title: Endogenous sink-source interactions and soil nitrogen regulate leaf life-span in an evergreen shrub.
abstract: How the balance between exogenous and endogenous nitrogen for shoot growth varies with soil nitrogen availability, and its consequences on leaf life-span, have rarely been studied within a single species in the field. In this study, we investigated two Rhododendron ferrugineum populations with contrasting leaf life-span. Soil nitrogen availability and nitrogen resorption of different leaf age classes were assessed, as were the interactions between plant compartments, using (15)N labelling and sink organ suppression. The population growing on poorer soil had a shorter leaf life-span (17.9 vs 21.5 months) and a higher net contribution of leaf reserves to shoot growth (32% vs 15%), achieved by faster nitrogen resorption and greater shedding of young nitrogen-rich leaves. For both populations, wood contributed to over 40% of shoot nitrogen demand. Both the negative relationship between current-year shoot mass and the percentage of 1-yr-old attached leaves and the delay of leaf shedding after bud removal suggest that shoot development has a strong effect on leaf life-span. Our results suggest that, contrary to the evolutionary response, plastic response to low soil nitrogen could reduce leaf life-span in evergreen plants. In addition, leaf life-span seems to be strongly influenced by the discrepancy between shoot nitrogen demand and soil nitrogen uptake rather than nitrogen demand alone.
authors.affiliation: Laboratoire Evolution et Diversité Biologique, CNRS-UMR 5174, Université Paul Sabatier, 31062 Toulouse Cedex 4, France.|Centre d'Etudes Spatiales de la Biosphère, CNES-CNRS-IRD-UMR 5639, Université Paul Sabatier, 18 Avenue Edouard Belin, bpi 2801, 31401 Toulouse Cedex 4, France.
authors.forename: C
authors.initials: C
authors.lastname: Marty
authors.affiliation: Centre d'Etudes Spatiales de la Biosphère, CNES-CNRS-IRD-UMR 5639, Université Paul Sabatier, 18 Avenue Edouard Belin, bpi 2801, 31401 Toulouse Cedex 4, France.
authors.forename: T
authors.initials: T
authors.lastname: Lamaze
authors.affiliation: Laboratoire Evolution et Diversité Biologique, CNRS-UMR 5174, Université Paul Sabatier, 31062 Toulouse Cedex 4, France.
authors.forename: A
authors.initials: A
authors.lastname: Pornon
mesh_terms: D001692:Biological Transport / Q000502:physiology; D016922:Cellular Senescence / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism*; D018520:Plant Shoots / Q000254:growth & development / Q000378:metabolism*; D029793:Rhododendron / Q000254:growth & development / Q000378:metabolism*; D012987:Soil; D014934:Wood / Q000378:metabolism
chemical_list: D012987:Soil; D009584:Nitrogen