Effect of silicate fertilizer on reducing methane emission during rice cultivation

Slag-type silicate fertilizer, which contains high amount of active iron oxide, a potential source of electron acceptor, was applied at the rate of 0, 2, 6, 10, and 20 Mg ha⁻¹ to reduce methane (CH₄) emission from rice planted in potted soils. Methane emission rates measured by closed chamber method decreased significantly with increasing levels of silicate fertilizer application during rice cultivation. Soil redox potential (Eh) decreased rapidly after flooding, but floodwater pH and soil pH increased significantly with increasing levels of silicate fertilizer application. Iron concentrations in potted soils and in percolated water significantly increased with the increasing levels of silicate fertilizer application, which acted as oxidizing agents and electron acceptors, and thereby suppressed CH₄ emissions. Silicate fertilization significantly decreased CH₄ production activity, while it increased carbon dioxide (CO₂) production activity. Rice plant growth, yield parameters, and grain yield were positively influenced by silicate application levels. The maximum increase in grain yield (17% yield increase over the control) was found with 10 Mg ha⁻¹ silicate application along with 28% reduction in total CH₄ flux during rice cultivation. It is, therefore, concluded that slag-type silicate fertilizer could be a suitable soil amendment for reducing CH₄ emissions as well as sustaining rice productivity and restoring the soil nutrient balance in rice paddy soil.     

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     

Effect of seedling transplanting date on methane emission from rice paddy soil during cultivation

In most temperate mono-rice cultivation systems like Korea, the local recommended transplanting date of rice (Oryza sativa L.) seedlings is proposed by the government agency considering climate, rice cultivar, rice productivity and quality, etc. Recently the transplanting of rice seedlings earlier than the recommended transplanting date (RTD) has been adopted by the local farmers to get high yield and to harvest earlier for higher market value. Earlier transplanting than RTD might influence methane (CH₄) emission due to the prolonged cultivation period, but its effect was not evaluated well so far. In this study, the effects of seedling transplanting date on CH₄ emission and rice productivity were investigated for two years in a general paddy soil. The 30-day old seedlings were transplanted on the local RTD (every June 15) as the control, and at 30 and 15 days before and 15 days after the RTD for comparison. There was no difference on CH₄ flux pattern among the treatments, but the earlier transplanting before the RTD significantly (P ?≤?0.05) increased total CH₄ emissions during rice cultivation due to the extended soil flooding period and improved plant growth. Rice grain yield was increased by earlier transplanting, but the values were not significantly different from those of transplanting practices on RTD and 15 days before RTD. Therefore, among all the treatments, the lowest total CH₄ emission per grain yield was observed in the RTD treatment. Conclusively, rice transplanting following the RTD, rather than early or late transplanting, could be more effective to minimize CH₄ emission without significantly decreasing the rice productivity.     

Soil respiration, nitrogen mineralization and uptake in barley following cultivation of grazed grasslands

 Soil tillage was studied as a strategy to synchronize N mineralization with plant demand following ploughing of two types of grazed pastures [ryegrass/white clover (Lolium perenne/Trifolium repens) and pure ryegrass]. The swards were either rotovated and ploughed or ploughed only. Soil respiration, as determined by a dynamic chamber method, was related to net N mineralization and to plant N uptake in a subsequent spring barley crop (Hordeum vulgare). Diurnal variations in temperature were important for the CO₂ flux and care must be taken that temperatures during measuring periods are representative of the daily mean. Soil tillage increased the CO₂ flux considerably compared with untilled soil with total emissions of 2.6 and 1.4 t C ha^–1, respectively, from start of April to end of June. Sward type or rotovation did not markedly influence accumulated emissions. Rotovation significantly increased the content of nitrate in the soil until 43 days after rotovation, showing that net N mineralization occurred rapidly during this period, in spite of low soil temperatures (5–10  °C). Rotovation increased barley grain yield by 10–12% and N-uptake by 14%. For both sward types, rotovation caused an extra N-uptake in harvested plant material of about 12 kg ha^–1. The availability of soil inorganic N at the early stages of barley was important for the final yield and N-uptake. The results indicated that soil biological activity was not enhanced by rotovation and that the yield effect of rotovation was mainly caused by quicker availability and better synchrony between N mineralization and plant uptake due to earlier start of decomposition. Received: 3 May 2000     

Potassium application reduces methane emission from a flooded field planted to rice

