ABSTRACT
Arbuscular mycorrhizal (AM) fungi are an essential component of natural soil-plant systems. While it is possible to design systems de void of AM fungi, as in greenhouse production, for example, it is clear that cropping systems that fully utilize AM symbiosis are the most efficient, sustainable, and environmentally sound large-scale methods for food production. The contribution of AM fungi to soil structural quality-which promotes water infiltration, limits erosion, and creates soil heterogeneity that is conducive to biodiversity-is well recognized. Most important, AM fungi can extract soil nutrients and water efficiently, allowing good crop yields to be produced from soils with limited fertility. Thus, AM fungi are essential for the de sign of cropping systems that have a low impact on the environment. Advances in molecular biology techniques have made it possible to develop diagnostic tools to estimate the potential contribution of AM fungi in a soil to a given crop yield. The determination of soil mycorrhizal potential as a component of routine soil testing will lead to more accurate fertilizer recommendations and the safe reduction of
fertilizer inputs. The production of good yields with reduced fertilizer use will translate into reduced nutrient seepage from farmland into the environment. A good understanding of how AM fungi contribute to plant nutrient uptake will facilitate the calibration of fertilizer rec ommendations in accordance with this novel soil testing approach as well as the design of efficient and environmentally sound cropping systems. This chapter summarizes the current state of knowledge of nutrient and water uptake by AM fungal mycelia.
