Roles of Arbuscular Mycorrhizas in Plant Phosphorus Nutrition: Interactions between Pathways of Phosphorus Uptake in Arbuscular Mycorrhizal Roots Have Important Implications for Understanding and Manipulating Plant Phosphorus Acquisition

In this Update, we review new findings about the roles of the arbuscular mycorrhizas (mycorrhiza = fungus plus root) in plant growth and phosphorus (P) nutrition. We focus particularly on the function of arbuscular mycorrhizal (AM) symbioses with different outcomes for plant growth (from positive to negative) and especially on the interplay between direct P uptake via root epidermis (including root hairs when present) and uptake via the AM fungal pathway. The results are highly relevant to many aspects of AM symbiosis, ranging from signaling involved in the development of colonization and the regulation of P acquisition to the roles of AM fungi in determining the composition of natural plant assemblages in ecological settings and their changes with time.