2018 ASHS Annual Conference

Root-zone salinity was provided to Carica papaya ‘Sunrise’ (papaya) seedlings and grafted Manilkara zapota ‘Ponderosa’ (sapodilla) plants as diluted ocean water or NaCl solution in order to determine the ionomic responses of root, stem, and leaf tissues. Sand culture was employed and the two salinity treatments were supplied to the intolerant papaya plants at 8 d·S^-1 and to the tolerant sapodilla plants at 20 d·S^-1. The control plants received dilute nutrient solution at 1 d·S^-1. All experimental units were harvested after 6 weeks of exposure for papaya or 10 weeks of exposure for sapodilla. In papaya, sodium concentration of leaves was greater for ocean water than for NaCl, and chloride concentration of leaves was greater for NaCl than for ocean water. In sapodilla, sodium concentration of leaves was similar between the two salinity treatments, but chloride concentration of leaves was greater for ocean water than for NaCl. Compared to control plants, sodium:potassium of papaya leaves increased 25-fold for NaCl and 41-fold for ocean water; and sodium:potassium of sapodilla leaves increased 5-fold for NaCl and 10-fold for ocean water. Other leaf stoichiometric traits such as nitrogen:phosphorus and nitrogen:potassium were also dissimilar between the two forms of salinity. For both species, root and stem sequestration of sodium was greater in ocean water plants, but root and stem sequestration of chloride was greater in NaCl. These results indicate that previously published analyses of ionomics following exposure to NaCl do not sufficiently reflect true ionomics of plants exposed to salinity stress associated with oceanic coastal environments. The covariance structure of essential nutrients within plant tissue cannot be adequately understood if NaCl exposure is used to study coastal salinity conditions. Many published studies of plant responses to coastal saline conditions should be revisited if NaCl was used to impose the saline conditions.