Physiological responses to salinity among warm-season turfgrasses of contrasting salinity tolerance

There is increasing need to understand physiological mechanisms of warm-season turfgrass species for potential use in salt-affected soils due to increased use of recycled water for irrigation in arid and semi-arid regions. Greenhouse screenings previously conducted during 2014 and 2015 at Texas A&M University, College Station, TX, and determined relative salinity tolerance among 45 experimental genotypes representing four warm-season turfgrass species under salinity levels ranging from 2.5 to 45 dS m(-1). From that study, eight genotypes (two genotypes representing the highest and lowest relative salinity tolerance from each of four species) were advanced for additional evaluations aimed at characterizing physiological responses to salinity in this study. Genotypes included 'Celebration(R)' and 'UGB79' bermudagrass (Cynodon spp.), 'DALZ1313' and 'Zeon' zoysiagrass (Zoysia spp.), 'UGP3' and 'UGP38' seashore paspalum (Paspalum vaginatum), and 'Floratam' and 'Palmetto' St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze]. Grasses were grown in the greenhouse and sub-irrigated daily for 4 weeks at salinity levels of 2.5, 15 and 30 dS m(-1). Responses including visual turf quality, shoot growth rates, salt excretion rates, root and shoot tissue nutrient concentrations, as well as root and shoot Na:K were characterized. Results showed that all grasses adjusted osmotically under increasing salinity levels. However, differences in Na:K were noted among species, with bermudagrass and seashore paspalum genotypes maintaining proportionally lower Na:K in roots and shoots than zoysiagrass and St. Augustinegrass under salinity stress. Salt excretion rates also increased at increasing salinity in zoysiagrass and bermudagrass, with greater salt excretion observed in the salinity-tolerant genotypes of each species. The results demonstrate that salt tolerance is complex, and show a variety of salt tolerance mechanisms are employed by these warm-season species.