In a field study, potassium (K) applied as muriate of potash (MOP) significantly reduced methane (CH₄) emission from a flooded alluvial soil planted to rice. Cumulative emission was highest in control plots (125.34 kg CH₄ ha⁻¹), while the lowest emission was recorded in field plots receiving 30 kg K ha⁻¹ (63.81 kg CH₄ ha⁻¹), with a 49% reduction in CH₄ emission. Potassium application prevented a drop in the redox potential and reduced the contents of active reducing substances and Fe²⁺ content in the rhizosphere soil. Potassium amendment also inhibited methanogenic bacteria and stimulated methanotrophic bacterial population. Results suggest that, apart form producing higher plant biomass (both above- and underground) and grain yield, K amendment can effectively reduce CH₄ emission from flooded soil and could be developed into an effective mitigation option, especially in K-deficient soils.     

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.     

Methane emission from paddy fields in Taiwan

 In order to investigate the effect of environmental conditions on CH₄ emission from paddy fields in Taiwan, four locations, two cropping seasons and two irrigation systems were studied. CH₄ emission was high at the active tillering and the booting stages in the first cropping season, whereas it was low at the transplanting and the ripening stages with an intermittent irrigation system. CH₄ emission was high at the transplanting stage in the second cropping season, and decreased gradually during rice cultivation. Daily temperature and light intensity increased gradually during rice growth in the first cropping season (February–June), while it was reversed in the second cropping season (August–December). The seasonal CH₄ emission from paddy fields ranged from 1.73 to 11.70 g m^–2, and from 10.54 to 39.50 g m^–2 in the first and second cropping seasons, respectively. The seasonal CH₄ emission in the second cropping season was higher than that in the first cropping season in all test fields. The seasonal CH₄ emission was 32.65 mg m^–2 in the first cropping season of the National Taiwan University paddy field with continuous flooding, and it was 28.85 mg m^–2 in the second cropping season. The annual CH₄ emission ranged from 12.3 to 49.3 g m^–2 with an intermittent irrigation system, and the value was 61.5 g m^–2 with a continuous flooding treatment. The annual CH₄ emission from paddy fields was estimated to be 0.034 Tg in 1997 from 364,212 ha of paddy fields with an intermittent irrigation system, which was less than the 0.241 Tg calculated by the IPCC method with a continuous flooding treatment Received: 23 February 2000     

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.     

小麦植株在麦田CH4交换中的作用及光照的影响

采用密闭箱/气相色谱法对中国科学院山东禹城实验站的麦田CH4通量进行观测,研究了土壤CH4通量、光照和遮光情况下的土壤-植物系统CH4通量,及植物、光照等因素对CH4通量的影响.试验采用小暗箱测定土壤CH4通量,采用暗箱和明箱测定土壤-植物系统CH4通量,同步观测了生物量、5 cm土壤温度、土壤水分及土壤NH4+含量.结果表明,麦田土壤和土壤-植物系统CH4通量均无明显的日变化,但季节变化显著;小麦的存在使土壤-植物系统CH4通量的季节波动加剧;小麦植株和光照促进麦田土壤-植物系统对CH4的吸收.此外,本研究发现在野外观测中,采用明箱覆盖土壤以及植物进行观测更能真实反映有植被覆盖的地表CH4通量状况.     

Is burial of wheat straw in ditches a way to reduce CH4 emissions from rice cultivation?

Abstract

Burial of wheat straw in ditches and incorporation of wheat straw are the two main ways of returning wheat straw prior to rice cultivation in China. To examine the effect of burying wheat straw in ditches on CH₄ emissions from rice cultivation, a field experiment was conducted at Yixing, Jiangsu, China in 2004. CH₄ flux was measured using a closed-chamber technique in three treatments (CK, no wheat straw application; WI, evenly incorporating 3.75 t ha^?1 wheat straw into the 0.1 m topsoil; WD, burying 3.75 t ha^?1 wheat straw in 0.14-m deep by 0.25-m wide ditches). Seasonal CH₄ emissions ranged from 49.7 to 218.4 kg CH₄ ha^?1. The application of wheat straw in these two ways significantly increased CH₄ emissions by 4.0-fold and 4.4-fold, respectively (P < 0.05). Although CH₄ flux from the non-ditch area in the WD treatment was as low as that in the CK treatment, it was counter-balanced by extremely high CH₄ flux from the ditch, which was approximately 6.0-fold as much as that from WI, leading to comparability between treatments WI and WD in total CH₄ emissions (P > 0.05). No significant difference was observed between the three treatments in grain yield (P > 0.05). The results indicated that burial of wheat straw in ditches is not a way to reduce CH₄ emission from rice cultivation.     

