Controlling CH4 Emissions Research Articles

Effects of Fallow Season Water and Straw Management on Methane Emissions and Associated Microorganisms

The effects of fallow season water and straw management on methane (CH4) emissions during the fallow season and the subsequent rice-growing season are rarely reported, and the underlying microbial mechanisms remain unclear. A field experiment was conducted with four treatments: (1) fields flooded in both the fallow and rice seasons (FF), (2) fields drained in the fallow season and flooded in the rice season (DF), (3) FF with straw retention (FFS), and (4) DF with straw retention (DFS). The CH4 emissions in fields under different water and straw treatments were monitored using the static closed chamber method. Methanogenic and methanotrophic communities in these fields were examined using terminal restriction fragment length polymorphism (T-RFLP) analysis based on the mcrA gene and pmoA gene encoding methyl coenzyme M reductase and particulate methane monooxygenase, respectively. The results showed that CH4 emissions were significantly affected by water management, straw retention, season, and their interactions. Over 80% of CH4 emissions occurred during the rice season. Field drainage during the fallow season reduced CH4 emissions by 47.0% and 53.8% with and without straw during the rice season, respectively. Water management altered the abundance and composition of methanogens and methanotrophs, whereas the effects of straw retention were less pronounced. The quantitative polymerase chain reaction (qPCR) assay revealed that field drainage in the fallow season decreased the mcrA gene abundance by 30.0% and 23.2% with and without straw in rice season, respectively, and increased the pmoA gene abundance by 108.9% and 213.7% with and without straw in rice season, respectively. CH4 flux was significantly positively associated with mcrA gene copy number and the ratio of mcrA to pmoA gene copy number, whereas it was significantly negatively correlated with the pmoA gene copy number. Results indicated that fallow drainage greatly decreased CH4 emission not only during the fallow season but also during the subsequent rice season by altering the community composition of methanogens and methanotrophs. These findings provide scientific insight into the role of water and straw management in controlling CH4 emissions through microbial community dynamics.

Spatio-temporal variations in activity of aerobic methane oxidation and community structure of methanotrophs in sediment of Wuxijiang River

Rivers are hotspots for methane (CH4) emissions, and aerobic methane oxidation is a crucial process in controlling emissions. The spatio-temporal heterogeneity of river environment can greatly affect the methane oxidation process. However, currently, few studies have focused on the spatio-temporal changes in activity of methane oxidation and the associated microbiome in riverine ecosystems, which hinders a comprehensive understanding the role of this process in reducing emissions of CH4. Here, we investigated the variations in methane oxidation activity and community of methanotrophs in sediment of a mountain river across different reaches and seasons. The potential methane oxidation rate ranged from 24.11 to 493.03 nmol CH4 g-1 (sediment) d-1, which was significantly greater in sediment obtained during the winter than in that obtained during the summer. Moreover, the rate in middle reaches was significantly greater than that in upper and lower reaches in summer. The abundance of pmoA gene of methanotrophs ranged from 2.45×10⁶ to 2.98×10⁷ copies g-1 (sediment), which was also significantly greater in winter than in summer and showed significant variations among reaches. Additionally, methanotrophic diversity and community composition exhibited significant variations across both reaches and seasons, and the relative abundance of Methylococcus and Methylocystis was closely associated with methane oxidation activity. Sediment NH4+ content, pH and temperature were potentially crucial factors affecting the activity or methanotrophic community. In conclusion, it is necessary to consider both temporal and spatial scales to improve our understanding of the significance and driving mechanisms of methane oxidation in controlling CH4 emissions from rivers.

Emerging research on characterizing the potential of cable bacteria for CH4 mitigation

Methane (CH4) contributes an essential portion for global warming as a pivotal greenhouse gas. Microorganisms are identified as an effective way to mediate and control CH4 emission. Cable bacteria is a promising microorganism to mitigate CH4, however, the studies of distribution, abundance and function for CH4 reduction of cable bacteria in inland water still remain unclear. In this paper, we propose the probable CH4 mitigation metabolism within cable bacteria in anoxic condition, and present the future research directions about the application potential of cable bacteria in CH4 reduction. The viewpoint will help to understand the significant role of cable bacteria in CH4 mitigation and provide a potential way to control CH4 emissions in inland freshwater ecosystem.

