Phenology and allocation of belowground plant carbon at local to global scales

244 Pages·2015·6.42 MB·English

by  Vika Zafrin

BOSTON UNIVERSITY

GRADUATE SCHOOL OF ARTS AND SCIENCES

Dissertation

PHENOLOGY AND ALLOCATION OF BELOWGROUND PLANT CARBON AT
LOCAL TO GLOBAL SCALES

by

ROSE Z. ABRAMOFF

B.A., Amherst College, 2009

Submitted in partial fulfillment of the

requirements for the degree of

Doctor of Philosophy

2015
UMI Number: 3711420
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Approved by

First Reader _________________________________________________________
Adrien C. Finzi, Ph.D.
Professor of Biology

Second Reader _________________________________________________________
Lucy Hutyra, Ph.D.
Assistant Professor of Earth & Environment

Third Reader _________________________________________________________
Jennifer Talbot, Ph.D.
Assistant Professor of Biology
ACKNOWLEDGEMENTS
I thank my thesis advisor, Adrien Finzi, whose guidance was critical to the
development of my research interests, expertise, and this document. I think him for
holding my work to a high standard, and for challenging me to think broadly and
critically. Because of his continuing support, I feel prepared to begin a career in research.
I also thank my committee members: Lucy Hutyra, Pamela Templer, Richard Primack,
Nathan Phillips, and Jennifer Talbot, for years of thoughtful discussion, advice, and
encouragement. This work is also a product of their guidance.
The field work, lab work, and image analysis presented here could not have been
completed without the help of the following students, who enriched my experience by
allowing me to mentor them for their own independent projects, projects supporting this
thesis, and in their next steps in science: Amanda Alon, Samuel Knapp, Johanna Recalde,
Arline Gould, and Aubree Woods. I also thank my labmates Allison Gill, Pat Sorensen,
Mustafa Saifuddin, and Marc-Andre Giasson, for field work help, invaluable discussion
and advice, and all the good times. To my fellow EBE and Biogeosciences graduate
students, too many to name, I thank you for your support, inspiration, friendship, cookies,
and beer.
Lastly, I would like to thank my family, and especially my parents, for a creative
and intellectual childhood, for the privileges they have afforded me, and for their
unconditional love.

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PHENOLOGY AND ALLOCATION OF BELOWGROUND PLANT CARBON AT
LOCAL TO GLOBAL SCALES
(Order No. )
ROSE Z. ABRAMOFF
Boston University Graduate School of Arts and Sciences, 2015
Major Professor: Adrien C. Finzi, Professor of Biology

ABSTRACT
Forests play an important role in mitigating climate change by removing carbon
dioxide (CO ) from the atmosphere via photosynthesis and storing it in plant tissues and
2
soil organic matter (SOM). Plant roots are a major conduit for transporting recently fixed
CO belowground, where carbon (C) remains in SOM or returns to the atmosphere via
2
respiration of soil microbes. Compared to aboveground plant processes related to the C
cycle, there is little understanding of how belowground plant-C allocation to roots,
symbiotic root fungi and secretions into the soil influence the gain or loss of C from the
soil. Further, the uncertainty in the timing and amount of root growth that occurs in
forests is a barrier to understanding how root activity responds to global change and feeds
back to the C cycle. Therefore, the objective of my research is to quantify the timing and
magnitude of C allocation to roots and soil via data compilation, field studies and
modeling across broad spatial scales. Using data compilation at the global scale, I show
that root and shoot phenology are often asynchronous and that evergreen trees commonly
have later root growth compared to deciduous trees using meta-analysis across four
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biomes. At the plot scale, field studies in a mid-latitude forest demonstrate that deciduous
stands allocate more C belowground earlier in the growing season compared to a conifer
stand. The difference in phenology between stands can be attributed to the timing of root
growth. At the root scale, zymographic analysis demonstrates that microbial extracellular
enzyme activity is concentrated near the surface of roots and that the rhizosphere can
extend well beyond 2 mm from the root surface. Finally, I developed a new model of
microbial physiology and extracellular enzyme activity to assess how climate change
may affect plant – microbe interactions and soil organic matter decomposition. I show
that increases in temperature and the quantity of C inputs substantially alter
decomposition. Collectively, these results demonstrate the importance of belowground
allocation to the C cycle of terrestrial ecosystems.

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TABLE OF CONTENTS

ACKNOWLEDGEMENTS ............................................................................................... iv
ABSTRACT ........................................................................................................................ v
TABLE OF CONTENTS .................................................................................................. vii
LIST OF TABLES ............................................................................................................ xii
LIST OF FIGURES ........................................................................................................ xvii
LIST OF ABBREVIATIONS ........................................................................................ xxvi
CHAPTER ONE: INTRODUCTION ................................................................................. 1
Dissertation Overview .................................................................................................... 7
CHAPTER TWO: ARE ABOVE AND BELOWGROUND PHENOLOGY IN SYNC? 11
Abstract ......................................................................................................................... 11
Introduction ................................................................................................................... 12
A compilation of available data .................................................................................... 13
Primary Data Findings .................................................................................................. 14
Some Implications of the Data ...................................................................................... 16
Moving Forward ........................................................................................................... 20
Acknowledgements ....................................................................................................... 21
Supplementary Information .......................................................................................... 28
Paper selection .......................................................................................................... 28
vii
Gross and net root production ................................................................................... 28
Offset......................................................................................................................... 29
Monthly root and shoot growth................................................................................. 30
Temperature and precipitation data .......................................................................... 30
Supplementary Information Reference Guide .......................................................... 46
CHAPTER THREE: SEASONALITY AND PARTITIONING OF ROOT
ALLOCATION TO RHIZOSPHERE SOILS IN A MID-LATITUDE FOREST ........... 54
Abstract ......................................................................................................................... 54
Introduction ................................................................................................................... 56
Materials and Methods .................................................................................................. 58
Study Site .................................................................................................................. 58
Root Production and Biomass ................................................................................... 59
Root Respiration ....................................................................................................... 62
Nonstructural Carbohydrates .................................................................................... 63
Root Exudation ......................................................................................................... 63
Total Belowground C Flux ....................................................................................... 64
Data Analysis ............................................................................................................ 66
Results ........................................................................................................................... 67
Root Production and Biomass ................................................................................... 67
Root Respiration ....................................................................................................... 69
Nonstructural Carbohydrates and Root Exudation ................................................... 70
Total Belowground C Flux ....................................................................................... 70
viii
Discussion ..................................................................................................................... 71
Phenology of Root Growth and Mortality ................................................................ 72
Environmental Controls over Root Growth and Respiration .................................... 73
Nonstructural Carbohydrates and Root Exudation ................................................... 74
Total Belowground C Flux ....................................................................................... 76
Summary ................................................................................................................... 78
Acknowledgements ....................................................................................................... 78
CHAPTER FOUR: WHERE DOES THE RHIZOSPHERE END? SPATIALLY
RESOLVED MEASUREMENTS OF IN SITU SOIL EXTRACELLULAR ENZYME
ACTIVITY ........................................................................................................................ 95
Abstract ......................................................................................................................... 95
Introduction ................................................................................................................... 97
Methods......................................................................................................................... 99
Site description.......................................................................................................... 99
Results ......................................................................................................................... 105
Visual inspection ..................................................................................................... 105
Coarse image resolution .......................................................................................... 106
Fine image resolution .............................................................................................. 107
Very fine image resolution...................................................................................... 108
Discussion ................................................................................................................... 108
Rhizosphere extent across stand types and enzyme classes .................................... 109
Effects of image analysis resolution ....................................................................... 109
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