研究課題
樹木の幹に生息するメタン生成微生物群集の物理的・生化学的環境(の解明)
Elucidation of the physical and biochemical environment of methane-producing microbial communities living in tree trunks
研究組織
| 代表者 | EPRON Daniel, Kyoto University, Graduate School of Agriculture |
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| 共同研究者 | NISHIMURA Hiroshi, Kyoto University, RISH COURSEUT Nathan (exchange student) Kyoto University, GS Agriculture / Université de Lorraine (Nancy, France) |
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研究概要
CH4 is the second most important anthropogenic greenhouse gas and rise of atmospheric CH4 concentration has accelerated these last years. In addition to global warming, CH4 oxidation in the troposphere leads to ozone production, which is harmful to human health and crop yields. Forests are a well-known carbon sinks, which mitigate the rise in atmospheric CO2 and hence global warming. Soils in upland forests are the largest biological sink for atmospheric CH4, providing a valuable ecosystem service. However, trees emit CH4 and it is necessary to take into account the role of the trees in addition to that of the soil to establish a complete methane balance of a forest ecosystem. Mountain forests cover nearly two-thirds of Japan land area, but we still know little about the role of trees in their CH4 budget.
CH4 that accumulates in the trunk of living trees can be produced endogenously by methanogenic archaea. We recently discovered that methanogenic archaea were present in wood samples of several species sampled from the Ashiu forest. However, little is known about factors that shape and control the composition and activity of microbial communities inhabiting the trunks. The onset of wood decay in mature tree trunks is the starting point of complex biochemical processes.
We hypothesize that cellulose and pectin degradation in heartwood provides carbohydrates which are substrates for fermentation that produces acetate, CO2 and H2 used by the methanogenic archaea under anoxic conditions. We also postulate that phenolic compounds, either constitutive or produced by lignin degradation, act as antibiotic substances against methanogenic microbes. Our goal is therefore to characterize the physical and biochemical environment in which CH4 production occurs.
Sampling will be conducted in the Ashiu experimental forest on sugi and buna trees. Wood cores will be sampled immediately after measuring trunk CH4 flux. A stainless tube will be inserted in each hole resulting from the coring and plugged with a rubber septum. Gas will be drawn from inside the tube through the septum into a syringe and injected to our gas analyser (CO2, CH4). Wood core segments representing the inner and outer heartwood and the sapwood will be cut from all the wood cores extracted from the trunks, sealed in glass vials flushed with an incubation mixture (10% CO2 and 1% H2 in N2) to estimate the potential CH4 production capacity of wood by drawing and analysing gas from each vial at regular intervals. The wood core segments will be used to characterize the wood microenvironment (wetness, density, osmolyte content, pH) and extract water-soluble and ethanol-soluble organic compounds (carbohydrates, acetate, methylated compounds, secondary metabolites) to be analysed colorimetrically and by gas chromatography mass spectrometer. DNA will be extracted and purified before performing PCR amplifications to characterize microbial communities in tree trunks
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2024年7月30日作成
