Abstract. Methane is an important end product of degradation of organic matter in anoxic lake sediments. Methane is mainly produced by either reduction of CO2 or cleavage of acetate involving different methanogenic archaea. The contribution of the different methanogenic paths and of the diverse bacteria and archaea involved in CH4 production exhibits a large variability that is not well understood. Lakes in tropical areas, e.g. in Brazil, are wetlands with high potential impact on the global CH4 budget. However, they have hardly been studied with respect to methanogenesis. Therefore, we used samples from 16 different lake sediments in the Pantanal and Amazon region of Brazil to measure production of CH4, CO2, analyze the content of 13C in the products and in intermediately formed acetate, determine the abundance of bacterial and archaeal microorgansisms and their community composition and diversity by targeting the genes of bacterial and archaeal ribosomal RNA and of methyl coenzyme M reductase, the key enzyme of methanogenic archaea. These experiments were done in the presence and absence of methyl fluoride, an inhibitor of acetoclastic methanogenesis. While production rates of CH4 and CO2 were correlated to the content of organic matter and the abundance of archaea in the sediment, values of 13C in acetate, CO2, and CH4 were related to the 13C content of organic matter and to the path of CH4 production with its intrinsic carbon isotope fractionation. Isotope fractionation was small (average 10‰) for conversion of Corg to acetate-methyl, which was hardly further fractionated during CH4 production. However, fractionation was strong for CO2 conversion to CH4 (average 75‰), which generally accounted for >50% of total CH4 production. Canonical correspondence analysis did not reveal an effect of microbial community composition, despite the fact that it exhibited a pronounced variability among the different sediments.

Stable carbon isotope discrimination and microbiology of methane formation in tropical anoxic lake sediments

Use of efficient water saving techniques for production of rice in India under climate change scenario: A critical review

The use of plastic film in agriculture strongly affects the decomposition of soil organic carbon (SOC) and the release of methane (CH4) and nitrous oxide (N2O) by influencing soil biogeochemical processes. However, no systematic conclusions have been reached regarding the effect of plastic film mulching on SOC stocks and greenhouse gas (GHG) budgets. In this study, a meta-analysis compiling data from 150 studies was used to assess the effects of film mulching on SOC and soil GHG fluxes across different agricultural systems. In addition, the net global warming potentials (GWPs) of SOC, CH4 and N2O were calculated with the GWP approach. Plastic film mulching significantly promoted crop yield by 48.6%; did not affect SOC; reduced CH4 emissions from paddy fields by 64.2% and CH4 uptake in uplands by 16.1%; and increased soil N2O emissions by 23.9%. The effect of mulching on SOC and GHG fluxes varied among agricultural systems. Compared with the non-mulched field, the use of plastic film significantly increased SOC and decreased CH4 uptake in rainfed uplands but reduced SOC in irrigated uplands. In paddy fields, this practice significantly reduced the SOC stock and CH4 emissions but increased N2O emissions. Our results suggest that a low coverage ratio (

A meta-analysis of film mulching cultivation effects on soil organic carbon and soil greenhouse gas fluxes

Effects of long-term no tillage and straw return on greenhouse gas emissions and crop yields from a rice-wheat system in central China

Paddy-upland rotation with Chinese milk vetch incorporation reduced the global warming potential and greenhouse gas emissions intensity of double rice cropping system

Tillage with the incorporation of stubble is a common practice in rice cultivation, but its effect on the net global warming potential (GWP) and greenhouse gas intensity (GHGI) is poorly documented. A three-year field experiment in a double-cropping rice system was conducted to investigate the rate of sequestration of soil organic carbon, CH4 and N2O emissions, the net GWP and the GHGI. Two timings of tillage with three amounts of stubble incorporation were prepared: winter tillage (tillage after the harvest of late rice) and spring tillage (tillage before the transplantation of early rice) with no (0 t ha−1), low (3.5 t ha−1) and high (5.2 t ha−1) amounts of stubble incorporation. The results showed that the rates of sequestration of soil organic carbon with the incorporation of stubble were 0.85–1.06 t C ha−1 yr−1 for winter tillage, 67–429% higher than for spring tillage. Winter tillage significantly increased CH4 and N2O emissions in the winter fallow season relative to spring tillage, whereas it tended to decrease both emissions in the early and late rice seasons, thus playing a small part in the annual emissions. The total CH4 and N2O emissions averaged 106.5–198.2 kg ha−1 yr−1 and 114.4–229.4 g N ha−1 yr−1, respectively. Significant decreases in the net GWP (46–82%) and GHGI (49–84%) were observed when changing the tillage practices with the incorporation of stubble from spring to winter. Compared with high levels of stubble incorporation, winter tillage with low levels of stubble incorporation significantly decreased both the net GWP and the GHGI. The total grain yield was 13.0–13.3 t ha−1 yr−1 for winter tillage, 3–5% higher than for spring tillage. These findings suggest that tillage with the incorporation of stubble in the winter fallow season, particularly with 3.5 t ha−1 stubble, is an effective strategy to mitigate the net GWP and GHGI while maintaining a high grain yield in the double-cropping rice system.

Winter tillage with the incorporation of stubble reduces the net global warming potential and greenhouse gas intensity of double-cropping rice fields

Achieving low methane and nitrous oxide emissions with high economic incomes in a rice-based cropping system.

Evaluation of methane and nitrous oxide emissions in a three-year case study on single rice and ratoon rice paddy fields

Responses of greenhouse gas emissions and soil carbon and nitrogen sequestration to field management in the winter season: A 6-year measurement in a Chinese double-rice field

Kaifu Song

Papers

Winter tillage with the incorporation of stubble reduces the net global warming potential and greenhouse gas intensity of double-cropping rice fields

Achieving low methane and nitrous oxide emissions with high economic incomes in a rice-based cropping system.

Evaluation of methane and nitrous oxide emissions in a three-year case study on single rice and ratoon rice paddy fields

Responses of greenhouse gas emissions and soil carbon and nitrogen sequestration to field management in the winter season: A 6-year measurement in a Chinese double-rice field

Reducing yield-scaled global warming potential and water use by rice plastic film mulching in a winter flooded paddy field