Australian Journal of Botany Australian Journal of Botany Society
Southern hemisphere botanical ecosystems
RESEARCH ARTICLE

Interactions Between Iron and Phosphorus in the Nutrition of Banksia ericifolia L.f var ericifolia (Proteaceae) in Soil-Less Potting Media

KA Handreck

Australian Journal of Botany 39(4) 373 - 384
Published: 1991

Abstract

Interactive effects of iron and phosphorus on the growth and appearance of Banksia ericifolia L.f. var. ericifolia seedlings were investigated. The seedlings were grown in a pinebark-based soil-less potting medium amended with 0-40 mg L-1 P added as single superphosphate and with Fe supplied either as FeSO4.7H2O (at 0-3 g L-1) or FeEDDHA (at 0-430 mg L-1).

Fe deficiency was the dominant visual effect on shoots; its severity increased as P supply increased. Classic symptoms of P toxicity (death of oldest leaves) were produced in plants at the highest levels of P supply and low Fe supply.

At each level of added P, Fe tended to lower %P in the shoots, mainly by allowing increased production of dry matter as Fe deficiency was overcome. The highest rate of FeSO4.7H2O addition reduced accumulation of P in the leaves and increased it in the stems. High P additions reduced accumulation of Fe into leaves. At non-toxic additions of P, young leaves had higher concentrations of P than did old leaves, but the reverse applied as P supply became excessive. The leaves of high quality plants contained less than about 0-14% P and more than 30 mg kg-1 Fe. P:Fe ratios for the leaves of such plants were in the range 14-53 (mean 23). Numbers of proteoid root clusters were greatest on plants in media of high Fe supply and low P and declined rapidly as P supply increased above the adequate range. No evidence was found for Fe stress leading to greater development of proteoid roots.

Quality scores of at least 85% of maximum were mainly confined to media giving < 3 mg L-1 P in 2 mM DTPA (1:1.5 volume) extracts and amended with at least 1.5 g L-1 FeSO4.7H2O or 215 mg L-1 FeEDDHA. Response in ferrous sulfate treatments was better correlated with extractable P and Fe than with totals added, but there was no difference with FeEDDHA treatments, because additions of FeEDDHA did not decrease extractable P and ferrous sulfate did.

http://dx.doi.org/10.1071/BT9910373

© CSIRO 1991


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