Selenium hyperaccumulation reduces plant arthropod loads in the field

Area of Science:

• Ecology
• Plant Science
• Biogeochemistry

Background:

• The elemental defense hypothesis posits that plants accumulate toxic elements for defense.
• Selenium (Se) is a toxic element with potential defensive properties against herbivores.
• Understanding Se's role in plant defense is crucial for ecological and evolutionary studies.

Purpose of the Study:

• To investigate the effectiveness of selenium (Se) as an arthropod deterrent in field conditions.
• To compare arthropod loads on Se hyperaccumulating plants versus nonhyperaccumulating plants.
• To explore the relationship between plant Se concentration and arthropod herbivory.

Main Methods:

• Field study over two growing seasons in Colorado, USA.
• Comparison of arthropod loads and species richness on Se hyperaccumulator species (Astragalus bisulcatus, Stanleya pinnata) and nonhyperaccumulator species.
• Measurement of Se concentrations in plants and collected arthropods.

Main Results:

• Se hyperaccumulating plants (1000–14000 μg Se g⁻¹ DW) had significantly fewer arthropods (approx. twofold) and arthropod species (approx. 1.5-fold) compared to nonhyperaccumulators (<30 μg Se g⁻¹ DW).
• Arthropods on Se-hyperaccumulating plants had 3–10 times higher Se concentrations than those on nonaccumulators, but >10 times lower than host plants.
• Some arthropod species exhibited high Se tolerance (>100 μg Se g⁻¹ DW), suggesting specialized feeding.

Conclusions:

• Results support the elemental defense hypothesis, demonstrating Se's efficacy as an arthropod deterrent.
• Plant Se hyperaccumulation significantly reduces arthropod abundance and diversity.
• Invertebrate herbivory pressure may have been a driving force in the evolution of Se hyperaccumulation in plants.