Differential responses to Na+/K+ and Ca2+/Mg2+ in two edaphic races of the Lasthenia californica (Asteraceae) complex: A case for parallel evolution of physiological traits

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Abstract
Sodium, potassium, calcium, and magnesium ion uptake physiology and tolerance to sodium and magnesium were characterized in two edaphic races (A and C) of two closely related species in the Lasthenia californica complex. Uptake rates of race A plants were 20-fold higher for Na+, and 2-fold higher for Ca (2+) and M (2+) than those of race C plants. Race A translocated c. 50% of absorbed Na+ to the shoot compared with < 30% in race C. For Ca2+ and Mg2+ corresponding values for the two races were > 95% and less than or equal to 50%, respectively. Germination, root growth and survivorship estimates indicated greater tolerance by race A to Na (+) and Mg (2+). Significant genotype treatment interactions were observed, suggesting that these races are genetically differentiated in their tolerance responses. The study suggests parallel evolution of physiological traits in populations belonging to the two species and points to intriguing correlations between the presence of sulfated flavonoids and the capacities for the uptake of and tolerance to specific ions.