Banksia species (Proteaceae) from severely phosphorus-impoverished soils exhibit extremem efficiency in the use and re-mobilization of phosphorus

Banksia species (Proteaceae) occur on some of the most phosphorus (P)-impoverished soils in the world. We hypothesized that Banksia spp. maximize P-use efficiency through high photosynthetic P-use efficiency, long leaf lifespan (P residence time), effective P re-mobilization from senescing leaves, and maximizing seed P concentration. Field and glasshouse experiments were conducted to quantify P-use efficiency in nine Banksia species. Leaf P concentrations for all species were extremely low (0.14–0.32 mg P g−1 DM) compared with leaf P in other species reported and low relative to other plant nutrients in Banksia spp.; however, moderately high rates of photosynthesis (13.8–21.7 µmol CO2 m−2 s−1), were measured. Some of the Banksia spp. had greater P proficiency (i.e. final P concentration in senesced leaves after re-mobilization; range: 27–196 µg P g−1 DM) than values reported for any other species in the literature. Seeds exhibited significantly higher P concentrations (6.6–12.2 mg P g−1 DM) than leaves, and species that sprout after fire (‘re-sprouters’) had significantly greater seed mass and P content than species that are killed by fire and regenerate from seed (‘seeders’). Seeds contained only small amounts of polyphosphate (between 1.3 and 6 µg g−1 DM), and this was not correlated with P concentration or fire response. Based on the evidence in the present study, we conclude that Banksia species are highly efficient in their use of P, explaining, in part, their success on P-impoverished soils, with little variation between species.Matthew D. Denton, Erik J. Veneklaas, Florian M. Freimoser and Hans Lamber

Reassessment of tissue Na+ concentration as a criterion for salinity tolerance in bread wheat

The definitive version is available at www.blackwell-synergy.comWheat is the most important crop grown on many of world's saline and sodic soils, and breeding for improved salinity tolerance (ST) is the only feasible way of improving yield and yield stability under these conditions. There are a number of possible mechanisms by which cereals can tolerate high levels of salinity, but these can be considered in terms of Na+ exclusion and tissue tolerance. Na+ exclusion has been the focus of much of the recent work in wheat, but with relatively little progress to date in developing high-yielding, salt-tolerant genotypes. Using a diverse collection of bread wheat germplasm, the present study was conducted to assess the value of tissue Na+ concentration as a criterion for ST, and to determine whether ST differs with growth stage. Two experiments were conducted, the first with 38 genotypes and the second with 21 genotypes. A wide range of Na+ concentrations within the roots and shoots as well as in ST were observed in both experiments. However, maintenance of growth and yield when grown with 100mM NaCl was not correlated with the ability of a genotype to exclude Na+ either from an individual leaf blade or from the whole shoot. The K+:Na+ ratio also showed a wide range among the genotypes, but it did not explain the variation in ST among the genotypes. The results suggested that Na+ exclusion and tissue tolerance varied independently, and there was no significant relationship between Na+ exclusion and ST in bread wheat. Consequently, similar levels of ST may be achieved through different combinations of exclusion and tissue tolerance. Breeding for improved ST in bread wheat needs to select for traits related to both exclusion and tissue tolerance.Yusuf Genc, Glenn K. McDonald, Mark Teste