Responses of CH_4 Emissions to Nitrogen Addition and Spartina alterniflora Invasion in Minjiang River Estuary, Southeast of China

The nitrogen （N） input and Spartina alterniflora invasion in the tidal marsh of the southeast of China are increasingly serious. To evaluate CH4 emissions in the tidal marsh as affected by the N inputs and S. alterniflora invasion, we measured CH4 emissions from plots with vegetated S. alterniflora and native Cyperus malaccensis, and fertilized with exogenous N at the rate of 0 （NO）, 21 （N1） and 42 （N2） g N/（m2.yr）, respectively, in the Shanyutan marsh in the Minjiang River estuary, the southeast of China. The average CH4 fluxes during the experiment in the C. malaccensis and S. alterniflora plots without N addition were 3.67 mg CHa/（m2.h） and 7.79 mg CH4/（m2-h）, respectively, suggesting that the invasion of S. alterniflora into the Minjiang River estuary stimulated CH4 emission. Exogenous N had positive effects on CH4 fluxes both in native and in invaded tidal marsh. The mean CH4 fluxes of NI and N2 treat- ments increased by 31.05% and 123.50% in the C. malaccensis marsh, and 63.88% and 7.55% in the S. alterniflora marsh, respectively, compared to that of NO treatment. The CH4 fluxes in the two marshes were positively correlated with temperature and pH, and nega- tively correlated with electrical conductivity and redox potential （Eh） at different N addition treatments. While the relationships between CH4 fluxes and environmental variables （especially soil temperature, pH and Eh at different depths） tended to decrease with N additions. Significant temporal variability in CH4 fluxes were observed as the N was gradually added to the native and invaded marshes. In order to better assess the global climatic role of tidal marshes as affected by N addition, much more attention should be paid to the short-term temporal variability in CH4 emission.

Super Rice Cropping Will Enhance Rice Yield and Reduce CH_4 Emission:A Case Study in Nanjing,China

A pot experiment was performed to learn the differences in plant productivity and OH4 emission between two rice cultivars, super rice variety Ningjing 1 and traditional variety Zhendao 11, which were currently commercially appUed 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.

Methane emissions from natural and drained peatlands in the Zoigê, eastern Qinghai-Tibet Plateau

Peatlands are one of the major natural sources of methane （CH4）, but the level of CH4 efflux is uncertain, especially in alpine peatlands. In this study, CH4 emission fluxes from natural and drained peatlands on the Qinghai- Tibet Plateau, southwest China, were measured from June to October in 2013 using the opaque static chamber technique and the Fast Greenhouse Gas Analyzer （DLT-100, Los Gatos Research Corp.）. CH4 emission fluxes ranged from 2.07 to 56.33 mg m^-2 h^-1 in natural peatlands and from 0.02 to 0.42 mg m^-2 h^-1 in drained peatlands. Mean CH4 emission flux was 19.13 mg m^-2 h^-1 in natural peatlands and 0.14 mg m^-2 h^-1 in drained peatlands. These results showed that drainage led to a significant decrease in CH4 emissions. CH4 emission fluxes for all sampling plots were significantly correlated with variation in water table depth for linear （R^2 = 0.453, P 〈 0.01） and exponential functions （R^2 = 0.429, P 〈 0.01）.

CH_4 emissions and reduction potential in wastewater treatment in China

The treatment of domestic and industrial wastewater is one of the major sources of CH_4 in the Chinese waste sector. On the basis of statistical data and country-specific emission factors, using IPCC methodology, the characteristics of CH_4 emissions from wastewater treatment in China were analyzed. The driving factors of CH_4 emissions were studied, and the emission trend and reduction potential were predicted and analyzed according to the current situation. Results show that in 2010, CH_4 emissions from the treatment of domestic and industrial wastewater were0.6110 Mt and 1.6237 Mt, respectively. Eight major industries account for more than 92% of emissions, and CH_4 emissions gradually increased from 2005 to 2010. From the controlling management scenario, we predict that in 2020, CH_4 emissions from the treatment of domestic and industrial wastewater will be 1.0136 Mt and 2.3393 Mt, respectively, and the reduction potential will be 0.0763 Mt and 0.2599 Mt, respectively.From 2010 to 2020, CH_4 emissions from the treatment of domestic and industrial wastewater will increase by 66% and 44%, respectively.

