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Project summary:
The aim of this project is to assess potential impacts of wild fire and forest harvesting operations on the net soil/atmosphere greenhouse gas (GHG) exchange in a wet temperate Eucalyptus obliqua forest system at the Warra Long Term Ecological Research site in Tasmania. This project specifically investigates if stand replacing wild fires and stand harvesting operations have an impact on soil atmosphere CH4 exchange and the diversity of methanotrophic soil bacteria. Methane uptake by soils is the largest terrestrial sink for this important greenhouse gas and understanding the processes that control methane uptake in soils will greatly improve ability to assess and improve greenhouse gas mitigation options in native ecosystems. Methane uptake in temperate forest soils is attributed to methanotrophic bacteria that are difficult to cultivate and therefore challenging to study in a laboratory environment. Our insight into the processes and factors that determine methane uptake in temperate forest soils worldwide is still very limited due to the lack of adequately sensitive trace gas and microbiological methods. Recent developments in real time gas measurement systems (e.g. FTIR and TDL) and high throughput population screening methods (T-RFLP and DNA-Sequencing) enable more precise and efficient research in this area.
The following methods will be used: Trace gas fluxes: Seasonal and spatial variation in soil GHG fluxes will be measured with 15 manual incubated soil chambers on each site in a closed chamber setup. Gas samples will be taken at fixed intervals after chamber closure and will be analysed on a gas chromatograph (GC) in the University of Melbourne laboratory in Creswick for the concentration of the gases methane, nitrous oxide and carbon dioxide. Fluxes can than be calculated out of the regression of gas concentration change with time. Soil biochemical properties: A suite of established methods will be used to assess surface soils (0-10cm depth) where most of the methane oxidation occurs at each site: Soil N and P status; pH; EC; bulk density (BD); gravimetric water content; volumetric water content; exchangeable anions and cations; soil total C/N and temperature. Soil diffusivity will be assessed using sulfur-hexa-fluoride (SF6) as an inert trace gas during chamber incubations. SF6 concentration will be analysed on a gas chromatograph (GC). Methanotrophic community structure: Terminal restriction fragment length polymorphism (T-RFLP) based on PCR amplification of the pmoA gene will result in high-resolution community fingerprints of the methanotrophs and will allow comparison of methanotroph communities between sites and treatments samples for DNA extraction will be collected for each site close to where soil trace gas fluxes are measured. We have established the T-RFLP methodology at the University of Melbourne Creswick laboratories. Clone library construction and DNA sequencing will also target the pmoA gene of selected samples. This will enable a detailed phylogenetic comparison of methanotrophic communities, identify novel methanotrophs, and directly compare the methanotrophs identified through this study with those identified by other researchers throughout the world.
Methodology: Not available
Datasets: None available.
Publications: None available.
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