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| Titel |
Needle age-related and seasonal photosynthetic capacity variation is negligible for modelling yearly gas exchange of a sparse temperate Scots pine forest |
| VerfasserIn |
M. Beeck, B. Gielen, I. Jonckheere, R. Samson, I. A. Janssens, R. Ceulemans |
| 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 ; 7, no. 1 ; Nr. 7, no. 1 (2010-01-14), S.199-215 |
| Datensatznummer |
250004374
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| Publikation (Nr.) |
 copernicus.org/bg-7-199-2010.pdf |
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| Zusammenfassung |
In this study, we quantified the predictive accuracy loss involved with
omitting photosynthetic capacity variation for a Scots pine (Pinus sylvestris L.) stand in
Flanders, Belgium. Over the course of one phenological year, we measured the
maximum carboxylation capacity at 25 °C (Vm25), the maximum electron
transport capacity at 25 °C (Jm25), and the leaf area index (LAI) of
different-aged needle cohorts in the upper and lower canopy. We used these
measurements as input for a process-based multi-layer canopy model with the
objective to quantify the difference in yearly gross ecosystem productivity
(GEP) and canopy transpiration (Ecan) simulated under scenarios in which
the observed needle age-related and/or seasonal variation of Vm25 and
Jm25 was omitted. We compared simulated GEP with estimations obtained from
eddy covariance measurements. Additionally, we measured summer needle N
content to investigate the relationship between photosynthetic capacity
parameters and needle N content along different needle ages.
Results show that Vm25 and Jm25 were, respectively, 27% and
13% higher in current-year than in one-year old needles. A significant
seasonality effect was found on Vm25, but not on Jm25. Summer needle
N content was considerably lower in current-year than in one-year-old
needles. As a result, the correlations between Vm25 and needle N content
and Jm25 and needle N content were negative and non-significant,
respectively. Some explanations for these unexpected correlations were
brought forward. Yearly GEP was overestimated by the canopy model by ±15% under all scenarios. The inclusion and omission of the observed
needle age-related Vm25 and Jm25 variation in the model simulations
led to statistically significant but ecologically irrelevant differences in
simulated yearly GEP and Ecan. Omitting seasonal variation did not yield
significant simulation differences. Our results indicate that intensive
photosynthetic capacity measurements over the full growing season and
separate simulation of needle age classes were no prerequisites for accurate
simulations of yearly canopy gas exchange. This is true, at least, for the
studied stand, which has a very sparse canopy and is exposed to high N
deposition and, hence, is not fully representative for temperate Scots pine
stands. Nevertheless, we believe well-parameterized process-based canopy
models – as applied in this study – are a useful tool to quantify losses of
predictive accuracy involved with canopy simplification in modelling. |
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