Arbuscular mycorrhizas (AM)¸ are associations formed between the roots of most terrestrial plant species and a specialized group of soil fungi. The formation of AM can have important impacts upon plant growth, nutrition and ecology. We have undertaken large scale surveys for AM in agricultural soils, with the aim of linking land management to impacts upon AM. We have also used a novel experimental system to study the effects of arbuscular mycorrhizal fungi (AMF) on plant growth and nutrition, soil ecology and nutrient cycling. We grew a mycorrhizal defective tomato mutant (rmc) and its mycorrhizal wildtype progenitor (76RMYC+) in both the field and glasshouse to study the biology of AM. This approach allows us to establish non-mycorrhizal controls without the use of non-specific fumigation/fungicide treatments in control plots, or use of constitutively mycorrhizal and non-mycorrhizal plant species. Thus, our approach allows us to study AM with the wider soil biota, and the many ecosystem services they provide, in tact. Results from our recent and ongoing research are discussed in the context of the role of AM in sustainable ecosystems.