Abstract
The goal of this study was to investigate how plant selenium (Se) hyperaccumulation may affect ecological interactions and whether associated partners may affect Se hyperaccumulation. The Se hyperaccumulator Astragalus bisulcatus was collected in its natural seleniferous habitat, and x-ray fluorescence mapping and x-ray absorption near-edge structure spectroscopy were used to characterize Se distribution and speciation in all organs as well as in encountered microbial symbionts and herbivores. Se was present at high levels (704-4,661 mg kg(-1) dry weight) in all organs, mainly as organic C-Se-C compounds (i.e. Se bonded to two carbon atoms, e.g. methylselenocysteine). In nodule, root, and stem, up to 34% of Se was found as elemental Se, which was potentially due to microbial activity. In addition to a nitrogen-fixing symbiont, the plants harbored an endophytic fungus that produced elemental Se. Furthermore, two Se-resistant herbivorous moths were discovered on A. bisulcatus, one of which was parasitized by a wasp. Adult moths, larvae, and wasps all accumulated predominantly C-Se-C compounds. In conclusion, hyperaccumulators live in association with a variety of Se-resistant ecological partners. Among these partners, microbial endosymbionts may affect Se speciation in hyperaccumulators. Hyperaccumulators have been shown earlier to negatively affect Se-sensitive ecological partners while apparently offering a niche for Se-resistant partners. Through their positive and negative effects on different ecological partners, hyperaccumulators may influence species composition and Se cycling in seleniferous ecosystems.
Highlights
The goal of this study was to investigate how plant selenium (Se) hyperaccumulation may affect ecological interactions and whether associated partners may affect Se hyperaccumulation
The A. bisulcatus plants collected in the field hyperaccumulated Se to concentrations ranging from 704 to 4,661 mg kg21 dry weight in different organs (Table I)
Within A. bisulcatus flowers, the highest Se level was measured in the sepals and petals, followed by pistils and stamens; immature seeds collected from developing seed pods had an intermediate Se level (Table I)
Summary
The goal of this study was to investigate how plant selenium (Se) hyperaccumulation may affect ecological interactions and whether associated partners may affect Se hyperaccumulation. The Se hyperaccumulator Astragalus bisulcatus was collected in its natural seleniferous habitat, and x-ray fluorescence mapping and x-ray absorption near-edge structure spectroscopy were used to characterize Se distribution and speciation in all organs as well as in encountered microbial symbionts and herbivores. Hyperaccumulators live in association with a variety of Se-resistant ecological partners. Among these partners, microbial endosymbionts may affect Se speciation in hyperaccumulators. Hyperaccumulators have been shown earlier to negatively affect Se-sensitive ecological partners while apparently offering a niche for Se-resistant partners. Selenium and Ecological Partnerships in Astragalus the leaf epidermis in organic forms with a C-Se-C configuration (i.e. Se bonded to two carbon atoms; Freeman et al, 2006b). A. bisulcatus showed specific Se sequestration in the leaf trichomes, in the form of C-Se-C compounds that were identified as MeSeCys and g-glutamyl-MeSeCys, using liquid chromatographymass spectroscopy (LC-MS; Freeman et al, 2006b)
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