Stochastic process determines the spatial variations in microbial community inhabiting terrestrial mud volcanoes across the Eurasian continent

Abstract. Terrestrial mud volcanoes (MVs) represent the surface expression of conduits tapping fluid and gas reservoirs in the deep subsurface. Such plumbing channels provide a direct, effective means to extract deep microbial communities fueled by geologically produced gases and fluids. The drivers accounting for the diversity and composition of these MV microbial communities distributed over a wide geographic range remain elusive. This study characterized microbial communities of 15 terrestrial MVs across a distance of ~10,000 km of the Eurasian continent to test the validity of distance control and physiochemical factors in explaining biogeographic patterns. Our analyses yielded diverse community compositions with a total of 28,928 amplicon sequence variances taxonomically assigned to 73 phyla. Although no cosmopolitan member was found, community variance between geographic locations was higher than within sites, generating a slope of distance–decay relationship exceeding those for marine seeps and MVs, and seawater columns. For comparison, physiochemical parameters explained 12 % of community variance, and specific geochemical parameters were correlated with specific taxa. Overall, the apparent lack of fluid exchange renders terrestrial MVs a patchy habitat with microbiome comprising specific colonists that are highly adapted to the local environmental context and restricted in terms of dispersal capability.