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| Titel |
COS as a proxy for photosynthesis: foliage and soil contributions to ecosystem COS flux |
| VerfasserIn |
Kukka-Maaria Erkkilä, Linda Kooijmans, Juho Aalto, Huilin Chen, Ivan Mammarella, Kadmiel Maseyk, Mari Pihlatie, Ulli Seibt, Wu Sun, Timo Vesala |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148976
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| Publikation (Nr.) |
 EGU/EGU2017-13286.pdf |
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| Zusammenfassung |
| Traditionally the photosynthetic sink of CO2 (described by gross primary production, GPP) is
defined from ecosystem scale measurements of CO2 flux taking into account respiration
defined from the nighttime CO2 flux data. The problem with this method is the accurate
determination of ecosystem respiration, since the respiratory processes can vary remarkably
between daytime and nighttime. Carbonyl sulfide (COS) has been suggested to be a useful
proxy for GPP since plants take up COS in a similar way as CO2 via their stomata. In
contrast to CO2, there is no back-flux (respiration) of COS by plants and GPP can be
calculated directly from COS flux measurements. However, leaf relative uptake (LRU)
ratio, that is used when converting COS flux into GPP with a linear relation, has
been treated as a constant and needs to be better determined for more accurate GPP
estimates.
This presentation shows the preliminary results of a measurement campaign organized in
Hyytiälä Scots pine (Pinus sylvestris) stand in southern Finland during the growing season
2016. COS fluxes from the soil were measured with soil chambers over different vegetations.
Pine and aspen branches were measured with branch chambers and ecosystem scale exchange
was monitored via eddy covariance measurements.
Preliminary results show night-time ecosystem uptake of COS (negative flux) that
is about 15% of the daily uptake. Soil chambers show constantly negative COS
fluxes, although there is no uptake of CO2 and the soil flux is about 25% of the
total ecosystem flux. Pine and aspen branches seem to be sinks of COS throughout
the day indicating open stomata during night-time. These findings suggest that
negative ecosystem COS flux can be explained by soil and vegetation uptake during
night-time.
From branch chamber measurements we were able to calculate the leaf relative uptake
(LRU) separately for aspen and pine. We find that LRU has an exponential correlation with
photosynthetic active radiation (PAR) when PAR<500μmol m−2s−1. On the other hand,
when PAR>500μmol m−2s−1, the LRU seems to be constant and for aspen LRU=1.7 and for
pine LRU=1.4. We find that the light dependency of LRU needs to be taken into account
when calculating GPP from COS measurements for better photosynthesis estimates. |
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