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Accueil du site → Doctorat → Italie → L’impatto dello stress idrico e delle alte temperature sull’emissione di isoprene, sulla fotosintesi e respirazione

Università degli studi della Tuscia - Viterbo (2008)

L’impatto dello stress idrico e delle alte temperature sull’emissione di isoprene, sulla fotosintesi e respirazione

Brilli, Federico

Titre : L’impatto dello stress idrico e delle alte temperature sull’emissione di isoprene, sulla fotosintesi e respirazione

Response of isoprene emission, photosynthesis and respiration to drought stress and rising temperatures

Auteur : Brilli, Federico

Université de soutenance : Università degli studi della Tuscia - Viterbo

Grade : Tesi di dottorato di ricerca 2008

Résumé
Isoprene is the most abundant volatile organic compounds (VOC) released by plants in the atmosphere (44% of the total amount of VOCs) (Gunther et al. 1995 ; Kesselmeier & Staudt, 1999). Isoprene influences the oxidative capacity of the troposphere (Zimmerman et al. 1978) and is a substrate for ozone production in polluted air (Chameides et al. 1988). Isoprene is mainly synthesized in the chloroplasts (Lichtenthaler 1999) from photosynthetic intermediates in a reaction catalyzed by isoprene synthase (ISPS) (Silver & Fall, 1995 ; Schnitzler et al. 1996). Incoming Global Change events leading to environmental stress conditions such as drought coupled with rising temperatures (and with high ozone concentration), may : - strongly influence isoprene biosynthesis with various consequences on its emission ; - have contrasting effects on biogeochemical carbon cycles regarding photosynthetic carbon assimilated (and respired) by forests. To investigate the impact of the interaction between rising temperatures and water stress on isoprene emission (IE), photosynthesis (A) and respiration (R), one-year-old Populus nigra L. saplings were first grown under two different temperatures (25 C° and 35 C°), and then exposed to progressive limiting soil water content. During progressive drought stress conditions, (IE), (A) and (R) were monitored and referred both to soil water availability (FASW) and to the amount of transpirable soil water (FTSW). Moreover, to investigate the biochemical regulation of (IE), proton-transfer-reaction mass spectrometer (PTR-MS) (Lindinger et al. 1998) was used to record the appearance of individually 13C-labeled atoms in the unfragmented isoprene molecule following exposure to air containing 13CO2. Experimental results showed that in well-watered non-stressed plants higher growing temperature (35 C°) doubled IE and decreased A by 30%, while R showed a not significant increase of 15%. These results pointed out that both IE and A did not acclimate to a 10 °C higher growing temperature whereas R seemed likely to acclimate (Ow et al. 2008). Drought did increase the (IE) to (A) ratio, because (IE) was inhibited with a slower kinetics than (A), both at 25 °C and at 35 °C. FTSW calculation addressed that the percentage of carbon lost as (IE) dramatically increased earlier at 35 °C than at 25 °C. In unstressed leaves (IE) was temporary stimulated when (A) dropped at progressively stronger levels of drought at both temperatures, before starting to decrease to minimum levels. In plants grown at 25 °C, even when carbon fixation by photosynthesis was compensated by respiratory processes under limiting soil water availability, isoprene was emitted at a 30% rate of the emission observed in irrigated controls. Differently from pre-stress conditions, at a severe drought stage only 16 – 42% of the (IE) was labeled by 13CO2 suggesting that extrachloroplastic carbon sources may increasingly supply carbon to isoprene when (A) became to be limited (Brilli et al. 2007). In severely drought-stress leaves, photosynthesis independent-(IE) was also independent of temperature, being the rate of emission similar at 25 °C and 35 °C. After re-watering, (IE) recovered as quickly as (A), but even if plants completely have recovered (A) recorded before drought stress, (IE) did not reach the pre-stress levels, particularly in leaves grown at 35 °C. Even though my experimental results supported previous evidences that isoprene emission is resistant to moderate drought stress conditions (Loreto & Sharkey, 1993 ; Fang et al. 1996, Brilli et al. 2007), for the first time it has highlighted that drought events are able to suppress temperature sensitivity of the process of isoprene biosynthesis, with important ecological consequences in reducing the emission of high emitters (Fortunati et al. 2008).

Mots Clés : Marcamento 13CO2 ; Isoprene ; Fotosintesi ; Respirazione ; Scambi gassosi ; PTR-MS ; AGR/05

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