Journal Article

Putting the P in <i>Ptilotus</i>: a phosphorus-accumulating herb native to Australia

M. H. Ryan, S. Ehrenberg, R. G. Bennett and M. Tibbett

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 103, issue 6, pages 901-911
Published in print April 2009 | ISSN: 0305-7364
Published online February 2009 | e-ISSN: 1095-8290 | DOI:
Putting the P in Ptilotus: a phosphorus-accumulating herb native to Australia

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  • Ecology and Conservation
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Background and Aims

Ptilotus polystachyus (green mulla mulla; ptilotus) is a short-lived perennial herb that occurs widely in Australia in arid and semi-arid regions with nutrient poor soils. As this species shows potential for domestication, its response to addition of phosphorus (P) and nitrogen (N) was compared to a variety of the domesticated exotic perennial pasture herb Cichorium intybus (chicory), ‘Puna’.


Pots were filled with 3 kg of an extremely nutrient-deficient sterilized field soil that contained 3 mg kg−1 mineral N and 2 mg kg−1 bicarbonate-extractable P. The growth and P and N accumulation of ptilotus and chicory in response to seven rates of readily available phosphorus (0–300 mg P pot−1) and nitrogen (N) (0–270 mg N pot−1) was examined.

Key Results

Ptilotus grew extremely well under low P conditions: shoot dry weights were 23, 6 and 1·7 times greater than for chicory at the three lowest levels of P addition, 0, 15 and 30 mg P pot−1, respectively. Ptilotus could not downregulate P uptake. Concentrations of P in shoots approached 4 % of dry weight and cryo-scanning electron microscopy and X-ray microanalysis showed 35–196 mm of P in cell vacuoles in a range of tissues from young leaves. Ptilotus had a remarkable tolerance of high P concentrations in shoots. While chicory exhibited symptoms of P toxicity at the highest rate of P addition (300 mg P pot−1), no symptoms were present for ptilotus. The two species responded in a similar manner to addition of N.


In comparison to chicory, ptilotus demonstrated an impressive ability to grow well under conditions of low and high P availability. Further study of the mechanisms of P uptake and tolerance in ptilotus is warranted.

Keywords: Phosphorus; nitrogen; hyperaccumulation; X-ray microanalysis; cell vacuole; Australian native plant; toxicity; domestication; phytoremediation; Ptilotus polystachyus; Cichorium intybus

Journal Article.  7313 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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