Salinity tolerance mechanisms of grasses in the subfamily Chloridoideae

Forage grasses and turfgrasses are increasingly being subjected to salinity stress, due to accelerated salinization of irrigated agricultural lands worldwide, and to increased use of reclaimed and other secondary water sources for irrigating turfgrass landscapes. The objective of this study was to examine salinity responses of a number of important forage and turfgrass genera in the subfamily Chloridoideae in attempt to gain understanding of salinity tolerance mechanisms operating in this subfamily. Grasses were exposed to salinities up to 600 mM NaCl in solution culture. Salinity tolerance decreased in the following order: Distichlis spicata var. stricta (Torr.) Beetle > Sporobolus airoides (Torr.) Torr. > Cynodon dactylon (L.) Pers. = Zoysia japonica Steud. > Sporobolus cryptandrus (Torr.) A. Gray. > Buchloe dactyloides (Nutt.) Engelm. > Bouteloua curtipendula (Michx.) Torr. Relative root length (RL) and relative root weight (RW) increased under saline conditions, relative to control, in salt tolerant grasses. Leaf sap osmolality, Na+, Cl-, and proline concentrations were negatively correlated and glycinebetaine was positively correlated with salinity tolerance. Bicellular salt glands were observed on leaves of all species. Salinity tolerance was positively correlated with Na+ and Cl- salt gland secretion rates. Within the subfamily Chloridoideae, salinity tolerance was associated with saline ion exclusion, facilitated by leaf salt gland ion secretion, and with accumulation of the compatible solute glycinebetaine.