Temporal Variations in Methane Emissions from a Restored Mangrove Ecosystem in Southern China

The role of coastal mangrove wetlands in sequestering atmospheric carbon dioxide has been increasingly investigated in recent years. While studies have shown that mangroves are weak sources of methane (CH4) emissions, measurements of CH4 fluxes from these ecosystems remain scarce. In this study, we examined the temporal variation and biophysical drivers of ecosystem-scale CH4 fluxes in China’s northernmost mangrove ecosystem based on eddy covariance measurements obtained over a 3-year period. In this mangrove, the annual CH4 emissions ranged from 6.15 to 9.07 g C m−2 year−1. The daily CH4 flux reached a peak of over 0.07 g C m−2 day−1 during the summer, while the winter CH4 flux was negligible. Latent heat, soil temperature, photosynthetically active radiation, and tide water level were the primary factors controlling CH4 emissions. This study not only elucidates the mechanisms influencing CH4 emissions from mangroves, strengthening the understanding of these processes but also provides a valuable benchmark dataset to validate the model-derived carbon budget estimates for these ecosystems.

The temporal variation of CH4 emissions embodied in Chinese supply chains, 2000–2020

Although the issue of embodied pollutants in China’s supply chains has garnered increasing attention, the dynamic changes occurring within them are unclear. Several existing studies analyze one-year or short-term data in supply chain. China’s overall CH4 emissions have risen from 41.1 Tg in 2000 to 60 Tg in 2020, so conducting long-term analyses can yield a deeper understanding of the dynamic changes across the entire supply chain from production to consumption. This study uses the environmentally extended input–output analysis (EEIOA) and structural path analysis (SPA) methods to investigate the dynamic variation of China’s embodied CH4 emissions in 20 industry sectors from 2000 to 2020, aiming to determine the key supply chain and key sectors. The results reveal that from the final demand perspective, consumption, investment and export drove 52.1%, 32%, and 15.9% of embodied CH4 emissions in 2020. The sector with the highest embodied CH4 emissions has changed from “Agriculture” in 2000 to “Construction” in 2010 to “Other service and activities” in 2020. The top listed supply chain path of embodied CH4 emissions has also evolved (starting from production to consumption) from “Agriculture → Rural consumption” in 2000 to “Agriculture → Food and tobacco → Urban consumption” in 2010 to “Agriculture → Urban consumption” in 2020. Notably, the high-ranked path, “Agriculture → Food and tobacco → Rural consumption”, shows that the embodied CH4 emission flowing between agriculture and the food industry cannot be ignored. The supply chain path “Coal Mining → Nonmetal Mineral Products → Construction → Capital Formation” has risen from 17th in 2000 to 3rd in 2020. Thus, it is necessary to control CH4 emissions from sectors upstream, which are predominantly influenced by the construction industry, and a coordinated effort between sectors is also required to effectively reduce emissions. By 2020, the CH4 emissions driven by urban consumption were 3.1 times that of rural consumption. This study provides a comprehensive analysis of China's supply chain over the past two decades. In particular, it suggests policy interventions by controlling critical supply chain paths and key sectors associated with embodied CH4 emission, thereby facilitating the coordinated reduction of anthropogenic CH4 emissions.

Does no-till crop management mitigate gaseous emissions and reduce yield disparities: An empirical US-China evaluation

Global agricultural systems face one of the greatest sustainability challenges: meeting the growing demand for food without leaving a negative environmental footprint. United States (US) and China are the two largest economies and account for 39 % of total global greenhouse gases (GHG) emissions into the atmosphere. No-till is a promising land management option that allows agriculture to better adapt and mitigate climate change effects compared to traditional tillage. However, the efficacy of no-till for mitigating GHG is still debatable. In this meta-analysis, we comprehensively assess the impact of no-till (relative to traditional tillage) on GHG mitigation potential and crop productivity in different agroecological systems and management regimes in the US and China. Overall, no-till in China did not change crop yields, although soil CO2 (8 %) and N2O (12 %) emissions decreased significantly, while soil CH4 emissions increased by 12 %. In contrast to Chinese no-till, a significant improvement in crop yields (up to 12 %) was recorded on US cropland under no-till. Moreover, significant decreases in soil N2O (21 %) and CH4 (12 %) emissions were observed. Of the three cropping systems, only wheat showed significant reduction in CO2, N2O and CH4 emissions in the Chinese no-till system. In the case of US, no-till soybean-rice and maize cropping systems demonstrated significant emission reductions for N2O and CO2, respectively. Interestingly, yields of no-till maize in China and rice in US exceeded those of other no-till cereals. In China, no-till on medium-texture soils resulted in significant reductions in GHG emissions and higher crop yields compared to other soil types. In both countries, the relatively higher crop yields under irrigated versus non-irrigated no-till and the significant yield differences on fine textured soils under US no-till are likely due to the substantial N2O reductions. In summary, crop yield disparities from no-till between China and the US were related to the insignificant effects on controlling CH4 emissions and successfully mitigating N2O, respectively. This study comprehensively demonstrates how cropping system and pedoclimatic conditions influence the relative effectiveness of no-till in both countries.

