Abstract
The grey mangrove, Avicennia marina, grows in coastal zones in which salinity is frequently associated with iron deficiency. Its response to these combined stresses has not yet explored. The current study aims to assess the physiological and biochemical effects of iron deficiency (ID), salt stress (SS) and their combination (ID + SS) on A. marina seedlings. Iron deficiency reduced growth at non-saline treated plants by 27% while its deleterious effect was mitigated by the supply of 600 mM NaCl, mainly through the increase of photosynthetic pigment contents, iron accumulation in leaves, and intrinsic water use efficiency (iWUE), and the maintain of iron use efficiency (FeUE). Iron deficiency restricted iron accumulation in leaves (31%), iron absorption efficiency (FeAE) (38%), photosynthetic activity and pigment contents, and enhanced FeUE (48%) at saline treated plants. Otherwise, salinity enhanced growth (47%), root volume (20%), Fe accumulation in leaves (8%), and pigment contents at Fe-deficient plants. However, it reduced their FeAE (18%), transpiration rate (77%) and stomatal conductance (86%). Equally, it increased Na and Cl accumulation, the net photosynthetic assimilation rate and iWUE at Fe-deficient. Interestingly, the combined stresses had no additive effects and stressed plants (ID +SS) had comparable biomass to that of the control.