Phenotypic plasticity is stronger than adaptative differentiation among Mediterranean stone pine provenances

Abstract

The Mediterranean stone pine, Pinus pinea L., seems to be well adapted to the different climate zones of its distribution range that spans four thousand kilometres along the Northern shore of the Mediterranean Sea. But recent molecular studies revealed it to be extremely genetically depauperate for a widespread tree. In this context, a provenances trial should elucidate whether any differentiation in adaptative traits can be identified between 34 accessions covering its natural range. The presence of strong spatial autocorrelations throughout four test sites required iterative nearest-neighbours adjustments in their statistical analysis. No significant differences in survival or ontogeny were found between accessions, while height growth was slightly though significantly more vigorous in northern or inland provenances. But these differences were masked by a common, stable reaction norm in dependence on site and microsite. On the other hand, its strong developmental plasticity allows the stone pine to delay the heteroblastic phase change in order to survive in unfavourable conditions, a clear advantage in the limiting and unpredictable environments of Mediterranean ecosystems.