Comparison of Field Measurements of CH_4 Emission from Rice Cultivation in Nanjing, China and in Texas, USA

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. Key words CH4 emission - Rice paddies - Rice biomass production - Soil temperature This work was supported by grants from TECO/NASA, the United States, the Hundred Talents Program, Chinese Academy of Sciences and the National Key Basic Research Development Foundation (approved # G1999011805), China.

ESTIMATE OF METHANE EMISSIONS FROM RICE FIELDS IN CHINA BY CLIMATE-BASED NET PRIMARY PRODUCTIVITY

Rice fields provide food for over half of the world population but are also an important source of atmospheric CH(4). Using the climate-based GIS empirical model and the meteorological data collected from 600 meteorological stations in China, with county as the basic unit, the net primary productivity (NPP) of rice fields in China in 1990, 1995, 1998, and 2000 were estimated to be in the range from 202.19x10(12)g C in 1990 to 163.46x10(12)g C in 2000. From the measured data of the factors affecting CH(4) emission and NPP, the conversion ratio of the NPP into CH(4) emission for the rice fields of China was determined to be 1.8%. Using this ratio and estimated NPP, the CH(4) emissions from rice fields of China in 1990, 1995, 1998, and 2000 were estimated to be 7.24x10(12), 6.31x10(12), 6.77x10(12) and 5.85x10(12)g CH(4), respectively.

Relationships Between Abundance of Microbial Functional Genes and the Status and Fluxes of Carbon and Nitrogen in Rice Rhizosphere and Bulk Soils

Rapid nitrogen(N) transformations and losses occur in the rice rhizosphere through root uptake and microbial activities. However,the relationships between rice roots and rhizosphere microbes for N utilization are still unclear. We analyzed different N forms(NH+4,NO-3, and dissolved organic N), microbial biomass N and C, dissolved organic C, CH4 and N2O emissions, and abundance of microbial functional genes in both rhizosphere and bulk soils after 37-d rice growth in a greenhouse pot experiment. Results showed that the dissolved organic C was significantly higher in the rhizosphere soil than in the non-rhizosphere bulk soil, but microbial biomass C showed no significant difference. The concentrations of NH+4, dissolved organic N, and microbial biomass N in the rhizosphere soil were significantly lower than those of the bulk soil, whereas NO-3in the rhizosphere soil was comparable to that in the bulk soil. The CH4 and N2O fluxes from the rhizosphere soil were much higher than those from the bulk soil. Real-time polymerase chain reaction analysis showed that the abundance of seven selected genes, bacterial and archaeal 16 S rRNA genes, amoA genes of ammonia-oxidizing archaea and ammonia-oxidizing bacteria, nosZ gene, mcrA gene, and pmoA gene, was lower in the rhizosphere soil than in the bulk soil, which is contrary to the results of previous studies. The lower concentration of N in the rhizosphere soil indicated that the competition for N in the rhizosphere soil was very strong, thus having a negative effect on the numbers of microbes. We concluded that when N was limiting, the growth of rhizosphere microorganisms depended on their competitive abilities with rice roots for N.

Methane emissions from livestock in East Asia during 1961−2019

Context:East Asia is a crucial region in the global methane(CH4)budget,with significant contributions from the livestock sector.However,the long-term trend and spatial pattern of CH4 emissions from livestock in this region have not been fully assessed.Methods:Here,we estimate CH4 emissions from 10 categories of livestock in East Asia during 1961-2019 following the Tier 2 approaches suggested by the 2019 Refinement to the IPCC 2006 Guidelines.Results:livestock-sourced CH4 emission in 2019 was 13.22[11.42-15.01](mean[minimum%maximum of 95-confidence interval]Tg CH4 yr-1,accounting for an increase of 231%since 1961.The contribution of slaughtered populations to total emissions increased from 3%in 1961 to 24%in 2019.Spatially,the emission hotspots were mostly distributed in eastern China,South Korea,and parts of Japan,but they tend to shift northward after 2000.Conclusion:It is necessary to use dynamic emission factors and include slaughtered populations in the estimation of livestock CH4 emissions.Regions including Northern China,Mongolia,and South Korea deserve more attention in future CH4 mitigation efforts.

