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Modeling plants and global environmental change
Dr Andrew LeakeyDepartment of Plant BiologyUniversity of Illinois at U-C
What is a model?
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
How much do I weigh?
What data would inform your estimate?Height, BMI
What data would help improve your accuracy?
Is your estimate perfect?
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
What do we want to simulate/predict?
Future CO2 concentration and temperature
What do we want to simulate/predict?
GENERAL CIRCULATION MODELS (GCMs)
Components of theclimate system considered: •atmosphere •ocean •cryosphere •biosphere •geosphere
Soil and detritus1500 GtC
Geological reserves5000-10000 GtC
Based on K.L. Griffin, Columbia U. 2002; Canadell et al PNAS 2007; IPCC 2001
The Global
Carbon Cycle
Atmosphere 780 GtC
Photosynthesis 120 GtC yr-1
PlantRespiration 59 GtC yr-1
SoilRespiration 58 GtC yr-1
Fossil Fuels8.4 GtC yr-1
Physiochemical diffusion
Land use change
1.5 GtC yr-1
550 GtC
Ocean38,000 GtC
90 GtC yr-1
92 GtC yr-1
+ 4.1 GtC yr-1
+2.8 GtC yr-1
+ 2.2 GtC yr-1
How do ecosystems play a role?
An example of an ecosystem model (Century)
This sub-model is an example of an important empirical model in plant biology
Open stomata Closed stomata•Stomata regulate how much water is lost from the leaf and how much CO2 enters the leaf.
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 poresLow stomatal conductance = closed pores
CO2
H2O
Ball et al.(1987) modelgs = g0 + m(A.h/ca) Where:gs is stomatal conductanceg0 is a constantm is slope of lineA is photosynthetic rateh is relative humidityca is atmospheric [CO2]
Straight liney = b + m(x)
Ball et al. modelgs = g0 + m(A.h/ca)
x
y m
b
A.h/ca
gs
g0
m
An example of an ecosystem model (Century)
This sub-model is an example of an important mechanistic model in plant biology
How do enzymes work?
Model of leaf photosynthesis
• Presented by Farquhar, von Caemmerer & Berry in 1980
0.5 dc oA v v R • 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
CO2 fi
xatio
n by
Rub
isco
CO2 concentration inside the leaf
{stimulation
Elevated CO2 stimulates photosynthesis by increasing the substrate concentration (CO2) for the carboxylation reaction of Rubisco
Ambient CO2
Elevated CO2
How do we improve our modeling capability?
1.Better understanding of mechanisms2.More data to parameterize (inform) models3.More data to test model predictions
How do we achieve this? Experiments!
Soybean Free Air gas Concentration Enrichment Facility (SoyFACE)
www.soyface.uiuc.edu
20 meters
Open Field vs Glasshouse
Experiments
Global change experiments on crops in the field
ChampaignSoybean/MaizeCO2/ºC/H2O
HorshamWheatCO2/N/H2O
JiangsuRice/WheatCO2/N
TsukubaRiceCO2
KEYLocationPlant SpeciesTreatments Fig. 1
MaricopaWheat/SorghumCO2/H2O/N
Wheat
Soybean
% change in crop yields in 2080 considering altered temperature, rainfall and socio-economics PLUS carbon dioxide fertilization of plant growth
Too optimistic??!!
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.