Modeling plants and global environmental change

Dr Andrew LeakeyDepartment of Plant BiologyUniversity of Illinois at U-C

leakey@illinois.edu

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.