Читать книгу Physiology of Salt Stress in Plants - Группа авторов - Страница 12

The threat of global warming is not limited only to the earthen atmosphere but slowly progressing toward the lithosphere. Attenuation of vegetative health due to the assimilation of brine substances is referred to as saline toxicity. The destruction caused solely due to the elevated level of sodium chloride (NaCl) is characterized as sodicity and is rather attainable to reclaim. Contrarily, the assorted salt stress enforces salinity, which makes land barren(Gul et al. 2015). Since the Green Revolution, the salinity footprint is engulfing the terrestrial territory quite rampantly. Presently, around one‐tenth of the earth's crust accounting nearly 46 M ha has turned non‐fertile (Hossain 2019). Excessive groundwater abstraction in the high zones may lead to premature desertification. The Indian Council of Agricultural Research (ICAR) predicted in a geospatial study that the coastal districts will be left with no aquifer water by 2050 without any technical interference (ICAR 2015). This further booms the inland intrusion of saline water. Figures are even more agitating, precisely in coastal regions. The rising sea levels often cause waterlogging in different parts of the world, precisely places located at lower elevations (EL‐Raey et al. 1995). India, with a coastline length of approximately 7516 km, is presently under immense risk of temporary submergence. Saline water logging abnormally elevates the sodicity and thereby turns the lands nonproductive or unfertile.

The other reason that may trigger the soil sodicity is extreme groundwater abstraction. The negative aquifer pressure in the coastal regions causes brackish water intrusion and vertical rise by capillary action (Dillon et al. 2009). Whereas, the increase in soil salinity is a complex phenomenon. Studies showcased the discharge of industrial effluents into the water bodies successively raising the dissolved salt content resulting in increased salinity while utilized in irrigation. The other foremost reason for soil salinity involves drying out. Overutilization has already caused drying of a significant chunk of sweet water resources. In the absence of the desired water quality, farmers are moving toward alternate sources with high saline concentration, leading to the salinity of agricultural lands (Staniforth and Davies 2018).

The impact of salt stress is found to be most severe on agricultural crops. The primary issues involve the non‐germination of seeds, reduced leaf surface area, retarded plant growth, strength, hampered yield, etc. Elevated soil salinity hampers the plants in various ways such as osmotic stress (OS), ionic toxicity, retarded cell division, reduced photosynthesis, to name a few. The inclusive impact of all the above factors boosts the mortality rate (Lauchli and Grattan 1970).

Immediate exposure to higher saline medium primarily increases the OS, causing reduced leaf surface area (i.e. due to repressed cell division and growth). Whereas, prolonged exposure imparts ionic stress leading to stomatal closure, immature senescence of mature leaves, chlorosis, necrosis, etc. The reduced biomass negatively affects photosynthesis and plant growth (Darko et al. 2019). In contrast, exposure to elevated sodicity, especially NaCl,affects the enzymatic system and augments cell swelling. The mutual impact leads to suppressed energy synthesis. Furthermore, excess exposure hinders all the growth‐oriented processes like metabolism and protein synthesis (Acosta‐Motos et al. 2017).

Therefore, prolonged exposure provoked the development of a defense mechanism in some species against salt stress and toxicity either by excluding through cells or by enhancing the salt tolerance. Additionally, synthetic species with transgenic properties are also synthesized by genetic engineering by altering the levels of gene expression (Carillo et al. 2011).