espm 111 carbon part 2 ecophysiology of leavesnature.berkeley.edu/biometlab/espm111/espm...

3/13/2013

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ESPM 111 Ecosystem Ecology

Carbon Cycle, part 2Ecophysiology of Leaves

• Dennis Baldocchi– ESPM

– UC Berkeley

Courtesy of Rob Jackson, Duke

3/13/2013


Outline

• Photosynthetic Pathways and Cycles• Environmental Physiology of Photosynthesis

– Light– Temperature– CO2

– Nutrients– Soil Moisture and Water Deficits

• Respiration

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6CO2 + 6H2O + (light) (C6H12O6) + 6O2

Basic Photosynthesis Stoichiometry


Physiological Attributes of Plants

• photosynthetic pathway– C3

– C4

– CAM

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Photosynthesis:A balance between Supply and Demand

• Biochemical limitation: carboxylation rate• Light limitation• Enzyme limitation

• Physical limitation: delivery of CO2 to leaf• Diffusion through Leaf Boundary Layer• Diffusion through Stomatal Pores• Potential Gradient between free Atmosphere and

substomatal Cavity

Critical Steps in C3 PhotosynthesisCalvin-Benson Cycle

• Light Reactions– Chlorophyll, in chloroplasts, captures photons

– Light energy is used to produce chemical energy in the forms of NADPH and ATP

– Oxygen is produced

• Dark Reactions– A 3-C compound, PGA, is formed at the first Carboxylation step via

the reaction between CO2 and RUBP, a C5 compound, and its subsequent cleaving (C6 => 2 C3)

– The enzyme RUBISCO catalyzes the reaction between CO2 and RUBP

– RUBISCO has an affinity for both CO2 and O2, with the later leading to photorespiration, a loss of CO2

– RUBISCO accounts for about 9 to 25% of the N in a leaf

– Chemical Energy (NADPH & ATP) is used to regenerate RUBP


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ESPM 111, Ecosystem Ecology

C3 Photosynthesis, The Calvin-Benson Cycle

CO2

(CH2O)n

PCR Cycle

PGA

RUBPCarboxylase/oxygenase

RUBPRegeneration

O2

Photorespiration,PCO

CO2

ADP

ATP

RUBP

Triose-P

ADPATP

NADP+ + H+

NADPH

ESPM 111 Ecosystem EcologyAllen and Martin, 2007 Nature

Light (‘Hill’) Z Reactions:PS II and Ps I

680 nm

700 nm

• Visible solar energy (400 to 700 nm) is absorbed by pigments

• This energy is converted into high energy compounds, ATP and NADPH, by photosystems II and I (PS II and I)

– Photosystem II uses 680 nm energy to generate ATP (non-cyclic electron transport)

– PS I uses 700 nm solar energy to generate NADPH (cyclic electron transport).

– Excess energy is lost as heat or fluorescence.

• 8 Photons per CO2 molecule fixed

Using Solar Energy for Life

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C4 leaf

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/C4leaf.gif

Critical Steps in C4 Photosynthesis

• The enzyme PEP Carboxylase catalyzes a reaction between CO2 and phosophenolpyruvate (PEP) to form a C4 compound

• The C4 compound is transported into the specializes cells, the bundle sheaths, and is decarboxylated

• CO2 is released into an environment and photosynthesis is completed via the C3 cycle

• Photorespiration is low; RUBISCO favors CO2 in this environment because the ratio between CO2:O2 is high


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Mesophyll

CO2

(CH2O)n

PCRCycle

PGA

RUBPCarboxy

lase

RUBP

CO2

C4acids

OAA

PEPCarboxylase

PEP

CO2

C3 acids

Mesophyll Bundle Sheath

C4 Photosynthesis

ESPM 111 Ecosystem EcologyEdwards et al 2010 Science

C3 vs C4 Grass Distribution

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O’Leary, 1988 Bioscience

C3 vs C4: Isotopes and Ci/Ca

C3

C4

Tool to Study Advance and Retreat of C3 Grasslands During Ice Age

ESPM 111 Ecosystem EcologyAdapted from Ehleringer et al. 1997

Why are CA Hot Grasslands Compose of C3 grasses?

CA annual Grasslands experience cool wet winter growing season

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Ehleringer et al, Oecologia

C3 vs C4 Photosynthesis:Light Use Efficiency, CO2 and Temperature


C3 C4 CAM:day

CAM:night

internal [CO2] 0.7 Ca 0.4 Ca 0.5 Ca ?

