Root exudates of Banksia species from different habitats – a genus-wide comparison

Summary of final report on the Australian Flora Foundation funded project:

Erik J. Veneklaas, Hans Lambers and Greg Cawthray
School of Plant Biology, University of Western Australia, Crawley WA 6009, Australia.
Ph: +61 8 9380 3584
Fax: +61 8 9380 1108
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.