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Accueil du site → Doctorat → États-Unis → 2011 → Drought Tolerance in Quercus douglasii in the California Mediterranean Savanna : A study of photosynthetic functional responses, limitations, and changes during annual seasonal drought

University of California, Berkeley (2011)

Drought Tolerance in Quercus douglasii in the California Mediterranean Savanna : A study of photosynthetic functional responses, limitations, and changes during annual seasonal drought

Osuna, Jessica Lee

Titre : Drought Tolerance in Quercus douglasii in the California Mediterranean Savanna : A study of photosynthetic functional responses, limitations, and changes during annual seasonal drought

Auteur : Osuna, Jessica Lee

Université de soutenance : University of California, Berkeley

Grade : Doctor of Philosophy (PhD) 2011

Résumé partiel
Quercus douglasii , blue oak, is endemic to the California mediterranean-type climate region characterized by annual summer drought. Because blue oak is winter deciduous, an understanding of the strategy for surviving under current climate conditions is vital to improving the predictions for survival and adaptation to predicted climate change. This is especially important because the region may experience strengthened climate-change type drought, a decrease in precipitation accompanied by higher temperatures. As such, this dissertation was focused on studying the ecophysiology of Quercus douglasii by intense measurements of the seasonal trends in leaf structure and function, photosynthetic functional response to three environmental variables (PAR, CO2, and temperature), leaf water potentials, and the limitation imposed on photosynthetic carbon fixation by stomatal and internal (mesophyll) conductance. The study was realized in situ in a grazed oak-grass savanna near Ione, CA, USA, in multiple years and on multiple trees of different water use strategies (i.e. both isohydric and anisohydric). Instantaneous gas-exchange and leaf-fluorescence was measured with the Li-Cor 6400-40 in order to estimate photosynthetic capacity via photosynthetic response curves to CO2, mitochondrial respiration in the dark during the day (Rd) via photosynthetic light response curves, as well as instantaneous maximum rates of photosynthesis, stomatal conductance, and transpiration. Additionally, by combining gas-exchange and fluorescence measurements, I calculated internal conductance (the conductance of CO2 from the intercellular airspaces to the site of carboxylation, also referred to as mesophyll conductance) employing the `variable J’ method. In order to estimate the relative contribution of electron transport to each photosynthesis and alternative electron sinks, I conducted photosynthetic response curves under 2% O2. I also developed and utilized a novel method of performing photosynthetic response curves to leaf temperature in in situ. Finally, I routinely measured leaf water potential in the mid-day and pre-dawn, leaf mass, area, nitrogen content, chlorophyll content, and leaf absorptance. The results from this study indicate that the majority of photosynthetic carbon fixation occurs during the spring when photosynthetic capacity of blue oaks is exceptionally high (Vcmax = 118 μmol m-2 s-1) and prior to the extreme drop of mid-day leaf water potential brought on by the onset of the summer drought. During this peak period, stomatal and internal conductances also peaked and the negative response of photosynthesis to increased leaf temperatures was minimal especially in the isohydric individual. During the summer drought when trees increasingly rely on the water table, mid-day leaf water potentials reached -5.1 MPa. While values of photosynthesis and conductance were low in all individuals, the isohydric individual displayed less suppression. In the anisohydric species, values approached zero toward day of year 200 and photosynthesis decreased nearly linearly with an increase in temperature and leaf-to-air vapor pressure difference, approaching 0 at 40°C. In all individuals in all years, Rd normalized to 25°C decreased exponentially from an initial value around 3 μmol m-2 s-1 throughout the season.

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Page publiée le 13 mai 2012, mise à jour le 2 octobre 2017