Crop Fertilization in a CO2

enriched world: is it good to be C3

David M. RosenthalCCAFS Science Workshop, Cancun, Dec 1 and 2, 2010

Outline

• Plant responses to elevated CO2 and other agents of climate change at SoyFACE

• Why is photosynthesis of crop plants in the field stimulated less by CO2 than predicted by theory?

• Some approaches to optimize (adapt) photosynthesis to global change

Recent evidence indicates atmospheric [CO2] is increasing more rapidly than the most aggressive

IPCC AR4 projection .

How does elevated CO2 stimulate photosynthesis that is the basis for the projected increases in yield?

Rubisco is not the most efficient enzyme

Energy conversion in C3 and C4 plants

Zhu et al 2008

SoybeanMaize

SoyFACE Experiment

20 meters

350

550

750

0:00 6.00 12:00 18:00 0.00

Fumigation

On

96% of minute

averages within ±10%

[CO2] (µmol mol-1)

Time (h)

Increased photosynthesis in C3 crops grown at elevated CO2 increases yield

Long, Ainsworth, Leakey, Nosberger, Ort (2006) Science 312, 1918-21

Percent Change in Elevated [CO2]

-40 -20 0 20 40 60 80 100 120

Asat

A'

gs

ci/ca

Vcmax

Jmax

Rubisco

Narea

Sugar

Starch

Leaf #

Plant Height

LAI

SLA

Biomass

Crop Yield

Meta analysis of C3 crops grown at elevated CO2 in FACE experiments

Ainsworth and Long (2005) New Phyt. 165:351=-372

Gleadow et al. (2009) Plant Biol 11:79-82

No CO2 stimulation in Cassava Greehouse Experiment

Cassava an increasingly important crop

July 19, 2010

CassavaFACEcv 60444

July 2, 2010

June 7, 2010

August 9, 2010

April 5, 2010

April 15, 2010

Growth at elevated [CO2] at SoyFACE stimulates cassava photosynthesis

Rosenthal et al. unpublished

pla

nt

Ambient CO2 Elevated CO2

Cassava canopies are larger at elevated CO2

Rosenthal et al. unpublished

Rosenthal et al. unpublished

AmbientElevated

Cassava harvested after only 3.5

months !

Ambient CO2 Elevated CO2 Rosenthal et al. unpublished

Rubisco is down regulated at elevated CO2 in cassava

Cassava leaf Carbon/Nitrogen ratio declines at elevated CO2

Rosenthal et al. unpublished

Growth at elevated [CO2] does not increase leaf or tuber cyanide content at SoyFACE

Miller, Gleadow unpublished

Long, Ainsworth, Leakey, Nosberger, Ort (2006) Science 312, 1918-21

“[CO2] Fertilization” of C3 crop photosynthesis falls short of theory

Why is photosynthesis of crop plants in the field stimulated less by CO2 than

predicted by theory?

400

320

240

160

80

0

400 320 240 160 80 0

Time before present, 103 years

Current value

Years below 280 ppm, 395 000 (96%)

Years below 240 ppm, 280 000 (67%)

Years below 200 ppm, 83 500 (20%)

Various sources ; Luthi et al (2008) NATURE 453: 379-382

Zhu et al. (2007) Plant Physiol 145: 513-526

Tobacco over-expressing SBPase grown at elevated [CO2]

SBP 11WT SBP 30

Over expression of SBPase enhances photosynthesis at elevated [CO2]

Rosenthal et al. unpublished

Over expression of SBPase enhances biomass formation at elevated [CO2]

Rosenthal et al. unpublished

CO2

C HHO

CH2OPO32-

C

COO-

HHO

CH2OPO32-

COO-

PGA

PGA

CH2OPO32-

C

COO-

HHO

PGA

O2

CH2OPO32-

COO-

2-phospho-glycolate

CH2OPO32-

C

C

C

CH2OPO32-

OH

H OH

H

O

Ribulose-1,5-bisphosphate

Non-green

algae

Terrestrial

C3

C4

ProkaryotesMutants

Current C3 crop Rubisco

Increase ?

Decrease ?

There is a trade off between ability of Rubisco to discriminate between CO2 and O2 Rubisco catalytic rate

= -10%

Lowering increases light saturated leaf photosynthesis but lowers light limited photosynthesis

C3 Average

Adding „foreign‟ Rubisco

Species Ac' = CANOPY

PHOTOSYNTH.

(mmol m-2

day-1

)

ε c

(% inc.)

Asat

( mol m-2

s-1

)

Current average C3 crop

(kcc = 2.5, = 92.5)

1040

0%

14.9

Amaranthus edulis (C4)

(kcc = 7.3, = 82)

1250

17%

28.3

Amaranthus edulis/current

(kcc = 7.3/2.5, = 82/92.5)

1360

31%

28.3

(2004) Plant Cell and Environment, 27, 155-165

(UN-IPCC 2001)

2000 2020 2040 2060 2080 210040

60

80

Ozo

ne

–P

art

s P

er

Bil

lio

n o

f A

ir

Rising tropospheric ozone 0.5 – 2.5 % per year

Relationship between Soybean Yield & Ozone

Fishman et al.2010 Atmospheric Environment

Summary• Growth at elevated [CO2] stimulated cassava

photosynthesis.

• Rubisco was down regulated in cassava at elevated [CO2], consistent lower leaf N (no change in cyanide content).

• Fresh and dry tuber biomass significantly increased with [CO2], as did harvest index.

• Cassava responded similarly to other C3 plants treated with elevated [CO2].

• CO2 stimulation of photosynthesis is less than predicted by theory.

- lack of adaptation to rapid increase in [CO2]

- inhibition due to increasing levels of tropospheric O3

- increased rates of respiration in CO2-grown plants

- temperatures above optimum for photosynthesis.

SoyFACE 2010

CassavaFACE collaborators:Becky Slattery (UIUC)Kat Grennan (UIUC)Bec Miller (Monash U)Ros Gleadow (Monash U)Claude Fauquet (ILTAB)

SBPase overexpression collaboratorsChristine Raines (U Exeter)Anna Locke (UIUC)Stephen Long (UIUC)