Plant and Soil

, Volume 238, Issue 1, pp 111–122

The pattern of carboxylate exudation in Banksia grandis (Proteaceae) is affected by the form of phosphate added to the soil

  • Hans Lambers
  • Damian Juniper
  • Greg R. Cawthray
  • Erik J. Veneklaas
  • Elsa Martínez-Ferri
Article

DOI: 10.1023/A:1014289121672

Cite this article as:
Lambers, H., Juniper, D., Cawthray, G.R. et al. Plant and Soil (2002) 238: 111. doi:10.1023/A:1014289121672

Abstract

Roots of a wide range of plant species exude carboxylates, e.g. citrate, into the rhizosphere, to mobilise sparingly available phosphate. We investigated the carboxylates in root exudates of Banksia grandisWilld. (Proteaceae), which occurs on severely phosphate-impoverished soils in Western Australia. Plants were grown in pots with a nutrient-poor quartz sand, with phosphate, at 25 μg P g−1, added as either K-phosphate, glycerol phosphate, Fe-phosphate or Al-phosphate.

Plants grown on Fe-phosphate or Al-phosphate formed `proteoid' or `cluster' roots, and exuded significant amounts of carboxylates. Plants grown on K-phosphate did not form cluster roots; their leaves were chlorotic, and some of these plants died during the experiment. Plants grown on glycerol phosphate did have cluster roots, but their leaves also became chlorotic, albeit later in the experiment.

Tri- and dicarboxylates (citrate, 60%; malate, 25%; trans-aconitate, 14%) were the major carboxylates in root exudates when P was supplied as Al-phosphate. The same tri- and dicarboxylates were also exuded when P was supplied as Fe-phosphate (31, 14 and 12%, respectively). In addition, these plants exuded monocarboxylates (lactate, 30%; acetate, 12%). We analysed the effect of the different carboxylates on the mobilisation of phosphate and Fe in two different types of soils. The ecological significance of the difference in exudate spectrum for the mobilisation of nutrients and for the detoxification of aluminium is discussed.

Because the leaves of plants grown with K-phosphate or glycerol-phosphate appeared chlorotic, we analysed the concentrations of P, Fe, Zn, Mn and Cu in these leaves. Only the concentration of total P was considerably higher in leaves of plants grown with K- or glycerol-phosphate than that in leaves of plants grown with Fe- or Al-phosphate. Both the concentration of total Fe and that of reduced Fe was the same in chlorotic leaves as that in leaves of plants grown with Fe- or Al-phosphate, which had a healthy appearance. It is concluded that P-induced chlorosis was not due to a lack of total or reduced Fe; it may have been due to precipitation of Fe by phosphate.

acetate aconitate aluminium Banksia grandis carboxylates chlorosis citrate cluster roots exudation iron lactate malate phosphate Proteaceae proteoid roots 

Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  • Hans Lambers
    • 1
    • 2
  • Damian Juniper
    • 2
  • Greg R. Cawthray
    • 2
  • Erik J. Veneklaas
    • 2
  • Elsa Martínez-Ferri
    • 2
  1. 1.Plant Sciences, Faculty of AgricultureThe University of Western AustraliaCrawleyAustralia
  2. 2.Plant EcophysiologyUtrecht UniversityUtrechtThe Netherlands

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