Plant diversity and different groups of belowground organisms have been shown to influence the
characteristics of plant communities and their associated aboveground organisms; however, little is
known about the interactions and combined effects of these biotic factors. Furthermore, while plant
species richness has received a lot of attention, intraspecific diversity has only recently come into the
focus of community ecology. The objective of this study was to determine whether the addition of
beneficial soil organisms (arbuscular mycorrhizal fungi (AMF) and anecic earthworms (Lumbricus
terrestris L.) and different levels of plant cultivar diversity interactively influence productivity, weed
establishment, leaf damage by herbivores and pathogens, and the diversity of aboveground herbivores in
legume-grass communities. Our results indicated that the addition of AMF increased aboveground plant
productivity and tended to decrease the diversity of aboveground herbivores. Earthworms attenuated the
effect of AMF addition on AMF root colonization, but had no effect on plant productivity or herbivore
diversity. Weed biomass was significantly lower in plant communities with high cultivar diversity
compared to low cultivar diversity. We did not find interactive effects of the two soil organism groups and
plant cultivar diversity. Our results demonstrate the independent roles and additive positive effects of
AMF and plant cultivar diversity on functions such as productivity and resistance against weeds in the
field. We suggest that AMF and plant cultivar diversity manipulations may be applied more frequently in
agriculture management programs that aim for sustainable yield enhancement and biocontrol of
herbivores and weeds.