Site conditions exert more control than genetic differentiation on modulation of secondary growth and climate sensitivity of Pinus pinaster

The adaptive potential and genetic background of tree species will determine their performance and vitality under changing climate conditions. How environment and genotype influence secondary growth and their climate sensitivity in boreal and temperate conifers has been fairly studied. Provenance studies assessing the genetic variation in plasticity of radial growth, however, are scarce in Mediterranean tree species. We explored the impact of climate on tree-ring growth in Pinus pinaster based on plantation sites and genetic background. We assessed the climate sensitivity, plastic response of growth, and intraspecific genetic differentiation of pines from 10 provenances planted in two trials in south-central Spain. Trees from areas with a climate similar to that of the planting sites showed greater growth rates. Higher within-site than among-site similitude in inter-annual growth variation was evidenced by similar growth patterns in each trial test, irrespective of seed provenance. We found positive growth responses to mild conditions in late winter, and to wet and cloudy conditions in spring and early summer. Greater site-dependent than genetically-driven control was observed on growth sensitivity to climate. Central Spanish seed sources were better able to withstand the combination of stressful environmental conditions in the test sites. Inter-site environmental variation was the factor that explained a higher number of growth responses to climate variation. The significant “genetic × environment” interaction on radial growth suggested that genotypic determinants were strongly modulated by plastic adaptations due to local conditions. The site-dependent relationships of provenance climate responses with the conditions at origin also reflected the prevailing local adaptation to site constraints. Since plastic response of P. pinaster trees to local environment has more influence than its genetic predisposition, assessing the spatio-temporal variation of growth sensitivity to climate becomes increasingly important.