Vegetal protein hydrolysates mitigate NaCl salinity in Salvia officinalis by improving growth, nutrient status and essential oil yield

Salinity stress is an important factor affecting the growth and production of secondary metabolites in medicinal and aromatic plants. Vegetal protein hydrolysates (VPHs) have emerged as eco-friendly biostimulants capable of improving plant tolerance to abiotic stresses. Accordingly, to evaluate the effectiveness of VPHs in mitigating salinity stress in sage (Salvia officinalis L.), a pot experiment was conducted as a factorial experiment in a completely randomized design with three replications, using three salinity levels (0, 50, and 100 mM sodium chloride (NaCl)) and five VPHs treatments (applied as foliar application at concentrations of 2 and 4 mL L− 1, fertigation at concentrations of 1.5 and 3 mL L− 1, and control). The results indicated that under salinity treatments, growth parameters, relative water content (RWC), chlorophyll content, photosynthetic performance, leaf nutrient concentrations, potassium to sodium (K/Na) ratio, and essential oil (EO) content and yield were significantly reduced. In contrast, sodium (Na) and chlorine (Cl) levels increased significantly. Application of VPHs significantly improved growth, RWC, photosynthetic parameters, nutrient uptake, K/Na ratio, and EO yield under saline conditions. Fertigation treatments were generally more effective than foliar applications in alleviating the effects of salinity. The EO yield decreased by 14.81% and 40.74% under salinity levels of 50 and 100 mM, respectively, compared to the treatment without salinity. In contrast, the EO yield increased by 64.7% and 35.29% when VPHs were applied as fertigation at concentrations of 1.5 and 3 mL L⁻¹, respectively, and by 23.53% and 17.65% when VPHs were used as foliar application at concentrations of 2 and 4 mL L⁻¹, respectively, compared to the treatment without VPHs application. The main components of the EO were α-Thujone, Camphor, β-Thujone, and 1,8-Cineole, which responded differently to salt stress and VPHs treatment. These findings demonstrate that VPHs, particularly when applied via fertigation, represent a promising and sustainable strategy to maintain productivity and EO yield of sage under salinity stress.