The Effect of Soil Nutrients on the Production of Proteoid Roots by Hakea Species

Abstract

The mode of the proteoid root response curve occurs at a considerably lower level of nitrogen or phosphorus than that of the response curve for non-proteoid roots. As a consequence, the relationship between proteoid and non-proteoid roots can be regarded as passing through four phases as nutrient availability increases: (a) an increase in proteoid root production as non-proteoid root growth increases; (b) a decrease in proteoid root production as non-proteoid root growth increases; (c) a decrease in proteoid root production as non-proteoid root growth decreases; (d) an absence of proteoid roots as non-proteoid root growth decreases. Only the first two phases are considered relevant to plants growing under field conditions. It is concluded that nutrient concentration in a number of soils, especially nitrogen availability, largely determines the relative contribution of proteoid roots to the root systems of two species of Hakea.