Page 212 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 9. Long-term warming effects on permafrost soil microbial communities
Figure 5. Shift of functional composition at pathway level over long-term incubation for the active layer (AL), transition layer (TL), and permafrost (PF). Carbon cycle (methane) includes both CH4 production and aerobic CH4 oxidation.
To assess the functional changes in more detail, we analyzed relative abundance changes for key functional marker genes (Table S3) of the major biogeochemical cycles (Fig. 6). The analysis of individual key functional genes showed general agreement with the analysis on whole pathway level as described before. For acetogenesis (the Wood-Ljungdahl pathway), the change in Acetyl-CoA synthase subunit gamma (acsC) in TL was most pronounced, but this was not reflected in the change observed for carbon monoxide dehydrogenase catalytic subunit (cooS). The cooS sequences were affiliated with Chloroflexi (35-61%), Proteobacteria (33- 51%) and Actinobateria (2-22%). For methanogenesis, there was an overall decrease in relative abundance of the gene encoding for methyl-coenzyme M reductase subunit alpha (mcrA) in all layers, which matched with the shift in functional composition (Fig. 5) and the overall decrease in methanogenic archaea that was observed in the 16S rRNA gene relative abundance (Fig. 3).
Within the nitrogen cycle, different pathways showed distinct responses to long-term warming. Relative abundances of nitrate reduction genes (periplasmic nitrate reductase subunit alpha napA, and nitrate reductase subunit alpha narG) increased in AL but decreased in TL and PF.
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