Comparative salinity tolerance and salt tolerance mechanisms of seashore paspalum ecotypes

Salinity stress (water quality and quantity issues) on turfgrass areas is a major problem worldwide and is not limited to coastal areas, but includes environmentally-related water shortages and use of recycled (effluent) water. One strategy to alleviate salinity stress is to develop and use turfgrass species or cultivars with enhanced salinity tolerance. This study was undertaken to determine the relative salinity tolerance of 94 seashore paspalum ( Paspalum vaginatum Swartz) ecotypes, to establish assessment criteria for salinity tolerance, and to identify the significant tolerance mechanisms associated with the most salt-tolerant ecotypes. A nutrient/sand culture system was used to grow seashore paspalum ecotypes under greenhouse conditions at the University of Georgia Experimental Station in Griffin, GA. Salinity treatments ranged from 1.1 to 41.1 dSm−1 (study 1 in 1997) or to 49.7 dSm−1 (study 2 in 1998). Many seashore paspalum ecotypes exhibited diverse and halophytic growth responses, and expressed superior salinity tolerance compared to bermudagrass cultivars. For salinity tolerance evaluation of halophytic turfgrass, comprehensive assessment of turf shoot, root, and crown components across salinity regimes was suggested. Shoot water (Ψ) and solute potential (Ψ_s) decreased in all ecotypes as salinity increased, but turgor pressure (Ψ _p) exhibited a quadratic response for the more salt-tolerant ecotypes and a linear decrease for less tolerant types. All paspalums were ion-accumulating types with efficiency to maintain ample shoot K and Ca contents even at EC _w50. As salinity increased, chlorophyll pigments decreased significantly only at EC_w50 and initial chlorophyll fluorescence (Fo) increased. Maximum (Fm) and variable (Fv) fluorescence and fluorescence ratio (Fv/Fm) tended to decrease. Reflectance over the PAR spectrum was enhanced as salinity increased but decreased at longer spectrums ≥760nm. Salt-tolerant ecotypes have high vegetation indices (IRR and NDVI) and low stress indices (Stress 1 and Stress 2) relative to less tolerant types. Osmotic adjustment by organic osmolytes was evident but contribution to a lower Ψ_s was less than contributions by inorganic ions (K, Na, Cl). More tolerant ecotypes maintain higher water content and were able to allocate organic compounds beyond the osmoregulation requirement to plant biomass production. Multiple regression analyses indicated that salinity tolerance was related to maintenance of total water potential (Ψ) and high shoot K content, the positive IRR and the negative Stress 1 indices, and proline synthesis.