Plant size and intraspecific variability in vascular epiphytes Dissertation zur Erlangung des naturwissenschaftlichen Doktorgrades der Bayerischen Julius-Maximilians-Universität Würzburg vorgelegt von Gerold Schmidt aus Lindenberg im Allgäu Würzburg, September 2000 Eingereicht am: ...................................................................................................... Mitglieder der Prüfungskommission: Vorsitzender: .......................................................................................................... Gutachter: ............................................................................................................... Gutachter: ............................................................................................................... Tag des Promotionskolloquiums: ........................................................................... Dokumenturkunde ausgehändigt am: ..................................................................... ACKNOWLEDGEMENT First, and this is not for formal reasons, I want to thank my advisor Dr. Gerhard Zotz. As a source of constant inspiration and motivation he contributed profoundly to this thesis. Neither the enormous distance from continent to continent nor the vicinity from door to door was an obstacle for an excellent advisorship. I am also grateful for his patient way of introducing me into the ‘art of writing papers’. And then there are all the helping hands that assisted (sometimes for money, sometimes for chocolate) during the field work in Panama. These hands belong Edgardo Garrido, Jonathan Gonzales, Malte Jordy, Jaxelis Mendoza, Sabine Stuntz, Vera Thomas, and Christian Ziegler. – Thanks guys! Thanks as well to all the reliable co-workers in Würzburg, like Susanne Fischer and Ephraim Hoffmann, who assisted in experiments, while Astrid Boots and Frida Reisberg conducted the nutrient analyses. A prerequisite for effective (field-)work during my time in Panama was the infrastructure provided by the Smithsonian Tropical Research Institute. Thanks, in particular, to ‘Cajar’ (boat mechanic), Oris Acevedo (scientific coordinator of BCI) and Steve Paton, who provided all climate data. Financially, this thesis was supported by a stipend of the ‘Graduierten Kolleg’ and the Deutsche Forschungsgemeinschaft’ (SFB 251, Universität Würzburg). Natural sciences are interesting, thrilling and fascinating. This is even more so if science is not the only topic to focus on. Therefore a special ‘Thank You’ to - as representatives – some of the distracters: Hubbi (the banana vine-dresser), Sabine (the big-tree conquest buddy), Jonathan (...wenn es dunkel ist, möchte ich leuchten...), Paul (for being Poll), Malte (the crater companion), and ... Vera (my love). The final thanx go out to my parents for the everlasting certainty of providing support whenever support is needed. I II Table of contents TABLE OF CONTENTS Acknowledgement..................................................................................................... I Table of contents..................................................................................................... III Chapter 1: Introductory Overview........................................................................... 1 THE SIZE OF AN ORGANISM ................................................................................................ 1 ORGANISM SIZE AND PERFORMANCE IN THE ANIMAL KINGDOM ......................................... 2 ORGANISM SIZE AND PERFORMANCE IN THE PLANT KINGDOM ........................................... 2 VASCULAR EPIPHYTES AS STUDY ORGANISMS.................................................................... 3 SCOPE OF THE DISSERTATION............................................................................................. 4 Chapter 2: Photosynthetic capacity increases with plant size in an epiphytic orchid: an exceptional case or a widespread phenomenon among tropical vascular epiphytes? ................................................................................................. 5 CHAPTER ABSTRACT .......................................................................................................... 5 INTRODUCTION .................................................................................................................. 5 METHODS .......................................................................................................................... 6 Field site and study organism.................................................................................. 6 Gas exchange and leaf nitrogen content.................................................................. 7 Shoot water content and plant leaf area................................................................... 7 RESULTS ............................................................................................................................ 7 DISCUSSION ..................................................................................................................... 10 APPENDIX ........................................................................................................................ 13 Chapter 3: Ecophysiological consequences of differences in plant size – in situ carbon gain and water relations for an epiphytic bromeliad........................15 CHAPTER ABSTRACT ........................................................................................................ 15 INTRODUCTION ................................................................................................................ 15 METHODS ........................................................................................................................ 16 Field site and study organism................................................................................ 16 Morphometry and anatomy ................................................................................... 17 Physiological measurements during the drought experiment................................ 17 Other measurements .............................................................................................. 18 Data analysis.......................................................................................................... 20 RESULTS .......................................................................................................................... 20 Size-related morphometrical and anatomical features .......................................... 20 Size-related changes in leaf physiological parameters during drought................. 23 DISCUSSION ..................................................................................................................... 28 Shift between life forms ........................................................................................ 28 Size differences in the water-impounding phase................................................... 29 III Chapter 4: Growth in two epiphytes – analysis of whole-plant performance under natural and controlled conditions with special consideration of plant size............................................................................................................................31 CHAPTER ABSTRACT ........................................................................................................ 31 INTRODUCTION ................................................................................................................ 31 METHODS ........................................................................................................................ 32 Habitat and study species ...................................................................................... 32 Census data............................................................................................................ 33 Determination of size categories ........................................................................... 33 Controlled environment......................................................................................... 34 Growth and data analysis ...................................................................................... 34 RESULTS .......................................................................................................................... 34 Phenology.............................................................................................................. 34 Plant size and vegetative growth ........................................................................... 36 Mortality................................................................................................................ 39 DISCUSSION ..................................................................................................................... 40 Chapter 5: Annual carbon balance of an epiphytic bromeliad – a model links leaf physiology and plant growth.......................................................................... 43 CHAPTER ABSTRACT ........................................................................................................ 43 INTRODUCTION ................................................................................................................ 43 METHODS ........................................................................................................................ 44 Field site and study organism................................................................................ 44 Measurements of maximal tank water content and diel