Publication Date:
2014-05-01
Description:
Partitioning of CO 2 exchange into canopy ( F A ) and soil ( F R ) flux components is essential to improve our understanding ecosystem processes. The stable isotope C 18 OO can be used for flux partitioning, but this approach depends on the magnitude and consistency of the isotope disequilibrium ( D eq ), i.e. difference between the isotope compositions of F R ( δ A ) and F A ( δ R ). In this study high temporal resolution isotopic data were used: 1) to test the suitability of existing steady state and non-steady models to estimate H 2 18 O enrichment in a mixed forest canopy, 2) to investigate the temporal dynamics of δ A using a big-leaf parameterization, and 3) to quantify the magnitude of the C 18 OO disequilibrium ( D eq ) in a temperate deciduous forest throughout the growing season and to determine the sensitivity of this variable to the CO 2 hydration efficiency ( θ eq ). A departure from steady state conditions was observed even at mid-day in this study, so the non-steady state formulation provided better estimates of leaf water isotope composition. The dynamics of δ R was mainly driven by changes in soil water isotope composition, caused by precipitation events. Large D eq values (up to 11‰) were predicted; however the magnitude of the disequilibrium was variable throughout the season. The magnitude of D eq was also very sensitive to the hydration efficiencies in the canopy. For this temperate forest during most of the growing season, the magnitude of D eq was inversely proportional to θ eq , due to the very negative δ R signal, which is contrary to observations for other ecosystems investigated in previous studies.
Print ISSN:
0148-0227
Topics:
Biology
,
Geosciences
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