Abstract
Daytime isoprene emissions were measured over a black spruce forest in Saskatchewan (Canada) during the Boreal Ecosystem Atmosphere Study of 1994. The relaxed eddy-accumulation (REA) technique was used to measure isoprene fluxes in parallel with gradient measurements, which are required for using the gradient transport (GT) theory. The average isoprene flux was 2.29 mg C m−2 h−1 in late July and decreased to 0.54 mg C m−2 h−1 in early September. The senescent needles and lower ambient air temperature were most likely the cause of the lower isoprene emissions measured in September. A relationship of isoprene flux with air temperature was derived at the canopy scale because canopy temperature is not readily available. High isoprene emissions were observed at temperatures above 25°C. These were most likely in relation to thermoprotection of photosynthesis. The diurnal trends measured by GT and REA were similar. Isoprene fluxes measured using GT were 63% lower than those using REA. The underestimation resulted from having the lower GT inlet in the roughness sublayer, in which the flux–gradient relationships are not valid. Measuring the gradient at about two canopy height, with a reduced spacing from 10 to 3 m, would reduce the underestimation of the scalar flux, but it would also reduce the isoprene concentration differences by five to six times compared to those obtained with the REA technique. Previously, black spruce has been assigned to the highest emitting class of spruce forest for inventory purposes;however, the authors’ results suggest that the boreal zone black spruce should be assigned a standard emission rate of 6 rather than 18 μg C g−1 h−1.
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Claims 12
Claim · model-written summary
The average isoprene flux over the black spruce stand was 2.29 mg C m-2 h-1 in late July.
- Taxon
- Black Spruce
Picea marianat0 - Outcome
- average isoprene fluxe0
- Value
- 2.29 mg C m−2 h−1e0
- Qualifier
- late Julye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The average isoprene flux was 2.29 mg C m−2 h−1 in late July and decreased to 0.54 mg C m−2 h−1 in early September”
t0“Black Spruce Stand”
Claim · model-written summary
The average isoprene flux decreased to 0.54 mg C m-2 h-1 in early September.
- Taxon
- Black SprucePicea marianat0
- Outcome
- isoprene fluxe0
- Direction
- decreasede0
- Value
- 0.54 mg C m−2 h−1e0
- Qualifier
- early Septembere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The average isoprene flux was 2.29 mg C m−2 h−1 in late July and decreased to 0.54 mg C m−2 h−1 in early September”
t0“Black Spruce Stand”
Claim · model-written summary
Senescent needles and lower ambient air temperature were most likely the cause of the lower isoprene emissions measured in September.
- Taxon
- Black SprucePicea marianat0
- Organ / stage
- senescent needlese0
- Treatment
- lower ambient air temperaturee0
- Outcome
- lower isoprene emissionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The senescent needles and lower ambient air temperature were most likely the cause of the lower isoprene emissions measured in September”
t0“Black Spruce Stand”
Claim · model-written summary
A relationship of isoprene flux with air temperature was derived at the canopy scale.
- Taxon
- Black SprucePicea marianat0
- Treatment
- air temperaturee0
- Outcome
- isoprene fluxe0
- Qualifier
- canopy scalee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A relationship of isoprene flux with air temperature was derived at the canopy scale”
t0“Black Spruce Stand”
Claim · model-written summary
High isoprene emissions were observed at temperatures above 25 degrees C.
- Taxon
- Black SprucePicea marianat0
- Treatment
- temperatures above 25°Ce0
- Outcome
- High isoprene emissionse0
- Direction
- Highe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“High isoprene emissions were observed at temperatures above 25°C”
t0“Black Spruce Stand”
Claim · model-written summary
The high isoprene emissions at temperatures above 25 degrees C were most likely related to thermoprotection of photosynthesis.
- Taxon
- Black SprucePicea marianat0
- Outcome
- High isoprene emissionse0
- Qualifier
- thermoprotection of photosynthesise0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“High isoprene emissions were observed at temperatures above 25°C. These were most likely in relation to thermoprotection of photosynthesis”
t0“Black Spruce Stand”
Claim · model-written summary
The diurnal trends of isoprene flux measured by gradient transport (GT) and relaxed eddy accumulation (REA) were similar.
Verbatim
e0“The diurnal trends measured by GT and REA were similar”
Claim · model-written summary
Isoprene fluxes measured with GT were 63% lower than those measured with REA.
Verbatim
e0“Isoprene fluxes measured using GT were 63% lower than those using REA”
Claim · model-written summary
The GT underestimation resulted from the lower GT inlet being in the roughness sublayer, where flux-gradient relationships are not valid.
- Taxon
- Black SprucePicea marianat0
- Outcome
- underestimatione0
- Qualifier
- lower GT inlet in the roughness sublayere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The underestimation resulted from having the lower GT inlet in the roughness sublayer, in which the flux–gradient relationships are not valid”
t0“Black Spruce Stand”
Claim · model-written summary
Measuring the gradient at about two canopy heights with spacing reduced from 10 to 3 m would reduce the underestimation of the scalar flux.
- Taxon
- Black SprucePicea marianat0
- Outcome
- underestimation of the scalar fluxe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Measuring the gradient at about two canopy height, with a reduced spacing from 10 to 3 m, would reduce the underestimation of the scalar flux”
t0“Black Spruce Stand”
Claim · model-written summary
The reduced gradient spacing would also reduce the isoprene concentration differences by five to six times compared with those obtained with the REA technique.
Verbatim
e0“it would also reduce the isoprene concentration differences by five to six times compared to those obtained with the REA technique”
Claim · model-written summary
Boreal zone black spruce should be assigned a standard emission rate of 6 rather than 18 ug C g-1 h-1.
- Taxon
- black sprucePicea marianae0
- Outcome
- standard emission ratee0
- Value
- 6 rather than 18 μg C g−1 h−1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the boreal zone black spruce should be assigned a standard emission rate of 6 rather than 18 μg C g−1 h−1”