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| Titel |
Towards a consistent approach of measuring and modelling CO2 exchange with manual chambers |
| VerfasserIn |
Vytas Huth, Shrijana Vaidya, Mathias Hoffmann, Nicole Jurisch, Anke Günther, Laura Gundlach, Ulrike Hagemann, Lars Elsgaard, Jürgen Augustin |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250134205
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| Publikation (Nr.) |
 EGU/EGU2016-14904.pdf |
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| Zusammenfassung |
| Determining ecosystem CO2 exchange with the manual closed chamber method has been
applied in the past for e.g. plant, soil or treatment on a wide range of terrestrial ecosystems.
Its major limitation is the discontinuous data acquisation challenging any gap-filling
procedures. In addition, both data acquisition and gap-filling of closed chamber data have
been carried out in different ways in the past. The reliability and comparability of the
derived results from different closed chamber studies has therefore remained unclear.
Hence, this study compares two different approaches of obtaining fluxes of gross
primary production (GPP) either via sunrise to noon or via gradually-shaded mid-day
measurements of transparent chamber fluxes (i.e. net ecosystem exchange, NEE) and opaque
chamber fluxes (i.e., ecosystem respiration, RECO) on a field experiment plot in NE
Germany cropped with a lucerne-clover-grass mix. Additionally, we compare three
approaches of pooling RECO data for consecutive modelling of annual balances of NEE,
i.e. campaign-wise (single measurement day RECO models), seasonal-wise (one
RECO model for the entire study period), and cluster-wise (two RECO models
representing low-/high-vegetation-stage data) modelling. The annual NEE balances of the
sunrise to noon measurements are insensitive towards differing RECO modelling
approaches (-101 to -131 g C m−2), whereas the choice of modelling annual NEE
balances with the shaded mid-day measurements must be taken carefully (-200 to
425 g C m−2). In addition, the campaign-wise RECO modelling approach is very sensitive
to daily data pooling (sunrise vs. mid-day) and only advisable when the diurnal
variability of CO2 fluxes and environmental parameters (i.e. photosynthetically
active radiation, temperature) is sufficiently covered. The seasonal- and cluster-wise
approaches lead to robust NEE balances with only little variation in terms of daily data
collection. We therefore recommend sunrise to noon measurements and data pooling
from adjacent measurement campaigns as long as pooling over e.g. harvest events
and significant changes in plant development can be omitted. If, e.g. for extensive
treatment comparisons, the sunrise to noon measurements are not feasible due to
their higher workload, data pooling accounting for plant development is necessary. |
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