Tissue Na+ and K+ Accumulation as a Means for Understanding the Salt Tolerance Mechanisms in Lolium perenne L. and Festuca rubra subsp. rubra L.

The physiological mechanisms of Na⁺ and K⁺ transport in cool season turf grasses are poorly understood. The objective of the present study is to investigate the mechanisms involved in salt tolerance by analyzing the Na⁺ and K⁺ accumulation patterns in L.  perenne and F. rubra subsp. rubra accessions. Two salt tolerant and two salt sensitive accessions from each species were grown in ebb and flow hydroponics trays with half strength Hoaglands solution and NaCl. The concentration of NaCl was gradually increased from 0-15000 mg L^-1 for L. perenne and 0-7500 mg L^-1 for F. rubra. Tissue samples collected from roots, stems, young leaves and old leaves were digested with concentrated HNO₃ and analyzed for Na⁺ and K⁺ content in an inductively coupled plasma mass spectrometry (ICP-MS). In stems and young leaves of L. perenne, Na⁺ content was found to be 34% and 37% higher respectively in sensitive accessions than in tolerant ones. In F. rubra sensitive accessions, Na⁺ was 48% and 339% higher in stems and young leaves respectively than in tolerant accessions. In L. perenne, a K⁺/Na⁺ ratio of 0.25 was found in young leaves of tolerant accessions compared to a ratio of 0.03 in sensitive ones. In F. rubra, a K⁺/Na⁺ ratio of 3.36 was found in young leaves of tolerant accessions compared to a ratio of 0.77 in the sensitive accessions. The ability of tolerant accessions to limit the accumulation of Na⁺ in growing parts, greater K⁺ uptake and enhanced K⁺/Na⁺ discrimination can be suggested as important salt tolerance mechanisms in L. perenne and F. rubra. The low rates of Na⁺ accumulation in growing leaves can be attributed to restricted Na⁺ uptake from the soil and entry to the xylem stream or to enhanced Na⁺ removal from the transpirational stream as it travels to the leaves.