Aspects of the Mineral Nutrition of the Western Australian Christmas Tree (Nuytsia floribunda (Labill.) R. Br.), With Special Reference to the Main Root

Abstract

A study was made of the shape, dimensions and possible nutritional significance of the main root of the hemi parasite Nuytsia floribunda. Levels of nitrogen, phosphorus, potassium, sulfur, calcium, magnesium, sodium, iron, manganese, zinc and copper were determined in the main root: haustoria, xylem sap, mucilage, trunk and leaves. The main root was approximately turnip-shaped and there was no evidence of a tap-root. Haustoria were confined to the top 15-20 cm of the soil and were attached to a variety of woody and herbaceous host plants. Haustoria contained the highest levels of nitrogen and phosphorus, the trunk and main root the highest levels of calcium, magnesium and sodium. Potassium and sodium accounted for 75% of the minerals in xylem sap. calcium and magnesium for 60% of the minerals in mucilage which exuded from wounds in the main root. Concentration gradients of most minerals existed across the main root. Nitrogen, phosphorus, potassium, sulfur and sodium were more concentrated in the outer zone of the root, calcium, magnesium, manganese and copper in the central part. Nuytsia appears to draw on stored nutrients in some situations. Conservative estimates suggested that nutrient reserves in the main root could not provide the amounts required for flower and fruit production. It was concluded that reproductive and vegetative growth draws on reserves in organs other than the main root and the extensive lateral root system may be important in this respect.