The role of biotic interactions in determining phenotypic and genotypic variation in metal hyperaccumulation and hypertolerance in two model Brassicaceae species

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Metal hyperaccumulation and metal hypertolerance (mh) are common traits in many Brassicaceae species. However, neither its ecological consequences nor the role of ecological interactions on natural trait variation have been studied. Here, we focus on two genetic model species (Arabidopsis halleri, Noccaea caerulescens) to study the causes and consequences of natural variation in this trait with a special focus on the role of negative and positive plant-plant interactions. To that end, we combine field and greenhouse studies, high-end molecular tools, quantitative genetics and experimental approaches of community ecology. In phase 1, we investigated the idea that a trade-off between competitive ability and stress tolerance exists in this system, affecting the performance of individual plants and determining the extent of genetic and phenotypic variation. We hypothesized that facilitation in populations and communities with metal accumulating plants will enable coexistence of different genotypes within the populations, especially under stressful conditions, i.e on soils with high content of heavy metals. Our field results and the first measurements from the competition experiments provide initial support for this hypothesis. In phase 2, we propose to expand our efforts to embrace the entire range of positive and negative interactions in our two model species. Particularly, we propose to explore the potentially contrasting outcomes of mh in plant-plant interactions under different environments, namely facilitation due to phytoremediation vs. elemental allelopathy due to phytoenrichment. Additionally, we propose to investigate several aspects of cooperative interactions in A. halleri, whose clonal propagation is likely to play a key role in mh, and we will contrast this with the patterns found in the second, non-clonal species. We will also investigate plant-herbivore interactions and their potential effect on mh levels within clonal vs. non-clonal plants. Finally, we will obtain estimates of heritability of mh in N. caerulescens. Our overall findings from both project phases will enable us to evaluate the role of phenotypic and genetic variation in mh for biotic interactions in natural habitats, and vice-versa, to determine the importance of such interactions in driving intra- and interspecific variation in metal hyperaccumulation and -tolerance.