We want to learn which groups of soil microorganisms are responsible for particular biogeochemical processes and to understand the reason why. As a model we investigate biogeochemical processes involved in the exchange of climatically relevant trace gases (CH4, N2O, H2) between soil and atmosphere. A particular focus is on processes in flooded rice fields. Our experimental approach includes analytical chemical techniques and isotopic tracer studies (14C, 13C) for investigating the biogeochemical cycling of microbial substrates and effectors in soil and in microbial cultures. The molecular characterization of rRNA genes and different functional genes serves for elucidating the composition of microbial communities, including transcript analysis, fluorescent in situ hybridization (FISH), and stable isotope probing (SIP) for identification of metabolically active populations. A particular focus is on the investigation of the microbiology and biogeochemistry of the global cycle of methane, an important greenhouse gas.
Methanogenic archaea of the order Methanocellales (Rice Cluster I) were found to dominate the formation of methane on rice roots. There is some initial evidence that roots colonized with methanogens other than Methanocellales produce less methane. This is a promising aspect for the application of synthetic microbial communities to mitigate methane emission from rice fields. Therefore, we want to manipulate the microbial community on rice roots to understand the role of the various groups of microbes for the formation and emission of the greenhouse gas methane. Since rice fields are one of the main anthropogenic sources of methane, it is important to understand the role of microbial community composition for this process. Rice roots are colonized with a microbial community that eventually decomposes root exudates to methane. The operation of this process is crucial for the extent of methane emission from rice fields. The composition of the root microbial community does not appear to be random. For example, why are the Methanocellales an important group of methanogens? Can they be replaced by other methanogenic species? What effect would this have on methane emission? These are questions we investigate using rice microcosms with manipulated bacterial and archaeal communities.