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
Vertical flux of carbon dioxide (F C ) over a prairie grassland What causes the Midday minimum in August?
Notice how low the CO 2 concentration was in 1969 !
NEE = A + R A = Gross Photosynthesis (-) R = Total Ecosystem Respiration (+)
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
Daytime NEE Gross Photosynthesis – Total Ecosystem Respiration NEE ( mol CO 2 m -2 s -1 ) Photosynthetically-active radiation ( mol m -2 s -1 )