Rewetting increases vegetation cover and net growing season carbon uptake under fen conditions after peat-extraction in Manitoba, Canada

The moss layer transfer technique has been developed to restore the carbon sequestration function and typical vegetation of Sphagnum-dominated peatlands after peat extraction in North America. However, the technique does not lead to successful bryophyte establishment when applied to peatlands with a richer residual fen peat. Therefore, we evaluated an alternative method of active rewetting and passive vegetation establishment using vegetation surveys and carbon dioxide and methane (CH4) flux measurements at a post-extracted fen in southern Manitoba, Canada. After one growing season post-rewetting, wetland vegetation established and the site was a net carbon sink over the growing season. However, high abundance of Carex lasiocarpa 10 years post-treatment led to higher CH4 emissions than the reference ecosystem. Successful establishment of wetland vegetation is attributed to the area being surrounded by undisturbed fens that can provide a local source of plant propagules. Bryophyte expansion was less successful than vascular plants, likely due to episodic flooding and shading from the sedge communities. Therefore, careful management of water levels to just below the peat surface is needed if reference vegetation community recovery is the goal of restoration. Water level management will also play a key role in controlling CH4 emissions to maximize carbon sequestration potential.

Methane emissions from rice paddies globally: A quantitative statistical review of controlling variables and modelling of emission factors

Greenhouse gas (GHG) modelling tools or the Intergovernmental Panel on Climate Change (IPCC) inventory methods are often used to identify suitable mitigation strategies for GHG emissions from rice, since measuring them in field is challenging and costly. Here we report an up-to-date quantitative review on methane (CH4) emission from rice paddies using information obtained from peer-review articles. Statistical analysis was conducted on the factors controlling CH4 emissions and a generalised additive model (GAM) was developed to estimate emission factors (EFs). Results showed that emissions were strongly linked to water regime, soil texture and organic amendment practices. Fields that were rainfed during the dry season or saturated emitted 70% and 56% that of continuously flooded fields, while applying straw off-season instead of within-season could decrease emissions by 48%. An independent dataset was used to evaluate the new model performance against existing models with the new model showing R2 values of 0.47 (n: 169), compared to 0.01–0.09 (n: 169) for the existing models. New baseline EFs was estimated at global, regional, and Country scale with result showing that using different pre-season water management when calculating baseline EFs at country level is vital in order to reflect the variation between tropical and temperate rice regions accurately. Our findings shows that the new model is more sensitive in capturing differences in management practices between tropical and temperate rice, and their impacts on CH4 emissions with baseline EF calculations accounting for these differences providing sound mitigation strategies.

Microbial sensitivity to temperature and sulfate deposition modulates greenhouse gas emissions from peat soils.

Peatlands are among the largest natural sources of atmospheric methane (CH4 ) worldwide. Microbial processes play a key role in regulating CH4 emissions from peatland ecosystems, yet the complex interplay between soil substrates and microbial communities in controlling CH4 emissions as a function of global change remains unclear. Herein, we performed an integrated analysis of multi-omics data sets to provide a comprehensive understanding of the molecular processes driving changes in greenhouse gas (GHG) emissions in peatland ecosystems with increasing temperature and sulfate deposition in a laboratory incubation study. We sought to first investigate how increasing temperatures (4, 21, and 35°C) impact soil microbiome-metabolome interactions; then explore the competition between methanogens and sulfate-reducing bacteria (SRBs) with increasing sulfate concentrations at the optimum temperature for methanogenesis. Our results revealed that peat soil organic matter degradation, mediated by biotic and potentially abiotic processes, is the main driver of the increase in CO2 production with temperature. In contrast, the decrease in CH4 production at 35°C was linked to the absence of syntrophic communities and the potential inhibitory effect of phenols on methanogens. Elevated temperatures further induced the microbial communities to develop high growth yield and stress tolerator trait-based strategies leading to a shift in their composition and function. On the other hand, SRBs were able to outcompete methanogens in the presence of non-limiting sulfate concentrations at 21°C, thereby reducing CH4 emissions. At higher sulfate concentrations, however, the prevalence of communities capable of producing sufficient low-molecular-weight carbon substrates for the coexistence of SRBs and methanogens was translated into elevated CH4 emissions. The use of omics in this study enhanced our understanding of the structure and interactions among microbes with the abiotic components of the system that can be useful for mitigating GHG emissions from peatland ecosystems in the face of global change.

