2. Plant Canopies and Carbon Dioxide Flux At night: - flux directed from canopy to the atmosphere - respiration from leaves, plant roots, soil Daytime:- CO 2 assimilation rate exceeds respiration rate Seasonal Variation in Temperate Environments Spring: Assimilation increases with leaf area index and increasing solar radiation availability/day length Midsummer: F c drops despite sun, due to soil moisture depletion – flux higher in morning Winter: Small, negative flux

3. Vertical flux of carbon dioxide (F C ) over a prairie grassland What causes the Midday minimum in August?

4. Notice how low the CO 2 concentration was in 1969 !

5. NEE = A + R A = Gross Photosynthesis (-) R = Total Ecosystem Respiration (+)

6. Night-time NEE = Total Ecosystem Respiration NEE (  mol CO 2  m -2  s -1 ) Soil Temperature at 5cm depth (  C) Mer Bleue Bog, Eastern Ontario

7. Daytime NEE Gross Photosynthesis – Total Ecosystem Respiration NEE (  mol CO 2  m -2  s -1 ) Photosynthetically-active radiation (  mol  m -2  s -1 )

9. Fluxnet-Canada Carbon Flux Stations Coastal conifers Southern boreal conifers and hardwoods Boreal mixedwood Balsam fir Eastern peatland Western peatland