title: Phosphorus deficiency affects the allocation of below-ground resources to combined cluster roots and nodules in Lupinus albus.
abstract: Lupins can rely on both cluster roots and nodules for P acquisition and biological nitrogen fixation (BNF), respectively. The resource allocation (C, N and P) between cluster roots and nodules has been largely understudied during P-deficient conditions. The aim of this investigation was therefore to determine the changes in resource allocation between these organs during fluctuations in P supply. Lupinus albus was cultivated in sand culture for 3 weeks, with either sufficient (2 mM high) or limiting (0.1 mM low) P supply. Although variation on P supply had no effect on the total biomass, there were significant differences in specialised below-ground organ allocation to cluster roots and nodule formation. Cluster root formation and the associated C-costs increased during low P supply, but at sufficient P-supply the construction and growth respiration costs of cluster roots declined along with their growth. In contrast to the cluster root decline at high P supply, there was an increase in nodule growth allocation and corresponding C-costs. However, this was not associated with an increase in BNF. Since cluster roots were able to increase P acquisition under low P conditions, this below-ground investment may also have benefited the P nutrition of nodules. These findings provide evidence that when lupins acquire N via BNF in their nodules, there may be a trade-off in resource allocation between cluster roots and nodules.
authors.affiliation: Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
authors.forename: Rochelle
authors.initials: R
authors.lastname: Thuynsma
authors.affiliation: Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa; World Agroforestry Centre, East Asia Node, 132 Lanhei Rd, Kunming 650201, China. Electronic address: alexvalentine@mac.com.
authors.forename: Alex
authors.initials: A
authors.lastname: Valentine
authors.affiliation: Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
authors.forename: Aleysia
authors.initials: A
authors.lastname: Kleinert
mesh_terms: D018506:Gene Expression Regulation, Plant; D031297:Lupinus / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010758:Phosphorus / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D010758:Phosphorus
keywords: Cluster roots; Nodules; Phosphorus deficiency; Resource allocation; White lupin