for salinity tolerance: a case study with tetraploid wheat. Plant Soil 253: 201–218.39 Munns, R. and Tester, M. (2008). Mechanisms of salinity tolerance. Annu. Rev. Plant Biol. 59: 651–681.
40 Munns, R., Schachtman, D., and Condon, A. (1995). The significance of a two‐phase growth response to salinity in wheat and barley. Aust. J. Plant Physiol. 22: 561.
41 Naidoo, S. and Olaniran, A.O. (2013). Treated wastewater effluent as a source of microbial pollution of surface water resources. Int. J. Environ. Res. Public Health 11: 249–270.
42 Nosetto, M., Jobbágy, E., Tóth, T., and Di‐Bella, C. (2007). The effects of tree establishment on water and salt dynamics in naturally salt‐affected grasslands. Oecologia 152: 695–705.
43 Parida, A.K. and Das, A.B. (2005). Salt tolerance and salinity effects on plants: a review. Ecotoxicol. Environ. Saf. 60: 324–349.
44 Patel, R. (2013). The long green revolution. J. Peasant Stud. 40: 1–63.
45 Pingali, P.L. (2012). Green revolution: impacts, limits, and the path ahead. Proc. Natl. Acad. Sci. 109: 12302–12308.
46 Rasool, S., Hameed, A., Azooz, M.M. et al. (2013). Salt stress: causes, types and responses of plants. In: Ecophysiology and Responses of Plants Under Salt Stress (eds. P. Ahmad, M.M. Azooz and M. Prasad), 1–24. New York: Springer.
47 Savci, S. (2012). An agricultural pollutant: chemical fertilizer. Int. J. Environ. Sci. Dev. 3: 77–80.
48 Shahid, S.A. and Rahman, K.U. (2011). Soil salinity development, classification, assessment, and management in irrigated agriculture. In: Handbook of Plant and Crop Stress (ed. M. Pessarakli), 24–36. Oxfordshire: Taylor and Francis.
49 Shahid, S.A., Zaman, M., and Heng, L. (2018). Soil salinity: historical perspectives and a world overview of the problem. In: Guideline for Salinity Assessment, Mitigation and Adaptation Using Nuclear and Related Techniques (eds. S.A. Shahid, M. Zaman and L. Heng), 43–53. Basel, Switzerland: Springer, Cham.
50 Sharma, D.K. and Singh, A. (2015). Salinity research in India‐ achievements, challenges and future prospects. Water Energy Int. 58: 35–45.
51 Shrivastava, P. and Kumar, R. (2015). Soil salinity: a serious environmental issue and plant growth promoting bacteria as one of the tools for its alleviation. Saudi J. Biol. Sci. 22: 123–131.
52 Singer, M.A. and Lindquist, S. (1998). Multiple effects of trehalose on protein folding in vitro and in vivo. Mol. Cell 1: 639–648.
53 Singh, A., Krause, P., Panda, S.N., and Flugel, W.A. (2010). Rising water table: a threat to sustainable agriculture in an irrigated semi‐arid region of Haryana, India. Agric. Water Manag. 97: 1443–1451.
54 Sultana, N., Ikeda, T., and Kashem, M.A. (2001). Effect of foliar spray of nutrient solutions on photosynthesis, dry matter accumulation and yield in seawater‐stressed rice. Environ. Exp. Bot. 46: 129–140.
55 Thomas, J.C. and Bohnert, H.J. (1993). Salt stress perception and plant growth regulators in the halophyte Mesembryanthemumcrystallinum. Plant Physiol. 103: 1299–1204.
56 Velasco, J., Gutiérrez‐Cánovas, C., Botella‐Cruz, M. et al. (2019). Effects of salinity changes on aquatic organisms in a multiple stressor context. Philos. Trans. R. Soc. B: Biol. Sci. 374: 20180011.
57 Williams, W.D. (1998). Salinity as a determinant of the structure of biological communities in salt lakes. Hydrobiologia 381: 191–201.