Krantz ananatomy NO YES Succulent

carboxylase RuBP PEP RuBp PEP

photorespiration YES NO

Fixation product PGA C4 acids PGA C4 acids

CO2 compensation pt 30 -80 ppm < 10 ppm 50 ppm < 5 ppm

optimum temperature 15-30 C 25-40C 35 C

Max Ps (mmol m-2 s-1) 14-40 18-55 6 8

Response at full sunlight saturated Linear Saturated

Enhancement in low O2 yes no yes No

Quantum req. 15-22 19

Quantum yield 0.052 0.064

Carbon isotope fractionation, per mill

-26 (-23 to -33) -14 -30 to -10 -30 to -10

Comparative EcoPhysiology

Adapted from Jones, 1992

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Resistance -Analog


Flexas et al 2008, Plant, Cell, Environ

( )

( ) ( ) ( )

a c

le a f m e s o p h y ll c h lo ro p la s t

b a s s s i m i c

C CA

r r r

g C C g C C g C C


A= V - 0.5V - Rc o d

Leaf Photosynthesis

Leaf photosynthesis (A) is a function of:

Rate of carboxylation (Vc), which is the minimum of the rates associate with regeneration of RuBP by electron transport and the

saturation of RUBISCO by CO2,

Rate of oxygenation (Vo, photorespiration) which is governed by the competition between CO2 and O2 for RUBISCO

Rate of dark respiration (Rd)

(all have units of mol m-2 s-1).

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A-Ci Curve: C3 Leaf

From Chapin et al


Light Response Curve, C3 Leaf

From Chapin et al

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[CO2] (ppm)

0 200 400 600 800 1000

Car

bo

xyla

tio

n r

ate

(m

ol

m-2

s-1

)

0

10

20

30

40

50

60

Ci

supply~stomatal conductance (gs)

Wc : demand limited by RUBISCO saturation

Wj : demand limited by RuBP regeneration

by electron transport


After Wullschleger. 1993

Vcmax

0 20 40 60 80 100 120 140 160

Jmax

0

50

100

150

200

250

300

350

Maximum rate of Carboxylation, Vcmax, scales with maximum rate of electron transport, Jmax

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Wohlfarht 1999mountain grassland species

Pml (mol m-2 s-1)

0 10 20 30 40 50 60

Vcm

ax

(m

ol

m-2

s-1

)

0

20

40

60

80

100

Vcmax=2.36+1.66 Pmx

r2=0.87

Vcmax scales with maximum photosynthesis at saturating light and ambient CO2, Pml


Seasonality of Model Parameters:e.g. Photosynthetic Capacity

DOY

100 150 200 250 300 350

Vcm

ax

0

20

40

60

80

100

120

140

Quercus alba (Wilson et al)Quercus douglasii (Xu and Baldocchi)

Live Fast, Die YoungIn Stressed Environments

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Jack pine (NSA)Data of Hank MargolisQp = >1000 mol m-2 s-1

Leaf Temperature (C)

-10 0 10 20 30 40

A (m

ol m

-2 s

-1)

0

1

2

3

4

Photosynthesis and Temperature

Berry and Bjorkman 1980, Ann Rev Plant Physiol

Stress Physiology• Adaptation is a response to long-term changes which result in inheritable

genetic alterations. These alterations are stable and will remain in the population over generations.

• Acclimation is a response induced by an environmental change which causes a phenotypic alteration over a single generation time without any compositional change in the genetic complement

– Stomata close to limit water loss

– Temperature optimum shifts with warmer temperatures

• Tolerance– Blue oaks are able to photosynthesize despite super severe water deficits (below

-5.0 Mpa)

• Avoidance– CA grasses adopt annual life strategy. Survive dry summer in the form of

dessicated seeds

– Blue oaks develop deep roots that tap into the ground water

• Huner et al 1993 Photosyn ResESPM 111 Ecosystem Ecology

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Ps and Temperature Acclimation

Berry and Bjorkman 1980, Ann Rev Plant Physiol


Mean Summer Temperature (C)

5 10 15 20 25 30

Tem

pera

ture

Opt

imum

fo

r C

anop

y C

O2

upta

ke (

C)

