Mechanisms for Electron Uptake by Methanosarcina acetivorans during Direct Interspecies Electron Transfer

The conversion of organic matter to methane plays an important role in the global carbon cycle and is an effective strategy for converting wastes to a useful biofuel. The reduction of carbon dioxide to methane accounts for approximately a third of the methane produced in anaerobic soils and sediments as well as waste digesters.

Tree stem greenhouse gas emissions from forested closed landfill sites

<p>Tree planting has the potential to increase carbon sequestration and is used as a common management strategy on former landfill sites to improve their visual appeal and manage issues such as leachates from decomposing organic matter. Tree stems mediate methane (CH<sub>4</sub>) emissions to the atmosphere from anaerobic soils, bypassing bacterial populations that would otherwise break down CH<sub>4</sub> before it is released to the atmosphere. This process has been observed in wetland forests but has yet to be measured in a landfill context. We examined whether trees emitted more CH<sub>4</sub> and carbon dioxide (CO<sub>2</sub>) on a closed UK landfill site relative to a more natural, comparable control site to determine the importance of this natural phenomenon in a managed environment. CH<sub>4</sub> and CO<sub>2</sub> fluxes from tree stem and soil surfaces were measured using flux chambers and an off-axis integrated cavity output spectroscopy analyser. Temporal and seasonal variations in greenhouse gas emissions from landfill tree stems were also investigated, as well as the impact of different landfill management techniques including site closure methods and tree species planted. Analyses showed that tree stem emissions from landfill were larger than from trees in the non-landfill control site. However, there was high variability in the greenhouse gas fluxes from trees on the landfill. Findings from this investigation suggest that conditions associated with landfill construction may increase CH<sub>4</sub> emissions from trees planted on their surface after closure of the site. Trees planted on former landfill sites may therefore result in additional CH<sub>4</sub> emissions to the atmosphere.</p>

The occurrence and ecology of microbial chain elongation of carboxylates in soils

Chain elongation is a growth-dependent anaerobic metabolism that combines acetate and ethanol into butyrate, hexanoate, and octanoate. While the model microorganism for chain elongation, Clostridium kluyveri, was isolated from a saturated soil sample in the 1940s, chain elongation has remained unexplored in soil environments. During soil fermentative events, simple carboxylates and alcohols can transiently accumulate up to low mM concentrations, suggesting in situ possibility of microbial chain elongation. Here, we examined the occurrence and microbial ecology of chain elongation in four soil types in microcosms and enrichments amended with chain elongation substrates. All soils showed evidence of chain elongation activity with several days of incubation at high (100 mM) and environmentally relevant (2.5 mM) concentrations of acetate and ethanol. Three soils showed substantial activity in soil microcosms with high substrate concentrations, converting 58% or more of the added carbon as acetate and ethanol to butyrate, butanol, and hexanoate. Semi-batch enrichment yielded hexanoate and octanoate as the most elongated products and microbial communities predominated by C. kluyveri and other Firmicutes genera not known to undergo chain elongation. Collectively, these results strongly suggest a niche for chain elongation in anaerobic soils that should not be overlooked in soil microbial ecology studies.

The thermal response of soil microbial methanogenesis decreases in magnitude with changing temperature

Microbial methanogenesis in anaerobic soils contributes greatly to global methane (CH4) release, and understanding its response to temperature is fundamental to predicting the feedback between this potent greenhouse gas and climate change. A compensatory thermal response in microbial activity over time can reduce the response of respiratory carbon (C) release to temperature change, as shown for carbon dioxide (CO2) in aerobic soils. However, whether microbial methanogenesis also shows a compensatory response to temperature change remains unknown. Here, we used anaerobic wetland soils from the Greater Khingan Range and the Tibetan Plateau to investigate how 160 days of experimental warming (+4°C) and cooling (−4°C) affect the thermal response of microbial CH4 respiration and whether these responses correspond to changes in microbial community dynamics. The mass-specific CH4 respiration rates of methanogens decreased with warming and increased with cooling, suggesting that microbial methanogenesis exhibited compensatory responses to temperature changes. Furthermore, changes in the species composition of methanogenic community under warming and cooling largely explained the compensatory response in the soils. The stimulatory effect of climate warming on soil microbe-driven CH4 emissions may thus be smaller than that currently predicted, with important consequences for atmospheric CH4 concentrations.

