Strategy to Mitigate Recurring Water Deficit in Black Pepper Using Melatonin, Ascophyllum nodosum, Lithothamnium calcareum

Water deficit is one of the main limiting factors in agricultural production, affecting the growth and photosynthetic performance of plants. The aim of this study was to evaluate the effects of foliar applications of melatonin, A. nodosum and L. calcareum on black pepper, ‘Bragantina’, subjected to three cycles of water deficit, on physiological per-formance, carbohydrate allocation and vegetative growth. The results showed that the applied solutions contributed to the recovery of damage caused by water stress. The first cycle of water deficit affected the electron transfer quantum yield, resulting in the re-duction of φP0 and PIABS. However, the damage to the photosynthetic apparatus was recovered in subsequent cycles. Water stress reduced chlorophyll indices, possibly as a strategy to minimize photo-oxidative damage. Plants treated with melatonin and L. calcareum maintained a stable leaf expansion rate and showed greater water recovery, standing out in the second and third cycles of water deficit.