Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: April 15, 2008
Publication Date: December 15, 2008
Repository URL: http://hdl.handle.net/10113/48049
Citation: Vance, C.P. 2008. Plants without arbuscular mycorrhizae. In: White, P.J., Hammond, J.P., editors. Ecophysiology of Plant-Phosphorus Interactions. Volume 7. Dordrecht, The Netherlands: Springer Publishing. p. 117-142. Technical Abstract: P is second to N as the most limiting element for plant growth. Plants have evolved a number of effective strategies to acquire P and grow in a P-limited environment. Physiological, biochemical, and molecular studies of P-deficiency adaptations that occur in non-mycorrhizal species have provided striking new insights into how plants respond to P-deficiency and which traits appear important in acquiring P. Because inexpensive P fertilizer is a limited resource and because many farmers of the world cannot afford P fertilizer, it is imperative that plant biologists discover strategies and approaches which will enhance efficiency of P acquisition and use. Although mycorrhizal symbioses are the most important adaptation for angiosperms to acquire scarce P, many plant families have species that either do not form or rarely form this pivotal association. This review will address adaptations and mechanisms for acquisition and use of scarce P in plants lacking effective mycorrhizal symbioses. The primary focus will be on root adaptations in species that develop specialized-complex roots (cluster and dauciform) in response to P-stress. Although not producing cluster or dauciform roots in response to P-deficiency, Arabidopsis will also be considered because it does not form mycorrhizal symbiosis and is a model species for evaluating plant adaptation to P-stress. Plants have evolved two broad strategies for improved P acquisition and use in nutrient-limiting environments: (1) those aimed at conservation of use; and (2) those directed toward enhanced acquisition or uptake. Processes that conserve the use of P involve decreased growth rate, increased growth per unit of P uptake, remobilization of internal P, modifications in carbon (C) metabolism that bypass P-requiring steps, alternative respiratory pathways, and alterations in membrane biosynthesis requiring less P. In comparison, processes that lead to enhanced P uptake include modified root architecture and greater root growth, prolific development of root hairs leading to expanded root surface area, enhanced expression of Pi transporter genes, and increased production and exudation of phosphatases and organic acids. These numerous adaptive responses to P-deficiency are not mutually exclusive and all may occur within a single species.