Symphyotrichum ericoides populations from seleniferous and nonseleniferous soil display striking variation in selenium accumulation

Symphyotrichum ericoides (Asteraceae) from naturally seleniferous habitat (Pine Ridge) was shown previously to have selenium (Se) hyperaccumulator properties in field and glasshouse studies, and to benefit from Se through protection from herbivory. To investigate whether Se hyperaccumulation is ubiquitous in S. ericoides or restricted to seleniferous soils, the S. ericoides Pine Ridge (PR) population was compared with the nearby Cloudy Pass (CP) population from nonseleniferous soil. The S. ericoides PR and CP populations were strikingly physiologically different: in a common garden experiment, PR plants accumulated up to 40-fold higher Se concentrations than CP plants and had 10-fold higher Se : sulfur (S) ratios. Moreover, roots of S. ericoides PR plants showed directional growth toward selenate, while CP roots did not. Growth of both accessions responded positively to Se. Each accession grew best on its own soil. Rhizosphere soil inoculum from the S. ericoides PR population stimulated plant growth and Se accumulation in both S. ericoides PR and S. ericoides CP plants, on both PR and CP soils. While the S. ericoides PR population hyperaccumulates Se, the nearby CP population does not. The capacity of S. ericoides PR plants to hyperaccumulate Se appears to be a local phenomenon that is restricted to seleniferous soil. Mutualistic rhizosphere microbes of the S. ericoides PR population may contribute to the hyperaccumulation phenotype.