The Evolution of Date Palm Tolerance to Salinity Stress via Arbuscular Mycorrhizal Fungi and Compost Application

Our study investigated the overtime mitigation of NaCl stress negative impact on growth performances of Phoenix dactylifera through the application of compost and/or arbuscular mycorrhizal fungi (AMF). The experiment was designed in eight treatments that include a control treatment (no AMF and compost application) and AMF and compost treatments supplemented alone or in dual application under 0 mM NaCl (absence of salt stress) and 240 mM NaCl (presence of salt stress) after two periods of cultivation (10 and 14 months). Our results indicate that date palm grown under 240 mM NaCl recorded enhanced sodium, chlorine, soluble sugars, proline, H2O2, and malondialdehyde (MDA) content; all together, they showed reduced growth fitness, leaf water potential, mycorrhizal colonization, phosphorus (P), nitrogen (N), potassium (K), calcium (Ca), and photosynthetic pigment contents. AMF and compost supplementation, applied alone or in combination, lessened the negative effect of salinity via various strategies including the improvement of N, P, K, and Ca uptake, water status, photosynthetic pigment concentrations, stomatal conductance, photosystem II efficiency, soluble sugars, proline content, antioxidant defense, and the decline of H2O2 and MDA production. The results also reveal that palms tolerance to salinity was gradually enhanced over time in supplemented plants and particularly when both biofertilizers were applied. Between the two periods of cultivation (10 and 14 months), growth traits and nutrients content were improved, and stress markers and toxic ions concentrations were reduced, while osmolyte content and antioxidant enzyme activity were regulated. In conclusion, this study pointed out the potential effect of the dual supplementation of compost and native AMF in alleviating the adverse impact of salinity stress on date palm with improved tolerance mechanisms over time.