Effects of hydrogeochemistry on the microbial ecology of terrestrial hot springs

Temperature, pH, and hydrochemistry of terrestrial hot springs play a critical role in shaping thermal microbial communities. However, the interactions of biotic and abiotic factors at this terrestrial-aquatic interface are still not well understood on a global scale, and the question of how underground events influence microbial communities remains open. To answer this, 11 new samples obtained from the El Tatio geothermal field were analyzed by 16S rRNA amplicon sequencing (V4 region), along with 191 samples from previous publications obtained from the Taupo Volcanic Zone, the Yellowstone Plateau Volcanic Field, and the Eastern Tibetan Plateau, with their temperature, pH, and major ion concentration. Microbial alpha diversity was lower in acid-sulfate waters, and no significant correlations were found with temperature. However, moderate correlations were observed between chemical parameters such as pH (mostly constrained to temperatures below 70degree celsius), SO42- and abundances of members of the phyla Armatimonadota, Deinococcota, Chloroflexota, Campilobacterota, and Thermoplasmatota. pH and SO42- gradients were explained by phase separation of sulfur-rich hydrothermal fluids and oxidation of reduced sulfur in the steam phase, which were identified as key processes shaping these communities. Ordination and permutational analysis of variance showed that temperature, pH, and major element hydrochemistry explain only 24% of the microbial community structure. Therefore, most of the variance remained unexplained, suggesting that other environmental or biotic factors are also involved and highlighting the environmental complexity of the ecosystem and its great potential to test niche theory ecological associated questions.

Automated summary

Temperature, pH, and hydrochemistry of terrestrial hot springs have a critical role in shaping thermal microbial communities. However, the interactions of biotic and abiotic factors at the terrestrial-aquatic interface on a global scale are not well understood, and the influence of underground events on microbial communities remains unknown. The study found moderate correlations between pH, SO42-, and the abundance of certain microbial phyla. pH and SO42- gradients were explained by phase separation and oxidation of sulfur in the steam phase. However, a large portion of the variance in microbial community structure remains unexplained, suggesting the involvement of other environmental or biotic factors.