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, which are distributed over a wide geographic range, remain
elusive. This study characterized the variation in microbial communities in
15 terrestrial MVs across a distance of ∼ 10 000 km on 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 (ASVs) taxonomically assigned to 73 phyla. While no true
cosmopolitan member was found, ∼ 85 % of ASVs were confined
within a single MV. Community variance between MVs appeared to be higher and
more stochastically controlled than within MVs, generating a slope of the
distance–decay relationship exceeding those for marine seeps and MVs as well as
seawater columns. For comparison, physiochemical parameters explained 12 %
of community variance, with the chloride concentration being the most
influential factor. Overall, the apparent lack of fluid exchange renders
terrestrial MVs a patchy habitat, with microbiomes diverging stochastically
with distance and consisting of dispersal-limited colonists that are highly
adapted to the local environmental context.