Short and long term salinity induced differences in growth and tissue specific ion regulation of Phragmites karka

Plant responses to salinity vary with concentration and duration of salt exposure. This study was designed to examine Phragmites karka responses under short (0-7 days) and long term (15-30 days) salinity treatments (0 mM NaCl - non saline, 100 mM NaCl - moderate and 300 mM NaCl - high) at growth and tissue specific ion regulation level. Plant growth was unchanged in short term exposure of moderate salinity, while shoot biomass decreased after long term exposure. However, growth rate decreased from short term exposure to high salinity with severe growth reduction (80 % of control) after prolonged exposure due to enhanced leaf senescence, associated with elevated hydrogen peroxide and malondialdehyde concentration. Accumulation of Na+ and Cl- was higher in root than leaf throughout the experiment. Sodium was unchanged in juvenile leaves under salinity, while increased Na+ in adult leaves correlated with leaf senescence. Chloride increased in all plant tissues from short term salt treatment, and contributed as major osmoticum under salinity. Nutrient selective absorption increased earlier (3rd day) than selective transport under salinity that helped to maintain nutrient homeostasis. In conclusion, P. karka can resist moderate salinity for long periods, by reduction of growth, Na+ sequestration in root and adult leaves, uses Cl- as major osmoticum, and increases selective nutrient transport. Moreover, the plant withstands short term exposure to high salinity without any damage symptoms whereas long term exposure to 300 mM NaCl is toxic for the plant, because of insufficient Na+ exclusion, premature leaf senescence, and enhanced reactive oxygen species production.