Effect of infiltration rate on methane emission properties in pot‐cultured rice under alternate wetting and drying irrigation

AbstractAlternate wetting and drying (AWD) irrigation is effective at reducing methane (CH4) emissions in rice cultivation. To investigate the effect of the infiltration rate on AWD effectiveness in terms of CH4 emissions, rice was cultivated in pots with three different infiltration rates under AWD. Under intermittent irrigation, the soil was more oxidative than is generally required for CH4 production (redox potential [Eh] > −150 mV), regardless of the infiltration rate. CH4 emission was suppressed by at least 37% compared to continuous flooding and no‐infiltration conditions; however, temporarily elevated emission caused by drainage below saturation was observed 1–2 h after the flooding receded. This result is important for accurately determining CH4 emissions in water management techniques such as AWD. CH4 emissions during the heading stage, including temporarily elevated emissions after flooding receded, were greatest under the highest infiltration rate (18 mm day−1). The infiltration rate did not affect the rate of soil Eh reduction; however, the total organic carbon concentration in the drainage water suggested that more carbon, a methanogen substrate, migrated to the bottom of the pot with increasing infiltration rate, which likely increased CH4 emissions. This study will aid in the examination of ponding water management techniques to control CH4 emissions in rice production.

Response of potential activity, abundance and community composition of nitrite-dependent anaerobic methanotrophs to long-term fertilization in paddy soils.

The process of nitrite-dependent anaerobic methane oxidation (n-damo) catalysed by Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria is a novel pathway in regulating methane (CH4 ) emissions from paddy fields. Nitrogen fertilization is essential to improve rice yields and soil fertility; however, its effect on the n-damo process is largely unknown. Here, the potential n-damo activity, abundance and community composition of M. oxyfera-like bacteria were investigated in paddy fields under three long-term (32 years) fertilization treatments, i.e. unfertilized control (CK), chemical fertilization (NPK) and straw incorporation with chemical fertilization (SNPK). Relative to the CK, both NPK and SNPK treatments significantly (p < 0.05) increased the potential n-damo activity (88%-110%) and the abundance (52%-105%) of M. oxyfera-like bacteria. The variation of soil organic carbon (OrgC) content and inorganic nitrogen content caused by the input of chemical fertilizers and straw returning were identified as the key factors affecting the potential n-damo activity and the abundance of M. oxyfera-like bacteria. However, the community composition and diversity of M. oxyfera-like bacteria did not change significantly by the input of fertilizers. Overall, our results provide the first evidence that long-term fertilization greatly stimulates the n-damo process, indicating its active role in controlling CH4 emissions from paddy fields.

Mitigation of methane emission in a rice paddy field amended with biochar-based slow-release fertilizer

Despite improving soil quality and reducing nitrogen (N) loss in paddy soil, replacing chemical fertilizer with organic fertilizer would significantly accelerate greenhouse gas emission in terms of methane (CH4). The application of slow-release fertilizer has been proposed an effective approach to control CH4 emissions, in addition to reducing N loss. Yet, the understanding of CH4 emissions from paddy fields with the additions of different fertilizers is still less known. Therefore, the effects of different fertilizer treatments, including chemical fertilizer treatment (CF), mixed chemical and organic fertilizer treatment (OF), biochar-based slow-release fertilizer treatment (SF), and no fertilizer control treatment (CK) on CH4 emissions and methanogenic community structure in paddy soils were investigated through a field experiment. Results showed that slow-release fertilizer addition significantly decreased CH4 emissions by 33.4%, during the whole rice growing season compared to those in OF. The cumulative CH4 emissions were in a significantly positive relation to soil NH4+-N. Slow-release fertilizer amendment decreased the relative abundances of Methanosarcina and Methanoregula and increased the relative abundances of hydrogenotrophic Methanocella and Rice Cluster I. Reduced CH4 emissions with slow-release fertilizer amendment might be mainly attributed to the different forms of N in the fertilizer and available potassium (K) in the paddy soil. Our findings produce novel insights into the application of slow-release fertilizer in controlling CH4 emissions from rice fields.

