Hydrochemical associations with microbial community structure in the Reshuigou hot springs, northeastern Qinghai-Tibet Plateau.

Geothermal hot springs provide important windows into the links among deep hydrothermal circulation, water-rock interaction, and microbial ecology in extreme environments. This study investigated six hot-spring water samples from Reshuigou, Guide County, Qinghai Province, by integrating hydrochemical analysis, PHREEQC mineral saturation calculations, microbial community profiling, RDA, PCoA environmental fitting, and Spearman correlation analysis. The Reshuigou waters were characterized by medium to high temperature, weak alkalinity, reducing conditions, and moderate to relatively high mineralization. Their hydrochemical facies were consistently of the Na+K/Cl-SO₄ type, reflecting deep-circulation water-rock interaction, sulfate and chloride inputs, silicate dissolution, and ion exchange. The microbial communities were dominated by Proteobacteria, Aquificota, Deinococcota, Chloroflexi, and Bacteroidota, with Hydrogenobacter, Thermus, Herbaspirillum, and Delftia as important genera. Phylum- and genus-level RDA accounted for 71.9 and 77.4% of the constrained community variation, respectively. Spearman analysis further showed an inverse relationship between Chloroflexi and ORP, a positive relationship between Chloroflexi and HCO₃⁻, and positive covariation of Proteobacteria with several major ions and mineralization indicators. Taken together, the results show that a shared deep-geothermal background establishes the regional community baseline, whereas temperature, redox state, mineralization, major-ion composition, and local discharge conditions jointly structure microbial differentiation among spring sites.