title: Fast growth involves high dependence on stored resources in seedlings of Mediterranean evergreen trees.
abstract: OBJECTIVE
  The carbon (C) and nitrogen (N) needed for plant growth can come either from soil N and current photosynthesis or through remobilization of stored resources. The contribution of remobilization to new organ growth on a whole-plant basis is quite well known in deciduous woody plants and evergreen conifers, but this information is very limited in broadleaf evergreen trees. This study compares the contribution of remobilized C and N to the construction of new organs in spring, and assesses the importance of different organs as C and N sources in 1-year-old potted seedlings of four ecologically distinct evergreen Mediterranean trees, namely Quercus ilex, Q. coccifera, Olea europaea and Pinus hapelensis.
  
  
  METHODS
  Dual (13)C and (15)N isotope labelling was used to unravel the contribution of currently taken up and stored C and N to new growth. Stored C was labelled under simulated winter conditions. Soil N was labelled with the fertilization during the spring growth.
  
  
  RESULTS
  Oaks allocated most C assimilated under simulated winter conditions to coarse roots, while O. europaea and P. halepensis allocated it to the leaves. Remobilization was the main N source (>74 %) for new fine-root growth in early spring, but by mid-spring soil supplied most of the N required for new growth (>64 %). Current photosynthesis supplied >60 % of the C in new fine roots by mid-spring in most species. Across species, the proportion of remobilized C and N in new shoots increased with the relative growth rate. Quercus species, the slowest growing trees, primarily used currently acquired resources, while P. halepensis, the fastest growing species, mainly used reserves. Increases in the amount of stored N increased N remobilization, which fostered absolute growth both within and across species. Old leaves were major sources of remobilized C and N, but stems and roots also supplied considerable amounts of both in all species except in P. halepensis, which mainly relied on foliage formed in the previous growing season to supply stored resources.
  
  
  CONCLUSIONS
  Seedlings of Mediterranean evergreen trees have distinct C and N storage physiologies, with relative growth rate driving the contribution of remobilized resources to new growth. These differences may reduce competition and facilitate species coexistence.
authors: Forest Ecology and Restoration Group, Departamento de Ciencias de la Vida, UD Ecología, Apdo. 20, Universidad de Alcalá, E-28805, Alcalá de Henares, Madrid, Spain and INRA Nancy, UMR 1137 INRA/UL Ecologie et Ecophysiologie Forestières, F-54280 Champenoux, France muscolaf@purdue.edu.
authors: Mercedes
authors: M
authors: Uscola
authors: Forest Ecology and Restoration Group, Departamento de Ciencias de la Vida, UD Ecología, Apdo. 20, Universidad de Alcalá, E-28805, Alcalá de Henares, Madrid, Spain and INRA Nancy, UMR 1137 INRA/UL Ecologie et Ecophysiologie Forestières, F-54280 Champenoux, France.
authors: Pedro
authors: P
authors: Villar-Salvador
authors: Forest Ecology and Restoration Group, Departamento de Ciencias de la Vida, UD Ecología, Apdo. 20, Universidad de Alcalá, E-28805, Alcalá de Henares, Madrid, Spain and INRA Nancy, UMR 1137 INRA/UL Ecologie et Ecophysiologie Forestières, F-54280 Champenoux, France.
authors: Patrick
authors: P
authors: Gross
authors: Forest Ecology and Restoration Group, Departamento de Ciencias de la Vida, UD Ecología, Apdo. 20, Universidad de Alcalá, E-28805, Alcalá de Henares, Madrid, Spain and INRA Nancy, UMR 1137 INRA/UL Ecologie et Ecophysiologie Forestières, F-54280 Champenoux, France.
authors: Pascale
authors: P
authors: Maillard
mesh_terms: D018533:Biomass; D002244:Carbon / Q000378:metabolism; D002247:Carbon Isotopes; D019083:Mediterranean Region; D009584:Nitrogen / Q000378:metabolism; D009928:Organ Specificity; D012621:Seasons; D036226:Seedlings / Q000254:growth & development*; D013045:Species Specificity; D014197:Trees / Q000254:growth & development*
chemical_list: D002247:Carbon Isotopes; D002244:Carbon; D009584:Nitrogen
keywords: 13C; 15N; Olea europaea; Pinus halepensis; Quercus coccifera; Quercus ilex; labelling; remobilization; reserves; spring growth