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| Titel |
Isoprene emissions track the seasonal cycle of canopy temperature, not primary production: evidence from remote sensing |
| VerfasserIn |
P. N. Foster, I. C. Prentice, C. Morfopoulos, M. Siddall, M. van Weele |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 13 ; Nr. 11, no. 13 (2014-07-01), S.3437-3451 |
| Datensatznummer |
250117497
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| Publikation (Nr.) |
 copernicus.org/bg-11-3437-2014.pdf |
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| Zusammenfassung |
| Isoprene is important in atmospheric chemistry, but its seasonal emission
pattern – especially in the tropics, where most isoprene is emitted – is
incompletely understood. We set out to discover generalized relationships
applicable across many biomes between large-scale isoprene emission and a
series of potential predictor variables, including both observed and
model-estimated variables related to gross primary production (GPP) and
canopy temperature. We used remotely sensed atmospheric concentrations of
formaldehyde, an intermediate oxidation product of isoprene, as a proxy for
isoprene emission in 22 regions selected to span high to low latitudes, to
sample major biomes, and to minimize interference from pyrogenic sources of
volatile organic compounds that could interfere with the isoprene signal.
Formaldehyde concentrations showed the highest average seasonal correlations
with remotely sensed (r = 0.85) and model-estimated (r = 0.80) canopy
temperatures. Both variables predicted formaldehyde concentrations better
than air temperature (r= 0.56) and a "reference" isoprene model that
combines GPP and an exponential function of temperature (r = 0.49), and far
better than either remotely sensed green vegetation cover, fPAR (r = 0.25) or model-estimated GPP (r = 0.14). Gross primary production in tropical regions was
anti-correlated with formaldehyde concentration (r = −0.30), which peaks
during the dry season. Our results were most reliable in the tropics, where
formaldehyde observational errors were the least. The tropics are of particular
interest because they are the greatest source of isoprene emission as well as
the region where previous modelling attempts have been least successful. We
conjecture that positive correlations of isoprene emission with GPP and air
temperature (as found in temperate forests) may arise simply because both
covary with canopy temperature, peaking during the relatively short growing
season. The lack of a general correlation between GPP and formaldehyde
concentration in the seasonal cycle is consistent with experimental evidence
that isoprene emission rates are largely decoupled from photosynthetic rates,
and with the likely adaptive significance of isoprene emission in protecting
leaves against heat damage and oxidative stress. |
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