Root exudates of Banksia species from different habitats
– a genus-wide comparison
Erik J. Veneklaas, Hans Lambers and Greg Cawthray
School of Plant Biology, University of Western Australia, Crawley WA 6009, Australia.
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7 February 2005 Grant details Final report
The genus Banksia is a uniquely Australian plant group. Banksias
dominate the physiognomy and ecology of several Australian plant communities.
Flowers and fruits of several species are successful export products.
The physiology of nutrient uptake is of great importance for this genus,
particularly since the soils on which Banksias occur are extremely low
in nutrients. All Banksias possess proteoid (cluster) roots that exude
a range of carboxylates into the rhizosphere. Carboxylates act to enhance
the availability of nutrients, particularly phosphorus, but the efficiency
of different carboxylates varies with soil type. We examined the hypothesis
that Banksia species with different soil preferences differ in the amount
and composition of rhizosphere carboxylates.
Our data show that, when grown in a standardised substrate, the 57 Banksia species studied exude roughly similar carboxylates into their rhizosphere, predominantly citrate. We found no evidence for phylogenetically determined differences, or correlations with species’ soil preferences. This may indicate that the conditions in the topsoil and litter layer in all Banksia habitats are sufficiently similar for these carboxylates to be effective. Alternatively, species differences were not expressed in the single substrate that was used. Ongoing research explores the ability of Banksias to adjust exudation patterns to contrasting soils, and the impact on growth and nutrient uptake.