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Description

Announcements • Feedback on phenology proposals has been posted to dropbox • Phenology data and weather data have been posted • We’ll be available during Monday and Tuesday labs for the remainder of the semester – sign up for a meeting slot (google sheets link posted later this week)

Today’s Lecture 1.How did photosynthesis evolve in response to variation in atmospheric CO2? 2.Do adaptations to high and low CO2 concentrations of the past influence plant distribution in the present? 3.Lab 5 questions

The response of C3 photosynthesis to CO2 40 35

Photosynthesis

30 25 20

0.1%

15 10

Current

5 0 0

100 200

300 400

500 600

700 800

900 1000 1100 1200 1300

-5

Atmospheric CO2 concentration (ppm)

The response of C3 photosynthesis to CO2 40 35

Photosynthesis

30 25 20

0.1%

15 10

Current

5 0 0

100 200

300 400

500 600

700 800

900 1000 1100 1200 1300

-5

Atmospheric CO2 concentration (ppm)

Photosynthesis is not adapted to current CO2

Rubisco evolved in a high CO2 environment Rubisco: Ribulose-1,5-bisphosphate carboxylase /oxygenase (1%)

(100%)

(0.1%) 4

3

2

1

0.6

0.4

0.2

0.0

Time before present, billion years [CO2] falls below C3 saturating levels c. 30 million years ago RF Sage (1999) C4 Plant Biology, Academic Press, NY

RUBISCO can bind with both CO2 and O2

Glucose Useless: Requires ATP to get rid of

How much does photorespiration affect photosynthesis?

2% O2 21% O2

H Lambers, FS Chapin, TL Pons (2008) Plant Physiological Ecology, 2nd Ed. Springer, New York

Atmospheric CO2 concentration (ppm) Fossil dating of C4 grass lineages

0.2% CO2 Saturation point for C3 photosynthesis (0.1 % or 1000 ppm CO2)

Appearance of C4 grass lineages follows drop in atmospheric CO2

Christin et al. (2008) Current Biology 18:37

C3 and C4 (“Kranz anatomy”)

Flaveria spp.

©W.L. Wagner. Courtesy of Smithsonian Institution, Dept. of Systematic Biology, Botany.

C3

C4

F. cronquistii

F. kochiana

•Both have bundle sheaths (*) •Note thicker cell walls and chloroplasts in C4 plant bundle sheaths McKown, A. D. , and N. G. Dengler. 2007. Key innovations in the evolution of Kranz anatomy and C4 vein pattern in Flaveria (Asteraceae). American Journal of Botany 94: 382–399.

C4 photosynthesis Chloroplasts in Heliotropium polyphyllum bundle sheaths. Brown stain indicates Rubisco.

Light

PEP carboxylase

Pyruvate (3C)

CO2

“CO2 pump”

4 carbon acids (malate) [CO2] ≈ 150 ppm Mesophyll cell with chloroplast

Calvin Cycle (Rubisco)

CO2

[CO2] >>5000 ppm Bundle-sheath cell with chloroplast Heliotropium Image courtesy of Patrick Vogan

C4 plants reach saturation at much lower atmospheric CO2 than C3 plants 60

C3

50 40

C4 30 20 10 0 -10 0

200

400

600

800

1000

1200

Atmospheric CO2 concentration (ppm) Pearcy, R. W., and J. Ehleringer. 1984. Plant Cell Environ. 7:1-13.

How common is C4 photosynthesis?

Taxonomically: 7600/300,000 = 2.5% Ecologically: 21% of all photosynthesis Agriculture: 30% of all photosynthesis

Lloyd J, Farquhar G.D. (1994) Oecologia 99:201–215

Where are C4 plants found?

Ehleringer, J.R., T.E. Cerling, and M.D. Dearing (eds.). 2005. A history of atmospheric CO2 and its effect on plants, animals, and ecosystems. Springer Verlag, New York.

Global Temperature Patterns

https://climatedataguide.ucar.edu/climate-data/global-surface-temperatures-best-berkeley-earth-surface-temperatures

Where are C4 plants found?

Ehleringer, J.R., T.E. Cerling, and M.D. Dearing (eds.). 2005. A history of atmospheric CO2 and its effect on plants, animals, and ecosystems. Springer Verlag, New York.

Global Moisture availability

World Water Assessment Program, http://wwap.cesr.de/

Summary: C4 photosynthesis is common in warm, sunny, and dry habitats

Why warm? Photorespiration increases with temperature in C3 plants

Laing et al. (1974) Plant Physiology 54:678

How does photorespiration influence the temperature habitat of C3 and C4 plants?

Quantum yield = CO2 fixed per unit light absorbed (slope) = photosynthetic light use efficiency Ehleringer, J.R., and D.R. Sandquist. 2010. Photosynthesis: physiological and ecological considerations, pages . In. L. Taiz and E. Zeiger (eds.), Plant physiology, 5th edition, Sinauer Associates, Sunderland, MA.

Why warm? C3 photosynthesis IS temperature sensitive C4 photosynthesis IS NOT temperature sensitive Quantum yield = CO2 fixed per unit light absorbed (slope) = photosynthetic light use efficiency Ehleringer J, Björkman O. 1977. Plant Physiology 59:86–90.

27.5 °C – crossover point...