Global warming has led to extensive permafrost degradation, particularly in thermally vulnerablepermafrost in the marginal or transitional zones of altitudinal or latitudinal permafrost. However,comprehensive knowledge about microbial communities in response to rapid permafrostdegradation at large (or interregional) scales remains elusive. In this meta-analysis, existingpublished data were utilized to identify the distributive and co-occurrence patterns of themicrobiome in two interregional locations: the Qilian Mountains on the northeasternQinghai-Tibet Plateau(NE-QTP) and the Xing'anling Mountainsin Northeast China(NE-China).Both areas are situated in the marginal zone of large permafrost units. The results reveal that therapidly degrading permafrost did not overshadow the regional biogeographic pattern of themicrobial community. Instead, the results show some distinctive biogeographic patterns, ascharacterized by different groups of characteristic bacterial lineages in each of the two regions. SoilpH has emerged as a crucial controlling factor on the basis of the available environmental data.Network-basedanalysessuggestagenerallyhighlevelofnaturalconnectivityforbacterialnetworkson the NE-QTP; however, it collapses more drastically than that in NE-China if the environmentalperturbations exceed the tipping point. These findings indicate that the biogeographic patterns ofthe bacterial community structure are not significantly altered by permafrost degradation. Thisresearch provides valuable insights into the development of more effective management methodsfor microbiomes in rapidly degrading permafrost.

Plant-associated microbiomes are structured by environmental conditions and plant associates, both of which are being altered by climate change. The future structure of plant microbiomes will depend on the, largely unknown, relative importance of each. This uncertainty is particularly relevant for arctic peatlands, which are undergoing large shifts in plant communities and soil microbiomes as permafrost thaws, and are potentially appreciable sources of climate change feedbacks due to their soil carbon (C) storage. We characterized phyllosphere and rhizosphere microbiomes of six plant species, and bulk peat, across a permafrost thaw progression (from intact permafrost, to partially- and fully-thawed stages) via 16S rRNA gene amplicon sequencing. We tested the hypothesis that the relative influence of biotic versus environmental filtering (the role of plant species versus thaw-defined habitat) in structuring microbial communities would differ among phyllosphere, rhizosphere, and bulk peat. Using both abundance- and phylogenetic-based approaches, we found that phyllosphere microbial composition was more strongly explained by plant associate, with little influence of habitat, whereas in the rhizosphere, plant and habitat had similar influence. Network-based community analyses showed that keystone taxa exhibited similar patterns with stronger responses to drivers. However, plant associates appeared to have a larger influence on organisms belonging to families associated with methane-cycling than the bulk community. Putative methanogens were more strongly influenced by plant than habitat in the rhizosphere, and in the phyllosphere putative methanotrophs were more strongly influenced by plant than was the community at large. We conclude that biotic effects can be stronger than environmental filtering, but their relative importance varies among microbial groups. For most microbes in this system, biotic filtering was stronger aboveground than belowground. However, for putative methane-cyclers, plant associations have a stronger influence on community composition than environment despite major hydrological changes with thaw. This suggests that plant successional dynamics may be as important as hydrological changes in determining microbial relevance to C-cycling climate feedbacks. By partitioning the degree that plant versus environmental filtering drives microbiome composition and function we can improve our ability to predict the consequences of warming for C-cycling in other arctic areas undergoing similar permafrost thaw transitions.