Shiva Khayyati - Master's student in Plant Physiology, Faculty of Science, Urmia University, West AzarbaijanProvince, Iran

Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization.Salts occur naturally within soils and water. Salination can be caused by natural processes such as mineralweathering or by the gradual withdrawal of an ocean. The electrical conductivity of the saturated moistureof these soils is more than ۴ millimos/cm at ۲۵oC. The percentage of exchangeable sodium in these soilsis less than ۱۵. Usually the pH is less than ۵.۸. The most important cations of these soils are calcium,magnesium and sodium, but rarely sodium makes up more than half of the dissolved cations. The mainanions are chloride (Cl-), sulfate and sometimes nitrate. In addition to soluble solutes, the amount of lesssoluble and insoluble solutes such as gypsum, calcium carbonate or magnesium is found in it. As a resultof water evaporation and remaining salt on the surface, white and separate spots are formed on thesurface of these soils. Therefore, some old scientists, including Hilgard, named these soils white alkali.Since the factors of weathering and soil formation do not have much effect on these soils and the profileof these soils is uniform, changes in the direction of depth are not observed. Due to the insufficient growthof plants, their humus content is low and therefore they have a light color. In this article, the aim is tofamiliarize with the reaction and how plants resist salinity. Salinity stress (regardless of the mechanism ofsoil disturbance) occurs due to excessive accumulation of cations in the soil solution. The presence ofthese salts causes damage to plants in two ways. Excessive accumulation of salt in the soil solutionincreases the osmotic pressure of the soil solution, and the plant faces a problem in absorbing water andsuffers a kind of physiological dryness or osmotic stress, and sometimes the presence of too many salts inthe soil causes ionic effects. Levitt separated salt stress from ionic stress; If the salt concentrationincreases so much that it reduces the water potential from ۰.۰۵ to ۰.۱ MPa, then the plant faces saltstress. If the salt concentration is not high, the existing stress is ionic and probably due to a specific ion.The tolerance of plants to salinity is not only quite variable among different species, but also changes ineach plant and under environmental conditions. Many factors related to plants, soil, water andatmosphere are combined with each other and affect the resistance of a plant to salinity. Therefore, thereaction of a plant to a certain concentration of salt cannot be predicted absolutely. However, plants canbe relatively compared to each other.

plant tolerance, salinity, Soil salinity, electrical conductivity of the saturated moisture