Phosphorus supply to vegetable crops from arbuscular mycorrhizal fungi: a review

Abstract

Increasing cost of inorganic P fertilizers manufactured from non-renewable phosphate rock and agro-environmental guidelines compel vegetable producers to re-evaluate and possibly reduce P fertilizer use in their operations. Greater reliance on arbuscular mycorrhizal (AM) fungi could compensate for lower P fertilizer inputs to vegetable crops. The objective of this review was to examine how AM fungi dependency and AM fungi-mediated P uptake in the Alliaceae, Fabaceae and Solanaceae families are affected by agronomic practices, soil biogeochemistry, and characteristics of the host plant and the AM fungal symbiont. Fertilization and geochemical reactions affecting the plant-available P concentration in the soil solution determine the degree of AM fungus colonization of roots, as well as the quantity of phosphate transferred to the plant via the hyphal network of AM fungi. The hyphae of AM fungi physically extend the rhizosphere into a larger soil volume and access more plant-available P; as well, AM fungi secrete organic acids and phosphatase enzymes than increase the plant-available P concentration. Feedback in the host-AM fungi system (mycorrhiza) due to plant morphology and physiology as well as mycorrhizal phenotype and high-affinity P transporters control the AM fungi-induced P uptake. Although inoculation with Glomus species is often beneficial for Alliaceae seedlings and transplants, gains in yield and better P nutrition of mycorrhizal vegetable crops can be achieved by boosting the indigenous AM fungus populations in agricultural fields with the following techniques: including mycorrhizal hosts in crop rotations or as intercrops and cover crops, reducing cultivation intensity and decreasing P fertilizer inputs.