Effects of nickel hyperaccumulation in Alyssum pintodasilvae on model arthropods representatives of two trophic levels

Abstract An experimental assessment of the defence hypothesis of nickel (Ni) hyperaccumulation in Alyssum was lacking. Also, to date no study had investigated the effects of hyperaccumulator litter on a detritivore species. We performed several experiments with model arthropods representatives of two trophic levels: Tribolium castaneum (herbivore) and Porcellio dilatatus (detritivore). In no-choice trials using artificial food disks with different Ni concentrations, T. castaneum fed significantly less as Ni concentration increased and totally rejected disks with the highest Ni concentration. In choice tests, insects preferred disks without Ni. In the no-choice experiment, mortality was low and did not differ significantly among treatments. Hence, this suggested a deterrent effect of high Ni diet. Experiments with P. dilatatus showed that isopods fed A. pintodasilvae litter showed significantly greater mortality (83%) than isopods fed litter from the non-hyperaccumulator species Iberis procumbens (8%), Micromeria juliana (no mortality) or Alnus glutinosa (no mortality). Also, isopods consumed significantly greater amounts of litter from the non-hyperaccumulator plant species. The behaviour of isopods fed A. pintodasilvae litter suggested an antifeedant effect of Ni, possibly due to post-ingestive toxic effects. Our results support the view that Ni defends the Portuguese serpentine hyperaccumulator A. pintodasilvae against herbivores, indicating that Ni can account both for feeding deterrence and toxic effects. The effects of hyperaccumulator litter on the detritivore P. dilatatus suggest that the activity of these important organisms may be significantly impaired with potential consequences on the decomposition processes

Do metal-rich plants deter herbivores? A field test of the defence hypothesis.

Some plant species growing on metalliferous soils are able to accumulate heavy metals in their shoots up to very high concentrations, but the selective advantage of this behaviour is still unknown. The most popular hypothesis, that metals protect plants against herbivores, has been tested several times in laboratory conditions, with contradictory results. We carried out the first large-scale test of the defence hypothesis in eight natural populations of the model Zn hyperaccumulator Thlaspi caerulescens J. and C. Presl (Brassicaceae). In two climatic regions (temperate, Belgium-Luxembourg, and Mediterranean, southern France), we worked in metalliferous and in normal, uncontaminated environments, with plants spanning a wide range of Zn concentrations. We also examined the importance of glucosinolates (main secondary metabolites of Brassicaceae) as antiherbivore defences. When exposed to natural herbivore populations, T. caerulescens suffered lower herbivory pressures in metal-enriched soils than in normal soils, both in Belgium-Luxembourg and in southern France. The trapping of gastropods shows an overall lower population density in metalliferous compared to normal environments, which suggests that herbivory pressure from gastropods is lower on metalliferous soils. In addition, foliar concentration of glucosinolates was constitutively lower in all populations from metal-enriched soils, suggesting that these have evolved towards lower investment in organic defences in response to lower herbivory pressure. The Zn concentration of plants had a protective role only for Belgian metallicolous plants when transplanted in normal soils of Luxembourg. These results do not support the hypothesis that Zn plays a key role in the protection of T. caerulescens against enemies. In contrast, glucosinolates appear to be directly involved in the defence of this hyperaccumulator against herbivores.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe