title: Nitrogen isotope ratios shift with plant size in tropical bromeliads.
abstract: We describe an ontogenetic shift in nitrogen (N) isotopic values in two rosette-forming epiphytic bromeliads. Leaf tissue N isotope values of small individuals of two bromeliad species (mean -6.2 per thousand ) differed from those of large individuals within each species (mean -0.5 per thousand ). Using references for potential N sources, we calculated the relative contribution of autochthonous (soil-derived through leaf litter) and allochthonous (atmospheric deposition) N with a two-member mixing model. Atmospheric sources contributed as much as 77-80% of the N in small individuals, whereas soil-derived N contributed 64-72% (conservative reference value) to 100% (less conservative reference value) of leaf tissue N in large plants. Shifts in N source with increasing plant size may be important aspects of rainforest complexity, an understudied aspect of ecosystem diversity.
mesh_terms: D031229:Bromeliaceae / Q000254:growth & development / Q000502:physiology*; D017753:Ecosystem; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000032:analysis / Q000493:pharmacokinetics; D018515:Plant Leaves / Q000737:chemistry; D012987:Soil; D014018:Tissue Distribution; D014329:Tropical Climate
chemical_list: D009587:Nitrogen Isotopes; D012987:Soil; D009584:Nitrogen