This Thesis Has Been Submitted in Fulfilment of the Requirements for a Postgraduate Degree (E.G
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This thesis has been submitted in fulfilment of the requirements for a postgraduate degree (e.g. PhD, MPhil, DClinPsychol) at the University of Edinburgh. Please note the following terms and conditions of use: • This work is protected by copyright and other intellectual property rights, which are retained by the thesis author, unless otherwise stated. • A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. • This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author. • The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author. • When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given. Linkages between leaf traits and productivity in two resource-limited ecosystems Isabel Cristina Chinchilla Soto Doctor of Philosophy The University of Edinburgh 2013 Declaration I declare that this thesis has been composed by myself and has been submitted for any other degree. The work described is my own, except where otherwise indicated. Cristina Chinchilla Soto i Acknowledgements I would like to thank my supervisor Mathew Williams for taking me on board. I do not think I could ever thank you enough for your time, your commitment to my project and for all the things you taught me. Thanks to everyone in my research group, particularly to Lorna Street who helped me with the field-set up for the experiment in Buxton. Thanks as well to the staff at the Crew Building, who answered my questions even when they were very busy. Thanks to my lovely friends at Uni that made my life special, particularly to the girls from all over the world: Toshie, Rossella, Joana, Aisling, Emal and Beth. I wouldn’t have made it this far without your encouraging words and your help along the way. Special thanks to Louise Beveridge and Christina Smith, for their invaluable help on the field. Your support and company on the long field days in Buxton and in Santa Rosa made my work a lot more fun. Thanks to everyone who contributed in the field work at the dry forest particularly to William Romero and Saul Chévez. Also to the personal in the Area de Conservacion Guanacaste, particularly to Roger Blanco Coordinator of the Research Program and to the kitchen staff who fed me so well. Additional thanks to Marco Vinicio Gutiérrez from the Universidad de Costa Rica (UCR) for providing equipment for this work, to Jose Araya for logistic support and to Jorge Leiva for helping me finding the plots. Thanks to Phil Grime and Jason Fridley for allowing me to develop my research in Buxton. I do not think I will see the grasses the same way after all that taxonomy. Andrew Askew thanks for all your logistic support. This work would not have been possible without financial support of the organizations that funded my PhD years. Thanks to the University of Edinburgh for awarding me an Overseas Research Scholarship (ORS), and to the School of Geosciences for granting me a Teaching Studentship. Additional thanks to the Universidad de Costa Rica (UCR) for additional financial support during this period. ii Thanks as well to the organizations that funded my research. To UNESCO- L’OREAL who granted me a Co-Sponsored Fellowship for Young Women in Life Sciences-2011, to the UCR and the National Council of Science and Technology of Costa Rica (CONICIT) for supporting my work in Costa Rica. Thanks to the University of Edinburgh Development Trust for funding part of my research in Buxton. Above all, thanks to my family for having faith in me once again and for all their support. Mom and Dad thanks for teaching me the value of hard work and dedication, and thanks for all the logistic help for my field work in Costa Rica. Thanks to Gaby, Nice, Fede and David for your encouraging words along the way. Nice, additional thanks for your help with my image processing. Special thanks to Johan Molina, for all your support, for living this adventure with me and for all your visits to Edinburgh, you made these four years a lot more fun. Thanks to all my friends in Costa Rica who were always asking about my progress and are waiting for my return. To all of you I dedicate this work. iii Abstract Leaf traits have long been used to classify and characterise species in natural ecosystems. In addition, leaf traits provide important information about plants’ strategies for the use of resources and can be used to improve our understanding of ecosystem level processes such as nutrient cycling and carbon allocation. To explore the linkages between leaf traits and productivity, we worked in two resource-limited ecosystems (a grassland and a forest), and used leaf traits to understand how species respond to changes in available resources and their relationship to ecosystem processes. We worked in a species rich limestone-grassland located in central England, which has been subjected to long-term climatic manipulation (winter warming, summer drought and extra summer rainfall). We characterised species composition in terms of their identity, abundance and leaf structural properties (nitrogen content and leaf mass per area (LMA)) in the main treatments and the control. We found that change in species abundance was the most important factor to understand the differences in productivity (above ground biomass and total foliar nitrogen). We then measured CO 2 exchange at ecosystem level, using a chamber technique, and assessed the treatments’ effect on the gross primary productivity (GPP) and ecosystem respiration ( Reco ). GPP and Reco were controlled by soil moisture and above ground biomass but also influenced by the conditions experienced during the growing season prior to the measuring period. Our second location was a post-disturbance chronosequence in a seasonally dry tropical forest in Costa Rica and we used leaf level gas exchange measurements to explore the role of nitrogen (N) and phosphorus (P) on the temporal-spatial variation of photosynthesis of dominant species. We found that photosynthetic efficiency was strongly linked to leaf N and P content, but that there was an important seasonal pattern on this relationship likely associated to P remobilization. Additionally we found seasonal changes in resources (water, nutrients) had a larger impact on the photosynthetic parameters than changes along the chronosequence. The two ecosystems studied for this thesis are contrasting in their physiognomy, species composition and climate, but are also characterised by species whose structural traits (high LMA and high C:N ratio) are likely to have a significant impact on the nutrient cycling processes. We iv learned that leaf traits provide important information about species strategies and their usage of resources and they can also aid to address questions at ecosystem level in time and space, either through simple aggregation or as emergent properties. Additionally, the traits explored are important input information to up-scale processes from leaf to the ecosystem level, a step needed to address the effect changes in resources will have on the seasonally dry tropical forest and grasslands, which represent a significant fraction of the total global carbon storage. v “Aprender a leer es lo más importante que me ha pasado en la vida". Mario Vargas Llosa , Nobel Prize Award Ceremony December 2010 vi Table of Contents Declaration .................................................................................................................... i Acknowledgements ...................................................................................................... ii Abstract ....................................................................................................................... iv Table of Contents ....................................................................................................... vii Chapter 1 . Introduction ............................................................................................... 1 Chapter 2 . Implications of leaf traits variation for grassland productivity in a long- term climate manipulation.......................................................................................... 24 Abstract ...................................................................................................................... 25 Introduction ................................................................................................................ 26 Methodology .............................................................................................................. 30 Results ........................................................................................................................ 35 Discussion .................................................................................................................. 47 Conclusions ................................................................................................................ 52 Chapter 3a . Soil moisture, leaf area index and inter-annual climatic variability control gross primary productivity in limestone grasslands in a field-scale climate manipulation experiment ........................................................................................... 60 Abstract ...................................................................................................................... 61 Introduction ...............................................................................................................