Unravelling the Intraspecific Variation in Drought Responses in Seedlings of European Black Pine (Pinus Nigra J.F. Arnold).

Understanding intraspecific variation in drought tolerance is essential for predicting the adaptive capacity of forest species under climate change. Yet, the molecular basis of this variation remains poorly understood in ecologically and economically important conifers. We integrated high-throughput phenotyping with metabolomics and transcriptomics under standardised soil drying to investigate drought responses across nine climatically distinct provenances of the conifer Pinus nigra. We tested whether drought tolerance-measured as decline in maximum quantum yield of the photosystem II (Fv/Fm)-varies among provenances, follows a climatic cline, and involves trade-off with growth. To identify the underlying molecular basis, we performed metabolomics and transcriptomics in four provenances representing contrasting drought tolerance. Drought tolerance varied significantly among provenances and was decoupled from growth, yet showed no differentiation along the climatic cline. Drought-tolerant provenances differed from sensitive ones in both constitutive abundance and drought-induced accumulation of the flavonoid pinostrobin and the diterpene hydroxydehydroabietic acid. Transcriptomic profiles further highlighted provenance-specific differences in gene expression related to flavonoids. Overall, these findings link phenotypic drought responses to molecular variation among provenances, providing insight into the molecular basis of drought responses in an important conifer species.