Role of root growth, arbuscular mycorrhiza, and root exudates for the efficiency in nutrient acquisition

Genotypic differences in nutrient acquisition are important determinants of nutrient efficiency. These differences can be related to root size and morphology and/or to root physiology. Root surface area can be enhanced through mycorrhizal associations. Root processes can affect rhizosphere pH and redox potential. In addition, root exudates affect rhizosphere chemistry. Exudation may be responsive to a particular nutrient deficiency. For example, P deficiency can induce the release of organic acids and/or acid phosphatases, and iron or Zn deficiencies result in the release of phytosiderophores by some species. Thus, in light of the diverse plant responses to nutrient-deficient soils, it will be necessary to identify the key mechanism(s) of tolerance in a particular field environment before initiating mass screening for a specific tolerance mechanism. (C) 1998 Elsevier Science B.V.