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Effects of High CO 2 on Plant Communities Ian Woodrow

Effects of High CO 2 on Plant Communities Ian Woodrow. Topics:. CO 2 measurements Primary CO 2 effects on plants Effects on plant communities. 1. CO 2 - Monitored at Several Locations. How do we know where the CO 2 comes from?. Plants discriminate against 13 CO 2.

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Effects of High CO 2 on Plant Communities Ian Woodrow

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  1. Effects of High CO2 on Plant Communities Ian Woodrow

  2. Topics: • CO2 measurements • Primary CO2 effects on plants • Effects on plant communities

  3. 1. CO2 - Monitored at Several Locations

  4. How do we know where the CO2 comes from?

  5. Plants discriminate against 13CO2 Plant tissue ground and analysed using a mass spectrometer (n.b. almost all trees are C3)

  6. CO2 Rise - Combustion of Old/New Plants

  7. 2. Primary Effects of CO2 - 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)

  8. Primary Effects of CO2 - Rubisco • Rubisco catalyses CO2 fixation (photosynthesis) • Rubisco also catalyses a low probability oxygenation reaction (photorespiration), which is more probable due to relatively high [O2]

  9. Primary Effects of CO2 - Rubisco O2 PGly (1) + RuBP + CO2 2 PGA 2 ATP + 2 NADPH (2) (3) ADP 2 ADP + 2 NADP 2 G3P ATP sugar • About 1 oxygenation for every 2.5 carboxylations • 0.5 CO2s lost per oxygenation 1/2 CO2

  10. Primary Effects of CO2 - Rubisco Leaf Response Today (intercellular [CO2] in ppm) • 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)

  11. Primary CO2 Response - Stomata

  12. Taking in CO2 ‘costs’ water H2O CO2 Plants effectively “trade” water for CO2

  13. A rise in CO2 causes stomata to close today Stomatal aperture [intercellular CO2]

  14. Stomata: major resistance to H2O transfer wa wi • 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)

  15. 3. Testing Effects of Primary Responses: FACE FACE = Free Air CO2Enrichment

  16. Testing Effects of Primary Responses: FACE

  17. Testing Effects of Primary Responses: FACE

  18. Measured 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)

  19. Measured 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)

  20. Measured responses: Tree FACEs

  21. Measured responses: Pine FACE

  22. OZFACE - Stomatal effects cause moisture rise

  23. Overall 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

  24. Uses in teaching • Sensor and communication technology • Data manipulation and processing (database) • Data acquisition system programming • Sampling strategies

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