CH_4 EMISSION FROM A CHINESE RICE PADDY FIELD

CH_4 emission rates have been measured continuously for the early rice of 1988 and late rices of 1987 and 1988 during entire growing seasons in a rice paddy field in Hangzhou,Zhejiang Province,China,by using an automatic sampling and analyzing system.During most parts of the seasons CH_4 emission rates showed strong diurnal variations.Bi-mode patterns with the highest value in the afternoon and a second peak at mid-night were generally found for the early rice,while the highest values were almost always found in the night for the late rice.Bi-mode patterns with a second peak in the afternoon were also found during the reproductive phase of the late rice plants.These diurnal variations may be explained by the diurnal variations of the soil temperature and the activity of rice plants.Strong seasonal variations with one peak in the tillering stage and two during the reproductive phase of rice plants were observed for all the three growing seasons.The seasonal variations may be explained by the activity of rice plants,availability of organic substrates in the soil,and the activity of soil bacteria related to soil temperatures,Fertilization did not show significant effects on the total seasonal CH_4 emissions but slightly changed the pattern of the seasonal variations of the CH_4 emission rates.Averaged over the measuring periods and 8 spots,CH_4 emission rates of 7.8 mg m^(-2) h^(-1) for the early rice and 28.6 mg m^(-2) h^(-1) for the late rice were obtained. Based on these measured data,the total global emission of CH_4 from rice paddies is estimated to be about 90 Tg/yr ranging from 70 to 110,accounting for 20% of the total source of CH_4.

Multi-regional input-output analysis for China＇s regional CH4 emissions

China is the largest CH4 emitter in the world. Given the importance of CH4 in greenhouse gas emission inventories, the characteristics ofChina＇s CH4 emissions at different scales deserve to be fully understood. Presented in this paper is an interprovincial input output embodi- ment analysis of China＇s regional CH4 emissions in 2007, based on the most recently available multi-regional input- output table, and relevant CH4 emissions data. The results show that the eastern, central and western areas contribute to 48.2%, 28.6%, and 23.3% of the national total embodied emissions, respectively. Guangdong has the highest level of embodied CH4 emissions among all of the 30 regions. The Agriculture sector produces the most embodied CH4 emissions in final demand, followed by the Construction, Food Production and Tobacco Processing, and Other Service Activities sectors. Significant net transfers of embodied CH4 emission flows are identified from the central and western areas to the eastern area via interregional trade. Shanxi is the largest interregional exporter of embodied CH4 emissions. In contrast, Guangdong is the largest interregional importer. Energy activities, agricultural activities, and waste management comprise 65.6%, 30.7%, and 3.7% of the total embodied CH4 emissions in interregional trade, respectively. By using consumption-based accounting principles, the emis- sion magnitudes, per capita emissions, and emission intensities of most eastern regions increase remarkably, while those of some central and western regions decrease largely. To achieve regional CH4 emission mitigation, comprehensive mitigation measures should be designed under consideration of regional transfer of emission responsibility.

