title: The reallocation of carbon in P deficient lupins affects biological nitrogen fixation.
abstract: It is not known how phosphate (P) deficiency affects the allocation of carbon (C) to biological nitrogen fixation (BNF) in legumes. The alteration of the respiratory and photosynthetic C costs of BNF was investigated under P deficiency. Although BNF can impose considerable sink stimulation on host respiratory and photosynthetic C, it is not known how the change in the C and energy allocation during P deficiency may affect BNF. Nodulated Lupinus luteus plants were grown in sand culture, using a modified Long Ashton nutrient solution containing no nitrogen (N) for ca. four weeks, after which one set was exposed to a P-deficient nutrient medium, while the other set continued growing on a P-sufficient nutrient medium. Phosphorus stress was measured at 20 days after onset of P-starvation. During P stress the decline in nodular P levels was associated with lower BNF and nodule growth. There was also a shift in the balance of photosynthetic and respiratory C toward a loss of C during P stress. Below-ground respiration declined under limiting P conditions. However, during this decline there was also a shift in the proportion of respiratory energy from maintenance toward growth respiration. Under P stress, there was an increased allocation of C toward root growth, thereby decreasing the amount of C available for maintenance respiration. It is therefore possible that the decline in BNF under P deficiency may be due to this change in resource allocation away from respiration associated with direct nutrient uptake, but rather toward a long term nutrient acquisition strategy of increased root growth.
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
authors.affiliation: Institute for Plant Biotechnology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa.
authors.forename: Mauritz
authors.initials: M
authors.lastname: Venter
authors.affiliation: Institute for Plant Biotechnology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa.
authors.forename: Jens
authors.initials: J
authors.lastname: Kossmann
authors.affiliation: Botany and Zoology Department, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. Electronic address: alexvalentine@mac.com.
authors.forename: Alexander
authors.initials: A
authors.lastname: Valentine
mesh_terms: D001692:Biological Transport; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D019069:Cell Respiration; D004734:Energy Metabolism; D031297:Lupinus / Q000254:growth & development / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D010758:Phosphorus / Q000172:deficiency* / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000254:growth & development / Q000502:physiology; D018517:Plant Roots / Q000254:growth & development / Q000502:physiology; D018526:Plant Transpiration
chemical_list: D002245:Carbon Dioxide; D010758:Phosphorus; D002244:Carbon; D009584:Nitrogen
keywords: Carbon and nitrogen costs; Nitrogen fixation; P deficiency; Photosynthesis; Respiration