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| Titel |
Modelling short-term variability in carbon and water exchange in a temperate Scots pine forest |
| VerfasserIn |
M. H. Vermeulen, B. J. Kruijt, T. Hickler, P. Kabat |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2190-4979
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| Digitales Dokument |
URL |
| Erschienen |
In: Earth System Dynamics ; 6, no. 2 ; Nr. 6, no. 2 (2015-07-30), S.485-503 |
| Datensatznummer |
250115472
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| Publikation (Nr.) |
 copernicus.org/esd-6-485-2015.pdf |
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| Zusammenfassung |
| The vegetation–atmosphere carbon and water exchange at one particular site
can strongly vary from year to year, and understanding this interannual
variability in carbon and water exchange (IAVcw) is a critical factor
in projecting future ecosystem changes. However, the mechanisms driving this
IAVcw are not well understood. We used data on carbon and water fluxes
from a multi-year eddy covariance study (1997–2009) in a Dutch Scots pine
forest and forced a process-based ecosystem model (Lund–Potsdam–Jena General Ecosystem Simulator; LPJ-GUESS) with local
data to, firstly, test whether the model can explain IAVcw and seasonal
carbon and water exchange from direct environmental factors only. Initial
model runs showed low correlations with estimated annual gross primary
productivity (GPP) and annual actual evapotranspiration (AET), while monthly
and daily fluxes showed high correlations. The model underestimated GPP and
AET during winter and drought events. Secondly, we adapted the temperature
inhibition function of photosynthesis to account for the observation that at
this particular site, trees continue to assimilate at very low atmospheric
temperatures (up to daily averages of −10 °C), resulting in a
net carbon sink in winter. While we were able to improve daily and monthly
simulations during winter by lowering the modelled minimum temperature
threshold for photosynthesis, this did not increase explained IAVcw at
the site. Thirdly, we implemented three alternative hypotheses concerning
water uptake by plants in order to test which one best corresponds with the
data. In particular, we analyse the effects during the 2003 heatwave. These
simulations revealed a strong sensitivity of the modelled fluxes during dry
and warm conditions, but no single formulation was consistently superior in
reproducing the data for all timescales and the overall model–data match
for IAVcw could not be improved. Most probably access to deep soil
water leads to higher AET and GPP simulated during the heatwave of 2003. We
conclude that photosynthesis at lower temperatures than assumed in most
models can be important for winter carbon and water fluxes in pine forests.
Furthermore, details of the model representations of water uptake, which are
often overlooked, need further attention, and deep water access should be
treated explicitly. |
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