The First Principles of IsopreneEmission and Modeling in a Future World

Russ MonsonUniversity of Colorado

I begin with a premise…

For the purpose of prognosis, it’s best to construct biogenic VOC emissions models with as direct a connection to the first-principles of biochemistry and physiology as is possible.

Temperature (°C)

Isop

rene

em

issi

on

(nm

ol m

-2 s-

1 )

Leaf emission

Isoprene synthase

‘Guenther algorithm’(Guenther, Monson and Fall, 1991, JGR)

minutes

T T )T-(T cexp C

s

sT1isoT R=

based on enzyme bioenergetics

T/ RTE

EeAnn −=

Ea

Kinetic energy

n/n

ET

20 C o

40 C o

100 C o

Maxwell-Boltzmann relationship

Temperature algorithm has foundations in transition-state bioenergetics

k = C exp Ea/RT

(Arrhenius model)

Guenther algorithm

T T )T-(T cexp C

s

sT1isoT R=

Light intensity (μmol m-2 s-1)

0 500 1000 1500 2000 2500

Isop

rene

em

issi

on ra

te (n

mol

m-2

s-1

)

0

5

10

15

20

25

30

35Populus tremuloides, leaf

Isoprene emission rate increases with light intensity(Monson and Fall, 1989, Plant Physiology)

22L1

L α1 cα CLL

+=

The ‘Guenther’ algorithm is based on the light dependence of photosynthetic electron transport

Pyruvate + Glyceraldehyde 3-P

NADPH

NADP + H+

CTP

Pi

2 ATP+CMP

2 ADP

ATP

ADP

DMADP

isopreneT T

)T-(T cexp1

T T )T-(T cexp

C

s

mT2

s

sT1

T

R

R

+=

22L1

L α1 cα C

LL

+=

isoprene synthase

(temperature)

(light)

The temperature and light algorithms have good biochemical justification

Is

= BER * CL

* CT

The Current Modeling Framework for PredictingIsoprene Emissions

T T )T-(T cexp1

T T )T-(T cexp

C

s

mT2

s

sT1

T

R

R

+=

22L1

L α1 cα CLL

+=

“Base” Emission Rate(emission factor)

Modeling the Response of VOC Emissions to Global Change

isoprene emission

temperature

increased [CO2 ]

NPP

climate

light

Model Logic

22L1

Liso α1 cα CLL

+=

T T )T-(T cexp1

T T )T-(T cexp

C

s

mT2

s

sT1

isoT

R

R

+=

Land Surface - DynamicGlobal Vegetation Model Species dynamics

This is not entirely justified on biochemical grounds, but no time to go into it now…

Instead, I want to focus on the CO2 response…

CO2 partial pressure (Pa)0 10 20 30 40 50

Isop

rene

em

issi

on ra

te (n

mol

m-2

s-1

)

10

15

20

25

30

35

40Populus tremuloides, leaf

Isopr

ene e

miss

ion ra

te(n

molm

-2s-1

)

photosynthesis rate

isoprene emission rate

(Monson and Fall, 1989, Plant Physiology)

CO2 partial pressure (Pa)

Elevated atmospheric [CO2 ] suppresses isoprene emissions

Rhinelander FACE, Wisconsin

Aspen trees, Wisconsin

0 1 2 3

Is (n

mol

m-2

s-1

)

0

10

20

30 p = 0.050a

b

Cont Hi CO2

Sweetgum trees, Tennessee

0 1 2 3

Is (n

mol

m-2

s-1

)

0

10

20

30

40p = 0.039a

b

Cont Hi CO2

Oak Ridge FACE site

Rhinelander FACE site

Monson, R.K. et al. (2007) Isoprene emission from terrestrial ecosystems in response to global change: Philosophical Transactions of the Royal Society, London A365: 1677-1695.

[CO2] (ppmv)(Ci range (μmol mol-1) in parenthesis)

I s (n

mol

m-2

s-1

)

0

10

20

30

40

520(272-337)

380(163-247)

240(161-176)

**

Liquidambar styraciflua

The Texas ‘CO2 Tube’Temple, Texas

n = 12

Intercellular CO2 concentration (μmol CO2 mol-1)0 100 200 300 400 500 600 700

I s (nm

ol C

m-2

s-1)

30

35

40

45

50400 ppmv treatment800 ppmv treatment

Intercellular CO2 concentration (ppmv)

Isop

rene

em

issi

on ra

te (n

mol

m-2

s-1 )

Growth Chamber Studies of the CO2 Effect

Populus tremuloides

Wilkinson, M.J., Monson, R.K., Trahan, N., Lee., S., Brown, E., Jackson, R.B., Polley, H.W., Fay, P. and Fall, R. (2008) Leaf isoprene emission rate as a function of atmospheric CO2 concentration. Global Change Biology (in press).

