On the Ecology of Selenium Accumulation in Plants.

Elizabeth A H Pilon-Smits

doi:10.3390/plants8070197

Abstract

Plants accumulate and tolerate Se to varying degrees, up to 15,000 mg Se/kg dry weight for Se hyperaccumulators. Plant Se accumulation may exert positive or negative effects on other species in the community. The movement of plant Se into ecological partners may benefit them at low concentrations, but cause toxicity at high concentrations. Thus, Se accumulation can protect plants against Se-sensitive herbivores and pathogens (elemental defense) and reduce surrounding vegetation cover via high-Se litter deposition (elemental allelopathy). While hyperaccumulators negatively impact Se-sensitive ecological partners, they offer a niche for Se-tolerant partners, including beneficial microbial and pollinator symbionts as well as detrimental herbivores, pathogens, and competing plant species. These ecological effects of plant Se accumulation may facilitate the evolution of Se resistance in symbionts. Conversely, Se hyperaccumulation may evolve driven by increasing Se resistance in herbivores, pathogens, or plant neighbors; Se resistance also evolves in mutualist symbionts, minimizing the plant’s ecological cost. Interesting topics to address in future research are whether the ecological impacts of plant Se accumulation may affect species composition across trophic levels (favoring Se resistant taxa), and to what extent Se hyperaccumulators form a portal for Se into the local food chain and are important for Se cycling in the local ecosystem.

Highlights

Plants accumulate and tolerate Se to varying degrees, up to 15,000 mg Se/kg dry weight for Se hyperaccumulators
Hyperaccumulators A. bisulcatus and S. pinnata contained up to 30% elemental Se (Se0) in their natural habitat, but only accumulated organic Se when grown from surface-sterilized seed in a greenhouse [48]
There are some general trends emerging from the various studies on the ecological effects of plant Se accumulation, which were already noted in our earlier review in 2012 [25], and have been supported by follow-up studies

Summary

Two Faces of Se in Biology—An Introduction to Se Benefits and Toxicity

Mammals and many other animals, as well as many prokaryotes and some algae, require Se for their essential metabolism, as a structural component of selenoproteins [1], which have a variety of redox functions vital for immune, thyroid, and reproductive health [2]. Some species called Se hyperaccumulators can tolerate tissue Se concentrations in the range of 1000–15,000 mg Se/kg DW and actively concentrate Se to these concentrations in all their organs while growing in their native seleniferous soils throughout the Western USA [11]. When plants grow in a Se-containing environment, they bioconcentrate the locally available Se in their tissues and, depending on the species, biotransform the inorganic Se to organic Se to a varying degree (Figure 1). This accumulated, organic/inorganic plant Se is recycled when the plants shed leaves or die, or in root exudation or through volatilization.

Plant–Herbivore

Effects

Plant–Pollinator Interactions

Plant–Microbe Interactions

Findings

Plant–Plant Interactions