Salt gland ion secretion: A salinity tolerance mechanism among five zoysiagrass species

Need for salinity tolerant turfgrasses is increasing because of government mandates requiring use of low quality secondary water sources for turfgrass irrigation. This study was done to elucidate salinity tolerance mechanisms of the Zoysia genus (zoysiagrass), which includes a number of important turfgrasses. Research objectives were to (i) determine the range in salinity tolerance among and within five zoysiagrass species, (ii) determine if salt secretion via leaf salt glands is an important salinity tolerance mechanism within the Zoysia genus, and (iii) determine if salinity tolerance is associated with the rate, or efficiency of leaf salt gland secretion. Fifty-seven zoysiagrass accessions and cultivars, representing five interfertile species, were grown in hydroponic tanks in a glasshouse. Salinity of treatment tanks was gradually raised prior to data collection to a final treatment level of 400 mM NaCl. Relative salinity tolerance was determined by changes in percent leaf firing and percent leaf dry weight relative to control plants. Relative percent leaf firing varied from 19 to 80% among entries, indicating a wide range in relative salinity tolerance. Bicellular leaf salt glands were observed in all species, lying recumbent to the leaf surface in parallel rows atop intercostal ridges. Relative salinity tolerance was negatively correlated with leaf sap Na⁺ concentration and positively correlated with leaf salt gland Na⁺ secretion rate and leaf gland density. This indicates that salinity tolerance in the Zoysia genus is associated with shoot saline ion exclusion via leaf salt gland secretion, which, in turn, is related to leaf salt gland density.