title: Nodules from Fynbos legume Virgilia divaricata have high functional plasticity under variable P supply levels.
abstract: Legumes have the unique ability to fix atmospheric nitrogen (N2) via symbiotic bacteria in their nodules but depend heavily on phosphorus (P), which affects nodulation, and the carbon costs and energy costs of N2 fixation. Consequently, legumes growing in nutrient-poor ecosystems (e.g., sandstone-derived soils) have to enhance P recycling and/or acquisition in order to maintain N2 fixation. In this study, we investigated the flexibility of P recycling and distribution within the nodules and their effect on N nutrition in Virgilia divaricata Adamson, Fabaceae, an indigenous legume in the Cape Floristic Region of South Africa. Specifically, we assessed tissue elemental localization using micro-particle-induced X-ray emission (PIXE), measured N fixation using nutrient concentrations derived from inductively coupled mass-spectrometry (ICP-MS), calculated nutrient costs, and determined P recycling from enzyme activity assays. Morphological and physiological features characteristic of adaptation to P deprivation were observed for V. divaricata. Decreased plant growth and nodule production with parallel increased root:shoot ratios are some of the plastic features exhibited in response to P deficiency. Plants resupplied with P resembled those supplied with optimal P levels in terms of growth and nutrient acquisition. Under low P conditions, plants maintained an increase in N2-fixing efficiency despite lower levels of orthophosphate (Pi) in the nodules. This can be attributed to two factors: (i) an increase in Fe concentration under low P, and (ii) greater APase activity in both the roots and nodules under low P. These findings suggest that V. divaricata is well adapted to acquire N under P deficiency, owing to the plasticity of its nodule physiology.
authors.affiliation: Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa.
authors.forename: Waafeka
authors.initials: W
authors.lastname: Vardien
authors.affiliation: Materials Research Department, iThemba LABS, National Research Foundation, PO Box 722, Somerset West 7129, South Africa.
authors.forename: Jolanta
authors.initials: J
authors.lastname: Mesjasz-Przybylowicz
authors.affiliation: Materials Research Department, iThemba LABS, National Research Foundation, PO Box 722, Somerset West 7129, South Africa; AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Al. A. Mickiewicza 30, 30-059, Krakow, Poland.
authors.forename: Wojciech J
authors.initials: WJ
authors.lastname: Przybylowicz
authors.affiliation: Materials Research Department, iThemba LABS, National Research Foundation, PO Box 722, Somerset West 7129, South Africa.
authors.forename: Yaodong
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria 0002, South Africa.
authors.forename: Emma T
authors.initials: ET
authors.lastname: Steenkamp
authors.affiliation: Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa. Electronic address: alexvalentine@mac.com.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Valentine
mesh_terms: D018533:Biomass; D007887:Fabaceae / Q000378:metabolism / Q000502:physiology*; D009586:Nitrogen Fixation; D010758:Phosphorus / Q000378:metabolism*
chemical_list: D010758:Phosphorus
keywords: Acid-phosphatase; Legume; N(2)-fixation; Phosphorus-deficient; Root-nodule