MODELS OF THE INTERACTIVE EFFECTS OF RISING OZONE,
CARBON DIOXIDE AND TEMPERATURE ON CANOPY CARBON DIOXIDE EXCHANGE AND
ISOPRENE EMISSION.
M.J. MARTIN
A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF BIOLOGICAL AND CHEMICAL SCIENCES
UNIVERSITY OF ESSEX
1997
Dedicated to the memory of my mother, Mrs. B.G. Violett.
ACKNOWLEDGEMENTS
I would like to express my thanks to Dr. Clare Stirling for the
opportunity of doing this PhD, and for her support during the initial stages of research.
I would also like to thank Professor Steve Long for his advice and supervision,
particularly during the writing of this thesis, together with Steve Humphries for the use
of the model WIMOVAC, and for his assistance with some aspects of the Visual Basic
programming code. I am also indebted to Dr. Peter Farage for the use of his experimental
data on the effects of acute ozone exposure on photosynthesis, and for useful discussions
during my time at Essex University, and to Dr. Ian McKee for the use of his data on
chronic ozone exposure effects on wheat.
In addition, I'd also like to express my appreciation to the Natural
Environmental Research Council for their financial support. However, the greatest thanks
must go to my family, for their support during the past few years of study, research and
thesis writing.
CONTENTS
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Page |
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ACKNOWLEDGEMENTS |
3 |
|
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CONTENTS |
4 |
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ABBREVIATIONS |
7 |
|
|
SUMMARY |
8 |
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CHAPTER ONE |
|
GENERAL INTRODUCTION |
|
1.1 The effects of global atmospheric
change on vegetation |
9 |
1.2 Tropospheric ozone |
10 |
1.3 Increased rates of isoprene emission |
15 |
1.4 Interactive effects |
16 |
1.5 Scales and types of model |
20 |
1.6 Aims and objectives |
22 |
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CHAPTER TWO |
|
A PROCESS-BASED MODEL TO PREDICT THE
EFFECTS OF ENVIRONMENTAL CHANGE ON LEAF ISOPRENE EMISSION RATES |
|
2.1 Introduction |
27 |
2.2 Model Theory |
31 |
2.2.1 Outline of model structure |
31 |
2.2.2 The supply of carbon for the
molecular skeleton of isoprene |
36 |
2.2.3 Phosphorylation and the availability
of ATP |
38 |
2.2.4 Isoprene synthase activity |
39 |
2.2.5 Summary |
40 |
2.3 Method |
41 |
2.3.1 Model overview |
41 |
2.3.2 Carbon dioxide assimilation model |
41 |
2.3.3 The rate of pyruvate formation in
the stroma |
44 |
2.3.4 Phosphorylation limitation of DMAPP
production |
46 |
2.3.5 Temperature dependency of isoprene
synthase reaction rate |
46 |
2.3.6 Model validation |
46 |
2.3.7 Sensitivity analysis |
48 |
2.3.8 Prediction of leaf isoprene emission
rates under increased temperature and
elevated [CO2] conditions |
51 |
2.4 Results |
52 |
2.4.1 Model simulation test results |
52 |
2.4.1.1 Response of isoprene emission
rates to photon flux density |
52 |
2.4.1.2 Response of isoprene emission
rates to CO2 concentrations |
52 |
2.4.1.3 Response of isoprene emission
rates to temperature |
57 |
2.4.2 Sensitivity analysis |
61 |
2.4.3 Isoprene emission rates under high
temperature and elevated [CO2] |
65 |
2.5 Discussion |
69 |
CHAPTER THREE |
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THE PREDICTED EFFECTS OF GLOBAL WARMING ON
ISOPRENE EMISSION FROM FOREST CANOPIES |
|
3.1 Introduction |
73 |
3.2 Methods |
76 |
3.2.1 Model equations |
76 |
3.2.2 Model simulations for validation |
80 |
3.2.3 Global warming prediction model
simulations |
84 |
3.3 Results |
86 |
3.3.1 Temperature regime |
86 |
3.3.1.1 Deciduous forest of the UK |
86 |
3.3.1.2 Deciduous forest of the USA |
86 |
3.3.1.3 Tropical rain forest of the Amazon |
87 |
3.3.2 Simulation of isoprene emission over
the course of one year |
87 |
3.3.3 Model simulations of future emission
rates |
91 |
3.3.3.1 Deciduous forest of the UK |
91 |
3.3.3.2 Deciduous forest of the USA |
94 |
3.3.3.3 Tropical rain forest of the Amazon |
94 |
3.4 Discussion |
97 |
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CHAPTER FOUR |
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A SIMPLE MODEL TO PREDICT THE EFFECTS OF
