Nutrient uptake responses and inorganic ion contribution to solute potential under salinity stress in halophytic seashore paspalums

There is increasing interest in superior halophytes for use on saline turfgrass, forage, and land reclamations sites. We investigated halophytic seashore paspalum (Paspalum vaginatum Swartz) ecotype responses for inorganic ion uptake in shoot tissues and to identify total and individual inorganic ion contributions to total solute potential (Psi(s) adjustment under increasing salinity. In a greenhouse study, nine ecotypes varying substantially in salinity tolerance were grown in nutrient/sand culture with six salinity levels up to 49.7 dS m(-1). Increasing salinity reduced uptake of K, Ca, and Mg, with Mg most affected. Sodium tissue content increased with salinity, but Cl increased and then declined as salinity increased. The least salt-tolerant ecotype, 'Adalayd', exhibited lower Cl uptake at high salinity compared to the most salt-tolerant types (SI 93-2, HI 101). Shoot and root growth were positively correlated to K tissue content and K was the primary ion for solute potential (Psi(s)) adjustment. Inorganic ions contributed 57 to 97% to Psi(s) adjustment with salt-tolerant ecotypes exhibiting less dependence on inorganic ions for T. adjustment apparently due to their ability to maintain synthesis of organic osmolytes under high salinity. In terms of physiological traits adapted for salt-screening protocols the following were not useful: tissue nutrient/element content; K/Na and Ca/Na tissue content ratios; and K or other ion contributions to total T, in percent or MPa units. Shoot tissue content relationships of K, Mg, and Ca to increasing salinity indicate the importance of nutritional programs for these nutrients on salt-affected sites.