Population divergence in heat and drought responses of a coastal plant: from metabolic phenotypes to plant morphology and growth.

Studying intra-specific variation in multi-stress responses is central for predicting and managing the population dynamics of wild plant species under rapid global change. Yet, it remains a challenging goal in this field to integrate knowledge on the complex biochemical underpinnings for the targeted 'non-model' species. Here, we studied divergence in combined drought and heat responses among Northern and Southern European populations of the dune plant Cakile maritima, by combining comprehensive plant phenotyping with metabolic profiling via FT-ICR-MS and UPLC-TQ-MS/MS. We observed pronounced constitutive divergence in growth phenology, leaf functional traits and defence chemistry (glucosinolates, alkaloids) among population origins. Most importantly, the magnitude of growth reduction under drought was partly weaker in southern plants and associated with divergence in plastic growth responses (leaf abscission) and the modulation of primary and specialized metabolites with known central functions not only in plant abiotic but also biotic stress responses. Our study indicates that divergent selection has shaped the constitutive and drought/heat-induced expression of numerous morphological and biochemical functional traits to mediate higher abiotic stress resistance in southern Cakile populations, and highlights that metabolomics can be a powerful tool to explore the mechanistic underpinnings of local adaptation in 'non-model' species.