Purpose <p>The relationship between plant and microbial diversity is well established, yet how the loss of plant functional groups (PFGs) influences microbial ecologicaladaptation remains unclear. This study aimed to investigate how the loss of specific PFGs Gramineae, Leguminosae, Forbs, and Cyperaceae affects microbial community assembly processes and their implications for soil nutrient cycling in grassland ecosystems.</p> Methods <p>We examined grassland soils subjected to the loss of different PFGs and analyzed microbial community composition, assembly mechanisms, and nutrient cycling functions. Microbial taxa were categorized into abundant and rare groups to compare their responses to environmental filtering under PFG loss. Community assembly processes were evaluated by distinguishing between stochastic and deterministic mechanisms, and their relationships with soil carbon, nitrogen, and phosphorus cycling were assessed.</p> Results <p>Our results showed that abundant bacterial taxa exhibited narrower environmental response thresholds than rare taxa and experienced stronger environmental filtering following PFG loss. As a result, the assembly of abundant taxa shifted from predominantly stochastic processes to a greater influence of deterministic processes, while rare taxa remained largely stochastic. This shift significantly affected carbon, nitrogen, and phosphorus cycling. Notably, Cyperaceae regulated the balance between deterministic and stochastic assembly processes in abundant taxa by influencing DOC content.</p> Conclusion <p>These findings demonstrate that distinct assembly responses of rare and abundant microbial taxa play a key role in regulating soil nutrient cycling. Our study highlights that PFG diversity, particularly the presence of Cyperaceae, is critical for maintaining microbial assembly dynamics and ecosystem stability in grassland systems.</p>