58 Williams, W.D. (2002). Environmental threats to salt lakes and the likely status of inland saline ecosystems in 2025. Environ. Conserv. 29: 154–167.
59 Yadav, S.K. (2010). Heavy metals toxicity in plants: an overview on the role of glutathione and phytochelatins in heavy metal stress tolerance of plants. S. Afr. J. Bot. 76: 167–179.
60 Yadav, S., Irfan, M., Ahmad, A., and Hayat, S. (2011). Causes of salinity and plant manifestations to salt stress. J. Environ. Biol. 32: 667–685.
61 Zhang, H., Xu, N., Wu, X. et al. (2018). Effects of four types of sodium salt stress on plant growth and photosynthetic apparatus in sorghum leaves. J. Plant Interact. 13: 506–513.
62 Zhu, J.K. (2007). Plant salt stress. In: Encyclopedia of Life Sciences. Chichester: Wiley doi:10.1002/9780470015902.a0001300.pub2.
2 Effects of Salt Stress on Physiology of Crop Plants: At Cellular Level
Vivekanand Tiwari1, Abhay Kumar2, and Pratibha Singh3
1 Department of Fruit Tree Sciences, Institute of Plant Sciences, Agricultural Research Organization (ARO) ‐ Volcani Institute, Rishon LeZion, Israel
2 Department of Biotechnology, ICAR‐National Research Centre on Litchi, Muzaffarpur, Bihar, India
3 Department of Botany, School of Life Sciences, Mahatma Gandhi Central University, Motihari, Bihar, India
2.1 Soil Salinity and Plants
Salt stress to plants occurs due to the accumulation of soluble salt in the plant rhizosphere beyond a threshold level, which can disturb the plants’ optimal metabolic homeostasis. This accumulation of the salt ions may happen either due to natural means such as the weathering of rocks, oceanic salt carried by the rain and wind, flooding of the seawater and leaching of saline water from the sea to the underground water resources of the coastal area, or by uneven irrigations and excess use of chemical fertilizers (Munns and Tester 2008). Natural weathering of parental rocks releases chloride salts of sodium, magnesium, and calcium, of which the most soluble and maximum proportion is sodium chloride (NaCl) (Szabolcs 1989). In general, the soil is defined as saline if its measured electrical conductivity (EC) is equal or higher than 4 dS/m, which is equivalent to 40 mM of NaCl concentration (Munns and Tester 2008). Since most cultivated crops are sensitive to salt stress, at soil salinity higher than 4 dS/m, the reduction in crop productivity due to salt stress accounts 50–80% (Zörb et al. 2019). The land area across the globe affected by the salinity is more than 800 million hectares and facing the problem of moderate to extreme salinity (Munns and Tester 2008). A total of 230 million hectares agriculture lands have a proper irrigation system and are the source of maximum crop productivity. Surprisingly, the salinity analysis of these irrigated agriculture lands revealed that approximately 20% (45 million hectares) is affected by salt stress (Munns and Tester 2008).
The increasing soil salinity affects the plants negatively for their growth, survival, and productivity. In saline soil, accumulation of salt ions triggers osmotic stress to the plant's root cells, which are then being absorbed by the plants to adjust the osmotic balance. The excess entry of the salt ions to the root cells creates the ionic imbalance at the cellular level. However, the halophytic plant species have adapted to thrive even under these adverse conditions of high salinity and can complete their life cycle under the extreme saline soil conditions. The halophytes have a better ability to tolerate the salt stress than a glycophyte (plants sensitive to salt stress) and can survive and grow well in the saline soil with soil salinity equivalent or higher than 200 mM NaCl (Flowers and Colmer 2008).
The effect of salt stress on plant physiology and its productivity depends on the level of soil salinity and how long plants get the stress. Immediately after the exposure to the salt stress, plants induce the signaling cascades to adjust their metabolic pathways. The
