The impact of solute leaching on the salt tolerance during germination of the common roadside plant Dipsacus fullonum subsp sylvestris (Dipsaceae)

Variation in salt tolerance during early seedling growth has been reported in seeds of Dipsacus fullonum subsp. sylvestris. Seeds collected from roadside populations displayed a greater salt tolerance than those from old fields; this salt tolerance was highly correlated with seed sodium ion (Na+) content. We hypothesized that the salt tolerance during germination was conferred through the deposition of Na+ in seeds by the maternal plant. To determine the role of Na+, we leached the soluble components from seeds before salt exposure and compared the salt tolerance of leached seeds and unleached seeds. Seeds from maternal families from the roadside showed higher salt tolerance than those from old fields. Leaching the seeds before salt exposure had no effect on the salt tolerance of old field families but caused some roadside families to lose salt tolerance. Roadside populations of D. fullonum appear to possess two distinct salt-tolerance strategies, osmotic stress tolerance conferred by seed composition and an inherent ability to tolerate highly saline conditions. This study reveals substantial diversity among D. fullonum populations in the roadside environment with variation not only in the ability to tolerate elevated salinity but also in the mechanism.