The impact of drought on plant metabolism in quercus species-from initial response to recovery

Oak species of the genus Quercus represent one of the most successful taxonomic groups from an evolutionary perspective. Knowing how oaks are capable of modulating their metabolism to tolerate water stress is a priority from an ecological point of view in a global change scenario. The great variability in production and accumulation of metabolites in oaks is related to differences in drought tolerance across species. This tolerance is defined by the ability to maintain water transport at low water potentials, the effectiveness of osmoregulation, and the capability to reduce oxidative damage caused by stress. General drought responses in oaks are the increase of soluble sugars and amino acids pools in leaves and woody organs, and the decrease of starch, which can help sustain water transport, cell turgor and cell-membrane stability, and the production of secondary metabolites, such as flavonoids, tannins, and terpenoids that act like antioxidants and protectors of the photosynthetic apparatus. Moreover, drought affects the quality and quantity of root exudates and biogenic volatile organic compounds. The production and emission of these metabolites depend on the sensitivity of plant physiology and metabolism to drought across oaks. The deep reorganization of primary and secondary metabolic pathways that fine-tunes cell functioning during drought episodes allows oaks to withstand long periods of limited water uptake and nutrient assimilation. Future studies combining other omics approaches with whole-plant physiology will help to unveil the potential coordination of plant metabolism and vascular transport in orchestrating drought tolerance.