Ecophysiology of the tree fern species Dicksonia antarctica Labill and Cyathea australis (R. Br.) Domin Liubov Vladimirovna Volkova Submitted in total fulfilment of the requirements of the degree of Doctor of Philosophy October 2009 Department of Forest and Ecosystem Science Melbourne School of Land and Environment The University of Melbourne Produced on archival quality paper Abstract Predictions of global warming and associated climate change indicate widespread in- creases in light intensities, temperatures, and the frequency and severity of droughts in south-eastern Australia. Understanding the ability of plants to respond and acclimate to these events is essential to predict species survival and potential impacts on biodiver- sity. This study focuses on two tree fern species – Dicksonia antarctica and Cyathea aus- tralis – two iconic understorey species of south-east Australian forests. These tree ferns belong to different families and are of contrasting origins, yet often grow together in south-eastern Australia, typically in shade, often along waterways. Their ecological im- portance is evident in the high epiphytic diversity on their trunks (ferns, mosses, bryo- phytes, liverwort etc), and the provision of nursery sites for many tree and shrub spe- cies. Both species are decreased by timber harvesting practices such as clearcut logging, with deaths continuing for up to five years in the post-harvest environment. Understand- ing the relative roles of changing light, water, and temperature in these ongoing declines is essential to conserving both tree fern populations and their dependent biota. The Thesis encompasses three controlled experiments and a field study. In the con- trolled experiments, the tree ferns were acclimated to contrasting growth light environ- ments (shade or moderate light) and then exposed to an environmental stress (i.e. light, heat, water deficit). The field study examined relationships between environmental variables (i.e. light, temperature, plant water status) and photosynthetic capacity pa- rameters of the tree ferns in their natural environment. Stress responses and acclimation potential of photosynthetic traits, water relation parameters, and frond traits of the tree ferns were studied using infra-red gas analysis, pigment determination techniques, and stable isotope methods. It was hypothesised that, consistent with their contrasting origins and micro-site prefer- ences, the two tree fern species would possess different physiological characteristics -i- and therefore respond differently to environmental stresses. It was also hypothesised that plants grown under contrasting light environments would have different reactions to and recoveries from environmental stresses. Overall, plants were able to sustain and recover from high light stress, while interactive effects of high light and heat were most detrimental to tree fern performance. Both spe- cies were susceptible to water stress, either alone or in combination with high light. The hypothesised different responses of the two species (associated with their different ori- gins) were not confirmed, and reaction to and recovery from stress was mainly unaf- fected by growth light environment. Both species had low acclimation potential to any of the applied environmental stresses. Overall, findings from this study indicate that combined effects of high light and heat most likely cause ongoing decline of tree ferns in post-harvest environments, and that the distribution of tree ferns will most likely con- tract under future climate scenarios of higher light, increased temperatures, and de- creased water availability. -ii- Declaration This is to certify that: the thesis comprises only my original work towards the PhD except where indicated in the Preface, due acknowledgement has been made in the text to all other material used, the thesis is less than 100,000 words in length, exclusive of tables, maps, bibliogra- phies and appendices Liubov Volkova -iii- Preface The climate chamber experiment, Chapter 3, was undertaken in Champenoux, France using facilities of the Institut National Reserche Agronomique (INRA). I planned, con- ducted the research, evaluated and presented the data. The results of the study were pre- sented at the International Eco-Fizz conference, 2007 (a poster) and published in the scientific journal Functional Plant Biology (Volkova L, Tausz M, Bennett LT, Dreyer E, 2009. „Interactive effects of high irradiance and moderate heat on photosynthesis, pigments, and tocopherol in the tree-fern Dicksonia antarctica’). M. Tausz and L.T. Bennett are the supervisors of my PhD work. Erwin Dreyer, the fourth co-author of the publication was a hosting party in INRA and supervised my activities. Professor Dreyer is also an honorary staff member of the Department of Forest and Ecosystem Science at The University of Melbourne. Chapter 4 (high light and water stress experiment) has been submitted for publication in co-authorship with my supervisors and Dr. Andrew Merchant (the University of Syd- ney). I declare that the execution of the experiment, data evaluation and presentation were solely my own work, and that A. Merchant gave useful tips on the experimental design and helped to organise the isotopic analysis of my samples. Chapters 2 and 5 are written in co-authorships with my supervisors M. Tausz and L.T. Bennett who helped with usual supervisory roles. -iv- Acknowledgements Personal financial support for this study was provided by a Melbourne Research Schol- arship. Expenses related to research activities (i.e. field study and construction of the controlled experiments) were partly covered by a research agreement with the Victorian Department of Sustainability and Environment (TA30874). I am personally grateful to my University supervisors, Ass. Prof. Michael Tausz and Dr Lauren Bennett, for their patience, ongoing support and encouragement during my study. I admire Michael for his ability to think globally and to give me confidence that everything is possible. I admire Ren for her strong personality, always prompt re- sponses; ability to carefully examine every detail; her great friendship and care when I needed it. She was (and is) the Woman, who made me deeply respect women in science. I am indebted to Erwin Dreyer (INRA, France) for his great deal of support and advice during my candidature; his personal friendship is very precious to me. I would like to thank Andrew Merchant for his advice and support throughout my study. My thanks to Chris Western for his patience, always good advice and for being my personal Counsel- lor at difficult times. I acknowledge staff and students at Creswick campus for their support. Thanks particu- larly to Thomas Wright for his friendship and ongoing help, and Raymond Dempsey for his help in the field. Thanks also to Matt Lee and Najib Ahmady for always providing reliable and timely results, and my thanks to all others. I am grateful to my family: husband, Fedor Torgovnikov, for his patience, support and help during my study. His ability to fix equipment and build constructions for my ex- periments was priceless. His patience with my often bad moods due to problems with experiments and understanding my difficulties made me able to finish this study. I thank my daughter, Katerina Torgovnikova, for her help with watering and re-potting plants and her patience with “always busy mum”. I am thankful to my parents-in-law, and most of all, I want to thank my mum, Svetlana Volkova, for teaching me to never give up and always reach my targets. -v- Table of Contents Abstract ...................................................................................................................... i Declaration .............................................................................................................. iii Preface ..................................................................................................................... iv Acknowledgements .................................................................................................... v Table of Contents ..................................................................................................... vi List of Figures .......................................................................................................... xi Chapter 1. Introduction .......................................................................................... 1 1.1. Environmental stresses: light, temperature and water deficit ...................... 1 1.2. Fundamental effects of high irradiance in interaction with high temperature or drought on plants ............................................................................. 1 1.3. Two tree ferns of contrasting origin ............................................................. 3 1.4. The tree ferns in mountain ash forests of south-eastern Australia ............... 5 1.5. Current knowledge of tree fern ecophysiology ............................................. 6 1.6. Thesis aims and outline ................................................................................. 8 Chapter 2. Effects of sudden exposure to high light on two tree fern species Dicksonia antarctica, and Cyathea australis, acclimated to different light intensities. ............................................................................................................ 11 (i) Abstract ....................................................................................................... 11 2.1. Introduction ...............................................................................................