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Accueil du site → Doctorat → États-Unis → 2007 → The importance of a Mediterranean type ecosystem in trace gas fluxes from the chaparral of Southern California

University of California, Davis and San Diego State University (2007)

The importance of a Mediterranean type ecosystem in trace gas fluxes from the chaparral of Southern California

Luo, Hongyan

Titre : The importance of a Mediterranean type ecosystem in trace gas fluxes from the chaparral of Southern California

Auteur : Luo, Hongyan

Université de soutenance : University of California, Davis and San Diego State University

Grade : Doctor of Philosophy (PhD) 2007

Résumé
Carbon flux measurements over a ca. 100-year old-growth chamise-dominated chaparral shrub ecosystem using eddy covariance techniques were conducted from 1996 to 2003. Results indicate carbon sinks, from -96 to -155 g C m-2 yr-1, under normal climate conditions, but were a weak sink of -18 g C m-2 yr-1 to a strong source of 207 g C m-2yr-1 as a consequence of a severe drought. The annual sink strength of carbon averaged -52 g C m -2 yr-1, which is comparable to many other ecosystems and indicates that, in contrast to previous thought, the old-growth chaparral shrub ecosystem can be a significant sink of carbon and, therefore, an important component of the global carbon budget. In the comparison experiments, a ca. 100-year chaparral stand (96 to 102-year old) demonstrated a substantial cumulative carbon sink of -391 g C m-2, while a ca. 10-year old chaparral (5 to 11-year old) stand exhibited a moderate carbon source of 114 g C m -2 over the measurement period. This caused the rejection to our hypothesis that young stand would be more productive than the old stand. The cumulative ET at the old stand was 2657 mm, which was higher than the value of 1885 mm at the young stand confirming earlier assumptions of lower water use in young stands. NEE and ET difference between the young stand and the old stand was likely due to the significantly higher soil temperature and higher soil moisture at the young stand than at the old stand. Measurements over the ca. 100-year chaparral ecosystem demonstrated that carbon uptake was largest in the growing season, but constrained in both the dry and winter seasons. The variability of water availability was the primary control on the intra and inter-annual variation of ecosystem carbon and water exchange. Air temperature increase resulted in a linear increase in seasonal carbon fixation and water loss during daytime. Nighttime ecosystem respiration increased as an exponential function with soil temperature in all seasons. Ecosystem dark respiration rates were similar in all seasons. The maximum carbon uptake rate was far larger in the growing season than other seasons.

Présentation (SAO/NASA)

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