| Popis: |
The methanotrophic bacteria are the only known biological sink for the third most important greenhouse gas methane, performing an important ecosystem function influencing global climate change. In the soil surface layer of water logged soils aerobic methanotrophs thrive at the oxic-anoxic interface attenuating the amount of potentially emitted methane. The highly diverse methanotroph community is shaping the interface characterized by overlapping methane and oxygen gradients by their own activity. However, how the different methanotrophs physically share their microhabitat at the interface is unknown. Here we highly resolved the vertical distribution and activity of methanotrophs at the interface. To assess the structure of the present and active methanotroph community the particulate methane monooxygenase gene pmoA was used as a functional and phylogenetic marker. For quantification of pmoA genes and transcripts a new method, the competitive-(reverse transcriptase)-t-RFLP was established. Only a subset of the methanotroph community was shown to be active and the major activity was confined to a small zone around the interface. The predominantly active methanotrophs were affiliated to Methylobacter and no transcripts of type II methanotrophs (Methylosinus, Methylocystis) were found. Hence, different species within this guild exploited different niches in the same microenvironment. Furthermore, the methanotrophs resistance to desciccation (up to 18 years) was tested. Longer-lasting droughts reduced methanotrophic diversity, and adversely affected methane oxidation upon rewetting. Type I methanotrophs showed relatively higher pmoA gene expression, while type II were more resistant to desiccation. Finally, we showed that high methane source strength aids the ability of the methanotroph community to recover from the effect of a strong disturbance. However, recovery of the type II community was independent of pmoA gene expression and source strength indicating facultative growth. Overall, the methanotroph community in the soil surface layer is highly diverse. This work contributed to understand the high and apparently redundant diversity by unravelling niche differentiation at the fine spatial resolution and evaluating the effect of different source strength. Moreover, the range of alternative substrates used for growth seems to be another important factor in the environment. |