ACUTE OZONE EXPOSURE ON WHEAT PHOTOSYNTHESIS |
|
4.1 Introduction |
104 |
4.2 Model theory and development |
107 |
4.3 Methods |
110 |
4.3.1 Model parameterisation: relating Vcmax to ozone uptake |
110 |
4.3.2 Predicting changes in stomatal
conductance |
116 |
4.3.3 Sensitivity analysis |
123 |
4.3.4 Predicting the interactive effects
of [CO2] and [O3] on photosynthesis |
123 |
4.3.5 Predicting the interactive effects
of [CO2] and [O3] on a wheat canopy |
124 |
4.4 Results |
127 |
4.4.1 Prediction of decline in Vcmax and stomatal closure |
127 |
4.4.2 Sensitivity analysis |
127 |
4.4.3 The interactive effects of [CO2] and [O3] on photosynthesis |
127 |
4.4.4 The interactive effects of [CO2] and [O3] on a wheat canopy |
131 |
4.5 Discussion |
134 |
CHAPTER FIVE |
|
A SIMPLE MODEL TO PREDICT THE EFFECTS OF
CHRONIC OZONE EXPOSURE ON WHEAT PHOTOSYNTHESIS |
|
5.1 Introduction |
139 |
5.2 Model theory and development |
143 |
5.3 Methods |
145 |
5.3.1 Determination of threshold
flux and coefficient of ozone damage |
145 |
5.3.2 Model testing |
153 |
5.3.2.1 Simulated interactive effects of
ozone and elevated [CO2] |
153 |
5.3.2.2 Testing the model against the cv.
Avalon |
153 |
5.3.3 Predicting the effects of chronic
ozone exposure on wheat productivity |
154 |
5.3.3.1 Parameterisation of ozone
variation during the growing season |
154 |
5.3.3.2 A simple canopy model to simulate
wheat growth |
157 |
5.4 Results |
160 |
5.4.1 Interactive effects of increased [O3] and [CO2] on Vcmax |
160 |
5.4.2 Model testing |
160 |
5.4.3 Effects of chronic ozone exposure
and elevated [CO2] on wheat productivity |
162 |
5.5 Discussion |
164 |
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CHAPTER SIX |
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GENERAL DISCUSSION |
|
6.1 Introduction |
169 |
6.2 Study findings and limitations |
170 |
6.2.1 Leaf isoprene emission rates |
170 |
6.2.2 Canopy isoprene emission rates |
172 |
6.2.3 Effects of acute ozone exposure |
174 |
6.2.4 Effects of chronic ozone exposure |
175 |
6.3 Model prediction |
176 |
6.4 Future work |
179 |
6.5 Hypotheses to test |
180 |
6.5.1 Interactive effects of ozone,
isoprene emission, elevated [CO2], and water
stress |
180 |
6.5.2 Relative ozone sensitivity, and the
values of Kz and FO3(0) |
181 |
6.6 Conclusion |
182 |
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REFERENCES |
183 |
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APPENDIX I |
|
Tables of model equations: |
|
Table A: Leaf CO2
assimilation rates and stomatal response |
196 |
Table B: Canopy macroclimate and
microclimate |
197 |
Table C: Rates of isoprene emission and
photorespiration |
199 |
Table D: Canopy isoprene emission |
200 |
Table E: Acute ozone |
201 |
Table F: Chronic ozone |
202 |
|
|
APPENDIX II |
|
Table of symbol definitions |
203 |
ABBREVIATIONS
A |
Assimilation rate (µmol m-2
s-1). |
Ca |
Atmospheric concentration of CO2 (µmol mol-1). |
Ci |
Intercellular concentration of CO2 (µmol mol-1). |
CO2 |
Carbon dioxide. |
[CO2] |
Concentration of carbon dioxide (µmol mol-1). |
Fiso |
Rate of isoprene emission from a leaf
(nmol m-2 s-1). |
F'isotot |
Amount of isoprene emitted from a canopy
in one year (kg km-2). |
F'O3eff |
Effective ozone dose (nmol m-2). |
F'O3tot |
Ozone uptake (mmol m-2). |
FO3(0) |
Threshold flux of ozone entering the leaf
(nmol m-2 s-1). |
gs |
Stomatal conductance to water (mmol m-2 s-1). |
gz |
Stomatal conductance to ozone (mmol m-2 s-1). |
g(0) |
Empirical (intercept) coefficient of
stomatal conductance. |
g(1)
|
Empirical (slope) coefficient of stomatal
conductance. |
Kz |
Empirical coefficient of sensitivity of Vcmax to F'O3eff in wheat. |
O3 |
Ozone. |
[O3] |
Concentration of ozone (µmol mol-1). |
Rubisco |
Ribulose-1, 5-bisphosphate
carboxylase/oxygenase. |
RubP |
Ribulose-1, 5-bisphosphate. |
Vcmax |
Maximum in vivo velocity of Rubisco
catalysed carboxylation (mmol m-2 s-1). |
SUMMARY
This thesis presents new process-based models to predict the response
of vegetation to interactive effects of concurrently changing environmental variables. The
combination of new process-based models with the biochemical mechanistic model equations
of photosynthesis and simple canopy models, allow the prediction of responses of isoprene
emission rates, wheat leaf CO2 assimilation, and wheat productivity
to various scenarios of climate and atmospheric change, consistent with changes predicted
by the "business as usual" scenario, IS92a.
Isoprene, a biogenic hydrocarbon emitted by many tree species, plays a
key role in atmospheric chemistry and is a major precursor to phytotoxic ozone. As
isoprene emission is highly temperature sensitive, the findings of the most recent
research into isoprene synthesis and emission were used to construct a process-based
model, to simulate the effects of environmental change on rates of isoprene emission from
leaves. This model was subsequently scaled up to the canopy level, using a simple
sunlit/shaded canopy model, and leaf energy budget equations.
A second new process-based model, based on published data, was
constructed to simulate the effects of acute ozone exposure on wheat leaf photosynthesis,
and was also subsequently scaled up to the canopy level. In addition, the model of acute
ozone effects was adapted to predict the effects of chronic ozone exposure on wheat
photosynthesis, and scaled-up to predict the interactive effects of elevated [CO2] and [O3] on wheat productivity. Predictions are
presented and discussed.
The research illustrates the need for process-based models to predict
the interactive effects of concurrently changing environmental factors on vegetation, in
order to quantify the feedback effects under future atmospheric and climate conditions.
