Nutrient Uptake by Different Parts of the Intact Roots of Plants

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Abstract
An apparatus is described for studying the uptake of ions by short segments of intact root systems grown in water culture. When the entire root systems of young cereal plants are supplied with o'I ppm, P or Sr the quantities of both ions accumulated in segments 3–5 mm long, or translocated from them to other tissues, are considerably smaller than those which move longitudinally in the cortex for short distances. This process, which is under metabolic control, causes ions to be released to the external solution from parts of the root a few mm distant from the site of entry. The contribution, to the nutrition of barley plants 3–4 weeks old, of different parts of the root system has been investigated. Between seminal axes, nodal axes, and laterals total uptake per unit length of root varies largely, though not entirely, with volume. The ratio in which phosphate and strontium are absorbed is not constant throughout the root system, the absorption of phosphate being relatively greater by laterals. Little translocation occurs from the apical 3 mm of roots and the fraction of the absorbed ions translocated to shoots from older root segments is considerably greater for nodal axes than for seminal axes or laterals. The significance of the distribution of absorbing power throughout the root system is considered in relation to the nutrition of plants grown in soil, especially when the rate of diffusion to the root surface may limit nutrient uptake.