Comparison of ionic concentration, organic solute accumulation and osmotic adaptation in Kentucky bluegrass and Tall fescue under NaCl stress

The need for salt-tolerant turfgrasses in arid and semi-arid regions has increased substantially owing to shortages of fresh water and to soil salinization. We hypothesized that salt tolerance in turfgrasses is achieved by ion regulation and the accumulation of compatible solutes. We investigated changes in ionic concentrations and compatible solutes in Kentucky bluegrass (Poa pratensis L.; a salt-sensitive species) and Tall fescue (Festuca arundinacea Schreb.; a moderately salt-tolerant species) in response to elevated sodium chloride (NaCl) concentration. Sodium (Na+) and chloride (Cl) concentrations in shoots and roots increased with increasing salinity in both turfgrasses. Kentucky bluegrass accumulated more Na+ and Cl under NaCl stress than did Tall fescue. NaCl stress induced more significantly mineral nutrient imbalances in Kentucky bluegrass than in Tall fescue. The concentrations of potassium (K+), calcium (Ca2+), magnesium (Mg2+) and nitrate in Tall fescue were much less affected than those in Kentucky bluegrass. The proline concentration increased significantly in both grasses with increasing salinity. The total soluble sugar (TSS) concentration of Tall fescue was significantly higher than that of Kentucky bluegrass under elevated NaCl concentration. Inorganic ions, especially Na+, were more important in osmoregulation for Kentucky bluegrass and Tall fescue to adapt to NaCl stress. The estimated contribution of K+ to osmotic potential ((s)) decreased with increasing salinity, and it was higher in Tall fescue than in Kentucky bluegrass. The estimated contribution of TSS to (s) was higher in Tall fescue than in Kentucky bluegrass under NaCl stress. These results indicate that Tall fescue tolerates salt better by inhibiting the accumulation of Na+ and Cl, which helps to maintain ion balance, and by accumulating sugars, which decrease the osmotic potential of the cytoplasm.