Heavy metals in mangrove sediments along the Selangor River, Malaysia

Mangroves are woody plants that grow at the interface between land and sea in tropical and subtropical latitudes where they exist in conditions of high salinity, extreme tides, strong winds, high temperature, and muddy anaerobic soils. The objectives of this study were to determine the selected heavy metals Copper (Cu), Zinc (Zn) and Lead (Pb) contamination in mangrove sediments at the Selangor River, Kampung Kuantan, Kuala Selangor, Selangor, Malaysia; and to compare heavy metals content in mangrove sediments between different plots and different sediment depths. Physical properties (sediment texture and sediment moisture) and chemical properties (pH water, electrical conductivity, and selected heavy metals) of sediments were determined by different plots and depths. The element of Pb was analyzed using the Inductively Coupled Plasma (ICP), whereas Cu and Zn using the Atomic Absorption Spectrometer (AAS). Data obtained were analyzed using the Statistical Analysis System (SAS) version 9.4 software. The results showed that the sediment texture was in the class of sandy clay, and soil moisture in all plots and at all depths were high. The contamination of sediment is affected by many factors, including soil pH and soil electrical conductivity. Cu, Zn and PB in sediment were determined around 1.00-10.60 mg/kg, 215.40-259.00 mg/kg and 18.83-28.59 mg/kg respectively, and were found to experience a significant difference between the plots, but not a significant difference between depths. The sediment in all plots and at all depths was contaminated with these heavy metals because of it being surrounded by residential and industrial areas, combined with particular recreational activities, agriculture and fishing along the Selangor River.

Identification of QTLS for NH4+ and NO3- use efficiency under water stress and non-stress conditions and expression analysis of glutamine synthetase and nitrate reductase in rice (Oryza Sativa L.)

Nitrogen (N) is one of the most critical inputs and the current average nitrogen use efficiency (NUE) in the rice field is approximately 33%, poorest among cereals. Predominant form of N in aerobic soils is nitrate (NO3-) while ammonium (NH4+) exists in anaerobic soils. Development of cultivars with improved NH4+ or NO3- use efficiency by harnessing inherent significant variability for NUE can be an important approach. Considering these facts, the present study was established with one hundred twenty two and selected thirty two recombinant inbred lines (RILs) of two indica genotypes, Danteshwari × Dagad deshi under three nitrogen forms and three environments. The trend analysis of NH4+-N and NO3--N dynamics revealed that NH4+-N concentration persisted more under anaerobic condition and NO3--N concentration under aerobic conditions. Three way-ANOVA showed high level of significance for variance components (G, N, E) and their interactions effects (GXN, GXE, NXE, EXNXG) for yield and NUE and their component traits. Mean performance of genotypes depicted higher values for agronomically important traits i.e. yield and NUE under NH4+ as compared to NO3--N and N0. The phenotypic and genotypic data was statistically analyzed for QTLs identification for yield and NUE traits. A total of 58 QTLs conferring the corresponding five traits were detected under three N forms and two environments. We also investigated the different members of AMT (Ammonium transporters), NRT (Nitrate transporters), GS (Glutamine Synthetase) and GOGAT (Glutamate Synthase) genes, involved in NUE and analyzed the expression pattern of each gene using gene-specific primer in young rice seedlings. Collectively, OsGln1;1, OsGln1;2, OsGln1;3, OsGln2, OsGlt1 and OsGlt2 manifested different and reciprocal responses to nitrate and ammonium supply. The activity of enzymes NR, NiR, GS and GOGAT was significantly affected by NH4+and NO3- treatment. These results assist us to identify NH4+ and NO3- responsive cultivars which could be used for cultivation and/or used as parent’s in future breeding program to produce better nitrogen use efficiency varieties under water stress and non-stress conditions.