Complementarity and selection effects suppress early- but facilitate late-stage invasion

Plant invasion is a major threat to biodiversity and ecosystem functioning. While native community diversity is often linked to greater invasion resistance, the underlying mechanisms—the roles of complementarity and selection effects across invasion stages—remain unclear. Here, we assembled native plant communities varying in species richness and introduced non-native seeds to quantify invasion performance at two stages: germination (early) and biomass production (late). We also quantified the complementarity and selection effects among native species before and after invasion to explore how diversity shapes invasion dynamics. Our results showed that higher native diversity generally exhibited stronger invasion resistance. Notably, complementarity and selection effects among natives significantly suppressed early non-native establishment (i.e., germination) but unexpectedly promoted later biomass accumulation. These findings underscore the importance of incorporating stage-dependent dynamics and community feedbacks into invasion frameworks, highlighting that maintaining both high diversity and dominant native species is critical for strengthening community resistance to invasion.