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An experiment was undertaken to investigate the effect of white clover inclusion in grass swards (GWc) compared with grass-only (GO) swards receiving high nitrogen fertilization and subjected to frequent and tight grazing on herbage and dairy cow productivity and enteric methane (CH4) emissions. Thirty cows were allocated to graze either a GO or GWc sward (n = 15) from April 17 to October 31, 2011. Fresh herbage [16 kg of dry matter (DM)/cow] and 1 kg of concentrate/ cow were offered daily. Herbage DM intake (DMI) was estimated on 3 occasions (May, July, and September) during which 17 kg of DM/cow per day was offered (and concentrate supplementation was withdrawn). In September, an additional 5 cows were added to each sward treatment (n = 20) and individual CH4 emissions were estimated using the sulfur hexafluoride (SF6) technique. Annual clover proportion (±SE) in the GWc swards was 0.20 ± 0.011. Swards had similar pregrazing herbage mass (1,800 ± 96 kg of DM/ha) and herbage production (13,110 ± 80 kg of DM/ha). The GWc swards tended to have lower DM and NDF contents but greater CP content than GO swards, but only significant differences were observed in the last part of the grazing season. Cows had similar milk and milk solids yields (19.4 ± 0.59 and 1.49 ± 0.049 kg/d, respectively) and similar milk composition. Cows also had similar DMI in the 3 measurement periods (16.0 ± 0.70 kg DM/cow per d). Similar sward and animal performance was observed during the CH4 estimation period, but GWc swards had 7.4% less NDF than GO swards. Cows had similar daily and per-unit-of-output CH4 emissions (357.1 ± 13.6 g of CH4/cow per day, 26.3 ± 1.14 g of CH4/kg of milk, and 312.3 ± 11.5 g of CH4/ kg of milk solids) but cows grazing GWc swards had 11.9% lower CH4 emissions per unit of feed intake than cows grazing GO swards due to the numerically lower CH4 per cow per day and a tendency for the GWc cows to have greater DMI compared with the GO cows. As a conclusion, under the conditions of this study, sward clover content in the GWc swards was not sufficient to improve overall sward herbage production and quality, or dairy cow productivity. Although GWc cows had a tendency to consume more and emitted less CH4 per unit of feed intake than GO cows, no difference was observed in daily or per-unit-of-output CH4 emissions. [ABSTRACT FROM AUTHOR]

Abstract: Methane and nitrous oxide emissions, their global warming potential, carbon efficiency ratio and related biogeochemical properties of a tropical soil planted to rice were investigated under different N management [i.e. urea-N (120kgN ha−1), rice straw (RS) (30kgN ha−1)+urea-N (90kgN ha−1), compost (C) (30kgN ha−1)+urea-N (90kgN ha−1) and poultry manure (PM) (30kgN ha−1)+urea-N (90kgN ha−1)]. CH4 fluxes were increased by 82.7%, 65.1%, 63.4% and 31.9% in RS+urea-N, C+urea-N, PM+urea-N and urea-N, respectively whereas percentage increase in cumulative N2O emission was 390.6, 371.8, 315.6, and 253.1 in PM+urea-N, urea-N, C+urea-N and RS+urea-N, respectively over control (no fertilizer amendment). However, increase of GWPs in different manure+urea-N over that of control were 85.5%, 69.2%, 68.8% and 37.6% in RS+urea-N, C+urea-N, PM+urea-N and urea-N, respectively. Microbial biomass carbon (MBC), readily mineralizable carbon (RMC) and fluorescence diacetate (FDA) hydrolysis activity were significantly affected by integrated N-management and followed the order of C+urea-N>PM+urea-N>RS+urea-N>urea-N>control. With considerably high microbial biomass C and microbial activity, high C efficiency ratio, high yield and low greenhouse gas intensity, C+urea-N could be a better option to mitigate CH4 and N2O emissions and to maintain soil biological quality and yield in tropical paddy. [Copyright &y& Elsevier]

Application of fine-textured and Ca-rich fly ash may be helpful in enhancing soil carbon content via protecting soil organic C (SOC) by organo-mineral complexation and via reducing CO2 emission by carbonation (e.g. formation of CaCO3). However, very limited information is available on the effects of fly ash application on gases loss of C and soil C content. In this study, to estimate the potential use of fly ash as a soil amendment for SOC enhancement purposes, the effects of fly ash application (0, 5, and 10 w/w %) on microbial biomass C (MBC), CH4 and CO2 emissions, and on soil C content were investigated. A 60-days incubation experiment was conducted with an acidic soil in the presence of organic input (pig manure compost, PMC; hairy vetch, HV) with contrasting substrate quality under changing water regime from water-logged to unsaturated via a transition period. Fly ash application did not affect MBC under water-unsaturated conditions, but reduced (P < 0.01) microbial growth under water-logged conditions, probably due to the increased solubility of a certain toxic element such as arsenic under the anaerobic conditions. Across the 60 days of incubation, the CO2 emission was reduced by fly ash regardless of organic input by 20.5-41.3%; meanwhile, a decline of CH4 emission by fly ash application was significant (P < 0.05) only in the HV treatment. Overall, fly ash application slowed down gases C loss and increased soil C content, probably due to the retardation of CH4 and CO2 emission as well as the addition of C contained in the fly ash. Biochemical (inhibition of microbial activity), chemical (formation of CaCO3 via carbonation), and physical (restriction of gas diffusion) mechanisms were suggested for the fly ash effects. [ABSTRACT FROM AUTHOR]

Methane (CH 4) is one of the dominant greenhouse gases (GHG) that is largely emitted from rice fields and thus, significantly contributes to global warming. Significant efforts have been made to find out suitable strategies to mitigate CH 4 emission from rice culture. However, the effectiveness of these management practices is often diverse with negative, no, or positive impacts making it difficult to adopt under a particular condition. The diversity of rice cultivation in terms of agro-climatic conditions and cultivation practices makes it difficult for providing specific recommendations. Here, we collected data from a total of 198 studies reporting 1052 observations. The management practices are categorized into five different management practices i.e. , water, organic and inorganic fertilizer management, crop establishment method, and agronomic practices while major categories were subdivided into different classes. To test statistically significant differences in the effectiveness between major management practices, an analysis of variance (ANOVA) was applied. The Gaussian and bootstrapping model were applied to find out the best estimate of the effectiveness of each practice. In addition, mechanisms controlling the CH 4 emission reductions were synthesized. Next, the adoption potentials of these practices were assessed based on the existing rice cultivation systems in Bangladesh. Our results showed that water and organic matter management were the most effective methods irrespective of the growing conditions. When these technologies are customized to Bangladesh, water management and crop establishment methods seem most feasible. Among the rice-growing seasons in Bangladesh, there is a larger scope to adopt these management practices in the Boro season (December to May), while these scopes are minimal in the other two seasons due to their rain-fed nature of cultivation. Altogether, our study provides fundamental insights on CH 4 reductions strategies from rice fields in Bangladesh. [Display omitted] • Methane emission from rice fields depends on growing conditions with implications for the adoption of location-specific agronomic management practices. • Meta-data analysis revealed that water, tillage, and fertilizer management practices are the most effective for CH 4 emission reduction. • Among the CH 4 reduction practices, water management and crop establishment methods seems most adoptable for Bangladesh. • Among rice growing seasons, there are larger scopes to adopt CH 4 reduction practices in Boro season. [ABSTRACT FROM AUTHOR]

