Effects of High COEffects of High CO22 on Plant Communities on Plant Communities

Ian WoodrowIan Woodrow

Topics:Topics:

• CO2 measurements

• Primary CO2 effects on plants

• Effects on plant communities

1. CO1. CO22 - Monitored at Several Locations - Monitored at Several Locations

How do we know where the COHow do we know where the CO22 comes from? comes from?

Plants discriminate against Plants discriminate against 1313COCO22

Plant tissue ground and analysed

using a mass spectrometer

(n.b. almost all trees are C3)

COCO22 Rise - Combustion of Old/New Plants Rise - Combustion of Old/New Plants

2. Primary Effects of CO2. Primary Effects of CO22 - Rubisco - Rubisco

• Ribulose 1,5-bisphosphate carboxylase/oxygenase• Catalyses net carbon fixation in all photosynthetic organisms (gate-keeper of C input to biosphere)• World’s most abundant protein (10 kg person-1)

Primary Effects of COPrimary Effects of CO22 - Rubisco - Rubisco

• Rubisco catalyses CO2 fixation (photosynthesis)

• Rubisco also catalyses a low probability oxygenation reaction (photorespiration), which is more probable due to relatively high [O2]

Primary Effects of COPrimary Effects of CO22 - Rubisco - Rubisco

• About 1 oxygenation for every 2.5 carboxylations

• 0.5 CO2s lost per oxygenation

RuBP + CO2 2 PGA

2 G3P

2 ATP + 2 NADPH

2 ADP + 2 NADP

ATP

ADP

(1)

(2)(3)

+O2 PGly

sugar

1/2 CO2

Primary Effects of COPrimary Effects of CO22 - Rubisco - Rubisco

• Net CO2 assimilation rate stimulated in most plants (except those with CO2 concentrating mechanisms - e.g. C4)

• Net rate = carboxylation - photorespiration - respiration• Photosynthesis and growth stimulated in most plants under high CO2 (glasshouse experiments)

(intercellular [CO2] in ppm)Today

Leaf

Response

Primary COPrimary CO22 Response - Stomata Response - Stomata

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Taking in COTaking in CO22 ‘costs’ water ‘costs’ water

CO2

H2O

Plants effectively “trade” water for CO2

A rise in COA rise in CO22 causes stomata to close causes stomata to close

0

200

400

600

800

1000

1200

0 250 500 1000

Conductance

[intercellular CO2]

Stomatal aperture

today

Stomata: major resistance to HStomata: major resistance to H22O transfer O transfer

• Stomata resist water vapour transfer from the inter-cellular air spaces to the atmosphere

• Drop in stomatal aperture cause drop in transpiration rate (E)

• Drop in E and rise in A result in rise in Water Use Efficiency (WUE)

wwii

wwaa

3. Testing Effects of Primary Responses: FACE3. Testing Effects of Primary Responses: FACE

FACE = Free Air CO2 Enrichment

Testing Effects of Primary Responses: FACETesting Effects of Primary Responses: FACE

Testing Effects of Primary Responses: FACETesting Effects of Primary Responses: FACE

Measured responses: Sorghum FACE - ArizonaMeasured responses: Sorghum FACE - Arizona

• Sorghum (a C4) grown for 2 consecutive years at 370 ppm and 570 ppm CO2 under well watered (ww) and water stressed (ws) conditions.

• High CO2 reduced E by 10% under ww and 4% under ws conditions

• High CO2 increased grain yield by 4% under ww and 16% under ws

• WUE rose by 9% (ww) and 19% (ws)

Measured responses: Cotton FACE - ArizonaMeasured responses: Cotton FACE - Arizona

• Cotten grown for 4 consecutive years at 370 ppm and 570 ppm CO2

• Cotton yields rose about 40% with no rise in water use (E)

• Wheat E decreased (5-8%), and grain yields increased by 10% (ww) and 20% (ws)

Measured responses: Tree FACEsMeasured responses: Tree FACEs

Measured responses: Pine FACEMeasured responses: Pine FACE

OZFACE - Stomatal effects cause moisture riseOZFACE - Stomatal effects cause moisture rise

Overall EffectsOverall Effects

• Almost all plant (on their own) do better under high CO2

• Due to Rubisco and water saving effects• Temperature rise can offset gains: favours photorespiration, enhances transpiration and respiration

• Chamber experiments examine CO2 - temp interaction

Uses in teachingUses in teaching

•Sensor and communication technology•Data manipulation and processing (database)•Data acquisition system programming•Sampling strategies