SignificanceIdentifying species assemblages that boost the provision of multiple ecosystem functions simultaneously (multifunctionality) is crucial to undertake effective restoration actions aiming at simultaneously promoting biodiversity and high multifunctionality in a changing world. By disentangling the effect of multiple traits on multifunctionality in a litter decomposition experiment, we show that it is possible to identify the assemblages that boost multifunctionality across multiple species mixtures originating from six biomes. We found that higher evenness among dissimilar species and the functional attributes of rare species as key biodiversity attributes to enhance multifunctionality and to reduce the abundance of plant pathogens. Our study identifies those species assemblages needed to simultaneously maximize multifunctionality and limit plant disease risks in natural and managed ecosystems.