Abstract: A pot experiment was performed to learn the differences in plant productivity and CH4 emission between two rice cultivars, super rice variety Ningjing 1 and traditional variety Zhendao 11, which were currently commercially applied in Nanjing, China. Similar seasonal changes of CH4 emission fluxes and soil solution CH4 contents were found between the tested cultivars. Although there was no significant difference in plant biomass production between the cultivars, the grain yield of Ningjing 1 was significantly higher by 35.0% (P < 0.05) than that of Zhendao 11, whereas the total CH4 emission from Ningjing 1 was 35.2% lower (P < 0.05). The main difference in the amounts of CH4 emission between the cultivars occurred in the period from the tillering stage to the heading stage. The biomass-scaled and yield-scaled CH4 emissions were respectively 3.8 and 5.2 mg/g for Ningjing 1, significantly lower than those for Zhendao 11 (7.4 and 12.8 mg/g, respectively). According to the relationships between the plant growth characteristics and the CH4 emission, a stronger root system contributed mainly to the lower CH4 emission of Ningjing 1, as compared with Zhendao 11. Our results demonstrated that super rice has advantages not only in grain productivity but also in CH4 emission mitigation. Further expansion of super rice cropping will enhance rice yield and reduce greenhouse gas emission in China. [Copyright &y& Elsevier]

Highlights: [•] Longer vetch cultivation increased nitrogenase activity of nodules. [•] It leads to the higher NO3-N content and enhanced N2O emission from rice paddy soil. [•] Harvesting vetch after 197 days significantly enhanced GWP during rice cultivation. [ABSTRACT FROM AUTHOR]

The objectives of this study were to clarify the effect of chemical fertilizer and manure application on methane (CH4) and nitrous oxide (N2O) emissions from intensively managed grassland on Andosols in Japan and to determine the controlling factors of the CH4and N2O emissions. The emission factors (EF) for both fertilizer- and manure-induced N2O emissions were calculated. Three experimental plots were set up in five grasslands across four climatic regions in Japan: one plot for treatment with chemical fertilizer (fertilizer plot); another plot for treatment with cattle manure and chemical fertilizer (manure plot), and the final plot was not treated with chemical fertilizer or manure (control plot). The type of chemical fertilizer was ammonium-based fertilizer or a combination fertilizer of ammonium and urea. CH4and N2O emissions were measured at the study sites for six years. For the manure plot, a supplement of chemical fertilizer was added to equalize the supply rate of mineral nitrogen (N) relative to that of the fertilizer plots. There were no significant differences in CH4emissions among the treatment plots, and the effect of fertilizer or manure application was not evident. CH4emissions tended to be larger at sites with higher soil moisture content. The application of chemical fertilizer or manure increased N2O emissions at all the sites, and there were significant differences among the sites and across different years. Background N2O emissions (N2O emissions at the control plot) had strong positive correlations with air temperature and precipitation, along with weak positive correlations with soil carbon and N content. Therefore, an empirical model (Background N2O emission = 0.298 × air temperature + 0.512 × soil N content −3.77) was established. Fertilizer-induced N2O emission factor (EF) had a positive correlation (R2 = 0.50,p < 0.01) with precipitation (Fertilizer-induced EF = 0.0022 × precipitation −1.3), and increasing precipitation enhanced N2O production through the denitrification process due to applied fertilizer N. There were no significant differences in manure-induced EFs among the sites, and the average was 0.36% except for an outlier. [ABSTRACT FROM PUBLISHER]

Abstract: Plants play an important role in CH4 emissions from wetlands. Vascular plants transport CH4 from the anaerobic zone to the atmosphere through their aerenchyma, thereby bypassing the aerobic zone and strongly increasing CH4 emission rates. However, most studies of the effect of plants on wetland CH4 emissions are based on observations made during the growing seasons. The effects in non-growing seasons are still unclear. In this study, we conducted a clipping experiment to investigate the effects of plants on CH4 emissions from a temperate marsh in the growing and non-growing seasons. The results show that the influence of plants on CH4 emissions from the wetland varied among different seasons. Plant-mediated CH4 accounted for 38% of the total fluxes in the plant-growing season. After the growing season, whether the plants transported CH4 from the soil to the atmosphere in situ was determined by the involved environmental conditions. In autumn, the plants did not transport CH4. This is because the CH4 diffused easily in the soil and water, rather than via the plants'' organs. In the surface soil freezing period, CH4 diffusion was blocked and accumulated under the frozen surface. The highly concentrated CH4 in the pore water was compelled to enter the organs of the plants and diffused by them. The ‘passive diffusion’ via plants transported 84% of the total CH4 emissions during this period. Nonetheless, the plants did not transport CH4 again in the deep soil freezing season. By synthesizing our data together with previous studies, we suggested that this is because the frozen soil layer was deep enough in this period to exceed the depth horizon of the plants'' roots and the CH4 in free water could not enter the plants'' organs. [Copyright &y& Elsevier]

Abstract: Paddy fields are one of the largest anthropogenic sources of global CH4 emission. A decrease in paddy CH4 emission can contribute significantly towards the control of global warming. Recent studies have demonstrated that the application of biochar in paddy soils has such a capability, but its underlying mechanism has yet to be elucidated. In this investigation, we studied CH4 emission, methanogenic archaeal, as well as methanotrophic proteobacterial communities, from microcosms derived from two paddy soils, Inceptisol and Ultisol. Both soils were amended with biochar at different pyrolysis temperatures (300 °C, 400 °C and 500 °C) at field condition. The soil CH4 flux was monitored across whole rice season in 2010; the functional guilds communities were analyzed by PCR–DGGE and real-time quantitative PCR (qPCR). It is found that paddy CH4 emissions significantly decreased under biochar amendments, which, interestingly, didn''t result from the inhibition of methanogenic archaeal growth. qPCR further revealed that biochar amendments (1) increased methanotrophic proteobacterial abundances significantly, and (2) decreased the ratios of methanogenic to methanotrophic abundances greatly. These results shed insight on the underlying mechanism of how biochar decreases paddy CH4 emission. This knowledge can be applied to develop a more effective greenhouse gas mitigation process for paddy fields. [Copyright &y& Elsevier]

Abstract: To simulate climate change impacts on pastures and domestic herbivores as well as feedbacks to the atmosphere in terms of greenhouse gas emissions, we have improved a process-based biogeochemical pasture model, PaSim. The overall aim was to simulate the meat and milk production of cattle (suckler cows with their calves, dairy cows and heifers) in response to climate and management, as well as feedbacks to the atmosphere through enteric methane emissions. Herbage intake at grazing was calculated from animal characteristics, herbage availability, diet digestibility and air temperature. With suckler cows, milk production and changes in daily liveweight and body condition were calculated from net energy balance. The net energy intake of dairy cows and their body reserves at turnout to pasture were used to simulate milk production at pasture, daily liveweight and body condition changes, taking into account cow energy requirements and intake capacity. Heifer growth was determined from heifer net energy intake and liveweight. Net energy intake was used to assess enteric methane production through a conversion factor, which depends both on the energy level of the diet and on the herbivore type. The model was assessed against experimental data for animal performance and methane emissions at grazing. Predictions show good agreement with observations. On average, the root mean square error was 6.5, 4 and 2.5% for the liveweights of suckler cows, suckler calves and heifers, respectively, 18% for dairy milk production and 12% for enteric methane emissions. By comparing this new version of the PaSim model to the previous version, we show that a greater accuracy in animal performance modelling improves the sensitivity of the model to interannual climate variability. However, long term (30 years) projections of climate change impacts on grasslands and of radiative feedbacks to the atmosphere are not significantly modified. The originality and the validity domain of the model are discussed. [Copyright &y& Elsevier]

