Temporal changes in soil properties and physiological characteristics of Atriplex species and Medicago arborea grown in different soil types under saline irrigation

Background and aims: Salinity stress tolerance is a complex polygenic trait composed of numerous sub-traits that operate at very different timescales. This work elucidates the time-dependence and physiological mechanisms conferring differential salinity stress tolerance between Atriplex lntiformis (halophyte) and Medicago arborea (glycophyte) exposed to prolonged NaCl treatments grown in various soil types. Methods: Plant (leaf sap Na+, K+ and Cl− concentrations and osmolality, chlorophyll content, stomatal conductance) and soil characteristic (pH, soil and leachate electrical conductivity) were measured at monthly intervals for up to five months of salinity treatments and then correlated with each other. Results and conclusions: The overall poor performance of salt-grown M. arborea (compared with A. lentiformis) was associated with several factors. This included: (i) its strong reliance on organic osmolytes (hence, associated carbon costs) for osmotic adjustment; (ii) poor K+ retention that compromised stomatal opening; (iii) its inability to prevent Na+ loading into the xylem; and (iv) its poor shoot tissue tolerance, most likely due to inability to provide efficient Na+ sequestration in vacuoles. Also, the salinity of sandy loam soil was only ~50% of the salinity of irrigation water suggesting the possibility of long-term usage of saline irrigation in soils with low clay content.