Physiological parameters of salinity tolerance in C(4) turfgrasses

Growth and physiological responses to salinity of 13 C{dollar}sb4{dollar} turfgrasses, and of a C{dollar}sb4{dollar} coastal salt marsh grass, were compared in an attempt to elucidate salinity tolerance mechanisms operating in these grasses. Relative shoot growth reduction with increasing salinity, as a percent of control, and also visual quality ratings, were used as indicators of salt tolerance. Sporobolus virginicus (L.) Kunth (a coastal salt marsh grass), seashore paspalum (Stenotaphrum secondatum Walt.), and Manilagrass (Zoysia matrella L.) consistently ranked as the most salt tolerant. The bermudagrasses (Cynodon spp. (L.) Pers., Burtt-Davey) were intermediate in salt tolerance, though the common bermudagrass Hawaii selections were more tolerant than the other bermudagrasses studied. Japanese lawngrass (Zoysia japonica Steud.) was salt sensitive, and centipedegrass (Eremochloa ophiuroides (Munro) Hack.) very salt sensitive, respectively. Root growth was stimulated by intermediate salinities in the bermudagrasses, seashore paspalum, and Manilagrass, and by high salinities in S. virginicus. Increased root growth may result in more efficient water and nutrient uptake under salinity stress. All grasses adjusted osmotically, maintaining sap osmolalities above that of salinity media. Though shoot Na{dollar}sp+{dollar} and Cl{dollar}sp-{dollar} accumulation was primarily responsible for osmotic adjustment, shoot dehydration also contributed. In grasses other than St. Augustinegrass, salinity tolerance was associated with exclusion of Na{dollar}sp+{dollar} and Cl{dollar}sp-{dollar} from shoots, coupled with shoot selectivity for K{dollar}sp+{dollar} over Na{dollar}sp+{dollar}. Seashore paspalum relied on selective ion uptake/exchange mechanism of the root cortex, while in S. virginicus, bermudagrasses, and Manilagrass shoot Na{dollar}sp+{dollar} and Cl{dollar}sp-{dollar} exclusion was aided by very active leaf salt glands. Shoot Na{dollar}sp+{dollar} and Cl{dollar}sp-{dollar} concentrations reached high levels in Japanese lawngrass and centipedegrass, resulting in shoot death at relatively low salinities. Growth stimulation at intermediate salinity, associated with ion accumulation and increased shoot succulence, typical halophytic responses, occurred in S. virginicus and St. Augustinegrass. St. Augustinegrass accumulated Na{dollar}sp+{dollar} and Cl{dollar}sp-{dollar} to much higher levels than other grasses, and maintained very high shoot succulence. Shoot ion concentrations were sufficiently high in all grasses at high external salinity to necessitate ion compartmentation in vacuoles. Proposed compatible solutes glycinebetaine and proline accumulated sufficiently to make substantial contributions to cytoplasmic osmotic adjustment in all grasses except centipedegrass.