In fast-growing herbs, grown with free access to nitrate, root respiration consumes about 8% of all photosynthates. In slower-growing herbs this is up to 50%. Slow-growing GA mutants also use relatively more carbon in root respiration. Therefore, slow growth is the cause, not the consequence, of a large consumption of carbon in root respiration. We investigated if variation in the contribution of the alternative respiratory path explains the relatively fast rates of root respiration of slow-growing plants. We also assessed respiratory costs for growth, maintenance and ion transport. We concluded that the large fraction of carbon required for root respiration in slow-growing plants is due to higher specific respiratory costs associated with nitrate uptake, accounted for by a high nitrate efflux expressed per net mole of nitrate taken up.

Soils in Western Australia are among the most phosphorus-impoverished in the world, and the southwest of Western Australia is a Global Biodiversity Hotspot. This unique environment offers an excellent opportunity to study root adaptations. A large proportion of species from these P-poor environments cannot produce an association with mycorrhizal fungi, but produce ‘root clusters'. The functioning of root clusters in Proteaceae has received considerable attention, but that of clusters in Cyperaceae has barely been explored. Root-cluster root growth is stimulated when at a very low P supply. Root clusters in Cyperaceae and Proteaceae are short-lived structures and release large amounts of carboxylates during an ‘exudative burst' at rates that are considerably faster than reported for nonspecialised roots of a wide range of species. Root clusters play a pivotal role in mobilisation of P from soil. Because the world P reserves are being depleted, there is a growing need for crops with a high efficiency of P acquisition. Some Australian native species have traits that would be highly desirable for future crops.