| Abstract: | Sitka spruce seedlings were grown with their root systems dividedbetween two contrasting nutrient regimes. One half of the rootsystem was supplied with a solution containing N, P, and K ata range of concentrations while the untreated half receivedwater only. High-nutrient treatments induced two flushes ofshoot growth resulting in a large shoot system, whereas plantsin the low-nutrient treatments flushed once only and showedsymptoms of nutrient deficiency. Root growth, assessed in terms of dry weight and diameter ofboth primary and woody tissues, was stimulated in the rootsto which the nutrients were actually applied, whereas in theuntreated roots on treated plants only the primary root diameterwas enhanced. However, internal nutrient concentrations on bothsides of the root system were related to the concentrationsapplied, though to a slightly lesser extent in the untreatedroots. Thus, the nutrients which had been internally translocatedto the untreated roots had little effect on their growth. The localized stimulation of xylem production in the woody rootsextended into the stem along a spiral pathway which was demonstratedby the movement of dye. Possible mechanisms are discussed by which differential rootgrowth is brought about by a localized supply of mineral nutrients. |
