Journal Article

Highly efficient uptake of phosphorus in epiphytic bromeliads

Uwe Winkler and Gerhard Zotz

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 103, issue 3, pages 477-484
Published in print February 2009 | ISSN: 0305-7364
Published online November 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcn231
Highly efficient uptake of phosphorus in epiphytic bromeliads

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Vascular epiphytes which can be abundant in tree crowns of tropical forests have to cope with low and highly intermittent water and nutrient supply from rainwater, throughfall and stem flow. Phosphorus rather than nitrogen has been suggested as the most limiting nutrient element, but, unlike nitrogen, this element has received little attention in physiological studies. This motivated the present report, in which phosphate uptake kinetics by leaves and roots, the subsequent distribution within plants and the metabolic fate of phosphate were studied as a step towards an improved understanding of physiological adaptations to the conditions of tree canopies.

Methods

Radioactively labelled [32P]phosphate was used to study uptake kinetics and plant distribution of phosphorus absorbed from bromeliad tanks. The metabolism of low molecular phosphorus metabolites was analysed by thin-layer chromatography followed by autoradiography.

Key Results

Uptake of phosphate from tanks is an ATP-dependent process. The kinetics of phosphorus uptake suggest that epiphytes possess effective phosphate transporters. The Km value of 1·05 µm determined for leaves of the bromeliad Aechmea fasciata is comparable with values obtained for the high affinity phosphate transporters in roots of terrestrial plants. In this species, young leaves are the main sink for phosphate absorbed from tank water. Within these leaves, phosphate is then allocated from the basal uptake zone into distal sections of the leaves. More than 80 % of the phosphate incorporated into leaves is not used in metabolism but stored as phytin.

Conclusions

Tank epiphytes are adapted to low and intermittent nutrient supply by different mechanisms. They possess an effective mechanism to take up phosphate, minimizing dilution and loss of phosphorus captured in the tank. Available phosphorus is taken up from the tank solution almost quantitatively, and the surplus not needed for current metabolism is accumulated in reserves, i.e. plants show luxury consumption. Young, developing leaves are preferentially supplied with this nutrient element. Taken together, these features allow epiphytes the efficient use of scarce and variable nutrient supplies.

Keywords: Epiphytic bromeliads; phosphorus uptake; forest canopies; luxury consumption; phytotelms; plant nutrition; Aechmea fasciata

Journal Article.  5530 words.  Illustrated.

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

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