Methane production in unamended and rice-straw-amended soil at different moisture levels

 CH₄ production in an alluvial soil, unamended or amended with rice straw (1% w/w), was examined under nonflooded [–1.5 MPa, –0.01 MPa and 0 MPa (saturated) and flooded (1 : 1.25 soil to water ratio)] conditions during a 40-day incubation in closed Vacutainer tubes. CH₄ production was negligible at –1.5 MPa, but increased with an increase in the moisture level. Addition of rice straw distinctly increased CH₄ production in the soil at all moisture levels including –1.5 MPa. Evidence, in terms of the drop in redox potential and Fe²⁺ accumulated, suggested that the addition of rice straw hastened the reduction of the soil, even under nonflooded conditions; thus its addition stimulated even the nonflooded soil to produce CH₄ in substantial amounts. Our results indicate that many currently unidentified sources of CH₄, possibly including organic-amended nonflooded soils, may make a significant contribution to the global CH₄ budget. Received: 10 July 1997     

Increased moisture and methanogenesis contribute to reduced methane oxidation in elevated CO2 soils

Awareness of global warming has stimulated research on environmental controls of soil methane (CH₄) consumption and the effects of increasing atmospheric carbon dioxide (CO₂) on the terrestrial CH₄ sink. In this study, factors impacting soil CH₄ consumption were investigated using laboratory incubations of soils collected at the Free Air Carbon Transfer and Storage I site in the Duke Forest, NC, where plots have been exposed to ambient (370 μL L⁻¹) or elevated (ambient + 200 μL L⁻¹) CO₂ since August 1996. Over 1 year, nearly 90% of the 360 incubations showed net CH₄ consumption, confirming that CH₄-oxidizing (methanotrophic) bacteria were active. Soil moisture was significantly (p < 0.01) higher in the 25–30 cm layer of elevated CO₂ soils over the length of the study, but soil moisture was equal between CO₂ treatments in shallower soils. The increased soil moisture corresponded to decreased net CH₄ oxidation, as elevated CO₂ soils also oxidized 70% less CH₄ at the 25–30 cm depth compared to ambient CO₂ soils, while CH₄ consumption was equal between treatments in shallower soils. Soil moisture content predicted (p < 0.05) CH₄ consumption in upper layers of ambient CO₂ soils, but this relationship was not significant in elevated CO₂ soils at any depth, suggesting that environmental factors in addition to moisture were influencing net CH₄ oxidation under elevated CO₂. More than 6% of the activity assays showed net CH₄ production, and of these, 80% contained soils from elevated CO₂ plots. In addition, more than 50% of the CH₄-producing flasks from elevated CO₂ sites contained deeper (25–30 cm) soils. These results indicate that subsurface (25 cm+) CH₄ production contributes to decreased net CH₄ consumption under elevated CO₂ in otherwise aerobic soils.     

Reduced net atmospheric CH4 consumption is a sustained response to elevated CO2 in a temperate forest

We compared, from 2004 through 2006, rates of soil–atmosphere CH₄ exchange at permanently established sampling sites in a temperate forest exposed to ambient (control plots; ∼380 μL L⁻¹) or elevated (ambient + 200 μL L⁻¹) CO₂ since August 1996. A total of 880 observations showed net atmospheric CH₄ consumption (flux from the atmosphere to the soil) from all static chambers most of the time at rates varying from 0.02 mg m⁻² day⁻¹ to 4.5 mg m⁻² day⁻¹. However, we infrequently found net CH₄ production (flux from the soil to the atmosphere) at lower rates, 0.01 mg m⁻² day⁻¹ to 0.08 mg m⁻² day⁻¹. For the entire study, the mean (±SEM) rate of net CH₄ consumption in control plots was higher than the mean for CO₂-enriched plots, 0.55 (0.03) versus 0.51 (0.03) mg m⁻² day⁻¹. Annual rates of 184, 196, and 197 mg m⁻² for net CH₄ consumption at control plots during the three calendar years of this study were 19, 10, and 8% higher than comparable values for CO₂ enriched plots. Differences between treatments were significant in 2004 and 2005 and nearly significant in 2006. Volumetric soil water content was consistently higher at CO₂-enriched sites and a mixed-effects model identified a significant soil moisture x CO₂ interaction on net atmospheric CH₄ consumption. Increased soil moisture at CO₂-enriched sites likely increases diffusional resistance of surface soils and the frequency of anaerobic microsites supporting methanogenesis, resulting in reduced rates of net atmospheric CH₄ consumption. Our study extends our observations of reduced net atmospheric CH₄ consumption at CO₂-enriched plots to nearly five continuous years, suggesting that this is likely a sustained negative feedback to increasing atmospheric CO₂ at this site.     

