Modifying Effects of Non–toxic Levels of Aluminium on the Uptake and Transport of Phosphate in Ryegrass

Apparent uptake and transport of H232PO4– from nutrient solutions containing 100 mmol m–3 phosphate were characterized asfunctions of time, concentration and pH in ryegrass seedlings. On a log/log plot, concentration versus uptake to the root resolvedinto two linear phases, suggesting a change in uptake mechanism or efflux at the break. These results were compared with those for 32P uptake and transport in solutions containing Al ranging from 0–185 mmol m–3. Al addition depressed pH, but becauseuptake of P was unaffected by pH below 5–0, no adjustments were attempted. Uptake time-courses revealed clearly the usualinitial adsorption shoulder in the uptake curve, increasing with Al concentration up to 37 mmol m–3. Beyond about 2 h, P uptaketo the root became linear, at rates increasing with external Al concentration up to 37 mmol m–3. Concentrations of Al muchabove 100 mmol m–3 were toxic. Al treatments did not affect P transport to the shoot and absorbed Al was confined to the root.The quantities of P and Al taken up into the root indicated storage in cortex cell vacuoles, locking up significant amounts of P.Experiments with tillering plants showed similar characteristics to those with seedlings. Sequestering of P with Al within the rootcortex cells was evident, particularly in plants which had been grown in nutrient containing Al from soon after germination. Aland P solution chemistry is discussed in the context of this work and the consequences of effects on P uptake for the economy ofphosphate poor upland soils were considered.