Gas exchange, chlorophyll fluorescence parameters and carbon isotope discrimination of 14 barley genetic lines in response to salinity

Barley is one of the most salt tolerant crop species, and differences between barley genotypes for salinity tolerance have been previously documented. Greenhouse experiments were conducted with barley seedlings (up to fourth leaf) from 14 genetic lines grown in control and saline (EC = 20 dS m−1) conditions. Some of these barley genotypes are parental lines to diverse mapping populations. Others have been bred and released for their tolerance to salinity. Gas exchange, chlorophyll fluorescence parameters, above ground dry matter and carbon isotope discrimination were measured to determine salinity tolerance. Two-week exposure to saline conditions decreased above-ground dry mass (AGDM), net photosynthesis (A), stomatal conductance (gs), internal CO2 concentration (Ci), efficiency of light harvesting of photosystem II (F′v/F′m)(F′v/F′m), photochemical quenching (qP), and carbon isotope discrimination (Δ) relative to control plants. Measurement of gs provided the best information to assess genetic differences in barley for absolute performance when subjected to salinity stress. Lines with the highest gs values under control conditions also showed some of the highest absolute values for A   and F′v/F′mF′v/F′m under saline conditions. All lines were enriched in 13C (lower Δ) with salinity, but Δ was of limited value to assess differences between lines. Salinity susceptibility indexes (SSI) were used to estimate the relative tolerance of lines to salinity. They varied considerably between parameters and provide only relative information that can be difficult to reconcile with above absolute values of performance under saline conditions.