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| Titel |
Use of the isotope flux ratio approach to investigate the C18O16O and 13CO2 exchange near the floor of a temperate deciduous forest |
| VerfasserIn |
E. Santos, C. Wagner-Riddle, X. Lee, J. Warland, S. Brown, R. Staebler, P. Bartlett, K. Kim |
| 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 ; 9, no. 7 ; Nr. 9, no. 7 (2012-07-02), S.2385-2399 |
| Datensatznummer |
250007174
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| Publikation (Nr.) |
 copernicus.org/bg-9-2385-2012.pdf |
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| Zusammenfassung |
| Stable isotopologues of CO2, such as 13CO2 and C18OO,
have been used to study the CO2 exchange between land and atmosphere.
The advent of new measuring techniques has allowed near-continuous
measurements of stable isotopes in the air. These measurements can be used
with micrometeorological techniques, providing new tools to investigate the
isotope exchange in ecosystems. The objectives of this study were to
evaluate the use of the isotope flux ratio method (IFR) near the forest
floor of a temperate deciduous forest and to study the temporal dynamics of
δ18O of CO2 flux near the forest floor by comparing IFR
estimates with estimates of δ18O of net soil CO2 flux
provided by an analytical model. Mixing ratios of 12C16O2,
13CO2 and C16O18O were measured within and above a
temperate deciduous forest, using the tunable diode laser spectroscopy
technique. The half-hourly compositions of the CO2 flux near the forest
floor (δ13CF and δ18OF) were calculated
by IFR and compared with estimates provided by a modified Keeling plot
technique (mKP) and by a Lagrangian dispersion analysis (WT analysis). The
mKP and IFR δ18OF estimates showed good agreement
(slope = 1.03 and correlation, R2 = 0.80). The δ13CF estimates
from the two methods varied in a narrow range of −32.7 and −23‰; the mean
(± SE) mKP and IFR δ13CF values were −27.5‰ (±0.2)
and −27.3‰ (±0.1), respectively, and were statistically identical
(p>0.05). WT analysis and IFR δ18OF estimates showed
better correlation (R2 = 0.37) when only turbulent periods (u*>0.6 m s−1) were included in the analysis. The large amount of data captured (~95 % of half-hour periods evaluated) for the IFR in comparison with mKP
(27 %) shows that the former provides new opportunities for studying
δ18OF dynamics within forest canopies. Values of δ18OF showed large temporal variation, with values ranging from
−31.4‰ (DOY 208) to −11.2‰ (DOY 221). Precipitation events caused
substantial variation (~8‰) in δ18OF over a period
of approximately 24 h. A diel trend of δ18OF was observed,
with more depleted values present during the daytime. Model simulations
indicate that the activity of the carbonic anhydrase enzyme was quite
variable during the evaluated period. These simulations indicate that more
frequent sampling of δ18O of soil water could improve the
estimates of δ18O of net soil CO2 flux. |
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