The Influence of Mineral Nutrition on the Root Development of Trees

Abstract

Sitka spruce seedlings were grown with their root systems divided between two contrasting nutrient regimes. One half of the root system was supplied with a solution containing N, P, and K at a range of concentrations while the untreated half received water only. High-nutrient treatments induced two flushes of shoot growth resulting in a large shoot system, whereas plants in the low-nutrient treatments flushed once only and showed symptoms of nutrient deficiency. Root growth, assessed in terms of dry weight and diameter of both primary and woody tissues, was stimulated in the roots to which the nutrients were actually applied, whereas in the un treated roots on treated plants only the primary root diameter was enhanced. However, internal nutrient concentrations on both sides of the root system were related to the concentra tions applied, though to a slightly lesser extent in the untreated roots. Thus, the nutrients which had been internally translocated to the untreated roots had little effect on their growth. The localized stimulation of xylem production in the woody roots extended into the stem along a spiral pathway which was demonstrated by the movement of dye. Possible mechanisms are discussed by which differential root growth is brought about by a localized supply of mineral nutrients.