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| Titel |
CO2 uptake of a mature Acacia mangium plantation estimated from sap flow measurements and stable carbon isotope discrimination |
| VerfasserIn |
H. Wang, P. Zhao, L. L. Zou, H. R. McCarthy, X. P. Zeng, G. Y. Ni, X. Q. Rao |
| 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 ; 11, no. 5 ; Nr. 11, no. 5 (2014-03-12), S.1393-1411 |
| Datensatznummer |
250117277
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| Publikation (Nr.) |
 copernicus.org/bg-11-1393-2014.pdf |
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| Zusammenfassung |
| A simple, nondestructive method for the estimation of canopy CO2 uptake
is important for understanding the CO2 exchange between forest and
atmosphere. Canopy CO2 uptake (FCO2) of a subtropical
mature \textit{A. mangium} plantation was estimated by combining sap flow
measurements and stable carbon isotope discrimination (Δ) in Southern
China from 2004 to 2007. The mechanistic relationship linking
FCO2, Δ in leaf sap, and sap flow-based canopy stomatal
conductance (Gs) was applied in our study. No significant
seasonal variations were observed in Δ or in the ratio of the
intercellular and ambient CO2 concentrations
(Ci/Ca), although diurnal
Ci/Ca varied between sunlit and shaded leaves. A
sensitivity analysis showed that estimates of FCO2 were more
sensitive to dynamics in Gs than in Ca and
Δ. By using seasonally and canopy averaged
Ci/Ca values, we obtained an acceptable estimate of
FCO2 compared to other estimates. FCO2 exhibited
similar diurnal variation to that of Gs. Large seasonal
variation in FCO2 was attributed to the responsiveness of
Gs to vapor pressure deficit, photosynthetically active
radiation, and soil moisture deficit. Our estimate of FCO2 for a
mature A. mangium plantation
(2.13 ± 0.40 gC m−2 d−1) approached the lower range of
values for subtropical mixed forests, probably due to lower mean canopy
stomatal conductance, higher Ci/Ca, and greater
tree height than other measured forests. Our estimate was also lower than
values determined by satellite-based modeling or carbon allocation studies,
suggesting the necessity of stand level flux data for verification.
Qualitatively, the sap flux/stable isotope results compared well with gas
exchange results. Differences in results between the two approaches likely
reflected variability due to leaf position and age, which should be reduced
for the combined sap flux and isotope technique, as it uses canopy average
values of Gs and Ci/Ca. |
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