Autochthonous Arbuscular Mycorrhizal Fungi Enhance Growth, Nutritional Homeostasis, and Antioxidant Machinery of Caper-Bush (Capparis spinosa L.) Plants Under Salt Stress

Abiotic pressures, such as high soil salinization, are among agricultural systems' most onerous challenges today. Using biostimulants, such as beneficial rhizospheric microorganisms, to support sustainable agriculture/horticulture has recently assumed greater importance.

This study investigates whether an indigenous arbuscular mycorrhizal fungi inoculum (AMF complex) can assist caper-bush (Capparis spinosa L.) plants in mitigating the adverse effects of NaCl-induced salinity stress (NSS). Two groups of plants, non-mycorrhizal (− AMF) and mycorrhizal (+ AMF), were exposed to NSS after a two-month acclimatization period in a greenhouse under non-saline conditions. NSS was induced by irrigating the plants with saline solutions of varying NaCl concentrations. Growth performance, nutrient uptake/homeostasis, physio-biochemical mechanisms, and antioxidant activity were comprehensively evaluated.

The results demonstrated that AMF inoculation significantly enhanced caper-bush plants' growth and stress tolerance under NSS. AMF-colonized plants exhibited higher growth parameters compared to non-mycorrhizal counterparts. Mycorrhizal dependency and colonization rates peaked at low to moderate salinity levels but decreased at higher NSS degrees. Photochemical efficiency (Fv/Fm) was ⁓14.5% higher in AMF-inoculated plants under severe salinity stress. Total chlorophyll content increased by ⁓60% at higher NSS levels. Nutrient uptake was notably improved, with phosphorus content rising by ⁓35.4% under control conditions and K⁺ content by ⁓29.6% under moderate NSS. Na⁺ levels and Na^+/K⁺ ratios were reduced by ⁓0.8-fold and ⁓0.7-fold, respectively. Enhanced antioxidant enzyme activities (CAT, SOD, G-POX, APX) and higher levels of osmolytes were also observed in AMF-inoculated plants, with CAT activity increasing by ⁓81.2% and proline and soluble sugar levels rising by ⁓42% and ⁓49%, respectively, under moderate NSS.

Overall, inoculating plants with the autochthonous AMF complex promoted photosynthesis performance, a protective antioxidant system, ionic homeostasis, and osmolyte accumulation, ultimately improving the caper bush's survival and tolerance under salt stress conditions.