AbstractWhile biodiversity is expected to enhance multiple ecosystem functions (EFs), the different roles of multiple biodiversity dimensions remain difficult to disentangle without carefully designed experiments. We sowed plant communities with independent levels of functional (FD) and phylogenetic diversities (PD), combined with different levels of fertilization, to investigate their direct and indirect roles on multiple EFs, including plant‐related EFs (plant biomass productivity, litter decomposability), soil fertility (organic carbon and nutrient pool variables), soil microbial activity (respiration and nutrient cycling), and an overall multifunctionality. We expected an increase in most EFs in communities with higher values of FD and/or PD via complementarity effects, but also the dominant plant types (using community weighted mean, CWM, independent of FD and PD) via selection effects on several EFs. The results showed strong direct effects of different dimensions of plant functional structure parameters on plant‐related EFs, through either CWM or FD, with weak effects of PD. Fertilization had significant effects on one soil microbial activity and indirect effects on the other variables via changes in soil abiotic properties. Dominant plant types and FD showed only indirect effects on soil microbial activity, through litter decomposition and soil abiotic properties, highlighting the importance of cascading effects. This study shows the relevance of complementary dimensions of biodiversity for assessing both direct and cascading effects on multiple EFs.