Nitrate-uptake restraint in Banksia spp. (Proteaceae) and Melaleuca spp. (Myrtaceae) from a severely phosphorus-impoverished environment

Aims South-western Australia has some of the most phosphorus (P)-impoverished soils in the world. Hakea prostrata (Proteaceae) has nitrate (NO3-)-uptake restraint, associated with its high P-use efficiency. This research explores how common this trait is in other Proteaceae and in co-occurring plant species in south-western Australia. Methods Banksia attenuata (Proteaceae), B. telmatiaea (Proteaceae), Melaleuca seriata (Myrtaceae) and M. rhaphiophylla (Myrtaceae) were grown with no NO3-, Medium (500 mu M) NO3- or High (2500 mu M) NO3- treatments with no other source of nitrogen (N). Plants were harvested after treatments. Leaf nitrate and phosphate concentrations were determined, as well as biomass, total N and total P concentrations of leaves, stems and roots separately. Results Banksia attenuata, B. telmatiaea and M. seriata had similar total N content when supplied with High NO3- as they did when supplied with Medium NO3-. All four species had the same low leaf NO3--N concentration in High and Medium NO3- treatments, no more than 6% of leaf total N. All species had similar leaf NO3- concentrations as those of plants growing in their natural habitat where the available soil nitrate concentration was much lower. These results are in sharp contrast with plants that are typically studied, for example Arabidopsis thaliana. Conclusions All four species exhibited NO3--uptake restraint to different degrees. Nitrate-uptake restraint appears a convergent trait common to many species that evolved in severely P-impoverished landscapes, allowing them to be more P-efficient.