Estimation of phosphorus uptake capacity by different zones of the primary root of soil‐grown maize (Zea mays L.)

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Abstract
A method is described which allows determination of the nutrient uptake capacity by different zones of individual roots of soil‐grown plants. Examples are given for phosphorus uptake by different zones of the primary root of maize. Agar strips with labelled phosphorus (32P) are placed on the soil‐root interface of root zones of different age. After 24 h autoradiographs are made of the soil‐root interface and phosphorus uptake rates determined by plant analysis.Along the primary root the relative phosphorus uptake capacity declines per unit root length from 100% in 1 day old root zones to about 25–30% in 26 day old root zones. The change in the extension of the phosphorus (32P) depletion zone along the root axis indicates that the uptake capacity for phosphorus of root hairs was maximal upto 4 days and declined thereafter. The decline in capacity for phosphorus uptake from apical to basal root zones probably reflects the decline in root hair viability. The relative high uptake capacity in basal root zones is therefore at least partially due to the uptake capacity of the cortical cells.