PHOSPHATE-UPTAKE AND TRANSPORT IN AGROSTIS-CAPILLARIS L - EFFECTS OF NONTOXIC LEVELS OF ALUMINUM AND THE SIGNIFICANCE OF P AND AL SPECIATION

Investigations on the effects of low levels of Al on B adsorption, upt ake and translocation in seedlings of the indigenous grass Agrostis ca pillaris were undertaken. Apparent uptake and transport of H-2 (PO4)-P -32 from nutrient solutions containing 10 or 100 mmol m(-3) phosphate were characterized as functions of time and concentration. Experiments on P-32 uptake and transport in solutions containing no Al (control) or Al ranging from 3.7 to 185 mmol m(-3) at pH ranging from 4.3 to 4.6 , showed that in 10 mmol m(-3) P, effects of Al at 3.7 and 37 mmol m(- 3) on the size of the initial uptake shoulder were small, but some inc rease in subsequent P uptake to the roots was observed, though transpo rt to the shoots was suppressed. With 37 mmol m(-3) Al in nutrient sol ution containing 100 mmol m(-3) P, the uptake shoulder was much increa sed above the control. Subsequent root uptake was stimulated but trans port was unaffected. Lack of toxicity of the Al concentrations used wa s indicated by a lack of significant effect on plant fresh weight. Abs orbed Al was almost totally retained in the root in all treatments. Sp eciation calculations showed that the major species in Al amended nutr ient solution at pH 4.4 were H2PO4-, Al3+ and AlHPO4+, together with s ubstantial amounts of AlSO4+ and soluble aluminium hydroxy complexes ( AlOH2+, Al(OH)(2)(+)), depending on the relative concentrations of P a nd Al. The effects of Al, with 10 mmol m(-3) P, on adsorption of compl exed P were partly accounted for in terms of preferential cell wall ad sorption of Al complexes not containing P. Conclusions were drawn abou t the P-economy of A. capillaris plants growing on soils with low leve ls of P and Al.