Plant Canopies and Carbon Dioxide Flux

At night: - flux directed from canopy to the atmosphere- respiration from leaves, plant roots, soil

Daytime: - CO2 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: Fc drops despite sun, due to soil moisture depletion – flux higher in morning

Winter: Small, negative flux

Vertical flux of carbon dioxide(FC) over a prairiegrassland

What causes theMidday minimum in August?

Notice how low the CO2 concentration was in 1969 !

NEE = A + R

A = Gross Photosynthesis (-)

R = Total EcosystemRespiration (+)

NEE = 0.1223 (soil temp) - 0.0525

R2 = 0.2477

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 5 10 15 20 25 30

Night-time NEE = Total Ecosystem RespirationN

EE

(m

ol C

O2

m-2s

-1)

Soil Temperature at 5cm depth (C)

Mer Bleue Bog,Eastern Ontario

-12

-8

-4

0

4

8

0 1000 2000

Daytime NEE Gross Photosynthesis – Total Ecosystem Respiration

NE

E (m

ol C

O2

m-2s

-1)

Photosynthetically-active radiation (molm-2s-1)

Fluxnet-Canada Carbon Flux Stations

Coastal conifers

Southern boreal conifers and hardwoods Boreal

mixedwood

Balsam fir

Eastern peatlandWestern

peatland

CO2 richDry, Cool

Low CO2

Humid, Warm