Abstract: As global changes and anthropogenic activities intensify, plant invasions are becoming increasingly prevalent, posing a significant threat to native biodiversity, including the soil microbiome. Protists play a crucial regulatory role in shaping the soil microbiome and are key contributors to nutrient cycling. However, the assembly and functional succession of soil protistan communities by invasion-induced habitat modification, particularly across different invasion stages, remain poorly understood. To address this gap, we employed a space-for-time substitution across five plant invasion duration gradients in a coastal wetland. Through metabarcoding sequencing, we traced the shifts in diversity, functional composition, and assembly of soil protistan communities resulting from the invasion of smooth cordgrass (Spartina alterniflora Loisel.). Our results revealed that soil protistan communities were restructured by the invasion, and the diversity and relative abundance of protistan consumers increased specifically, while other functional groups of protists were minimally affected. Co-occurrence patterns among protists, bacteria, and fungi shifted with invasion history, suggesting changes in potential ecological linkages within the temporally fluctuating microbial community. Although stochastic processes predominantly shaped protist assemblages across the invasion gradient, niche-based processes became more influential for the consumers’ community as duration progressed after the invasion. Our findings demonstrate that protists are key responsive indicators and trophic mediators in linking plant invasion to soil microbial diversity. The observed shifts in consumer and phototroph communities suggest broader implications for microbiome function, including the potential for enhanced predation-driven microbial turnover and phototrophic carbon fixation, with direct consequences for soil nutrient cycling.

Key words: plant invasion, protistan functional groups, community assembly, soil microbial diversity, estuarine wetlands