Abstract: Combination of divergent active principles to achieve broad-spectrum control is gaining popularity to manage the weed menace in intensive agriculture. However, such application could have non-target impacts on the soil processes affecting soil ecology and environmental interactions. A field experiment was conducted to investigate the impact of separate and combined applications of herbicides bensulfuron methyl and pretilachlor on the emission of N2O and CH4, and related soil and microbial parameters in a flooded alluvial field planted to rice cv Lalat. Single application of the herbicide bensulfuron methyl or pretilachlor resulted in a significant reduction of N2O and CH4 emissions while the combination of these two herbicides distinctly increased N2O and CH4 emissions. Cumulative N2O emissions (kg N2O–N) followed the order of bensulfuron methyl (0.35kgha−1)

To establish energetically and environmentally viable paddy rice-based bioethanol production systems in northern Japan, it is important to implement appropriately selected agronomic practice options during the rice cultivation step. In this context, effects of rice variety (conventional vs. high-yielding) and rice straw management (return to vs. removal from the paddy field) on energy inputs from fuels and consumption of materials, greenhouse gas emissions (fuel and material consumption-derived CO2 emissions as well as paddy soil CH4 and N2O emissions) and ethanol yields were assessed. The estimated ethanol yield from the high-yielding rice variety, “Kita-aoba” was 2.94 kL ha−1, a 32% increase from the conventional rice variety, “Kirara 397”. Under conventional rice production in northern Japan (conventional rice variety and straw returned to the paddy), raising seedlings, mechanical field operations, transportation of harvested unhulled brown rice and consumption of materials (seeds, fertilizers, biocides and agricultural machinery) amounted to 28.5 GJ ha−1 in energy inputs. The total energy input was increased by 14% by using the high-yielding variety and straw removal, owing to increased requirements for fuels in harvesting and transporting harvested rice as well as in collecting, loading and transporting rice straw. In terms of energy efficiency, the variation among rice variety and straw management scenarios regarding rice varieties and rice straw management was small (28.5–32.6 GJ ha−1 or 10.1–14.0 MJ L−1). Meanwhile, CO2-equivalent greenhouse gas emissions varied considerably from scenario to scenario, as straw management had significant impacts on CH4 emissions from paddy soils. When rice straw was incorporated into the soil, total CO2-equivalent greenhouse gas emissions for “Kirara 397” and “Kita-aoba” were 25.5 and 28.2 Mg CO2 ha−1, respectively; however, these emissions were reduced notably for the two varieties when rice straw was removed from the paddy fields in an effort to mitigate CH4 emissions. Thus, rice straw removal avers itself a key practice with respect to lessening the impacts of greenhouse gas emissions in paddy rice-based ethanol production systems in northern Japan. More crucially, the rice straw removed is available for ethanol production and generation of heat energy with a biomass boiler, all elements required for biomass-to-ethanol transformation steps including saccharification, fermentation and distillation. This indicates opportunities for further improvement in energy efficiency and reductions in greenhouse gas emissions under whole rice plant-based bioethanol production systems. [Copyright &y& Elsevier]

Few investigations have been made on the impact of elevated ozone (O) concentration on methane (CH) emission from rice paddies. Using open-top chambers in situ with different O treatments, CH emissions were measured in a rice paddy in Yangtze River Delta, China in 2007 and 2008. There were four treatments applied: charcoal-filtered air (CF), nonfiltered air (NF), and charcoal-filtered air with different O additions (O-1 and O-2). The mean O concentrations during the O fumigation were 19.7, 22.6, 69.6 and 118.6 ppb in 2007 and 7.0, 17.4, 82.2 and 138.3 ppb in 2008 for treatments CF, NF, O-1 and O-2, respectively. The rice yields, as compared with CF, were reduced by 32.8% and 37.1%, 58.3% and 52.1% in treatments O-1 and O-2 in 2007 and 2008, respectively. The diurnal patterns of CH emission varied temporally with treatments and there was inconsistence in diurnal variations in CH emissions from the paddy field. The daily mean CH emissions were significantly lower in treatments O-1 and O-2 than those in treatments CF and NF. Compared with CF treatment, CH emissions from the paddy field were decreased to 46.5% and 38.3%, 50.6% and 46.8% under treatments O-1 and O-2 in the whole growing seasons of 2007 and 2008, respectively. The seasonal mean CH emissions were negatively related with AOT40 (accumulative O concentration above 40 ppb; P < 0.01 in both years), but positively related to the relative rice yield (reference to CF; P < 0.01 in 2007 and P < 0.001 in 2008), aboveground biomass ( P < 0.01 in both years) and underground biomass ( P < 0.01 in 2007 and P < 0.05 in 2008). The decreased CH emission from the rice paddy due to an increased O exposure might partially mitigate the global warming potential induced by soil carbon loss under elevated O concentrations. [ABSTRACT FROM AUTHOR]

Field and incubation experiments were conducted during 2007-2009 to study the effect of drainage in the fallow season on CH production and emission from permanently flooded rice fields. It was found that drainage in the fallow season significantly affected the temporal variations of CH production and emission from permanently flooded rice fields. CH production and emission from permanently flooded rice fields (Treatment FF) mainly occurred during the rice season, where they were found to be much lower in the late fallow season. No CH flux was detected from drained fields (Treatment DF) in the fallow season. Compared with Treatment FF, Treatment DF was delayed not only its onset of CH production and emission, but also appearance of the highest peak of CH production during the rice season. A significant positive relationship was observed between CH production rates of paddy soil and corresponding CH fluxes ( P < 0.01). CH production in rice roots was the highest in rate at the rice booting stage, but was obviously lower at the rice tillering, grain filling and ripening stages, and the highest value reached at the same time as the peak of CH production occurred in the paddy soil. Drainage in the fallow season significantly decreased CH production and emission from Treatment FF. Compared with Treatment FF, Treatment DF was about 42-61% lower in mean CH production rate in the paddy soil during the rice season, and was reduced by approximately 56% in mean CH production rate in rice roots. Accordingly, Treatment DF was 20.6-30.2 g CH m, 39-52% lower than Treatment FF in total CH emission during the rice season, and 44-57% lower in annual total CH emission. Rice yield in Treatment DF tended to be 4-7% lower than that in Treatment FF. [ABSTRACT FROM AUTHOR]

