Modeling Photosynthetic Responses to Carbon Dioxide

Environmental Conditions

T

leaf

25

O

2

210

PPFD

1500

Photosynthetic Parameters

V

c,max

98

J

max

160

TPU

10.5

R

D

1.1

RuBP-Limited A Adjustments

T

o

55.6

Ω

30.2

α

0.85

β

0.5

θ

0.85

ΦPSII

0.73

Axes Limits

Max

C

i

1000.

Max A

55.

Rubisco

RuBP

TPU

A

This Demonstration simulates the response of photosynthesis

A

(

µmol

-2

m

-1

s

) to the intercellular concentration of

CO

2

C

i

(

μmol

-1

mol

). The equations are based on the leaf model of photosynthesis [1] that predicts

A

based on the most limiting of three processes: (1) the kinetics of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (or rubisco) for fixing

CO

2

, (2) the rate of RuBP regeneration associated with electron transport rates on the thylakoid membrane (RuBP), and (3) the rate in which inorganic phosphate, required for regenerating ATP from ADP, is released during the utilization of triose phosphate (TPU). While the functions associated with all three of these limiting processes are shown (Rubisco, RuBP, and TPU), the actual modeled rate of photosynthesis is the lowest of the three processes, with the exception of the portion of the curve below the intersection of rubisco and RuBP limited photosynthesis. Below this intersection, photosynthesis will always be rubisco-limited. The modeled rates of photosynthesis are indicated by the net photosynthesis curve

A

(solid black line). Vary the parameters or environmental conditions to see the impact on the modeled photosynthesis over the range of

C

i

. Temperature has a major effect on photosynthesis, and the equations from the original model [1] have been corrected with the temperature functions from [3] for rubisco-limited photosynthesis, [2, 4, 6] for RuBP-limited photosynthesis, and [5] for TPU-limited photosynthesis.