Salt Tolerance of Trifolium alexandrinum L. II. Ion Balance in Relation to Its Salt Tolerance

Abstract

Detailed analysis of K⁺, Na⁺ and Cl^- contents and the distribution of leaf-applied ²²NaCl and Na³⁶Cl in roots, stems, petioles and leaves of T. alexandrinum grown under a moderate salinity regime showed that this plant uses several mechanisms to cope with moderate salinity: (1) retranslocation of Na⁺ (and Cl^-) out of young leaves, maintaining salt concentrations which are low compared to stems and petioles; (2) predominant basipetal movement of leaf-exported Na⁺ and its extrusion into the medium; (3) establishment of a gradient of K⁺ :Na⁺ ratios along the plant axis providing highest K⁺ :Na⁺ in youngest stem parts and leaves; and (4) restricted transfer of Cl- from roots to shoots leading to moderate Cl^- contents distributed equally in stem tissues of different ages. The results are discussed with respect to the dynamic aspects of salt tolerance and the terminology of 'salt-includers' and 'salt-excluders',