Abstract: A field trial was performed to investigate the effect of biochar at rates of 0, 10 and 40tha−1 on rice yield and CH4 and N2O emissions with or without N fertilization in a rice paddy from Tai Lake plain, China. The paddy was cultivated with rice (Oryza sativa L., cv. Wuyunjing 7) under a conventional water regime. Soil emissions of CH4 and N2O were monitored with a closed chamber method throughout the whole rice growing season (WRGS) at 10 day intervals. Biochar amendments of 10tha−1 and 40tha−1 increased rice yields by 12% and 14% in unfertilized soils, and by 8.8% and 12.1% in soils with N fertilization, respectively. Total soil CH4-C emissions were increased by 34% and 41% in soils amended with biochar at 40tha−1 compared to the treatments without biochar and with or without N fertilization, respectively. However, total N2O emissions were sharply decreased by 40–51% and by 21–28%, respectively in biochar amended soils with or without N fertilization. The emission factor (EF) was reduced from 0.0042kgN2O-Nkg−1 N fertilized with no biochar to 0.0013kgN2O-Nkg−1 N fertilized with biochar at 40tha−1. The results show that biochar significantly increased rice yields and decreased N2O emission, but increased total CH4 emissions. Summary calculations based on this experiment data set provide a basis for estimating the potential reductions in GHG emissions that may be achieved by incorporating biochar into rice paddy soils in south-eastern China. [ABSTRACT FROM AUTHOR]

This study quantified spatiotemporal patterns of CH4 and N2O emissions from livestock and poultry production in Turkey between 1961 and 2007. CH4(enteric) (from enteric fermentation), CH4(manure) (from manure management), and N2O(AWM) (from animal waste management) emissions in Turkey were estimated at 1,164, 216, and 55 Gg in 1961 and decreased to 844, 187, and 39 Gg in 2007, contributing a share of roughly 2% to the global livestock-related CH4 emissions and %1.5 to the global N2O(AWM) emissions, respectively. Total CO2-eq emissions were estimated at 50.7 Tg in 1961 and declined from a maximum value of 60.7 Tg in 1982 to a minimum value of 34.5 Tg in 2003, with a mean emission rate of 48 Tg year − 1 due to a significant reduction in the number of ruminant livestock. The highest mean share of emissions belonged to West Black Sea (14% and 16%) for CH4(enteric) and CH4(manure) and to North East Anatolia (12% and %13) for N2O(AWM) and total CO2-eq emissions, respectively. The highest emission density was 1.7 Mg km − 2 year − 1 for CH4(enteric), 0.3 Mg km − 2 year − 1 for CH4(manure), and 0.07 Mg km − 2 year − 1 for the total CO2-eq emissions in the West and North East Anatolia regions and 0.09 Mg km − 2 year − 1 for N2O(AWM) in the East Marmara region. Temporal and spatial variations in CH4(enteric), CH4(manure), and N2O(AWM) emissions in Turkey were estimated using regression models and ordinary kriging at a 500-m resolution, respectively. [ABSTRACT FROM AUTHOR]

Although invasions by non-native species represent a major threat to biodiversity and ecosystem functioning, little attention has been paid to the potential impacts of these invasions on methane (CH4) emission and its 13C-CH4-isotope signature in salt marshes. An invasive perennial C4 grass Spartina alterniflora has spread rapidly along the east coast of China since its introduction from North America in 1979. Since its intentional introduction to the Jiuduansha Island in the Yangtze River estuary in 1997, S. alterniflora monocultures have become the dominant component of the Jiuduansha’s vegetation, where monocultures of the native plant Scirpus mariqueter (a C3 grass) used to dominate the vegetation for more than 30 years. We investigated seasonal variation in soil CH4 emission and its 13C-CH4-isotope signature from S. alterniflora and S. mariqueter marshes. The results obtained here show that S. alterniflora invasion increased soil CH4 emissions compared to native S. mariqueter, possibly resulting from great belowground biomass of S. alterniflora, which might have affected soil microenvironments and /or CH4 production pathways. CH4 emissions from soils in both marshes followed similar seasonal patterns in CH4 emissions that increased significantly from April to August and then decreased from August to October. CH4 emissions were positively correlated with soil temperature, but negatively correlated with soil moisture for both S. alterniflora and S. mariqueter soils (p < 0.05). The δ13C values of CH4 from S. alterniflora, and S. mariqueter soils ranged from -39.0‰ to -45.0‰, and -37.3‰ to -45.7‰, respectively, with the lowest δ13C values occurring in August in both marshes. Although the leaves, roots and soil organic matter of S. alterniflora had significantly higher δ13C values than those of S. mariqueter, S. alterniflora invasion did not significantly change the 13C- isotopic signature of soil emitted CH4 (p > 0.05). Generally, the CH4 emissions from both invasive S. alterniflora and native S. mariqueter soils in the salt marshes of Jiuduansha Island were very low (0.01–0.26 mg m-2 h-1), suggesting that S. alterniflora invasion along the east coast of China may not be a significant potential source of atmospheric CH4. [ABSTRACT FROM AUTHOR]

Abstract: A 3-year field experiment was conducted in Jiangsu Province, China from 2004 to 2006 to investigate CH4 and N2O emissions from paddy fields as affected by various wheat straw management practices prior to rice cultivation. Five methods of returning wheat straw, no straw, evenly incorporating, burying straw, ditch mulching and strip mulching, were adopted in the experiment. Evenly incorporating is the most common management practice in the region. Results showed that compared with no straw, evenly incorporating increased CH4 emission significantly by a factor of 3.9–10.5, while decreasing N2O emission by 1–78%. Methane emission from burying straw was comparable with that from evenly incorporating, while N2O emission from burying straw was 94–314% of that from evenly incorporating. Compared with evenly incorporating, CH4 emission was decreased by 23–32% in ditch mulching and by 32% in strip mulching, while N2O emission was increased by a factor of 1.4–3.7 in ditch mulching and by a factor of 5.1 in strip mulching. During the rice-growing season, the emitted N2O was negligible compared to that of emitted CH4. No significant difference in grain yield was observed between ditch mulching, burying straw, evenly incorporating and no straw. Compared with no straw, the grain yield was increased by 27% in strip mulching. Based on these results, the best management practice for returning wheat straw to the soil is strip mulching wheat straw partially or completely onto the field surface, as the method reduced CH4 emission from rice fields with no decrease in rice yield. [Copyright &y& Elsevier]

• The addition of fuel reforming gas simultaneously reduced NO X and HC emissions from natural gas engines. • CO emissions showed a trade-off to NOx and HC emission. • The addition of fuel reforming gas showed no damage of economic performance of the engine. • A promising on-board fuel reforming scheme for vehicles was proposed. Combustion, emission characteristics and the economic performance of a heavy-duty natural gas engine blended with different ratios of reformed gas were investigated, and the feasibility of applying the fuel partial oxidation catalytic reforming system on a heavy-duty natural gas engine was discussed. Experimental results showed that the use of Rh/γ-Al 2 O 3 as a catalyst of partial oxidation reaction of natural gas fuel requires low initial reaction inlet gas temperature, and it has good catalytic performance and durability, which makes it feasible to be applied on vehicles. Blending with reformed gas from partial oxidation reaction significantly reduces NO X and CH 4 emission and effectively reduces coefficient of variance of peak pressure. In additions, no significant change in fuel consumption was observed after blending with reformed gas, while CO emissions increased. In general, the combination of on-board fuel partial oxidation catalytic reforming system to improve the performance of natural gas engines has good prospects. [ABSTRACT FROM AUTHOR]

