This study investigates the relative influences of stochastic and deterministic processes in shaping subsurface microbial community composition. By integrating spatiotemporal data with phylogenetic metrics and null models, the researchers found that environmental filtering strongly determines community composition, with deterministic processes dominating in extreme environmental conditions. Phylogenetic analyses revealed that closely related taxa have more similar habitat associations, and ecologically similar taxa coexist more frequently than expected by chance. Environmental filtering thus plays a dominant role in structuring subsurface microbial communities. However, stochastic factors also influence community dynamics, particularly in temporally and spatially variable environments. The study highlights that the relative influence of deterministic and stochastic processes varies across environmental gradients, with deterministic processes being more influential at both ends of the gradient. Phylogenetic turnover was generally faster than expected, but most pairwise comparisons were not significantly non-random. The results suggest that general rules govern the relative influences of stochastic and deterministic processes across micro- and macro-organisms. The study emphasizes the importance of using phylogenetic information and null models to better understand microbial community assembly and dynamics. The findings contribute to a broader understanding of ecological processes in microbial systems and highlight the need for integrating phylogenetic approaches in microbial ecology.This study investigates the relative influences of stochastic and deterministic processes in shaping subsurface microbial community composition. By integrating spatiotemporal data with phylogenetic metrics and null models, the researchers found that environmental filtering strongly determines community composition, with deterministic processes dominating in extreme environmental conditions. Phylogenetic analyses revealed that closely related taxa have more similar habitat associations, and ecologically similar taxa coexist more frequently than expected by chance. Environmental filtering thus plays a dominant role in structuring subsurface microbial communities. However, stochastic factors also influence community dynamics, particularly in temporally and spatially variable environments. The study highlights that the relative influence of deterministic and stochastic processes varies across environmental gradients, with deterministic processes being more influential at both ends of the gradient. Phylogenetic turnover was generally faster than expected, but most pairwise comparisons were not significantly non-random. The results suggest that general rules govern the relative influences of stochastic and deterministic processes across micro- and macro-organisms. The study emphasizes the importance of using phylogenetic information and null models to better understand microbial community assembly and dynamics. The findings contribute to a broader understanding of ecological processes in microbial systems and highlight the need for integrating phylogenetic approaches in microbial ecology.