Keystone K-Strategists Shape Microbial Co-Occurrence Networks in Shale-Gas Wellpad Soils in the Field, Sichuan Basin, China

Shale-gas extraction imposes persistent, low-intensity, multi-factor disturbances on terrestrial soil ecosystems, driven by flowback-fluid-derived salinization, drilling-residue deposition, and moderate petroleum hydrocarbon contamination. However, microbial community assembly mechanisms and the corresponding ecological strategies under such combined chronic perturbations remain insufficiently understood. This study employed 16S rRNA gene sequencing, quantitative PCR, and molecular ecological network (MEN) analysis to characterize the soil microbiome within the Changning shale-gas field, Sichuan Basin, China. The results revealed that microbial communities in shale-gas wellpad soils formed highly modular (M = 0.786), non-random “small-world” co-occurrence networks, indicating intrinsically stable microbial systems. Via Zi-Pi topological classification, six low-abundance (<0.63%) keystone taxa were identified: three module hubs (OTU11572, OTU14908, OTU11976) and three connectors (OTU8845, OTU13035, OTU8962), phylogenetically affiliated with Acidobacteriota, Chloroflexi, and Actinobacteriota. These keystone organisms exhibited typical K-strategy traits, including high network connectivity (degree = 21–24), metabolic stability, and dependence on inter-taxa cooperative interactions. Significant positive correlations were detected between these K-strategy keystone species and anaerobic functional genes (nirS, nirK, dsrAB) responsible for denitrification and sulfate reduction, highlighting their adaptation to fluctuating redox environments generated by drilling-cutting accumulation. Distance-based redundancy analysis (Db-RDA) further demonstrated that electrical conductivity (representing salinization stress from flowback-water intrusion) and soil organic matter acted as the dominant environmental filters shaping microbial community composition, outweighing the influence of labile inorganic nutrients. Overall, this work provides novel evidence that K-selection dominates microbial community assembly under chronic soil disturbance associated with shale-gas extraction. Keystone K-strategists sustain modular network stability through the combination of metabolic plasticity and anaerobic respiratory adaptation. These findings expand r/K-selection theory to anthropogenically disturbed soil habitats and offer theoretical guidance for soil ecological restoration and risk assessment for shale-gas exploiting regions.