Estimates of methane emissions from Chinese rice fields using the DNDC model

Methane (CH4) emissions from rice fields across China were estimated using the DNDC (DeNitrification-DeComposition) model. The results showed that the CH4 emissions from Chinese rice fields in 2012 were estimated to be 8.20 Tg CH4 yr−1 (ranging from 4.80 to 11.40 Tg CH4 yr−1); the values from early, late, and single cropping rice were 1.12, 2.86, and 4.23 Tg CH4 yr−1. Rice fields in AEZ (agricultural ecosystem zoning) 7 (southeastern China) and AEZ 6 (central and southwestern China) were the two major sources, accounting for 92% of the total CH4 emissions in China. The CH4 emissions in AEZ 7 mainly originated from double cropping rice fields, while single cropping rice fields dominated the CH4 emissions in AEZ 6. The CH4 emission hotspots were in the Sichuan Basin of AEZ 6B (southwestern China), AEZ 6A (central China, except for Henan Province), AEZ 7 (except parts of Fujian and Zhejiang Provinces), and Heilongjiang Province. At the national scale, water management (positive correlation), air temperature (positive correlation), and the soil clay content (negative correlation) were the three dominant factors controlling the CH4 fluxes in paddy fields. These results provide an understanding of the spatial distribution of CH4 emissions from paddy fields and will help the government formulate policies to control CH4 emissions at a regional scale.

Methane Emissions during the Tide Cycle of a Yangtze Estuary Salt Marsh

Methane (CH4) emissions from estuarine wetlands were proved to be influenced by tide movement and inundation conditions notably in many previous studies. Although there have been several researches focusing on the seasonal or annual CH4 emissions, the short-term CH4 emissions during the tide cycles were rarely studied up to now in this area. In order to investigate the CH4 emission pattern during a tide cycle in Yangtze Estuary salt marshes, frequent fixed-point observations of methane flux were carried out using the in-situ static closed chamber technique. The results indicated that the daily average CH4 fluxes varied from 0.68 mgCH4·m−2·h−1 to 4.22 mgCH4·m−2·h−1 with the average flux reaching 1.78 mgCH4·m−2·h−1 from small tide to spring tide in summer. CH4 fluxes did not show consistent variation with both tide levels and inundation time but increased steadily during almost the whole research period. By Pearson correlation analysis, CH4 fluxes were not correlated with both tide levels (R = −0.014, p = 0.979) and solar radiation (R = 0.024, p = 0.865), but significantly correlated with ambient temperature. It is temperature rather than the tide level mainly controlling CH4 emissions during the tide cycles. Besides, CH4 fluxes also showed no significant correlation with the underground pore-water CH4 concentrations, indicating that plant-mediated transport played a more important role in CH4 fluxes compared with its production and consumption.

Mitigation Rice Yield Scaled Methane Emission and Soil Salinity Stress with Feasible Soil Amendments