Net

pho

tosy

nthe

sis

(μm

olm

-2s-1

) Isoprene emission rate (nm

olm-2s

-1)

Time (min)

We understand the biochemical reasons for these responses – PEP carboxylase

Rosenstiel, T., Potosnak, M., Griffen, K., Fall, R. and Monson, R.K. (2003) Elevated CO2 uncouples growth and isoprene emission in a model agriforest ecosystem. Nature 421: 256-259.

Substrate

Rea

ctio

n

Progressive amplification of positive influence of one substrate andnegative influence of a second substrate

k1 (G3P)

k2 (Pyr)

Ci

Is

G3P from old photosynthate

A possible mechanism for the CO2 response

( )( ) ( ) ⎥

⎦

⎤⎢⎣

⎡+

−= hh

h

i*i maxs

maxsci CCCIIC

Pyruvate + Glyceraldehyde 3-P

NADPH

NADP + H+

CTP

Pi

2 ATP+CMP

2 ADP

ATP

ADP

DMADP

isopreneT T

)T-(T cexp1

T T )T-(T cexp

C

s

mT2

s

sT1

T

R

R

+=

22L1

L α1 cα C

LL

+=

PEPPi

PEP

Pi

isoprene synthase

(temperature)

(light)

(CO2 )

( )( ) ( ) ⎥

⎦

⎤⎢⎣

⎡+

−= hh

h

i*i maxs

maxsci CCCIIC

Is

= BER * CL

* CT

*Cci

Revised Modeling Framework for PredictingIsoprene Emissions

T T )T-(T cexp1

T T )T-(T cexp

C

s

mT2

s

sT1

T

R

R

+=

22L1

L α1 cα CLL

+=

“Base” Emission Rate(emission factor)

( )( ) ( ) ⎥

⎦

⎤⎢⎣

⎡+

−= hh

h

i*i maxs

maxsci CCCIIC

NCAR Community Climate System Model 3

Community Atmospheric Model (CAM3)

Community Land Model (CLM3.5)

NPP, Vegetation type

IPCC SRES A1B

[CO2 ]

Isoprene Emission Rate

Heald, C.L., Wilkinson, M.J., Monson, R.K., Alo, C.A., Wang, G. and Guenther, A. (2008) Response of the global isoprene emission rate to future changes in climate and atmospheric CO2 concentration. Global Change Biology (in press).

MEGAN Emission Model

isoprene emission rate

Isoprene emission in present day and future without CO2 effect (left) or with CO2 effect (right). The effect of CO2 on NPP is not included.

Without CO2 effect climate warming causes a 37% increaseWith CO2 effect climate warming results in an 8% decrease

We find that the direct effect of [CO2 ] can completely compensate for the effect of climate warming on isoprene emissions

Without CO2 effect climate + CO2 causes a 166% increaseWith CO2 effect climate + CO2 results in a 78% increase

We find that the direct effect of [CO2 ] can significantly reduce the effect of increasing NPP on isoprene emissions

isoprene emission

temperature

increased [CO2 ]

NPP

climate

light

Model Logic

22L1

Liso α1 cα CLL

+=

T T )T-(T cexp1

T T )T-(T cexp

C

s

mT2

s

sT1

isoT

R

R

+=

Species dynamics

Temperature adjustmentto base emission rate

CO2 adjustmentto base emission rate (not possible from first principles)

(not possible fromfirst principles)

CO2

( )( ) ( ) ⎥

⎦

⎤⎢⎣

⎡+

−= hh

h

i*i maxs

maxsci CCCIIC

Two points from today’s talk:

1. We currently have access to relatively accurate equations for describing the short- term responses of isoprene emission to light, temperature and [CO2 ] at the leaf scale.

2. There is much work to be done in defining the longer-term effects and interactions among forcing variables.

Acknowledgements

University of ColoradoMick WilkinsonRay FallTodd RosenstielNicole Trahan

Colorado State UniversityColette Heald