Four helophyte species growing under salt stress: their salt of life?

We studied the capacity of pre-germinated seedlings of four helophyte species to develop under conditions of chronic and temporary salt stress in waterlogged sediments: Typha latifolia L., Phragmites australis (Cav.) Trin. ex Steud., Scirpus lacustris sap. lacustris L., and Scirpus maritimus L. Salinity levels were 1.8 parts per thousand S and 18 parts per thousand S, applied constantly during four months, or for one or three weeks in otherwise freshwater conditions. The chronic salt stress treatment at 18 parts per thousand S led to a rapid die-off of both I: latifolia and S. lacustris ssp. lacustris. The other two species only barely survived, hardly forming new vertical shoots. At 1.8 parts per thousand S, the consequences were less, and limited to I: latifolia and S. lacustris sap, lacustris. Both levels of short-term salinity stress were well-tolerated by P. australis and S, maritimus, while mortality of I latifolia and S. lacustris ssp. lacustris was significantly increased after the three weeks, 18 parts per thousand S treatment. The surviving individuals of these two species after this treatment also showed a more than 50% reduction in their total biomass compared to the control plants. Remarkably, after the three weeks 18 parts per thousand S treatment, all species apart of I latifolia showed a short period in which the growth rate of the number of new shoots was significantly increased. This increase was sufficient to restore the same development pattern as observed in the control plants. (C) 1998 Elsevier Science B.V. All rights reserved.