• Afforestation increases soil methane uptake compared to contiguous herbaceous land. • Maximum methane uptake driven by afforestation varies with stand age and density. • Afforestation effect on soil methane fluxes was mediated by their effect on soil water balance. • Modifying rotation time and stand stocking, afforestation may increase its potential as a CH 4 sink. Evidence suggests that tree plantations change soil methane (CH 4) fluxes (magnitude and/or direction of the fluxes) compared to herbaceous land (i.e. afforestation effect) due to the effect of trees increasing methanotroph bacteria abundance and enhancing soil gas diffusivity. However, the magnitude of this afforestation effect is highly variable across studies. Here, we evaluated whether the variation in the afforestation effect depends on forestry management strategies, described by stand age and density, as well as taxonomic identity of the tree species, and the interaction with climatic conditions. To this end, we conducted a meta -analysis using 47 paired samples of afforested and contiguous herbaceous land from 14 studies located in different biomes worldwide. We found that afforestation predominantly increases the capacity of soil net CH 4 uptake (i.e. more negative fluxes) compared to herbaceous land, but the magnitude of this effect was highly heterogeneous across paired samples. This heterogeneity was explained by environmental conditions, but significant effects of forest stand age and density were also found proving the importance of forest management on this ecological service. Soil net CH 4 uptake following afforestation increases with increasing stand age. Although the stand stocking effect could be tested with a limited number of studies (24 out of the 47 paired samples), the results suggest that net CH 4 uptake decreases with tree stocking (stand density) in the range of values up to 1500 individuals per ha. No change in CH 4 fluxes was observed above this high stand density. Contrary to our expectations, no effect of taxonomic identity of the trees considering the most planted genera (Pinus and Eucalyptus) was observed in the average soil CH 4 fluxes. Furthermore, a significant correlation between the afforestation effect on soil water content and CH 4 flux suggests that the most plausible cause of the increased soil net CH 4 uptake is driven by the forest impact on soil desiccation, which in turn increases in sites with higher water limitation (i.e. higher potential evapotranspiration and high temporal rainfalls variations within the ranges of the available studies). Finally, our study provides evidence that by modifying rotation time and stand stocking, afforested land may increase its environmental service as a sink of atmospheric CH 4. [ABSTRACT FROM AUTHOR]

Coastal wetlands play an important role in nitrogen removal and are a vital blue carbon sink. The produced methane (CH 4) in coastal wetlands has been recently identified as a possible carbon source for denitrification process, providing a significant contribution to coastal nitrogen cycling. However, the in-situ correlation between CH 4 emissions and denitrification rate, as well as their coupling mechanism is still unclear. Here, we investigated the nitrogen removal pattern throughout a complete tidal cycle, quantified the in-situ linkage between CH 4 emissions and denitrification rate, and explored the associated microbial mechanisms in the eutrophic coastal wetland. The results showed that (1) the removal of nitrogen was driven by the tidal cycle (marsh flooding and drying), which involved two processes - physical interception and microbial denitrification; (2) the denitrification rate was linearly positively correlated to the CH 4 emission (R2 = 0.87, p < 0.0001); (3) nitrite- and nitrate-dependent denitrifying anaerobic methane oxidation (DAMO) coexisted in the wetland sediment, and promoted nitrogen removal by utilizing CH 4 as the carbon source for denitrification. Our findings suggested that CH 4 emission could enhance denitrification via DAMO in the field, and deepened the understanding of the dynamic nitrogen removal process within eutrophic coastal wetlands, and further indicated a strong interaction between coastal carbon and nitrogen cycling. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted to investigate CH4 emissions from a sandy paddy soil as influenced by rice cultivars and atmospheric CO2 elevation. The experiment with two CO2 levels, 370 μL L−1 (ambient) and 570 μL L−1 (elevated), was performed in a climatron, located at the National Institute for Agro-Environmental Sciences, Tsukuba, Japan. Four rice cultivars were tested in this experiment, including IR65598, IR72, Dular and Koshihikari. Tiller number, root length and grain yield were clearly larger under elevated CO2 than under ambient CO2. IR72 and Dular showed significantly higher tiller number, root length and grain yield than Koshihikari and IR65598. Average daily CH4 fluxes under elevated CO2 were significantly larger by 10.9–23.8% than those under ambient CO2, and varied with the cultivars in the sequence Dular ≧ IR72>IR65598 ≧ Koshihikari. Dissolved organic C (DOC) content in the soil was obviously higher under elevated CO2 than under ambient CO2 and differed among the cultivars, in the sequence IR72>Dular>Koshihikari>IR65598. The differences in average daily CH4 fluxes between CO2 levels and among the cultivars were related to different root exudation as DOC content, root length and tiller number. This study indicated that Koshihikari should be a potential cultivar for mitigating CH4 emission and simultaneously keeping stable grain yield, because this cultivar emitted lowest CH4 emission and produced medium grain yield. [ABSTRACT FROM AUTHOR]

Abstract: The wetlands play an important role in carbon storage, especially at high latitudes, at which they store nearly one-third of global soil carbons. However, few studies have investigated the emissions of CO2, CH4 and N2O in the long-term, especially effects of freeze–thaw cycles on these gases emissions in freshwater marsh ecosystems. In this paper, we collected greenhouse gas emission data from a freshwater marsh area in China for 4 years, evaluated their release variables and speculated on their potential atmospheric impact. For this paper, we report on the CO2, CH4 and N2O emission rates recorded from June 2002 to November 2005 in the Sanjiang Plain of northeast China. We measured their interannual variations and fluctuations, as well as factors affecting their emissions, and estimated their regulation and freeze–thaw cycle impacts. Our results revealed obvious CO2 and CH4 emission fluctuations during the winter months, and during the freeze–thaw cycle, and a strong interannual variation during the growing season. Overall, we documented a close relationship between the CO2 and CH4 emissions, implicating some regulatory commonality. We determined that the marsh was a N2O sink during the winter, but a significant source of N2O during the freeze–thaw cycle as the temperature increased, especially in early summer. During the thaw–freeze period, the N2O levels were positively correlated with the water depth. Additionally, water depth greatly governed the interannual variation of the N2O emissions from the marshes during the thaw–freeze period. [Copyright &y& Elsevier]

Abstract: We measured methane (CH4) emissions from the stem surfaces of mature Fraxinus mandshurica var. japonica trees in a floodplain forest. Flux measurements were conducted almost monthly from May to October 2005, and positive CH4 fluxes were detected throughout the study period, including the leafless season. The mean CH4 flux was 176 and 97μgCH4 m−2 h−1 at the lower (15cm above the ground) and upper (70cm above the ground) stem positions, respectively. The CH4 concentration was lower in soil gas than in ambient air to a depth of at least 40cm. One possible source of CH4 emitted from the stems might be the dissolved CH4 in groundwater; maximum concentrations were 10,000 times higher than atmospheric CH4 concentrations. Our results suggest that CH4 transport from the submerged soil layer to the atmosphere may occur through internal air spaces in tree bodies. [Copyright &y& Elsevier]

Abstract: In this paper, CH4 flux was measured from Nov. 2002 to Oct. 2005, to estimate CH4 emissions in winter and during freeze–thaw period, and interannual variation in CH4 emissions in freshwater marsh in northeast China. The results showed that there was an obvious CH4 emission (0.1–2.3 mg m−2 h−1) in the freshwater marsh in winter. Flux of CH4 in winter (November to March the next year) was about 3.8%, 5.5%, and 2.2% of the whole year in 2003, 2004, and 2005, respectively. Emission of CH4 significantly increased during the freeze–thaw period (April–June), and was about 30.8%, 20.9%, and 20.6% of the whole year in 2003, 2004, and 2005, respectively. Standing water depth greatly governed interannual variation of CH4 emissions from marshes during the thaw–freeze period. Interannual variation of CH4 emissions was significant during the growing season (p <0.05). Standing water depth during April to June was a primary factor, which affected the interannual variation of CH4 flux during the growing season. Precipitation during the preceding non-growing season affected CH4 emission indirectly via standing water depth. [Copyright &y& Elsevier]

