Ecological aspects of plant selenium hyperaccumulation

Abstract

Hyperaccumulators are plants that accumulate toxic elements to extraordinary levels. Selenium (Se) hyperaccumulators can contain 0.1-1.5% of their dry weight as Se, levels toxic to most other organisms. In this review we summarise what is known about the ecological functions and implications of Se (hyper)accumulation by plants. Selenium promotes hyperaccumulator growth and also offers a plant several ecological advantages through negative effects on Se-sensitive partners. High tissue Se levels reduce herbivory and pathogen infection, and high-Se litter deposition can inhibit neighbouring plants. There is no evidence for a cost of hyperaccumulation in terms of reproductive functions or pollinator visitation. Hyperaccumulators offer a niche for Se-tolerant herbivores, pollinators, microbes and neighbouring plants. They may even facilitate these partners through Se enrichment: neighbouring plants with elevated Se levels enjoy enhanced growth and reduced herbivory. Through combined negative and positive effects on ecological partners, Se hyperaccumulators likely affect local plant, microbial and animal species composition and richness, favouring Se-tolerant species at different trophic levels. By locally concentrating Se and altering its chemical form, Se hyperaccumulators likely play an important role in Se entry into, and Se cycling through, seleniferous ecosystems. These findings are of significance since they provide insight into the ecological reverberations of Se hyperaccumulation, and shed light on the possible selection pressures that have led to the evolution of this fascinating phenomenon. Better ecological insight will also help in the management of seleniferous areas and the agricultural production of Se-rich crops for phytoremediation or biofortification.

Effects of selenium on the growth and photosynthetic characteristics of flue-cured tobacco (Nicotiana tabacum L.)

“…Generally, most cultivated plants contain less than 25 mg Se kg −1 DWs and are considered to be non-accumulators [31]. More recently, it was revealed that most plant species growing on seleniferous soils contain <10 mg Se kg −1 DWs, and experience toxicity at levels above ~100 mg Se kg −1 DWs [32]. Therefore, from our results it can be suggested that the flue-cured tobacco had a low tolerance to high Se levels, an should be classified as a Se non-accumulator.…”

Effect of sulphate on selenium uptake and translocation in rape (Brassica napus L.) supplied with selenate or selenite

“…Excessive intake of Se causes garlic breath odor, hair and nail loss, skin and nervous system disorders, and other symptoms (Zhu et al 2009). Additionally, the concentrations of Se in most plants are above 100 mg kg −1 , which also cause damage (El Mehdawi and Pilon-Smits 2012). Therefore, controlling the uptake of Se by plants from the environment (soils) is crucial to reduce the health risk of both Se toxicity and deficiency.…”

Selenium Distribution and Speciation in the Hyperaccumulator Astragalus bisulcatus and Associated Ecological Partners

“…Several studies suggest that Se hyperaccumulation evolved as a defense mechanism against herbivory. Se can protect plants from a wide variety of Se-sensitive invertebrate and vertebrate herbivores, due to deterrence and toxicity (for review, see Boyd, 2007Boyd, , 2010Quinn et al, 2007;El Mehdawi and Pilon-Smits, 2012). Se has been shown to protect plants from aphids (Hurd-Karrer and Poos, 1936;Hanson et al, 2004), moth and butterfly larvae (Vickerman et al, 2002;Hanson et al, 2003;Freeman et al, 2006a), crickets and grasshoppers , thrips and spider mites , and prairie dogs Freeman et al, 2009).…”