Metabolic filtering as a putative mechanism linking soil metabolome and microbial community assembly along a lake...

Climate-driven lake expansion across the Qinghai-Tibet Plateau induces profound edaphic shifts, but how these abiotic changes shape soil microbial assembly remains unclear. Soil metagenomics and metabolomics were integrated along a 0-10 km spatial gradient at Gahai. Redundancy analysis (RDA) identified moisture (NDWI) and salinity (SI) as primary ecosystem drivers. Structural equation modeling (SEM) provided exploratory evidence consistent with a mediation pathway (P = 0.64, CFI = 1, RMSEA = 0), in which environmental factors potentially influenced microbial community structure indirectly, via reshaping the soil metabolome rather than through a direct path. Moisture availability exerted a strong negative effect on soil metabolic profiles (λ = -0.93), leading to a pronounced negative correlation between the metabolome and microbial community (λ= -0.97). Multi-omics integration attributed this pattern to stress-induced accumulation of defensive metabolites, including Feruloylputrescine and 3-Methylthiopropyl-desulfoglucosinolate. These compounds showed significant negative correlations with dominant genera (e.g., Candidatus Kryptobacter). This "metabolic filtering" is hypothesized to selectively limit the presence of non-adapted taxa based solely on correlational SEM and network analyses, supporting our tentative hypothesis that increasing environmental stress may promote a transition from competitive interactions toward patterns consistent with stronger deterministic filtering. Our exploratory findings suggest that the soil metabolome acts as a functional interface mediating microbial adaptation and strategic resource allocation to lake expansion in this high-altitude saline-alkali system. However, due to regional heterogeneity, these patterns provide a theoretical baseline for plateau lake ecosystems and should be applied with caution to broader geographic areas.