Cluster-root formation and carboxylate release in Euplassa cantareirae (Proteaceae) from a neotropical biodiversity hotspot

© 2015, Springer International Publishing Switzerland.Background and Aims: Euplassa cantareirae is a Neotropical Proteaceae, native to the Restinga forest in Brazil and it experiences a wide array of adverse environmental conditions, especially seasonal flooding and low nutrient availability. We aimed to investigate the effects of phosphorus (P) supply on plant growth and cluster root formation, as well as to characterize the main carboxylates released by the cluster roots of this species. Methods: We conducted a greenhouse experiment where seedlings were grown in a sandy soil and watered three times a week with nutrient solution with the following P concentrations: 0, 10, 50 or 100 μM. Cluster-root production per plant, tissue P concentrations, growth parameters and carboxylate release were recorded and analyzed. Results: Remarkably, cluster-root formation, biomass production and leaf P concentration did not depend on P supply. These results differ from what have been found for almost all other investigated species, except for one other plant that inhabits a similar habitat in south-western Australia, Viminaria juncea (Fabaceae). The carboxylates that were found in the rhizosphere were similar to those reported before for other Proteaceae. Conclusions: Euplassa cantareirae is a Neotropical Proteaceae producing cluster roots, and contrary to what is known for other family members, it does not appear to regulate its cluster-root formation, growth and leaf P concentration by the soil P availability.