Physiological and Biochemical Responses of Apple (Malus domestica Borkh.) to Biostimulants Application and Substrate Additives under Salinity Stress

Abstract

The issue of high concentration of salt in soil is not restricted to coastal areas, but also expands to cultivated lands, complicating, or even intercepting, the growth of plants. The objective of this paper is to study the effect of zeolite, compost and effective microorganisms (EM), seaweed extract, and ceramic powder on MM106 apple (Malus domestica Borkh.) plants in normal and saline conditions. More specifically, the weight of the dry matter of the plants, physiological parameters, proline, carbohydrate, carotenoid, phenolic, and flavonoid concentrations in leaf tissues and antioxidant capacity were determined. At the end of the experiment, it was ascertained that the plants of the treatments which included zeolite or EM exhibited the highest dry matter weight of the leaves in normal (5.07 g and 4.68 g, respectively) and saline conditions (4.14 g and 3.02 g, respectively), while the leaf dry weight in the control treatment was 4.37 g in the absence and 2.34 g in the presence of NaCl. Furthermore, these treatments resulted in significantly higher proline concentration in plant leaves under salinity with values of 5.63 in the EM treatment, 2.44 in the zeolite treatment, and 0.75 μmol/g of leaf fresh weight in the control. At the same time, the application of ceramic powder in combination with effective microorganisms led to the highest rate of photosynthesis in salinity conditions (12.8 μmol CO2/m2s), while the seaweed extract spraying was associated with low stomatal conductance in all treatments (0.09–0.13 mol H2O/m2s). Overall, the application of effective microorganisms appeared to associate more with plant vigor in both normal and salinity conditions. In this context, the implementation of EM could improve the growth of potted plants, but it could also be used in orchards before and after their establishment.