Sea level rise and saline water intrusion have been affecting land use and crop production especially rice in the coastal areas of major rice growing countries including Bangladesh. The upward trend in salinity intrusion has been hampering crop production, particularly rice cultivation in the coastal areas of Bangladesh. Therefore, an experiment was conducted on rice planted saline soils under the Nethouse at Bangladesh Agricultural University, Mymensingh to improve the properties of salt affected soils for rice cultivation as well as controlling methane (CH4) emissions with feasible soil organic amendments and recommended inorganic fertilizers. The experimental treatments were arranged under 25 mM NaCl, 50 mM NaCl and 75 mM NaCl salinity levels with different combinations of NPKSZn, biochar, phosphogypsum and Trichocompost. It was found that CH4 emission rates were suppressed with phospho-gypsum and biochar amendments within the salinity level 25 mM to 50 mM, beyond this salinity level (at 75 mM), soil amendments were not effective to control CH4 emissions. From panicle initiation to grain ripening stages treatment T4 (100% NPKSZn + 75 mM NaCl stress) showed the highest CH4 emission rate, while lower CH4 emission rate was recorded in T5 (100% NPKSZn + 25 mM NaCl stress + Phospho-gypsum) and T8 treatment (100% NPKSZn + 50 mM NaCl + Phospho-gypsum). In case of seasonal total CH4 emission, Phospho-gypsum was found most effective to mitigate total CH4 emissions followed by biochar and trichocompost amendments in all salinity levels, probably due to the improved soil redox potential status (Eh), decreased electrical conductivity (EC), increased SO42-, NO3- , Mn4+ etc. in the rice rhizosphere. Rice growth and yield components were badly affected by increasing salinity levels. Phospho-gypsum, biochar and trichocompost amendments increased plant height, panicles number/hill, shoot biomass and grain yield/hill at 25 mM NaCl stress condition. However, salinity stress 50 mM to 75 mM severely affected rice growth and yield components, eventhough phospho-gypsum, biochar and trichocompost were applied. Among the amendments, phosphogypsum and biochar significantly decreased yield scaled CH4 emission (GHGI) in salinity levels 25 mM to 75 mM. After harvesting rice, the overall soil properties such as organic matter content, available P, available S, exchangeable K+ and Ca2+, K+/Na+, Ca2+/Na+ ratios etc. were increased with the biochar, phospho-gypsum and trichocompost amendments. The highest ratios of K+/Na+ and Ca+/Na+ were found in the extract of saline soil at 25 mM with phospho-gypsum amendments followed by biochar and trichocompost amendments. Furthermore, soil SO42-, NO3- , Mn4+ and Fe3+ contents in rice root rhizosphere were increased in the amended saline soils, which caused significant reduction in seasonal methane emissions. Therefore, it could be concluded that the combined application of phospho-gypsum and biochar with the recommended NPKSZn fertilizers in saline soils may be a good practice for increasing tolerance to salinity in rice by increasing K+/Na+, Ca2+/Na+ ratios, while decreasing yield scaled CH4 emission (GHGI) in salinity levels 25 mM to 75 mM.

Methane emissions during different freezing-thawing periods from a fen on the Qinghai-Tibetan Plateau: Four years of measurements

How methane (CH4) fluxes from alpine peatlands, especially during freeze-thaw cycles, affect the global CH4 budget is poorly understood. The present research combined the eddy covariance method, incubation experiments and high-throughput sequencing to observe CH4 flux from an alpine fen during thawing-freezing periods over a period of four years. The response of CH4 production potential and methanogenic archaea to climate change was analyzed. We found a relatively high mean annual cumulative CH4 emission of 37.7 g CH4-C m−2. The dominant contributor to CH4 emission was the thawing period: warmer, longer thawing periods contributed 69.1-88.6% to the annual CH4 budget. Non-thawing periods also contributed, with shorter frozen-thawing periods accounting for up to 18.5% and shorter thawing-freezing periods accounting for up to 8.8%. Over the course of a year, emission peaked in the peak growing season and at onset of thawing and freezing. In contrast, emission did not vary substantially during the frozen period. Daily mean emission was highest during the thawing period and lowest during the frozen period. Diurnal patterns of CH4 emission were similar among the four periods, with peaks ranging from 12:00 to 18:00 and the lowest emission around 00:00. Water table and temperature were the dominant factors controlling CH4 emissions during different thawing-freezing periods. Our results suggest that CH4 emission from peatland will change substantially as CH4 production, microbial composition, and patterns of thawing-freezing cycles change with global warming. Therefore, frequent monitoring of CH4 fluxes in more peatlands and in situ monitoring of methanogenesis and related microbes are needed to provide a clear picture of CH4 fluxes and the thawing-freezing processes that affect them.

Microbial mechanisms related to the effects of bamboo charcoal and bamboo vinegar on the degradation of organic matter and methane emissions during composting.

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 (CH4) emissions during composting. BC+BV resulted in the highest degradation of OM. BV was most effective treatment in controlling CH4 emissions and it significantly reduced the abundance of the mcrA gene. Methanobrevibacter, Methanosarcina, and Methanocorpusculum were closely related to CH4 emissions during the thermophilic composting period. PICRUSt analysis showed that BC and/or BV enhanced the metabolism associated with OM degradation and reduced CH4 metabolism. Structural equation modeling indicated that BC+BV strongly promoted the metabolic activity of microorganisms, which had a positive effect on CH4 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.

