Comparative effects of mineral fertilization, mycorrhizal biofertilizer, and organic biostimulants on growth and physiological response of olive trees ( Olea europaea L. cv. Koroneiki) under salinity stress

Intensive olive cultivation without adequate nutrient inputs can deplete soil fertility and limit productivity. In Tunisia, fertilization practices remain poorly regulated, with excessive inputs in irrigated orchards and insufficient fertilization in rain-fed systems. Under salinity stress, these practices are rarely adapted to local constraints, further affecting productivity, nutrient efficiency, and sustainability. This study directly compared conventional mineral fertilization, a commercial arbuscular mycorrhizal fungus (AMF)-based biofertilizer, and a commercial organic biostimulant in olive plants (Olea europaea L. cv. Koroneiki) exposed to saline irrigation with 100 mM NaCl, corresponding to approximately 5.84 g L−1 NaCl. Salinity reduced vegetative growth, biomass accumulation, water status, chlorophyll content, and photosynthetic performance, confirming its strong constraint on young olive plants. Both biological inputs improved shoot elongation, biomass production, chlorophyll status, and gas exchange, while the AMF-based biofertilizer showed the most consistent alleviation effect under saline conditions. This treatment also sustained nutrient acquisition and contributed to ionic regulation, particularly through improved K and Ca nutrition and modified Na partitioning between shoots and roots. Overall, this comparative approach highlights biofertilizers and biostimulants as promising alternatives or complementary tools to mineral fertilization for improving nutrient management, physiological performance, and resilience of salt-affected olive systems in Mediterranean regions.