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Do volatile organic compound emissions of Tunisian cork oak populations originating from contrasting climatic conditions differ in their responses to summer drought?

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Abstract:

The intrinsic variability of volatile organic compound emissions and photosynthetic parameters in response to two drying cycles was investigated on Quercus suber L. saplings originating from three Tunisian populations native to contrasting climates. Emissions mainly included monoterpenes plus traces of sesquiterpenes and methylsalicylate that steadily decreased during the experiment unrelated to treatments. Instead, monoterpene emissions increased by 30% during a first moderate drought and remained enhanced after rewatering, while CO2–H2O gas exchange was reduced by 30%. A second severe drought decreased monoterpene emissions to about two third of controls, strongly inhibited gas exchange and photochemical efficiency, and caused a partial loss of chlorophyll. Rewatering led to only partial recovery of emissions and photosynthetic parameters of stressed plants whose biomasses and leaf nitrogen and chlorophyll contents were lower than in control plants. There was no clear difference among populations in volatile organic compound emissions or photosynthetic parameters. However, the population inhabiting the most arid region had intrinsically smaller leaves with lower specific leaf masses and higher drought-related leaf losses than populations native to less arid climates. These results indicate an adaptive shift from stress-tolerating towards stress-avoiding ecotypes under arid climates involving mainly morphological adaptations without apparent differentiation in volatile organic compound production, probably because of its high phenological plasticity.

La variabilité des émissions foliaires de composés organiques volatils et des paramètres photosynthétiques ont été étudiés au cours de deux cycles de desséchement sur des plants de Quercus suber L. provenant de trois populations tunisiennes adaptées à des différentes conditions climatiques. Les composés organiques volatils émis étaient principalement des monoterpènes, plus, indépendamment du traitement, des traces de sesquiterpènes et méthyle-salicylate. Un premier desséchement modéré réduisant les échanges gazeux en CO2–H2O de 30%, a augmenté de 30% les émissions de composés organiques volatils qui sont restées élevées après réhydratation. Un second dessèchement plus sévère a réduit les émissions d’environ 30% accompagné d’une forte inhibition des échanges gazeux et de l’efficience photochimique et d’une perte partielle de chlorophylle. Après réhydratation les émissions et les paramètres photosynthétiques ont partiellement récupéré. Les biomasses aériennes et souterraines finales ainsi que l’azote foliaire et la teneur en chlorophylle des plantes stressées étaient inférieurs à ceux des témoins. Les émissions de composés organiques volatils et les paramètres photosynthétiques n’étaient pas nettement différents entre populations. Cependant, la population provenant du site le plus aride présentait des feuilles plus petites de poids spécifique plus faible, et des pertes de feuilles plus importantes après le stress que les populations adaptées à des sites moins arides. Ces résultats pourraient indiquer l’évolution adaptative d’une stratégie de tolérance au stress vers une stratégie d’évitement du stress sous climat aride impliquant surtout des adaptations morphologiques sans différence apparente dans la production de composés organiques volatils, probablement à cause d’une grande plasticité phénologique.

Document Type: Research Article

Publication date: 2008-12-01

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  • Published since 1971, this monthly journal features articles, reviews, notes and commentaries on all aspects of forest science, including biometrics and mensuration, conservation, disturbance, ecology, economics, entomology, fire, genetics, management, operations, pathology, physiology, policy, remote sensing, social science, soil, silviculture, wildlife and wood science, contributed by internationally respected scientists. It also publishes special issues dedicated to a topic of current interest.
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