Impact of effective microorganisms on the amount of leaf and root elements of almond rootstocks under salinity stress

Introduction
Almond (Prunus dulcis Mill.) is one of the oldest and most critical dry fruits in the world and belongs to the Rosacea family. Salinity is one of the increasing problems in the world and it covers a large part of our country, so identifying work methods against abiotic stress is a major challenge. Salinity stress affects the absorption of nutrients. In the conditions of salinity stress, the occurrence of changes in the amount of absorption, distribution and transfer of nutrients in the plant parts or the physiological inactivation of the parts of the plant that are involved in the absorption of nutrients cause disturbance in the nutritional balance of the plant. Salinity first leads to a decrease in water absorption and then causes a disturbance in the absorption of nutrients in the plant, which leads to plant damage. Absorption of water and nutrients in plants are closely related, and the factors that limit water absorption may also cause tension in the absorption of nutrients. In the conditions of salinity stress, the decrease in the absorption of nutrients is caused by the decrease in the efficiency of the roots in the absorption of nutrients and the competition between sodium and chlorine ions with elements such as calcium and potassium. The use of almond-specific hybrids such as GF677, GF557, Titan, Hansen, and GN15 is beneficial for achieving salinity and drought tolerance. However, botanists need faster and more complete methods to cope with intense environmental stresses. Using effective microorganisms (EMs) is one of these options that increases plant resistance to environmental stresses through increasing metabolism. Therefore, this study was conducted to select new salinity-resistant rootstocks and investigate the effect of different levels of salinity and EM' treatments on the number of various nutrients in the leaf and root of almond seedlings.
 
Materials and Methods
This research was carried out in the Department of Horticulture, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili in 2016. A pot experiment was carried out as a factorial based on the randomized complete block design (RCBD) with three replications. Almond rootstocks, two years old, healthy, and with the same growth ability, were provided. In March, they were removed from polyethylene pots and transformed into seven kg plastic pots containing equal amounts of cultivated soil and peat moss and each pot was considered as one repeat. The used soil texture was sandy loamy with pH = 6.8, EC = 1.63 ds m⁻¹, 179 ppm of K, 71 ppm of P, 0.17 % of total N, and 1.41 % of C. The experimental treatments included: effective microorganisms concentrations containing EM0: zero, EM1: 10, EM2: 20, and EM3: 30 ml L^-1 and salinity in four levels: B0: zero, B1: 60, B2: 120, and B3: 180 mM NaCl, that were applied on almond rootstocks: C0: Sangi almond seedling, C1: GF677, and C2: GN15. From the 5th of May and for two months, EMs have been applied once a week with irrigation water and soil application. The pots were irrigated with water containing various NaCl levels every two days, from the 5th of July for 60 days. Drainage water was removed from the bottom of the pot at each irrigation with saline water. The plant roots were thoroughly washed with ordinary water to minimize EC and pH changes due to salt accumulation in the planting bed each week. At the beginning of the experiment, to prevent the occurrence of sudden stress on plants, salinity stress increased by increasing the amount of 15 mM NaCl daily. To evaluate these conditions, on the studied almond rootstocks, nutrient elements such as sodium, chlorine, potassium, calcium, and nitrogen, and the potassium/sodium ratio of leaf and root were measured.
 
Results and Discussion
Analysis of the variance (ANOVA) showed that in the treatment of EMs, the interaction of the year and the rootstocks was significant on calcium leaf. The simple effects of treatments in all studied elements were statistically significant. The results showed that the sodium chloride of leaves and chlorine and roots increased with increasing salinity stress. Three tested rootstocks with stress expansion, but the GF677 and seedling rootstock had the lowest sodium and chloride in the leaf and root. With increasing salt stress levels, concentrations of potassium, calcium, nitrogen, and potassium/sodium ratio of leaves and roots, decreased in all three rootstocks but these indices were higher in the GF677 and seedling almond.
 
Conclusion
Among the evaluated traits elements, the leaf nitrogen, and potassium/sodium content were good markers to study and examine the salinity of almond rootstocks. The application of biofertilizers improved all studied indices in each of the three studied rootstocks and the best result in the Ems experiment was related to the GF677, the level of 30 ml per liter of EMs, and zero mM of salinity. Based on this, the GF677 hybrid was tolerant to salt stress conditions, and seedling almond and GN15 were placed in the next positions, respectively.