Sugar Maple (Acer Saccharum Marsh.) Provenances Differ with Climate of Origin in Survival, Growth, and Traits Along a Climate Gr
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Sugar maple (Acer saccharum Marsh.) provenances differ with climate of origin in survival, growth, and traits along a climate gradient: implications for the species’ distribution under climate change A DISSERTATION SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA BY Rachel Cope Putnam IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Dr. Peter B. Reich and Dr. G. David Tilman, Advisors December 2015 © Rachel Putnam 2015 ACKNOWLEDGEMENTS I gratefully acknowledge my advisors, Peter Reich and David Tilman, for all their support and guidance, and for encouraging me to think big and to tackle the questions that interest me most. Thanks as well to my committee members: Rebecca Montgomery, for helpful conversations and guidance along the way, and Sarah Hobbie, whose support I have felt and appreciated long before her role on the committee became official. I wish to acknowledge all those who helped with field and lab work, especially those volunteers who made the phenology component of this research possible, and the land managers at each site who made it possible for this research to be conducted. Specific contributions are recognized in each chapter. This research was supported by a STAR fellowship from the U.S. Environmental Protection Agency, and by funding from the Wilderness Research Foundation, the Alexander & Lydia Anderson Fellowship Fund, the James W. Wilkie Fund for Natural History, the Carolyn M. Crosby Fellowship Fund, the Rothman Fellowship Fund of the Dept. of Ecology, Evolution, and Behavior, and a Thesis Research Grant from the University of Minnesota. The Reich and Tilman lab groups have been a wonderful source of camaraderie and inspiration. Special thanks to Nick Fisichelli, Sascha Lodge, Laura Williams, and Peter Wragg, and to Cindy Buschena for all manner of support over the years. Finally, I thank my family, an ever-present source of grounding, support, and encouragement. Above all, thanks to Allison: from Arkansas to Ontario, you’ve been there every step of the way. Deep thanks for your unfailing support and patience. i DEDICATION To all the teachers in my life, from whom I have learned so much. ii ABSTRACT Plant ranges, broadly constrained by climate, may be further shaped by interspecific interactions and intraspecific variation in growth and traits. Changing climate and species composition in plant communities lends urgency to the need to better define the factors determining species’ distributions. This research seeks to determine the effects of temperature and neighbors on sugar maple (Acer saccharum) seedling survival, growth, biomass allocation, and functional traits, and whether this response varies with populations’ climate of origin. I first examine survival and growth of forest-planted seedlings across a natural climate gradient and beyond range limits to determine whether populations’ climate of origin and contrasting neighbor density and light environments affect performance. I find no evidence of climate or competition limitation beyond range margins for populations grown near their region of origin, but populations differ in survival and net growth in a manner consistent with local adaptation and contrasting growth strategies: the northern population has high survival across sites but lower mass than the southern population, which has low survival and growth facilitated by neighbors at northern sites. I then examine whether patterns of root biomass allocation of these same seedlings is affected by climate of the planting site or each populations’ region of origin. I find higher root mass in southern population seedlings than in similarly sized northern population seedlings, and higher root mass fraction at colder sites in the southern (but not northern) population. Finally, I use growth chambers to examine the effects of temperature and light on growth rate and traits for three climatically distinct populations. Growth rate declines with increasing latitude of origin and is lower in the temperature treatment corresponding to the climate of origin for the southern population. High-latitude populations have low SLA and LMF, but populations do not differ in photosynthetic rates. In conclusion, I find potentially adaptive differences in populations’ growth, survival, and plant traits but no direct evidence of climate or competition limitation across the range. This study highlights intraspecific variation in growth and traits, its relevance at range limits, and the need to identify whether reproductive or phenological traits also vary within species. iii TABLE OF CONTENTS Acknowledgements……………………………………………………………………...…i Dedication……………………………………………………………………………...