Methane (CH 4 ) and nitrous oxide (N 2 O) 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 CH 4 emission by 24.22% but increased N 2 O 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 CH 4 emission, above +100 mV with significant N 2 O emission, and +100 to -100 mV with little CH 4 and N 2 O emissions. Intermittently draining the field increased soil oxidation, with a decrease in CH 4 emission and an increase in N 2 O emission. In general the mid‐season drainage slightly increased the populations of methanotrophs, nitrifiers, and denitrifiers but decreased that of methanogens. [ABSTRACT FROM AUTHOR]

Methane production potential (MPP) of rice soil, defined here as the mean value of methane production rate (MP-R) of rice soil over a given period in which the substrate for methanogenesis is presumably depleted, significantly affects CH4 emission to the atmosphere. To expand our understanding of how MPP was affected in soils grown with different rice cultivars ( Yanxuan, 72031 and 9516) and its consequence on CH4 emission, the changing pattern of MP-R was elucidated in the present study. On an entire rice growing scale, the MPP of planted soil was significantly higher than that of unplanted soil, and the MPP of 72031 rice soil was 9.42 µg CH4 kg (d.w.s)−1 h−1, significantly lower than Yanxuan (18.2 µg CH4 kg (d.w.s)−1 h−1) and 9516 rice soils (17.7 µg CH4 kg (d.w.s)−1 h−1). Yanxuan and 9516 soils had a similar MP-R changing pattern, which was distinct from 72031 soil. On a temporal scale of the representative rice growing stages (i.e. early tillering, late tillering, panicle initiation, ripening and harvesting stages), the MPP of rice soils varied widely among rice cultivars, and MPP coincided well with CH4 emission regardless of rice cultivars. No clear pattern was observed in soil redox potential (soil E h), or in above-ground biomass of rice cultivars to MPP and CH4 emission. [ABSTRACT FROM AUTHOR]

This article focuses on the seasonal and spatial changes of CH4 emission from the natural reed marsh of Liaohe Delta, China. Field experiments showed that this natural wetland acts as a CH4 sink in spring (-30- 1000 μ/m².h), a strong source in summer (400-3000 μg/m².h) and a weak source in autumn (<400 μg/m².h). Reed plants play an important role in transportation and emission of methane produced in soil. According to our field measurement data, CH4 emission is positively related to temperature, and negatively related to Eh value and water depth. The activity of methanogenic bacteria is higher in the rhizosphere and surface layer, and thus contributes more in CH4 emission than other layers. [ABSTRACT FROM AUTHOR]

Outdoor pot experiments with various paddy soils representing five soil types were conducted at Nanjing Agricultural University during the 2000 and 2001 rice-growing seasons. Eighteen soils and ten out of the eighteen soils were involved in the 2000 and the 2001 experiment, respectively. Two treatments were designed as mineral fertilization (MF) and mineral fertilizer + wheat straw incorporation (MF + WS) for the 2001 experiment. Seasonal average rate of CH4 emission from different soils ranged from 1.96 to 11.06 mg m-2 h-1 in the 2000 experiment, and from 0.89 to 5.92 mg m-2 h-1 for the MF treatment in the 2001 experiment, respectively. Incorporation of wheat straw enhanced considerably CH4 emission with an average increment of 7.09 mg m-2 h-1. CH4 emissions from the two-year experiment were negatively correlated to soil available and total copper concentration. A further investigation showed that CH4 emission from the MF treatment was positively related to the dissolved organic carbon (DOC) in the soil (r=0.904, p<0.001), and that the DOC was negatively correlated to the concentrations of available copper (r=-0.844, p<0.01) and total copper (r=-0.833, p<0.01), respectively. Nevertheless, the incorporation of wheat straw did not enhance the soil DOC, and the relationship between CH4 emission and soil DOC was not statistically significant (r=0.470, p<0.20). It was concluded that higher concentration of copper in the soils resulted in lower soil DOC and thus reduced CH4 emission when there was no additional organic matter input. Incorporation of wheat straw did not affect soil DOC and available copper concentration but enhanced CH4 emission. [Copyright &y& Elsevier]

To identify the key soil parameters influencing CH4 emission from rice paddies, an outdoor pot experiment with a total of 18 paddy soils was conducted in Nanjing Agricultural University during the 2000 rice growing season. The seasonal average rate of CH4 emission for all 18 soils was 6.42±2.70 mg m−2 h−1, with a range of 1.96 to 11.06 mg m−2 h−1. Correlation analysis indicated that the seasonal average of CH4 emission was positively dependent on soil sand content and negatively on total N as well as NH4 +-N determined before rice transplanting. Copper content of soils had a significant negative impact on CH4 emission. No clear relationship existed between CH4 emission and soil carbon content. In addition, soil type cannot explain the variability in CH4 emission. Soil parameters influencing CH4 emission were different as rice growth and development proceeded. A further investigation suggested that the seasonal average rate of CH4 emission could be quantitatively determined by a linear combination of soil NH4 +-N, available copper, the ratio of available to total sulphur, and the ratio of available to total iron. Moreover, the average rates of CH4 emission in the vegetative, reproductive and ripening stages could be also respectively described by a linear combination of different soil variables. [ABSTRACT FROM AUTHOR]

CH4 emission and its relevant processes involved (i.e. CH4 production, rhizospheric CH4 oxidation and plant-mediated CH4 transport) were studied simultaneously to comprehensively understand how rice cultivars ( Yanxuan, 72031, and 9516) at growth stages (early and late tillering, panicle initiation, ripening, and harvest stage) affect CH4 emission in a paddy soil. Over the entire rice-growing season, Yanxuan had the highest CH4 emission flux with 5.98 μg CH4 m−2 h−1 followed by 72031 (4.48 μg CH4 m−2 h−1) and 9516 (3.41 μg CH4 m−2 h−1). The highest CH4 production rate of paddy soils planted to Yanxuan was observed with 18.0 μg CH4 kg{ (d.w.soil)} h−1 followed by the soil planted to 9516 (17.5 μg CH4 kg{ (d.w.soil)} h−1). For each cultivar, both rhizospheric CH4 oxidation ability and plant-mediated CH4 transport efficiency varied widely with a range of 9.81–76.8% and 15.5–80.5% over the duration of crop growth, respectively. Multiple regression analyses showed that CH4 emission flux was positively related with CH4 production rate and rice plant-mediated CH4 transport efficiency, but negatively with rhizospheric CH4 oxidation ( R2=0.425 for Yanxuan, P<0.01; R2=0.426 for 72031, P<0.01; R2=0.564 for 9516, P<0.01). The contribution of rice plants to CH4 production seems to be more important than to rhizospheric CH4 oxidation and plant-mediated transport in impact of rice plants on CH4 emission. [ABSTRACT FROM AUTHOR]

