JXB Advance Access originally published online on July 28, 2003
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Journal of Experimental Botany, Vol. 54, No. 390, pp. 2015-2024,
September 1, 2003
© 2003 Oxford University Press
Cavitation, stomatal conductance, and leaf dieback in seedlings of two co-occurring Mediterranean shrubs during an intense drought
Received 17 October 2002; Accepted 22 May 2003
1 CEAM-Department de Ecologia, Universitat d’Alacant, POB 99, E-03080 Alacant, Spain
2 Department de Ecologia, Universitat d’Alacant, POB 99, E-03080 Alacant, Spain
3 CEAM, C/Ch. Darwin 14, Parque Tecnológico, E-46980 Paterna, Spain
4 Unidad de Recursos Forestales, SIA-DGA, POB 727, E-50080 Zaragoza, Spain
* To whom correspondence should be addressed. Fax: +34 965 903 464. E-mail: a.vilagrosa{at}ua.es
Seedling shrubs in the Mediterranean semi-arid climate are subjected to intense droughts during summer. Thus, seedlings often surpass their limits of tolerance to water stress, resulting in the loss of hydraulic conductivity due to xylem cavitation. The response in terms of stomatal conductance, vulnerability to cavitation, leaf dieback, and survival were analysed in two co-occurring seedlings of mastic tree (Pistacia lentiscus L.) and kermes oak (Quercus coccifera L.) during an intense drought period. Both species reacted to drought with steep decreases in stomatal conductance before the critical water potential brought about the onset of cavitation events. Q. coccifera showed wider safety margins for avoiding runaway embolism than P. lentiscus and these differences could be related to the particular drought strategy displayed by each species: water saver or water spender. The limits for survival, resprout capacity and leaf dieback were also analysed in terms of loss of conductivity. By contrast with previous studies, the species showing higher seedling survival in the presence of drought also showed higher susceptibility to cavitation and operated with a lower safety margin for cavitation. Both species showed a leaf specific conductivity (LSC) threshold below which leaf biomass had to be regulated to avoid runaway embolism. However, each species displayed a different type of response: P. lentiscus conserved total leaf area up to 100% loss of LSC, whereas Q. coccifera continuously adjusted leaf biomass throughout the drought period in order to maintain the LSC very close to the maximum values recorded without loss of conductivity. Both species maintained the capacity for survival until the loss of conductivity was very nearly 100%.
Key words: Drought stress, leaf dieback, Mediterranean shrubs, stomatal conductance, survival, xylem cavitation.
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