited effects on methanotrophic abundance were found in the N treatment, compared to the stimulated effects from the NK and NPK+C treatments. The fertilizers of nitrogen, potassium, and the crop residues could be important factors controlling the abundance and community composition of the methanotrophs in the paddy soil. Recommendations and perspectives  Methanotrophs are a fascinating group of microorganisms playing an important role in the biogeochemical carbon cycle and in the control of global climate change. However, it is still a challenge for the cultivation of the methanotrophs, although three isolates were obtained in the extreme environments very recently. Therefore, future studies will be undoubtedly conducted via molecular techniques just like the applications in this study.     

Methane fluxes and nitrogen dynamics from a drained fenland peat

 Rates of methane uptake were measured in incubation studies with intact cores from adjacent fenland peats that have been under arable management and woodland management for at least the past 30 years. On two separate occasions the woodland peat showed greater rates of uptake than the arable peat. These rates ranged from 23.1 to 223.3 μg CH₄ m^–2 day^–1 for the woodland peat and from 29.6 to 157.6 μg CH₄ m^–2 day^–1 for the arable peat. When the peats were artificially flooded there was a decrease in the rate of methane oxidation, but neither site showed any net efflux of methane. ¹⁵N isotopic dilution was used to characterise nitrogen cycling within the two peats. Both showed similar rates of gross nitrogen mineralisation (3.58 mg N kg^–1 day^–1, arable peat; 3.54 N kg^–1 day^–1, woodland peat) and ammonium consumption (4.19 arable peat and 4.70 mg N kg^–1 day^–1 woodland peat). There were significant differences in their inorganic ammonium and nitrate pool sizes, and the rate of gross nitrification was significantly higher in the woodland peat (4.90 mg N kg^–1 day^–1) compared to the arable peat (1.90 mg N kg^–1 day^–1). These results are discussed in the light of high atmospheric nitrogen deposition. Received: 1 December 1997     

基于DNDC模型模拟江汉平原稻田不同种植模式条件下温室气体排放

稻田被认为是温室气体CH_4和N_2O的主要排放源之一。湖北省江汉平原地区水稻常年种植面积约8×105 hm2,占湖北省水稻种植面积的40%左右。研究江汉平原地区稻田温室气体排放特征,对于评估区域稻田温室气体排放以及稻田温室气体减排具有重要意义。目前,DNDC模型已被广泛应用于模拟和估算田间尺度的温室气体排放,DNDC模型与地理信息系统(Arc GIS)结合,可进行区域尺度的温室气体排放模拟与估算。本研究以湖北省典型稻作区江汉平原为研究区域,运用DNDC模型模拟和估算江汉平原稻田区域尺度的温室气体排放。设置大田定点观测试验,监测中稻-小麦(RW)、中稻-油菜(RR)、中稻-冬闲(RF)3种种植模式下稻田温室气体CH_4和N_2O的周年排放特征。通过田间观测值与DNDC模拟值的比较进行模型验证,并利用获取DNDC模型所需的气象、土壤、作物及田间管理等区域数据,模拟江汉平原稻田不同种植模式下温室气体CH_4和N_2O的排放量。田间试验表明,江汉平原稻田RW、RR和RF模型的CH_4排放通量为-2.80~39.78 mg·m-2·h-1、-1.74~42.51 mg·m-2·h-1和-1.57~55.64 mg·m-2·h-1,N_2O周年排放通量范围分别为0~1.90 mg·m-2·h-1、0~1.76mg·m-2·h-1和0~1.49 mg·m-2·h-1;CH_4排放量RW和RR模式显著高于RF模式,N_2O排放量为RF显著低于RW和RR模式。模型验证结果表明,不同种植模式温室气体排放实测值与模拟值比较的决定系数(R2)为0.85~0.98,相对误差绝对值(RAE)为8.29%~16.42%。根据DNDC模型模拟和估算的结果,江汉平原区域稻田CH_4周年的排放量为0.292 9 Tg C,N_2O周年的排放量为0.009 2 Tg N,不同种植模式稻田CH_4排放量表现为RWRRRF,N_2O排放量表现为RWRFRR,增温潜势(GWP)表现为RWRRRF。不同地区稻田CH_4排放量表现为监利县荆门市公安县天门市仙桃市洪湖市松滋市汉川市潜江市石首市荆州市江陵县赤壁市嘉鱼县,N_2O排放量表现为监利县荆门市公安县洪湖市仙桃市天门市汉川市潜江市松滋市荆州市江陵县赤壁市石首市嘉鱼县。本研究结果表明DNDC模型能较好地应用于模拟江汉平原稻田温室气体排放,RR和RF模式相比RW模式可有效减少温室气体CH_4和N_2O的排放。