Tolerance to Salinity and Manganese in Three Common Roadside Species

Abstract

Roadside soils are contaminated with a variety of substances toxic to plants, including manganese ($$\mathrm{Mn}\,^{++}$$) from the use of the antiknocking agent methylcyclopentadienyl manganese tricarbonyl in gasoline and salt from the use of de‐icing salts. We investigated whether roadside populations of three species (Asclepias syriaca L., Dipsacus sylvestris Huds., and Hesperis matronalis L.) were more tolerant of these contaminants during germination than populations located in a more benign environment; i.e., old fields. We used field‐collected maternal families because the life history of the three species, two monocarpic perennials and one perennial, prevented us from growing the plants for one generation in a common environment. Family responses to the treatments are therefore a combination of genetic traits and maternal environmental effects. Consequently, we measured several traits likely to be affected by the maternal environment, including seed size and the quantity of sodium ions (Na+) leached from seeds during germination. Roadside populations of neither A. syriaca nor D. sylvestris demonstrated any adaptation to elevated $$\mathrm{Mn}\,^{++}$$ levels during germination. However, one roadside population of H. matronalis did display a low level of $$\mathrm{Mn}\,^{++}$$ tolerance. There was no relationship between the seed characteristics and $$\mathrm{Mn}\,^{++}$$ tolerance in H. matronalis. Roadside populations of neither A. syriaca nor H. matronalis demonstrated any adaptation to high soil salinity during germination. However, roadside populations of D. sylvestris did display tolerance to elevated salinity levels. Salt tolerance in roadside populations of D. sylvestris appeared to be highly related to both seed size and $$\mathrm{Na}\,^{+}$$ concentration of the seed leachate. The observed salt tolerance of roadside D. sylvestris seeds may be a maternal environmental effect rather than a genetic trait.