….ii Abstract………………………………………………………………………………..….iii Table of Contents…………………………………………………………………………iv List of Tables………………………………………………………………………..……vi List of Figures……………………………………………………………………………vii Introduction…………………………………………………………………………..……1 Chapter 1 Understanding range limits: effects of climate and biotic interactions on growth and survival of sugar maple (Acer saccharum Marsh.) along a north-south gradient……………………………………………………………………………………3 Summary…………………………………………………………………………..4 Introduction………………………………………………………………………..5 Research Methods………………………………………………………………..11 Results……………………………………………………………………………19 Discussion………………………………………………………………………..25 Conclusion……………………………………………………………………….40 Acknowledgements………………………………………………………………41 Tables and Figures………………………………………………………...……..42 Supplemental Information……………………………………………………….51 Chapter 2 Root biomass fraction of forest-planted sugar maple (Acer saccharum Marsh.) seedlings varies with climate of population origin across a latitude gradient…………...59 Summary…………………………………………………………………………………60 Introduction………………………………………………………………………61 Research Methods………………………………………………………………..65 Results……………………………………………………………………………69 Discussion………………………………………………………………………..71 Conclusion……………………………………………………………………….77 Acknowledgements………………………………………………………………78 Tables and Figures……………………………………………………………….79 Supplemental Information…………………………………………………….…86 iv Chapter 3 Variable trait response to temperature in sugar maple (Acer saccharum Marsh.) seedlings despite consistent differences in growth among provenances……….92 Summary…………………………………………………………………………93 Introduction………………………………………………………………………94 Research Methods………………………………………………………………..97 Results…………………………………………………………………………..100 Discussion………………………………………………………………………103 Conclusion……………………………………………………………………...106 Acknowledgements……………………………………………………………..107 Tables and Figures……………………………………………………………...108 Supplemental Information……………………………………………………...115 Conclusion……………………………………………………………………………...126 Bibliography……………………………………………………………………………129 v List of Tables Chapter 1 Table 1-1. Survival and growth models over three-year period…………………………42 Table 1-2. Spring and fall phenology data at a northern and southern site……………...43 Table S1-1. Planting site climate and soil characteristics………………………………..51 Table S1-2. Climate-of-origin data for the three populations……………………………52 Table S1-3. Site climate normals compared to 3-year average climate………………….53 Table S1-4. Seasonal patterns in mortality for two populations at all sites……………...54 Table S1-5. Annual and final survival models…………………………………………...55 Table S1-6. Annual height, diameter, and extension models……………………………56 Table S1-7. Annual difference from long-term temperature mean……………………....57 Chapter 2 Table 2-1. Effects of population, temperature, and shoot mass on root biomass………..79 Table S2-1. Root mass model including clip and light treatments………………………86 Table S2-2. Root mass model including three populations……………………………...87 Table S2-3. Frequency of soil moisture deficit at a northern and southern site…………88 Chapter 3 Table 3-1. Hypothesized growth, trait response to temperature, population, and light...108 Table 3-2. Climate-of-origin data for three populations (MN, MO, TN)………………109 Table 3-3. Growth and trait models and hypotheses……………………………………110 Table S3-1. Distribution of light values in “low-light” vs. “higher-light” chambers…..115 Table S3-2. RGR model that includes LMF……………………………………………116 Table S3-3. RGR model that includes LAR……………………………………………117 vi List of Figures Chapter 1 Figure 1-1. Growth and survival hypotheses…………………………………………….44 Figure 1-2. Range map of sugar maple and planting sites……………………………….45 Figure 1-3. Survival and height of 3 populations across sites…………………………...46 Figure 1-4. Survival and height between light and clip treatments across sites…………47 Figure 1-5. Site-specific percent survival over time for 3 populations…………………..48 Figure 1-6. Relationship between height and survival…………………………………...49 Figure 1-7. Clip treatment effect on seedling mass for 3 populations…………………...50 Figure S1-1. Climate of 3-year average compared to long-term average………………..58 Chapter 2 Figure 2-1. Map of sites used in root analysis…………………………………………...80 Figure 2-2. Allometric relationship between root and shoot mass………………………81 Figure 2-3. Site differences in root/shoot allometric relationship……………………….82 Figure 2-4. RMF across a temperature gradient for 2 populations………………………83 Figure 2-5. Population differences in proportion root mass across sites………………...84 Figure 2-6. Root mass proportion at three seedling size quartiles……………………….85 Figure S2-1. Comparison of 3-year average site weather data to climate normals……...89 Figure S2-2. Site-specific allometric relationships of two populations………………….90 Figure S2-3. Effects of clip and light treatments