The relative functional importance of rare and abundant species in driving relationships between biodiversity and ecosystem functions (BEF) remains unknown. Here, we investigated the functional roles of rare and abundant species diversity (multitrophic soil organism groups) on multifunctionality derived from 16 ecosystem functions in 228 agricultural fields relating to soil and crop health. The results revealed that the diversity of rare species, rather than of abundant species, was positively related to multifunctionality. Abundant taxa tended to maintain a larger number of functions than rare taxa, while rare subcommunity contributed more phylotypes supporting to the single ecosystem functions. Community assembly processes were closely related to the ecosystem functional performance of soil biodiversity, only observed in rare subcommunity. Higher relative contributions of stochastic assembly processes promoted the positive effects of diversity of rare taxa on multifunctionality, while reducing their diversity and multifunctionality overall. Our results highlight the importance of rare species for ecosystem multifunctionality and elucidate the linkage between ecological assembly processes and BEF relationships. IMPORTANCE The relative functional importance of rare and abundant species in driving relationships between biodiversity and ecosystem functions remains unknown. Here, we highlighted the importance of rare species for ecosystem multifunctionality. In addition, community assembly processes were closely related to the ecosystem functional performance of soil biodiversity in rare subcommunity. Stochastic assembly processes promoted the positive effects of diversity of rare taxa on multifunctionality, while reducing their diversity and multifunctionality overall. This study expands current understanding of the mechanisms underpinning the relationships between biodiversity and ecosystem functions and suggests that stochastic community assembly enhances BEF relationships.
Keywords: BEF; BEF relationships; community assembly; functional role; rare species.