Nutritional exchanges in the arbuscular mycorrhizal symbiosis: Implications for sustainable agriculture

The Glomeromycota – the fungi that form arbuscular mycorrhizas – are both abundant, representing perhaps 10 % or more of soil microbial biomass, and ecologically important, acting as major conduits in the principal elemental cycles. However, their basic biology is poorly understood, and the continuing lack of good genome descriptions is a serious stumbling block. In particular, the mechanism and regulation of transfer of sugars and mineral nutrients across the symbiotic interface merit further investigation. We extend a recent model for these transfers to cover nitrogen as well as phosphate, and discuss the implications of this more general model for the exploitation of arbuscular mycorrhizas in sustainable agriculture.