Arbuscular-mycorrhizal fungi: potential roles in weed management

The importance of interactions between arbuscular-mycorrhizal fungi (AMF) and weeds of agro-ecosystems is reviewed. Considerable evidence suggests that AMF can affect the nature of weed communities in agro-ecosystems in a variety of ways, including changing the relative abundance of mycotrophic weed species (hosts of AMF), and non-mycotrophic species (non-hosts). These effects may merely change the composition of weed communities without affecting the damage that these communities cause. However, it is quite plausible that interactions with AMF can increase the beneficial effects of weeds on the functioning of agro-ecosystems. Through a variety of mechanisms, weed:AMF interactions may reduce crop yield losses to weeds, limit weed species shifts, and increase positive effects of weeds on soil quality and beneficial organisms. If beneficial effects of AMF on the composition and functioning of weed communities can be confirmed by more direct evidence, then AMF could provide a new means of ecologically-based weed management. Intentional management will be required to increase diversity and abundance of AMF in many cropping systems, but these actions (e.g. conservation tillage and use of cover and green-manure crops) typically will confer a range of agronomic benefits in addition to potential improvements in weed management.