EFFECTS OF MODERATE WATER STRESS AND SHADING ON SURVIVAL, GROWTH AND RESOURCE ALLOCATION OF TWO CORK OAK (QUERCUS SUBER L.) PROVENANCES

Sixty-four plants of Cork oak (Quercus suber L.) originating from Spain and Tunisia provenances were grown under a combination of two light levels (15 % (moderate shade) versus 5 % (deep shade) of full-light) and two water regimes (well-watered versus moderate water stress) in a nursery in Spain. Ten response variables including seedling survival, height, diameter, height-to-diameter ratio, above- and below-ground biomass, total biomass, shoot-to-root ratio, number and length of growth unit were measured for each provenance. In average, seedling survival was 89 % and was independent of the studied factors (provenance, light, water regime). Seedling height was similar in both provenances, while diameter was significantly larger in the Spanish provenance. Water stress adversely affected the balance between height and diameter for the Spanish provenance, but not for the Tunisian provenance, while light, and independently of seedlings' provenance, affected 80 % (8/10) of traits studied. Thus, the Tunisian provenance seemed to be more tolerant to water stress while none of both provenances seemed to be more tolerant to shade. However, when considering both factors the Spanish provenance showed a better seedlings' acclimation to water stress under deep shade and may constitute accordingly a better material for afforestation as in Mediterranean conditions, as our results show, light and water stress may act in a coordinate manner. This variability would be mainly genetically controlled, as both provenances were cultivated under the same environmental conditions. Our results may be helpful in regeneration, cultivation and afforestation of cork oak.