The waterlogging/salinity interaction in higher plants revisited - focusing on the hypoxia-induced disturbance to K+ homeostasis

Salinity and waterlogging (root-zone hypoxia) are abiotic stresses that often occur together on saltland. It is widely recognised that these two factors interact to increase Na+ and/or Cl- concentrations in shoots, which can have adverse effects on plant growth and survival. This review expands on this understanding, providing evidence that the adverse effects of the interaction are also associated with a disturbance to plant K+ homeostasis. This conclusion is based on a comparative analysis of changes in ion concentrations and growth reported in the literature between species (glycophytes vs halophytes) and within a single species (Hordeum marinum L.). Comparisons between species show that hypoxia under saline conditions causes simultaneous increases in Na+ and Cl- concentrations and decreases in K+ concentrations in shoots and that these changes can all be related to changes in shoot dry mass. Comparisons between accessions of a single species (Hordeum maritima L.) strengthen the argument, with increases in Na+ and decreases in K+ being related to decreases in shoot relative growth rate.