Crop production in coastal areas is threatened by seawater intrusion, which increases soil salinity. Seawater intrusion will become a more prominent concern as sea level continues to rise with global climate change and overuse of groundwater. According to Stoner (1988), about 40,000 ha of arable lands are lost every year due to salinity and waterlogging. Excessive salinity in soil and irrigation water in combination with waterlogging can significantly reduce the productivity of many agricultural crops, especially those vegetables that are sensitive to salinity.
Salinity is one of the major abiotic stresses that threaten agricultural production. Increasing salinity in soil and irrigation water usually leads to a buildup in sodium (Na) and chloride (Cl) content and imposes water deficit detrimental to plants (Yamaguchi and Blumwald, 2005). Adverse effects associated with salinity include plant growth reduction, leaf burning, decreased photosynthesis, and potentially death (Munns and Tester, 2008). Salt tolerance varies among plant species or even cultivars within species. Akinci et al. (2004) observed that growth and development of eggplant cultivars at the germination and seedling stages were negatively affected by increasing NaCl from 50 mm to 150 mm, and ‘Kemer’ was more tolerant than ‘Pala’ and ‘Aydin Siyahi’. Furthermore, salt tolerance is frequently different from one growth stage to another. Sugar beet and tomato plants are more sensitive to salinity during germination and early growth, but moderately to highly salt tolerant at maturity (Ungar, 1996). The response of eggplant cultivars Kemer, Pala, and Aydin Siyahi to salinity varied also with plant growth stage with salt tolerance increasing as later growth stages progressed (Akinci et al., 2004).
Flooding is another major abiotic stress significantly impacting crop growth and productivity. An estimated $500–$600 million in agricultural production was lost due to flooding in eastern Australia in 2010–11, especially the production of cotton, fruit, grain sorghum, vegetables, and winter crops (ABARES, 2011). In general, flooding damages vegetables by reducing oxygen in the root zone, which inhibits aerobic processes. Flooding restricts respiration and gaseous exchange, ceases growth processes, reduces yields, or even leads to death and decay of crop plants (Visser et al., 2003). Johnson (2011) reported that most vegetable crops can recover if the flooding or waterlogging duration is less than 48 h. Longer flood periods will lead to root death and lower chances of recovery. Most vegetables are highly sensitive to flooding and genetic variation is high. Tomato ‘LA1579’ genotype is flooding sensitive, whereas genotype ‘CLN2498E’ and ‘CA4’ show high tolerance to flooding (Ezin et al., 2010).
Some plants have developed a mechanism that allows them to exclude salts from their shoots or tolerate accumulated salts in their tissue (Munns and Tester, 2008). However, the mechanism to exclude salts from shoots will break down and roots become “leaky” to salts because waterlogging makes plant roots oxygen deficient and thus decreases their production of energy (Qureshi and Barrett-Lennard, 1998). Barrett-Lennard (1986) observed that waterlogging and salinity interactively allow large and rapid accumulation of Na and Cl in plant shoots. Na content in wheat leaves continuously increased with salt and waterlogged treatment (Ibrahim et al., 2007).
Salt-waterlogged treatment also greatly reduced grain DW and number per plant in Triticum aestivum (wheat) ‘Pirsabak’, ‘Inqlab-91’, ‘SARC-6’, and ‘HD-2320’ (Ibrahim et al., 2007). In addition, there is substantial evidence that waterlogging under salt conditions increases leaf senescence. The combination of waterlogging and salinity (8.7 dS·m−1 NaCl) increased the numbers of senescenced leaves, but did not affect the rate of production of new leaves of squash (Cucurbita pepo) that grew in sand irrigation (Huang et al., 1995a, 1995b).
Little information is available on the tolerance of many vegetables at early stages of development to seawater flooding. The purpose of this study was to evaluate the plant growth responses of 10 common vegetable crops to SSW flooding for 24 h in a greenhouse. Gas exchange rates and leaf Na, potassium (K), calcium (Ca), and Cl accumulation of selected vegetables were also determined.
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