CH_4 Oxidation Potentials of Diferent Land Uses in Three Gorges Reservoir Area of Central Subtropical China

To compare the CH4 oxidation potential among different land uses and seasons, and to observe its response to monsoon precipi- tation pattern and carbon and nitrogen parameters, a one-year study was conducted for different land uses （vegetable field, tilled and non-tilled orchard, upland crops and pine forest） in central subtropical China. Results showed significant differences in CH4 oxidation potential among different land uses （ranging from -3.08 to 0.36 kg CH4 ha-1 year-l）. Upland with corn-peanut-sweet potato rotation showed the highest CH4 emission, while pine forest showed the highest CH4 oxidation potential among all land uses. Non-tilled citrus orchard （-0.72 ~ 0.08 kg CHa ha-1 year-1） absorbed two times more CH4 than tilled citrus orchard （-0.38 ~ 0.06 kg CH4 ha-1 year-l）. Irrespective of different vegetation, inorganic N fertilizer application significantly influenced CH4 fluxes across the sites （R2 ： 0.86, P -- 0.002）. Water-filled pore space, soil microbial biomass carbon, and dissolved nitrogen showed significant effects across different land uses （31% to 38% of variability） in one linear regression model. However, their cumulative interaction was significant for pine forest only, which might be attributed to undisturbed microbial communities legitimately responding to other variables, leading to net CH4 oxidation in the soil. These results suggested that i） natural soil condition tended to create win-win situation for CH4 oxidation, and agricultural activities could disrupt the oxidation potentials of the soils; and ii） specific management practices including but not limiting to efficient fertilizer application and utilization, water use efficiency, and less soil disruption might be required to increase the CH4 uptake from the soil.

CH_4 emission and conversion from A^2O and SBR processes in full-scale wastewater treatment plants

Wastewater treatment systems are important anthropogenic sources of CH4 emission. A full-scale experiment was carried out to monitor the CH4 emission from anoxic/anaerobic/oxic process （A2O） and sequencing batch reactor （SBR） wastewater treatment plants （WWTPs） for one year from May 2011 to April 2012. The main emission unit of the A2O process was an oxic tank, accounting for 76.2% of CH4 emissions; the main emission unit of the SBR process was the feeding and aeration phase, accounting for 99.5% of CH4 emissions. CH4 can be produced in the anaerobic condition, such as in the primary settling tank and anaerobic tank of the A2O process. While CH4 can be consumed in anoxic denitrification or the aeration condition, such as in the anoxic tank and oxic tank of the A2O process and the feeding and aeration phase of the SBR process. The CH4 emission flux and the dissolved CH4 concentration rapidly decreased in the oxic tank of the A2O process. These metrics increased during the first half of the phase and then decreased during the latter half of the phase in the feeding and aeration phase of the SBR process. The CH4 oxidation rate ranged from 32.47% to 89.52% （mean： 67.96%） in the A2O process and from 12.65% to 88.31% （mean： 47.62%） in the SBR process. The mean CH4 emission factors were 0.182 g/ton of wastewater and 24.75 g CH4/（person.year） for the A2O process, and 0.457 g/ton of wastewater and 36.55 g CH4/（person.year） for the SBR process.

Effect of calcium silicate on nutrient use of lowland rice and greenhouse gas emission from a paddy soil under alternating wetting and drying

In intensively irrigated rice cultivation,plant-available silicon(Si)is a crucial nutrient for improving rice productivity.As a source of Si,calcium silicate(CaSiO3)was amended to evaluate the effect of silicate fertilizer on rice production,nitrogen(N)use efficiency,and greenhouse gas(GHG)emission under alternating wetting and drying in a pot experiment using a tropical soil from a paddy field of the International Rice Research Institute(IRRI)in the Philippines.Four levels of CaSiO3 amendment,0,112.7,224.5,and 445.8 kg ha^-1,with the recommended N rate were tested.The results showed that although CaSiO3amendment of 112.7 kg ha^-1resulted in higher rice straw,improved N use efficiency,and reduced N2O emission,there was no difference in grain yield among the four levels of CaSiO3 amendment owing to relatively lower harvest index.Moreover,CaSiO3 amendment showed a reverse trend between CH4 and N2O emissions as it reduced N2O emission while led to significantly increased CH4 emission and global warming potential.Thus,CaSiO3 amendment was a possible alternative to improve N use efficiency and increase rice straw biomass,but it needs to be reviewed in line with grain yield production and GHG emission.It is also imperative to test an optimal method of silicate fertilizer amendment in future research in order to compromise a negative impact in tropical soils.