Simultaneous reduction of antibiotics leakage and methane emission from constructed wetland by integrating microbial fuel cell

In this study, a microbial fuel cell coupled with constructed wetland (CW-MFC) was built to demonstrate that integration of MFC can enhance antibiotics (sulfadiazine (SDZ) and ciprofloxacin (CIP)) removal in CWs and control CH4 emissions. Better COD and antibiotics removal performance was obtained in CW-MFC. Notably, both reactors can remove more than 90.00% of CIP. A decline in methane fluxes (by 15.29%) was also observed in CW-MFC compared with CW. The presence of Acorus tatarinowii had no obvious effect on antibiotics removal but the application of manganese ore substrate reduced methane emissions. Further study showed that Proteobacteria was enriched on the Mn substrate anode and the relative abundance of Methanothrix was declined. The results suggested that suppression of methanogenesis may be contributed to a low methane flux in CW-MFC. This study will facilitate the application of CW-MFC to treat antibiotics wastewater and control the ecological risks of greenhouse gas emissions.

Effects of Temperature and Light on Methane Production of Widespread Marine Phytoplankton

AbstractMethane (CH4) production in the ocean surface mixed layer is a widespread but still largely unexplained phenomenon. In this context marine algae have recently been described as a possible source of CH4in surface waters. In the present study we investigated the effects of temperature and light intensity (including daylength) on CH4formation from three widespread marine algal speciesEmiliania huxleyi,Phaeocystis globosa,andChrysochromulinasp. Rates ofE. huxleyiincreased by 210% when temperature increased in a range from 10°C to 21.5°C, while a further increase in temperature (up to 23.8°C) showed reduction of CH4production rates. Our results clearly showed that CH4formation ofE. huxleyiis controlled by light: When light intensity increased from 30 to 2,670 μmol m−2 s−1, CH4emission rates increased continuously by almost 1 order of magnitude and was more than 1 order of magnitude higher when the daylength (light period) was extended from 6/18 hr light‐dark cycle to continuous light. Furthermore, light intensity is also an important factor controlling CH4emissions ofChrysochromulinasp. andP. globosaand could therefore be a species‐independent regulator of phytoplankton CH4production. Based on our results, we might conclude that extensive blooms ofE. huxleyicould act as a main regional source of CH4in surface water, since blooming ofE. huxleyiis related to the seasonal increase in both light and temperature, which also stimulate CH4production. Under typical global change scenarios,E. huxleyiwill increase its CH4production in the future.

Nitrogen fertilizer application in the rice-growing season can stimulate methane emissions during the subsequent flooded fallow period

Winter-flooded rice paddy field (FR), characterized by water conserved in the field during the fallow period, is a typical cropping system in southwest China, leading to considerable methane (CH4) emissions. The effect of nitrogen (N) fertilization on CH4 emissions during rice-growing seasons is well studied in FR, further studies covering N fertilizer applied in the rice-growing seasons affects CH4 emissions during the subsequent fallow period is needed. Therefore, a field experiment was conducted in an FR of Sichuan province, China, with conventional N fertilized (CN) and N unfertilized (NN) treatments. The cumulative CH4 emission from CN treatment during the rice-growing season and the subsequent fallow period was 389 ± 29.4 and 158 ± 31.2 kg C ha−1, which were increased by 29.5% and 395% in comparison with the NN treatment, indicting N applied during the rice growing-season significantly facilitated CH4 emission during the subsequent fallow period. During the rice-growing season, higher CH4 emission from CN treatment could be attributed to elevated soil dissolved organic carbon (DOC) content that might have provided sufficient substrates for CH4 production. During the fallow period, as compared to NN treatment, higher CH4 emissions from CN treatment could be explained by greater linear regression slopes between CH4 fluxes, soil temperature and DOC to dissolved inorganic N (DIN) (DOC/DIN) ratio. Moreover, the structural equation model (SEM) described that the soil temperature exhibited the most significant effects on CH4 emissions for both treatments during the rice-growing season and subsequent fallow period. These findings are a major step forward to showing that N fertilizer applied in the rice-growing season could also affect CH4 emission during the subsequent fallow period, accompanying other soil parameters controlling CH4 emission.