Size-Dependent Variation of Carbon and Nitrogen Isotope Abundances in Epiphytic Bromeliads

P. Hietz; W. Wanek

doi:10.1055/s-2003-40730

Plant Biology, Table of Contents

Plant Biol (Stuttg) 2003; 5(2): 137-142
DOI: 10.1055/s-2003-40730

Original Paper

Georg Thieme Verlag Stuttgart · New York

Size-Dependent Variation of Carbon and Nitrogen Isotope Abundances in Epiphytic Bromeliads

P. Hietz¹ , W. Wanek²

¹Institute of Botany, BOKU University of Natural Resources and Applied Life Sciences, Vienna, Austria
²Institute of Ecology and Conservation Biology, University of Vienna, Vienna, Austria

Abstract

While atmospheric species of bromeliads have narrow leaves, densely covered with water-absorbing trichomes throughout their life cycles, many tank bromeliads with broad leaves, forming phytotelmata, go through an atmospheric juvenile phase. The effect of the different habits and the phase change in tank-forming bromeliads on water and nutrient relations was investigated by analysing the relationship between plant size, C/N ratios and the natural abundance of ¹³C and ¹⁵N in five epiphytic bromeliad species or morphospecies of a humid montane forest in Xalapa, Mexico. The atmospheric species Tillandsia juncea and T. butzii exhibited full crassulacean acid metabolism, with δ¹³C values (mean - 15.3 ‰ and - 14.7 ‰, respectively) independent of size. In Tillandsia species with C₃ photosynthesis, δ¹³C decreased with increasing plant size, indicating stronger drought stress in juveniles. The increase of the C/N ratio with size suggests that, at least in heteroblastic bromeliads, the availability of water is more limiting during early growth, and that limitations of nitrogen supply become more important later on, when water stored in the tank helps to bridge dry periods, reducing water shortage. δ¹⁵N values of the two atmospheric species were very negative (- 12.6 ‰ and - 12.2 ‰, respectively) and did not change with plant size. Tank-forming bromeliads had less negative δ¹⁵N values (c - 6 ‰), and, in species with atmospheric juveniles and tank-forming adults, δ¹⁵N values increased significantly with plant size. These differences do not appear to be an effect of the isotopic composition of N sources, but rather reflect N availability and limitation and stress-induced changes in ¹⁵N discrimination.

Key words

CAM - epiphyte - nitrogen - plant size - stable isotope abundance

Full Text

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P. Hietz

Institute of Botany BOKU University of Natural Resources and Applied Life Sciences

Gregor-Mendel-Straße 33

1180 Vienna

Austria

Email: hietz@edv1.boku.ac.at

Section Editor: H. Rennenberg