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Article << Previous     |     Next >>   Contents Vol 36(5)

Differential photosynthetic performance and photoprotection mechanisms of three Mediterranean evergreen oaks under severe drought stress

José Javier Peguero-Pina A, Domingo Sancho-Knapik A, Fermín Morales B, Jaume Flexas C, Eustaquio Gil-Pelegrín A D

A Unidad de Recursos Forestales, Centro de Investigación y Tecnología Agroalimentaria, Gobierno de Aragón, Apdo. 727, 50080 Zaragoza, Spain.
B Department of Plant Nutrition, Experimental Station of Aula Dei, CSIC, Apdo. 13034, 50080 Zaragoza, Spain.
C Laboratori de Fisiologia Vegetal, Departament de Biologia, Universitat de les Illes Balears, Carretera de Valldemossa, km 7.5, 07071, Palma de Mallorca, Balears, Spain.
D Corresponding author. Email: egilp@aragon.es
 
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Abstract

The ability of three Mediterranean oaks (Quercus coccifera L., Quercus ilex ssp. ballota (Desf.) Samp and Quercus suber L.) to cope with intense drought was investigated. Water stress reduced stomatal conductance and photosynthesis in these species. Drought-mediated changes in photosynthetic-related parameters allowed the characterisation of the specific photo-protective mechanisms. Specifically, Q. suber downregulated photosynthetic electron transport rates (ETR) closing PSII reaction centres (i.e. decreasing photochemical quenching) and through an antheraxanthin (A) + zeaxanthin (Z)-mediated diminished intrinsic PSII efficiency (Φexc.). These changes were lower in Q. coccifera and Q. ilex ssp. ballota, which decreased further ETR photo-inactivating PSII centres (evidenced by their low predawn Fv/Fm ratios at high water stress). The predawn Fv/Fm ratio decreased in Q. coccifera largely due to Fm decreases, whereas in Q. ilex ssp. ballota Fv/Fm decreases were due to F0 increases, below –4 MPa. These Fv/Fm decreases were well correlated with increases in the A + Z photo-protective pigments. An analysis of dark respiration and photorespiration as alternative electron sinks under intense drought stress also revealed interspecific differences. The largest imbalance between electrons generated and consumed increased potentially oxidative damage in Q. suber. Subsequently, only Q. suber showed loss of chlorophyll, which is one of the main targets of oxidative damage. Data suggest that Q. coccifera and Q. ilex ssp. ballota seem more able than Q. suber to withstand highly xeric conditions. Therefore, our results question the consideration of Mediterranean evergreen oaks as a homogeneous physiological group.

Keywords: morphological convergence, photoprotection, physiological performance, Quercus, summer aridity, water stress.


   
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