Résumé
The degree to which climate warming and increasing drought will alter isoprenoid emissions of Mediterranean forests remains unclear, because most studies were carried out on single factors with isolated plants thus neglecting possible factor interactions and indirect effects at plant and community level. We studied foliar isoprenoid emissions, phenology, growth and survival rates on Quercus pubescens (QP) and Quercus ilex (QI) saplings growing in competition with herbaceous species under three temperature treatments (ambient, +1.5, +3 degrees C) combined with two precipitation treatments (normal, -30% precipitation). Elevated temperature treatments significantly enhanced isoprenoid emissions of both species (similar to 70%). Most of this enhancement could be attributed to increases in the foliar emission capacities. Reduced precipitation tended to decrease isoprenoid emissions (similar to 20%), but this effect was variable depending on plant species, measurement period and interaction with temperature treatments. In QP, measured early summer, most of the emission variability was associated with that of photosynthesis while in QI, measured mid-summer, emissions and photosynthesis were rather uncoupled probably due to changes in resource allocation and persistent impairment of the primary metabolism caused by stress. Elevated temperature reduced sapling survival rates of both species (similar to 20 %) but increased longevity of QP leaves (similar to 18%). Leaf biomasses at plant and community level were not affected by treatments but were strongly reduced by the presence of herbaceous competitors. The results underline the complexity of potential plant responses to climate change to be considered for predicting the future evolution of isoprenoid emission in the Mediterranean region.