Tissue specific changes in elements and organic compounds of alfalfa (Medicago sativa L.) cultivars differing in salt tolerance under salt stress

Soil salinity is a global concern and often the primary factor contributing to land degradation, limiting crop growth and production. Alfalfa (Medicago sativa L.) is a low input high value forage legume with a wide adaptation. Examining the tissue-specific responses to salt stress will be important to understanding physiological changes of alfalfa. The responses of two alfalfa cultivars (salt tolerant 'Halo', salt intolerant 'Vernal') were studied for 12 weeks in five gradients of salt stress in a sand based hydroponic system in the greenhouse. The accumulation and localization of elements and organic compounds in different tissues of alfalfa under salt stress were evaluated using synchrotron beamlines. The pattern of chlorine accumulation for `Halo' was: root > stem similar or equal to leaf at 8 dSm(-1), and root similar or equal to leaf > stem at 12 dSm(-1), potentially preventing toxic ion accumulation in leaf tissues. In contrast, for 'Vernal', it was leaf > stem similar or equal to root at 8 dSm(-1) and leaf > root similar or equal to stem at 12 dSm(-1). The distribution of chlorine in 'Halo' was relatively uniform in the leaf surface and vascular bundles of the stem. Amide concentration in the leaf and stem tissues was greater for 'Halo' than 'Vernal' at all salt gradients. This study determined that low ion accumulation in the shoot was a common strategy in salt tolerant alfalfa up to 8 dSm 1 of salt stress, which was then replaced by shoot tissue tolerance at 12 dSm(-1).