Morphophysiological responses of comfrey (Symphytum officinale) to water deficit

Symphytum officinale, comfrey, is a medicinal plant known for its healing properties. On the growing conditions and physiological responses of this plant to stress are scarce. We aimed to assess the morphophysiological responses of comfrey to short-term severe water restriction (seven days) and to a control treatment under irrigation. Climatological data, growth parameters, pigment content, stomatal conductance, chlorophyll a fluorescence, Normalized Difference Vegetation Index, plant morphological responses, and anatomical differences of roots were evaluated. Symptoms of water deficit were evident from the third day onwards, such as leaf wilt and senescence of a greater quantity of leaves, as well as reduction of stomatal conductance. Photochemical activities were affected in the first days, with less intensity on the seventh day for the photosystem II performance index (PIabs). The plant aerial parts were more visually affected than the roots, which showed secondary growth after the water restriction imposition, a possible response of tuberization to drought. The water deficit affected the growth and metabolism of comfrey plants, but adjustments in photosynthetic apparatus and increased dry mass productivity indicated a possible adjustment to severe drought. Further experiments are needed to assess whether there is a viability of the root system after shoot senescence due to extreme drought.