Why Photosynthesis? Growth Respiration, and Maintenance Growth - - PDF document

6/13/2008 1

Marc van Iersel

Estimating Carbon Use Efficiency, Estimating Carbon Use Efficiency, Growth Respiration, and Maintenance Growth Respiration, and Maintenance Respiration from Crop Gas Exchange Respiration from Crop Gas Exchange Measurements Measurements The University of Georgia

2008 Meeting on controlled environment agriculture

Why Photosynthesis?

• Plants contain approximately:

– 40% C 45% O – 45% O – 6% H

• Leaf photosynthesis and plant growth or

yield are poorly correlated

Whole Crop Photosynthesis and Growth Whole Crop Photosynthesis and Growth

• Direct measure of C incorporated into the plant
• With continuous measurements, net carbon gain

can be determined can be determined

• Daily net carbon gain closely related to growth rate
• Cumulative carbon gain closely related to dry mass

Plexiglas chambers

Alan Lakso Cornell

Corelli-Grappadelli and Magnanini, 1993, HortScience

Fred Davies Texas A&M

6/13/2008 2

Soil-Plant-Atmosphere-Research chambers (SPAR) USDA Beltsville e rate

Diurnal CER

dark light dark

CO2 exchange

Rdark Pnet

Time (hours)

24

e rate

Daily Carbon Gain (DCG) (area 1 - area 2)

dark light dark dark light dark

CO2 exchange

Rdark Pnet

Time (hours)

1 2 2

24 24

Time (hours)

mol.m-2)

6 8 10

respiration photosynthesis

Cumulative Carbon Gain Time (days)

2 4 6 8 10 12 14

CCG (m

2 4

ght (g)

25 30 35 40 45

Whole Plant Photosynthesis and Growth

DW = 5.55 + 25.8 x CCG r = 0.99

Cumulative carbon gain (mol)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Dry wei

5 10 15 20 25

Case Study

• Marigold grown at 20 or 30 oC
• CO2 exchange measured for 60 days

6/13/2008 3

mol/plant/s)

40 60 80

30 oC 20 oC

Time (days after seeding) 10 20 30 40 50 60

Pnet (nm

20

van Iersel, 2005

• Physiol. Plant.

nmol/plant/s)

20 30

20 oC 30 oC

Time (days after seeding)

10 20 30 40 50 60

Rdark (n

10

20 oC

Data Interpretation

• Carbon-use efficiency =

Net amount of carbon incorporated into the plant G t f h t th t d d Gross amount of photosynthates produced e rate

Carbon Use Efficiency (area 1 - area 2)/(area 1 + area 3)

dark light dark dark light dark

CO2 exchange

Rdark Pnet Pgross

Time (hours)

1 3 2 2

24 24

Time (hours)

fficiency (mol.mol-1)

0 4 0.5 0.6 0.7

30 oC 20 oC

Time after seeding (days)

10 20 30 40 50 60

Carbon use ef

0.2 0.3 0.4

Growth and maintenance respiration

Photosynthates Growth Biomass (70%) Maintenance respiration coefficient (rm) Dry weight Maintenance respiration Growth Respiration (30%) Growth Growth respiration coefficient (rg)

6/13/2008 4

Growth and maintenance respiration

• R = Rm + Rg = rm x weight + rg x growth

R / i h h/ i h

• R / weight = rm + rg x growth/weight

IF rm and rg are constants, they can be estimated from linear regression = rm + rg x RGR

Calculations

• Growth rate and plant dry weight were

calculated from CO2 exchange measurements and carbon content of the plants plants

• RGR (growth rate / dry weight) and

specific respiration rate (Rdark / dry weight) were calculated from these data

Relative growth rate

(d-1)

0.15 0.20

20 oC 30 oC

Time (days after seeding)

10 20 30 40 50 60 70

RGR

0.00 0.05 0.10

Growth and maintenance respiration

ration (mg.g-1.d-1)

60 80 100 120

20 oC 30 oC

Specific respi

20 40

Time (days after seeding)

20 30 40 50 60

ation (mg.g-1.d-1)

80 100 120 140

30 oC

Growth and maintenance respiration

r

Specific respira

20 40 60

Q10

1.10

20 oC

Relative growth rate (g.g-1.d-1)

0.00 0.05 0.10 0.15 0.20 0.25 90

Rspec = rm + rg x RGR rm rg

Growth and maintenance respiration

mr (mg g-1 d-1) gr (g g-1) 20 oC 8.4 ± 0.6 0.56 ± 0.01 Temperature 30 oC 11.9 ± 0.5 0.50 ± 0.01 Q10 1.42 0.89 Maintenance respiration = mr × dry mass Growth respiration = gr × growth rate

6/13/2008 5

ance respiration (mg.d-1)

30 40 50 60

30o C 20o C

growth

Time (days)

20 30 40 50 60

Growth and maintena

10 20

20 C

ance respiration (mg.d-1)

30 40 50 60

30o C 20o C

growth

Time (days)

20 30 40 50 60

Growth and maintena

10 20

30o C 20 C 20o C

maintenance

Conclusions

• Continuous whole plant CER gives:

– Direct measure of growth – Physiological components of growth

• Carbon use efficiency
• growth respiration
• maintenance respiration

Thank you