Ecological Processes Underpinning Microbial Variability in Archean Granitoids Beneath the Deccan Traps: Evidence From...

The deep continental rocky biosphere harbours a diverse and active microbial ecosystem which mostly remains elusive. Here we investigate the ecological processes shaping the microbial species distribution and community assembly across the environmental gradients within the extreme realm of Archean granitic basement (down to ~3000 mbs) of the Koyna Seismic Zone (KSZ), Deccan Traps province, India. Amplicon-based metataxonomy reveals a predominance of bacteria with a few dominant taxa present across the depth, while a large number of rare taxa (< 0.01% abundance) remain localized. Multivariate analyses suggest a distinct partitioning of the KSZ microbial ecosystem into shallow, intermediate, and deeper zones, with a pronounced effect of depth, Fe₂O₃, TOC, and NO₂ ^- on community variability. Phylogenetic null models delineate high turnover among the microbial communities, highlighting the major role of dispersal limitation and variable selection in community assembly. Co-occurrence analysis shows high positive correlation indicating mutualistic association for efficient nutrient utilization and minimization of diversity loss. The potential influence of seismic activity on the microbial community assemblages in specific regions is inferred from correlating cohesion patterns with ⁴He and acetate concentrations. Overall results indicate that microbial communities within the granitoid basement of KSZ are shaped by variable environmental conditions, limited dispersion, and mutualistic interactions between them.