Emissions of trace gases (CO2, CO,CH4, and N2O) resulting from rice straw burning

Emissions of trace gases (CO₂, CO, CH₄, N₂O) resulting from rice straw burning were measured by using the open chamber method. The carbon contained in rice straw was mainly released to the atmosphere as CO₂. The percentage of CO₂-C emitted in total C in rice straw was in the range of 57–81%, followed by CO-C (5–9%). The percentages of CH₄-C and N₂O-N in total C and N in rice straw were in the range of 0.43–0.90 and 1.16–1.50%, respectively. In the case of the rice straw which had been left in the field for a period of one month after harvest, emission of imperfect combustible gases such as CO and CH₄ during burning increased slightly, while that of perfect combustible gas, CO₂, was reduced. The amount of CH₄ emission from rice straw burning was comparable to that from paddy fields.     

太湖地区不同水旱轮作方式下稻季甲烷和氧化亚氮排放研究

为准确编制我国稻田温室气体排放清单及制定合理减排措施提供基础数据,选择太湖地区典型水稻种植区江苏省苏州市,研究设计了休闲水稻(对照,CK)、紫云英水稻(T1)、黑麦草水稻(T2)、小麦水稻(T3)和油菜水稻(T4)5种水旱轮作方式,采用静态箱气相色谱法,开展了不同水旱轮作方式下水稻生长季田间甲烷(CH4)和氧化亚氮(N2O)排放监测试验。试验结果表明:不同水旱轮作方式下水稻生长季CH4排放通量呈先升高后降低的变化趋势,CH4排放峰值出现在水稻生育前期,移栽至有效分蘖临界叶龄期CH4累积排放量占全生育期排放总量的比例为65%~81%,而N2O仅在水稻烤田期间有明显排放。水旱轮作方式对稻季CH4和N2O排放有极显著(P 0.01)影响,CH4季节总排放量表现为T1(283.2 kg.hm 2)CK(139.5 kg.hm 2)T3(123.4kg.hm 2)T4(114.7 kg.hm 2)T2(100.8 kg.hm 2),N2O季节总排放量顺序为T1 T4 T3 T2 CK,依次为1.06kg.hm 2、0.87 kg.hm 2、0.81 kg.hm 2、0.72 kg.hm 2和0.53 kg.hm 2。T1处理稻季排放CH4和N2O产生的增温潜势最高[7 396 kg(CO2).hm 2],显著(P 0.05)高于其他处理,比CK[3 646 kg(CO2).hm 2]增加103%,T2[2 735kg(CO2).hm 2]较CK减少25%(P 0.05)。紫云英水稻轮作方式增加了太湖地区水稻生长季的温室效应。     

Potential contribution of Lumbricus terrestris L. to carbon dioxide, methane and nitrous oxide fluxes from a forest soil

 Potential effects of earthworms (Lumbricus terrestris L.) inoculated into soil on fluxes of CO₂, CH₄ and N₂O were investigated for an untreated and a limed soil under beech in open topsoil columns under field conditions for 120 days. Gas fluxes from L. terrestris, beech litter and mineral soil from soil columns were measured separately in jars at 17  °C. The inoculation with L. terrestris and the application of lime had no effect on cumulative CO₂ emissions from soil. During the first 3–4 weeks earthworms significantly (P<0.05) increased CO₂ emissions by 16% to 28%. In contrast, significantly lower (P<0.05) CO₂ emission rates were measured after 11 weeks. The data suggest that earthworm activity was high during the first weeks due to the creation of burrows and incorporation of beech litter into the mineral soil. Low cumulative CH₄ oxidation rates were found in all soil columns as a result of CH₄ production and oxidation processes. L. terrestris with fresh feces and the beech litter produced CH₄ during the laboratory incubation, whereas the mineral soil oxidised atmospheric CH₄. Inoculation with L. terrestris led to a significant reduction (P<0.02) in the CH₄ oxidation rate of soil, i.e. 53% reduction. Liming had no effect on cumulative CH₄ oxidation rates of soil columns and on CH₄ fluxes during the laboratory incubation. L. terrestris significantly increased (P<0.001) cumulative N₂O emissions of unlimed soil columns by 57%. The separate incubation of L. terrestris with fresh feces resulted in rather high N₂O emissions, but the rate strongly decreased from 54 to 2 μg N kg^–1 (dry weight) h^–1 during the 100 h of incubation. Liming had a marked effect on N₂O formation and significantly (P<0.001) reduced cumulative N₂O emissions by 34%. Although the interaction of liming and L. terrestris was not significant, N₂O emissions of limed soil columns with L. terrestris were 8% lower than those of the control. Received: 2 September 1999     