A pot experiment was carried out to investigate the effect of soil water content in the non-rice growth season (winter season) on CH4 emission during the following rice-growing period. The results showed that CH4 fluxes increased significantly with the increase of soil water content in the winter season, except air-dry water condition. The mean CH4 fluxes of treatments with soil water contents in the winter of 3.89–5.37% (air-dry), 25–35%, 50–60%, 75–85% and 107% (flooded) of field water capacity (FWC) were 13.04, 4.04, 8.61, 13.26 and 20.47 mg m−2 h−1, respectively. Antecedent soil water contents also markedly affected temporal variation patterns of CH4 fluxes and soil redox potential (Eh) during the rice-growing period. The higher soil water contents in the winter season were, the quicker soil Eh decreased, and the earlier CH4 emission occurred after rice transplanting, except air-dry water condition. Though the seasonal mean CH4 flux was significantly correlated with the seasonal mean soil Eh, the seasonal variation of CH4 fluxes was not always significantly correlated with soil Eh. For the treatment flooded in the fallow season, there was no significant correlation between CH4 flux and soil Eh, but there was significant correlation between CH4 flux and soil temperature during rice growth season. In contrast, for the other four treatments, it was soil Eh, not soil temperature that significantly affected the temporal variation of CH4 emissions. Soil water contents in the fallow season significantly influenced concentrations of soil labile organic carbon (including undecomposed plant debris), active Fe and Mn immediately before rice transplanting. The mean CH4 fluxes during rice-growing period were significantly correlated with soil labile organic carbon contents (positively) and contents of soil active Fe and Mn (negatively). [ABSTRACT FROM AUTHOR]

Field measurements of methane emission from rice paddies were made in Nanjing, China and in Texas, USA, respectively. Soil temperature at approximately 10 cm depth of the flooded soils was automatically recorded. Aboveground biomass of rice crop was measured approximately every 10 days in Nanjing and every other week in Texas. Seasonal variation of soil temperature in Nanjing was quite wide with a magnitude of 15.3°C and that in Texas was narrow with a magnitude of 2.9°C. Analysis of methane emission fluxes against soil temperature and rice biomass production demonstrated that the seasonal course of methane emission in Nanjing was mostly attributed to soil temperature changes, while that in Texas was mainly related to rice biomass production. We concluded that under the permanent flooding condition, the seasonal trend of methane emission would be determined by the soil temperature where there was a wide variation of soil temperature, and the seasonal trend would be mainly determined by rice biomass production if there are no additional organic matter inputs and the variation of soil temperature over the rice growing season is small. [ABSTRACT FROM AUTHOR]

Connecting external circuits can effectively inhibit the CH 4 emissions from constructed wetlands (CW). In this study, the effect of external circuits, plant roots position and external resistance value on the electrical, CH 4 emission and pollutant removing performance of sequencing batch constructed wetland-microbial fuel cell (CW-MFC) was investigated for the first time. After connecting external circuit, the CH 4 emission from rhizosphere-anode-closed (RAC) constructed wetland-microbial fuel cell (CW-MFC) and rhizosphere-cathode-closed (RCC) CW-MFC was significantly reduced by 49.39% and 74.19%, respectively. When the external resistance was 1000, the highest power density was observed in RAC CW-MFC with a number of 73.32 mW m−3. In comparison, CW-MFC with rhizosphere at cathode emitted less CH 4 , while CW-MFC with rhizosphere at anode had a better electrical performance. Based on the high-throughput sequencing analysis, dynamic community structure of bacteria and archaea and the related microbial processes in the anode and cathode of CW-MFC were studied. Proteobacteria , Bacteroidetes and Methanosaeta were observed to be dominant in CW-MFCs, and the circuit conditions, external resistance and rhizosphere location all played important roles in the microbial community structure of CW-MFCs. [Display omitted] ● Connecting closed circuits can reduce CH 4 emissions from CW-MFC by 74.19%. ● Sequencing batch CW-MFC with rhizosphere at cathode released less CH 4. ● External circuits affect microbial community and biochemical processes. ● The COD removal of CW-MFC was significantly affected by external circuits. [ABSTRACT FROM AUTHOR]

Lipid metabolism plays an important role in the energy economy of ruminants. However, its interactions of fat, rumen fermentation, gas emission, and microorganisms are not yet clear. This study evaluated the effect of adding raw oilseeds to high-forage diets on in vitro ruminal fermentation, gas composition, and microbial profile. Three isoenergetic and isoproteic experimental diets were designed and used as fermentation substrate: control treatment (CON group) was the basal diet lacking oilseeds, the other two treatments were the basal diet supplemented by 100 g/kg dry matter (DM) raw whole soybean (S group) and 50 g/kg DM raw flaxseed (F group), respectively. Data showed that the acetate, butyrate, and total VFA concentration of culture fluids in the S group were lower (p < 0.05) than in the F group. There was a tendency to a higher level (p = 0.094) of propionate concentration in the F group compared with the other two groups. The gas production in the F group was higher (p < 0.05) than in the control group. There was a lower abundance of Sutterella (p < 0.05) and a greater abundance of Butyrivibrio (p < 0.05) in both of the two oilseed treatments. Methanobrevibacter (p = 0.078) in the F group was the lowest. Our results suggested that CH4 emission could be inhibited with flaxseed supplementation by propionate production metabolism, biohydrogenation of unsaturated fatty acid (FA), and toxicity to Methanobrevibacter, while regarding soybean seed supplementation, the emission of CH4 was more likely to be reduced through biohydrogenation of unsaturated FA modulated by Butyrivibrio. [ABSTRACT FROM AUTHOR]

• Elevated CO 2 increases CH 4 emissions in an intermittently inundated marsh. • Elevated CO 2 decreases CH 4 emissions in a persistently inundated marsh. • Response of CH 4 emissions to elevated CO 2 is determined by hydrology and vegetation. • CH 4 emissions from wetlands under elevated CO 2 may have been grossly overestimated. Elevated atmospheric CO 2 may have consequences for methane (CH 4) emissions from wetlands, yet the magnitude and direction remain unpredictable, because the associated mechanisms have not been fully investigated. Here, we established an in situ macrocosm experiment to compare the effects of elevated CO 2 (700 ppm) on the CH 4 emissions from two wetlands: an intermittently inundated Calamagrostis angustifolia marsh and a permanently inundated Carex lasiocarpa marsh. The elevated CO 2 increased CH 4 emissions by 27.6–57.6% in the C. angustifolia marsh, compared to a reduction of 18.7–23.5% in the C. lasiocarpa marsh. The CO 2 -induced increase in CH 4 emissions from the C. angustifolia marsh was paralleled with (1) increased dissolved organic carbon (DOC) released from plant photosynthesis and (2) reduced (rate of) CH 4 oxidation due to a putative shift in methanotrophic community composition. In contrast, the CO 2 -induced decrease in CH 4 emissions from the C. lasiocarpa marsh was associated with the increases in soil redox potential and pmoA gene abundance. We synthesized data from worldwide wetland ecosystems, and found that the responses of CH 4 emissions to elevated CO 2 was determined by the wetland water table levels and associated plant oxygen secretion capacity. In conditions with elevated CO 2 , plants with a high oxygen secretion capacity suppress CH 4 emissions while plants with low oxygen secretion capacity stimulate CH 4 emissions; both effects are mediated via a feedback loop involving shifts in activities of methanogens and methanotrophs. [Display omitted] [ABSTRACT FROM AUTHOR]

