1. Modeling plants and global environmental change
Dr Andrew Leakey
Department of Plant Biology
University of Illinois at U-C

2. What is a model?

3. A model of the scientific method
A model has two characteristics:
It is a physical, mathematical, or logical representation of a system of entities, phenomena, or processes.
It is always a simplified representation of the real system which it describes.
A model of the scientific method

4. How much do I weigh? What data would inform your estimate? Height, BMI
What data would help improve your accuracy?
Is your estimate perfect?

5. Mathematical models can be either:
Empirical – mathematical description of observed phenomena, but without mechanistic basis.
Mechanistic – mathematical description that is based on the mechanism underlying the observed phenomena

6. What do we want to simulate/predict?
Future CO2 concentration and temperature

7. What do we want to simulate/predict?

8. GENERAL CIRCULATION MODELS (GCMs)
Components of the
climate system considered:
atmosphere
ocean
cryosphere
biosphere
geosphere

9. Physiochemical diffusion
How do ecosystems play a role?
The
Global Carbon
Cycle
Atmosphere 780 GtC
+ 4.1 GtC yr-1
Photosynthesis
120 GtC yr-1
Fossil Fuels
8.4 GtC yr-1
Plant
Respiration
59 GtC yr-1
Land use
change
1.5 GtC yr-1
550 GtC
Soil
Respiration
58 GtC yr-1
Physiochemical diffusion
92 GtC yr-1
90 GtC yr-1 +
2.8 GtC yr-1
Soil and detritus
1500 GtC
Geological reserves
GtC
Ocean
38,000 GtC
+ 2.2 GtC yr-1
Based on K.L. Griffin, Columbia U. 2002; Canadell et al PNAS 2007; IPCC 2001

10. An example of an ecosystem model (Century)
This sub-model is an example of an important empirical model in plant biology

11. Open stomata Closed stomata
Stomata regulate how much water is lost from the leaf and how much CO2 enters the leaf.

12. Plants must deal with a trade-off between carbon gain and water use.
Stomata regulate the exchange of CO2 and H2O vapor
Stomatal conductance is a measure of how easily CO2 and H2O vapor can move through the stomata
High stomatal conductance = open pores
Low stomatal conductance = closed pores
CO2
H2O

13. Ball et al.(1987) model
gs = g0 + m(A.h/ca)
Where:
gs is stomatal conductance
g0 is a constant
m is slope of line
A is photosynthetic rate
h is relative humidity
ca is atmospheric [CO2]

14. y m Straight line y = b + m(x) b Ball et al. model gs = g0 + m(A.h/ca)

16. An example of an ecosystem model (Century)
This sub-model is an example of an important mechanistic model in plant biology

17. How do enzymes work?

19. Model of leaf photosynthesis
Presented by Farquhar, von Caemmerer & Berry in 1980
A is photosynthetic CO2 uptake
vc is rate of carboxylation
vo is rate of CO2 loss due to oxygenation
Rd is rate of mitochondrial respiratory CO2 loss

20. { CO2 fixation by Rubisco CO2 concentration inside the leaf
Elevated CO2 stimulates photosynthesis by increasing the substrate concentration (CO2) for the carboxylation reaction of Rubisco {
stimulation
CO2 fixation by Rubisco
Elevated CO2
Ambient CO2
CO2 concentration inside the leaf

22. How do we improve our modeling capability?
Better understanding of mechanisms
More data to parameterize (inform) models
More data to test model predictions
How do we achieve this? Experiments!

23. Soybean Free Air gas Concentration Enrichment Facility (SoyFACE)

24. 20 meters

27. Open Field vs Glasshouse
Experiments

28. Global change experiments on crops in the field
Tsukuba
Rice
CO2
Jiangsu
Rice/Wheat
CO2/N
Maricopa
Wheat/Sorghum
CO2/H2O/N
Champaign
Soybean/Maize
CO2/ºC/H2O
KEY
Location
Plant Species
Treatments
Horsham
Wheat
CO2/N/H2O
Fig. 1

29. Soybean
Wheat

30. % change in crop yields in 2080 considering altered temperature, rainfall and socio-economics PLUS carbon dioxide fertilization of plant growth
Too optimistic??!! 30

31. Conclusions
Models allow us to simulate complex systems and make predictions about how they will operate under certain scenarios (like the future).
They aren’t perfect, but they are always being improved and generate valuable predictions.
Models and experimentation go hand in hand – each is more valuable when combined with the other.