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| Titel |
Trends in CO2 exchange over a deciduous forest based on continuous eddy covariance mesurements over 14 years |
| VerfasserIn |
Kim Pilegaard, Andreas Ibrom, Ebba Dellwik |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039692
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| Zusammenfassung |
| The CO2 exchange was measured by eddy covariance technique over a Danish mature beech
forest (Sorø) continuously from June 1996 to December 2009. The results show a significant
increase in annual net ecosystem exchange (NEE) of 30 g C m-2 y-1. Estimates of
ecosystem respiration (RE) and gross ecosystem exchange (GEE) were derived from NEE.
The trend in RE (-8 g C m-2 y-1) was not significant, but there was a significant
increase in GEE (22 g C m-2 y-1). An analysis of the seasonal changes in NEE
showed that the carbon uptake period (CUP), i.e. the period with net uptake increased
significantly by 1.7 d y-1, whereas the period with leaves on the trees (LP) stayed
constant. Light response curves for NEE revealed that the assimilation capacity of
the forest at maximum ambient light (F-) increased significantly by 0.7 μmol
m-2 s-1 per year, whereas there was no significant trend in the apparent quantum
yield.
Trends in the explaining variables were examined. No significant trends could be found in
temperature, light or precipitation, whereas there was a significant increase in global
atmospheric CO2 concentration (1.9 ppmv y-1).
Simulation of the NEE data from the Sorø forest by the model MAESTRA showed that
the increase in CO2 could only explain a small part of the increased uptake capacity of the
forest. A much larger part could be explained by an increase in N-content of the leaves. Such
an increase is not yet documented. In general the deposition of atmospheric N has decreased,
but the forest is already N-saturated and the availability of N in the soil might have increased
due to climate change. Other possibilities for explaining the observed trends are
discussed. |
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