Intraspecific grafting with selected scions and rootstocks was used to study drought tolerance in the recalcitrant Mediterranean conifer P. pinaster. Conifers store different terpene types in needles, stems and roots, which can be modified by drought, but most studies have focused on a single organ and over selected terpenes which limits understanding of the overall plant response. In this work, terpene profile (160 components among mono-, sesqui, di-terpenes and resin acids) as well as eco-physiological traits were assessed in needles, roots, and scion and rootstock stems to analyze the drought sensibility of scions and rootstocks on grafted P. pinaster trees. We used two scions from wet (Galicia) and dry (Oria) provenances grafted onto rootstocks showing differences in the efficiency of water use, grown under two different water regimes, well-watered and water stressed. Constitutively, organs showed clearly different qualitative and quantitative terpene profiles, such as a long-term optimized resources allocation, being neutral and acid diterpenes those more discriminant. Environmental factors may selectively affect the regulation of diterpene biosynthesis in needles, since scion provenances determined the variation of their profiles, mainly regarding again neutral and acid diterpenes. Different scion-conferred terpene phenotypes were observed in each organ, having a relevant role isoabienol content. Drought triggered needle/ root resin acids redistribution, which may provide higher protection to roots, correlated to the effective water stress endured by plants. Drought sensitivity of scion-rootstock combinations determined the intensity of drought-triggered changes in terpene levels in all organs, suggesting that chemical defense and drought tolerance are somehow interconnected.
