Demand for bioenergy has rapidly developed in recent decades, resulting in expansion of bioenergy cropping systems such as willow short rotation coppice (SRC). Increasing the number of willow genotypes in SRC can potentially enhance species diversity in the associated arthropod community, which may promote ecosystem functions within plantations. However, the ecology of SRCs and their effects on biodiversity have only rarely been investigated. Therefore, to study the role of plant genetic diversity (GD) in SRC, we established a replicated common garden experiment comprising genetic monocultures and mixtures of two, three and four different Salix genotypes used in commercial SRC. We sampled arthropods and examined the effect of GD across trophic groups, to test if the use of genotype mixtures increases arthropod richness and abundance. Species richness of total arthropods and of herbivores increased significantly with increasing GD, regardless whether data were pooled per plot or analysed on tree level. However, effects varied among willow genotypes as positive correlations between GD and different trophic groups were genotype-specific. We show that establishing and managing commercial willow SRCs with a mixture of varying genotypes can help to increase arthropod diversity within a bioenergy system that is a promising renewable energy source.