Impact of cyclic-mild-drought stress on the metabolism of Mentha spicata L.: A strategy to improve quality traits

Studying the impact of mild drought stress on plant productivity and product quality is essential in the context of climate change and dwindling water resources. Moreover, understanding how mild drought stress affects plants is crucial for sustainable agriculture, since it can potentially lead to the development of more efficient irrigation techniques, which, in turn, could enhance the resilience of agricultural systems, improve crop quality and reduce environmental impacts. In this contest, the study reports on the physiological and metabolic responses of spearmint (Mentha spicata L.) plants to cyclic-mild-drought stress. The research aimed to understand how plants adapt to water stress conditions and whether the nutraceutical and sensory characteristics of the plant can be enhanced by managing the water supply. Cyclic-mild-drought stress affected various physiological parameters of the plants [i.e. stomatal conductance, net photosynthesis, leaf temperature and leaf osmolality] but did not impact plant biomass and the photosynthetic machinery. Changes in leaf cation and anion concentration were not related to the observed changes in leaf osmolality, suggesting that the accumulation of organic compounds such as amino acids, sugars, organic acids, and phenolic acids mainly drove the osmotic adjustment. Finally, the comparison between the leaves' volatile profile of stressed and unstressed plants revealed that the cyclic-mild-drought stress significantly increased the concentration of carvone, the most representative and industrially important molecule produced by spearmint. Overall, the study's novelty is to provide insights into spearmint plants' physiological and metabolic responses to cyclic-mild-drought stress, highlighting potential strategies, after verification in open fields, to enhance plant productivity and quality by modulating water supply.