5

10

15

20

25

30

35

b[0] 3.192b[1] 0.923r ² 0.830

Analysis of E. Falge

GPP: Acclimation with Temperature

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Photosynthesis and Leaf Nitrogen

Field and Mooney, 1986


Reich et al 1997 PNAS

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Stomatal conductance adjusts to match photosynthetic capacity(or vice versa)

Schulze et al 1994 Ann Rev Ecol


Schulze 1986 Ann Rev Plant Physiol

Stomatal conductance and water deficits

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Quercus douglasii

Pre-dawn Water Potential (MPa)

-7 -6 -5 -4 -3 -2 -1 0

Vcm

ax

0

20

40

60

80

100

120

140

b[0]: 111.3b[1]: 22.69b[2]: 1.734r ² 0.7532

Vcmax scales with water deficits

Baldocchi and Xu, 2007 Adv Water Res


Canopy Photosynthesis

• Sunlight, and Environmental Conditions

• Leaf Area Index

• Leaf Clumping

• Leaf Angle Distribution

• Diffuse vs Direct Light

• Leaf Thickness and Photosynthetic Capacity

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Light and Photosynthesis:

Leaves, Canopies and Clumping

D 2 0 8 O a k le a f , f o r e s t f lo o rT le a f : 2 5 o CC O 2 : 3 6 0 p p m

Q p a r ( m o l m - 2 s - 1 )

0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0

A (m

ol m

-2 s

-1)

0

2

4

6

8

1 0

1 2

d a t a

m o d e l

model: clumped leaves

PPFD (mol m-2 s-1)

0 500 1000 1500 2000F

c (m

ol m

-2 s-1

)

-40

-30

-20

-10

0

10

measured

(a )

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0-5 0

-4 5

-4 0

-3 5

-3 0

-2 5

-2 0

-1 5

-1 0

-5

0

a b s o rb e d P A R (µ m o l m -2 s -1)

W H E A T

Fc (

mg

m-2

s-1

)

Dry Matter Production scales with Sunlight

ESPM 111 Ecosystem EcologyMonteith 1981 Phil Trans Roy Soc

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0 250 500 750 1000 1250 1500 1750 2000-0 .75

-0 .50

-0 .25

0 .00

0 .25

Q a (µ m ol m -2 s-1 )

Fc/

LA

I (m

g m

-2 le

af a

rea

s-1 )

C O R N

W H E A T

CO2 uptake-Light Response Curve: Role of C3 and C4 Crops

Linear Function and High r2 (~0.90)

Baldocchi, 1994, AgForMet


PPFD (mol m-2 s-1)

0 500 1000 1500 2000

NE

E (m

ol

m-2

s-1

)

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10Sunny daysdiffuse/total <= 0.3

Cloudy daysdiffuse/total >= 0.7

Temperate Broad-leaved ForestSpring 1995 (days 130 to 170)

Canopy Light Response Curves: Effect of Diffuse Light

Baldocchi, 1997, PCE

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Summary Points

• Leaf photosynthesis involves a set of light and dark reactions.

• The light reactions involve the harvesting of sunlight by chlorophyll and the transfer of electrons to the produce of biochemical energy compounds adenosine triphosphate (ATP) and nico-adenomine di-phosate (NADPH) via the process called photophosphorylation.

• The energy contained in molecules ATP and NADPH is subsequently used in the dark reactions to drive the photosynthetic carbon reduction cycle, or Calvin Cycle.

• There are three photosynthetic pathways, C3 (the most common), C4 and CAM.

• Photorespiration, due to the competitive affinity for CO2 and O2 by the enzyme RUBISCO, is an attribute of C3 photosynthesis.

– This leads to its lower efficiency than C4 photosynthesis– C4 plants circumvents this inefficiency by using a different enzyme to carboxylze CO2 (PEP carboxylase)

and by minimizing the diffusion of O2 deep in the leaf with its unique leaf anatomy (bundle sheaths).

• Rates of photosynthesis achieved by a leaf is a balance between the supply and the demand for carbon dioxide. The supply is related to the CO2 concentration in the air and its diffusion through the leaf boundary layer and stomata. The demand is controlled by the Michaelis-Menton kinetic reactions that are a function of CO2 at the chloroplast.

• Rates of photosynthesis are a function of light, temperature, CO2, moisture, leaf nutrition, and phytotoxics.

espm 111 carbon part 2 ecophysiology of leavesnature.berkeley.edu/biometlab/espm111/espm...

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