CMI Annual Report 2022

ultimately makes mineral-poor, peaty wetlands drastically
more methanogenic (Wilmoth et al., 2021). The researchers
have pieced together fragments of genetic information from
Sphagnum peat microbiomes to recreate microbial genomes.
This has allowed the researchers to show that transient
oxygenation selects for different keystone microorganisms at
multiple steps of the microbial food chain underlying peat
carbon conversion into methane (Figure 9.1, Reji et al., 2022).
Figure 9.1.
Compared to continuously
oxygen-free conditions,
additional methane
formation can occur when
transient oxygen exposure
triggers a shift in microbial
community succession
during microbial
degradation of complex
aromatic peat carbon (Reji
et al., 2022).
The current work (Reji et al., in preparation) examines
wetlands along a freshwater to saltwater continuum, including
organic-rich peat composed of a different plant (Tree Moss
instead of Sphagnum), mineral-soil marsh, and saltmarsh
sediments. The goal is to better constrain the effects of
hydrologically driven oxygen variability on methane
emissions from a greater diversity of wetlands. Results point to
highly variable responses of different wetland types to changes
in oxygen levels. Unlike in Sphagnum peat (Wilmoth et al.,
2021), methane emissions in Tree Moss peat were largely
unaffected by oxygen exposure (Figure 9.2a). While a similar
trend was observed for the freshwater marsh, saltmarsh
sediments did not release any methane. In contrast, CO 2
emissions were generally higher (up to ~threefold) in oxygenshifted
samples across all three wetland types. This was
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Carbon Mitigation Initiative Twenty-second Year Report 2022