Rice cultivation is the primary source of anthropogenic methane (CH 4), which dramatically impacts global climate change. A growing body of evidence shows that optimizing photosynthate distribution is important for increasing rice yields and mitigating CH 4 emissions. Therefore, the molecular rice breeding with a barley HvSUSIBA2 gene that confers elevated photosynthate flux to grains, is predicted to enhance rice yield and mitigate CH 4 emissions in paddies. Here, in a series of field experiments with differences in growing season and rice variety, we show that SUSIBA2 rice reduced CH 4 emissions from paddies. SUSIBA2 rice grown in the early rice season and late rice season showed similar mitigation effects, with reduction rates of 50.98% for early rice and 50.97% for late rice. The reduction rate of SUSIBA2 rice during the winter rice season was significantly lower (22.26%) than those of other rice seasons. The reduction rates also varied between rice varieties, and SUSIBA2 japonica rice showed a more significant CH 4 mitigation effect than SUSIBA2 indica rice. Further yield-scaled CH 4 emission analyses indicated that the SUSIBA2 effect did not mitigate CH 4 emissions at the expense of yield. Compared with the wild type, SUSIBA2 rice significantly reduced soil organic carbon properties and the abundance of CH 4 -related microbes, and altered methanogenic and methanotrophic communities, indicating that SUSIBA2 rice released less carbon to the soil, which reduced CH 4 production. Furthermore, a comparison of microbial communities between SUSIBA2 japonica and indica rice revealed different responses of methanogenic and methanotrophic communities, which may partly explain their differences in growth performance and CH 4 mitigation effect. Thus, our results show that SUSIBA2 rice substantially reduces CH 4 emissions and that SUSIBA2 can potentially mitigate the CH 4 emissions of japonica and indica rice under distinct cultivation conditions. Unlabelled Image • The CH 4 mitigation effect of the rice carrying a gene introduced from barley (SUSIBA2) in fields varied with growing season. • SUSIBA2 japonica rice shows a greater CH 4 mitigation effect than SUSIBA2 indica rice. • Altered soil C promoted different patterns of methanogenic and methanotrophic communities. [ABSTRACT FROM AUTHOR]

Improved mechanistic understanding of soil methane (CH4) exchange responses to shifts in soil moisture and temperature in forest ecosystems is pivotal to reducing uncertainty in estimates of the soil-atmospheric CH4 budget under climate change. We investigated the mechanism behind the effects of soil moisture and temperature shifts on soil CH4 fluxes under laboratory conditions. Soils from the Huai River Basin in China, an area that experiences frequent hydrological shifts, were sampled from two consecutive depths (0–20 and 20–50 cm) and incubated for 2 weeks under different combinations of soil moisture and temperature. Soils from both depths showed an increase in soil moisture and temperature-dependent cumulative CH4 fluxes. CH4 production rates incubated in different moisture and temperature in surface soil ranged from 1.27 to 2.18 ng g−1 d−1, and that of subsurface soil ranged from 1.18 to 2.34 ng g−1 d−1. The Q10 range for soil CH4 efflux rates was 1.04–1.37. For surface soils, the relative abundance and diversity of methanotrophs decreased with moisture increase when incubated at 5 °C, while it increased with moisture increase when incubated at 15 and 30 °C. For subsurface soils, the relative abundance and diversity of methanotrophs in all samples decreased with moisture increase. However, there was no significant difference in the diversity of methanogens between the two soil depths, while the relative abundance of methanogens in both depths soils increased with temperature increase when incubated at 150% water-filled pore space (WFPS). Microbial community composition exhibited large variations in post incubation samples except for one treatment based on the surface soils incubated at 15 °C, which showed a decrease in the total and unique species number of methanotrophs with moisture increase. In contrast, the unique species number of methanogens in surface soils increased with moisture increase. The analysis of distance-based redundancy analysis (db-RDA) showed that soil pH, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), microbial biomass carbon (MBC), NO3−-N, and NH4+-N mainly performed a significant effect on methanotrophs community composition when incubated at 60% WFPS, while they performed a significant effect on methanogens community composition when incubated at 150% WFPS. Overall, our findings emphasized the vital function of soil hydrology in triggering CH4 efflux from subtropical plantation forest soils under future climate change. [ABSTRACT FROM AUTHOR]

In this study, functional microbial sequencing, quantitative PCR, and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) were employed to understand the microbial mechanisms related to the effects of bamboo charcoal (BC) and bamboo vinegar (BV) on the degradation of organic matter (OM) and methane (CH 4) emissions during composting. BC + BV resulted in the highest degradation of OM. BV was most effective treatment in controlling CH 4 emissions and it significantly reduced the abundance of the mcrA gene. Methanobrevibacter , Methanosarcina , and Methanocorpusculum were closely related to CH 4 emissions during the thermophilic composting period. PICRUSt analysis showed that BC and/or BV enhanced the metabolism associated with OM degradation and reduced CH 4 metabolism. Structural equation modeling indicated that BC + BV strongly promoted the metabolic activity of microorganisms, which had a positive effect on CH 4 emissions. Together these results suggest that BC + BV may be a suitable composting strategy if the aerobic conditions can be effectively improved during the thermophilic composting period. Image 1 • BC and BV enhanced organic matter degradation and decreased CH 4 emissions. • BC + BV treatment resulted in the highest organic matter degradation. • CH 4 emissions and mcrA gene abundance were mostly decreased in BV treatment. • Methanobrevibacter was the most abundant methanogen and related to CH 4 emissions. • The aerobic conditions should be improved when simultaneously applying BC and BV. [ABSTRACT FROM AUTHOR]

• We apply a model coupling method to "reproduce" the field experiment process at 24 representative sites via model simulations. • The model coupling enriches and updates the rice genetic parameters. • The simulations demonstrate the feasibility of implementing water-saving irrigation methods across rice fields in China. • The expansion of "Alternate Wetting and Drying" method can lead to a "win-win" solution for the food-water-GHG emissions tradeoffs. Paddy rice cultivation is an important source of agricultural greenhouse gas emissions in China. The traditional flooded paddy rice fields not only use large amounts of irrigation water, but also produce significant methane (CH 4) emissions. To balance food security with environmental impacts of rice production, many water-saving irrigations technologies have been tested in the field to increase the drainage period during the rice growth cycle. However, whether these management solutions can be implemented at the regional scale needs to be further explored. Because it is too time-consuming and resource-intensive for field experiments to be carried out across large areas, we opt to assess the regional impacts of alternative irrigation schemes via computer modeling, by coupling the well-known DSSAT and DNDC models, which have been extensively validated in China. Irrigation methods tested include the traditional Continuous Flooding (CF), Midseason Drainage (MD) and Alternate Wetting and Drying (AWD). Simulation results show that compared with CF, water-saving irrigation methods can significantly reduce the CH 4 emission from paddy rice field, with slight or no loss in expected rice yields. AWD had the greatest effect in reducing irrigation water amounts and CH 4 emission. Compared with CF, CH 4 emission under the AWD were 60% - 71% lower in Northeast China sites and 34% - 65% lower in South China sites. At the same time, compared to CF, irrigation water use in AWD was reduced by 23% - 34% in northeast China sites and by 18% - 50% in south China sites. Our results suggest that policies that support expansion of AWD in paddy rice cultivation across China can lead to a "win-win" for the food-water-GHG emissions tradeoffs, and offer a viable solution for policy makers and stakeholders in China. [ABSTRACT FROM AUTHOR]