Effect of changes in substrate salinity on the elongation of Rosa hybrida L. ‘Kardinal’ stems

Abstract

Changes in stem elongation rates of Rosa hybrida L. ‘Kardinal’ stems were measured using linear displacement position sensors (LDPS) while plants were exposed to salinized nutrient solutions for 2 or 12 h. Greenhouse-grown plants were acclimated for at least 24 h in a growth chamber before treatment. While in the growth chamber under constant 25 °C and continuous light, plants were automatically irrigated based on substrate moisture tension with half-strength modified Hoagland’s nutrient solution in demineralized water (NS). In the 2 h exposure experiment, a pretreatment irrigation of NS was initiated at 1:00 a.m. and was followed 2 h later by an application of demineralized (deionized) water (DI), NS, or NS with NaCl to increase the solution electrical conductivity (EC) by 1, 2, 4, or 8 dS m −1 (+1, +2, +4, and +8, respectively). A post-treatment irrigation with NS followed after two more hours. The shoot elongation rate (SER) of plants treated with DI increased by 0.30 mm h −1 from 0.95 mm h −1, then returned to the pretreatment rate after the final irrigation. Treatment with NS resulted in a growth rate 0.10 mm h −1 greater than the pretreatment rate. This was unexpected and is probably due to a temperature effect caused by irrigating with cold solution. The +1 treatment had no effect on growth rate, but the higher concentrations resulted in decreases in SER of 0.12, 0.23, and 0.86 mm h −1, respectively. Shoot growth rates of salinized plants returned to or exceeded pretreatment rates after the final leaching irrigation. In a 12 h exposure experiment, the treatment solution was not leached and data was collected for 12 h after the treatment. Treatment with +2, +4, and +8 caused immediate, but temporary reductions in SER. Growth rates then increased and restabilized after 4–6 h. Stems of the +2 and +4 treated plants regained the pretreatment elongation rates, but +8 treated stems only partially recovered at 78% of the pretreatment rate.