Effect of intermittent drainage in reduction of methane emission from paddy soils in Hokkaido,northern Japan

ABSTRACT

Emission of methane (CH₄), a major greenhouse gas, from submerged paddy soils is generally reduced by introducing intermittent drainage in summer, which is a common water management in Japan. However, such a practice is not widely conducted in Hokkaido, a northern region in Japan, to prevent a possible reduction in rice grain yield caused by cold weather. Therefore, the effects of intermittent drainage on CH₄ emission and rice grain yield have not been investigated comprehensively in Hokkaido. In this study, we conducted a three-year field experiment in Hokkaido and measured CH₄ and nitrous oxide (N₂O) fluxes and rice grain yield to elucidate whether the reduction in CH₄ emission can be achieved in Hokkaido as well as other regions in Japan. Four experimental treatments, namely, two soil types [soils of light clay (LiC) and heavy clay (HC) textures] and two water management [continuous flood irrigation (CF), and intermittent drainage (ID)], were used, and CH₄ and N₂O fluxes were measured throughout the rice cultivation periods from 2016 to 2018. Cumulative CH₄ emissions in 2016 were markedly low, suggesting an initially low population of methanogens in the soils presumably due to no soil submergence or crop cultivation in the preceding years, which indicates a possible reduction in CH₄ emission by introducing paddy-upland crop rotation. Cumulative CH₄ emissions in the ID-LiC and ID-HC plots were 21–91% lower than those in the CF-LiC and CF-HC plots, respectively, whereas the cumulative N₂O emissions did not significantly differ between the different water managements. The amount of CH₄ emission reduction by the intermittent drainage was largest in 2018, with a comparatively long period of the first drainage for 12 days in summer. Rice grain yields did not significantly differ between the different water managements for the entire 3 years, although the percentage of well-formed rice grains was reduced by the intermittent drainage in 2018. These results suggest that CH₄ emission from paddy fields can be reduced with no decrease in rice grain yield by the intermittent drainage in Hokkaido. In particular, the first drainage for a long period in summer is expected to reduce CH₄ emission markedly.     

Carbon exchange in a freshwater marsh in the Sanjiang Plain, northeastern China

Northern wetlands are critically important to global change because of their role in modulating atmospheric concentrations of greenhouse gases, especially CO₂ and CH₄. At present, continuous observations for CO₂ and CH₄ fluxes from northern wetlands in Asia are still very limited. In this paper, two growing season measurements for CO₂ flux by eddy covariance technique and CH₄ flux by static chamber technique were conducted in 2004 and 2005, at a permanently inundated marsh in the Sanjiang Plain, northeastern China. The seasonal variations of CO₂ exchange and CH₄ flux and the environmental controls on them were investigated. During the growing seasons, large variations in net ecosystem CO₂ exchange (NEE) and gross ecosystem productivity (GEP) were observed with the range of −4.0 to 2.2 (where negative exchange is a gain of carbon from the atmosphere) and 0-7.6 g C m⁻² d⁻¹, respectively. Ecosystem respiration (RE) displayed relatively smooth seasonal pattern with the range of 0.8-4.2 g C m⁻² d⁻¹. More than 70% of the total GEP was consumed by respiration, which resulted in a net CO₂ uptake of 143 ± 9.8 and 100 ± 9.2 g C m⁻² for the marsh over the growing seasons of 2004 and 2005, respectively. A significant portion of the accumulated NEE-C was lost by CH₄ emission during the growing seasons, indicating the great potential of CH₄ emission from the inundated marsh. Air temperature and leaf area index jointly affected the seasonal variation of GEP and the seasonal dynamic of RE was mainly controlled by soil temperature and leaf area index. Soil temperature also exerted the dominant influence over variation of CH₄ flux while no significant relationship was found between CH₄ emission and water table level. The close relationships between carbon fluxes and temperature can provide insights into the response of marsh carbon exchange to a changing climate. Future long term flux measurements over the freshwater marsh ecosystems are undoubtedly necessary.     

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.