Plant-soil feedbacks in heavy metal soils

Heavy metal pollution is a major environmental problem. Metal pollutants are long lasting and can be toxic to organisms in all parts of an ecosystem, including humans. Restoring healthy ecosystems in metal contaminated sites is critical for human and environmental health. Plant-soil feedbacks (PSFs), in which plants affect other plants indirectly by modifying the soil they grow in, have been shown to affect many processes critical to successful restoration, but we know little about their generality across ecosystems or how metal contamination will affect them. I conducted a series of experiments to investigate different mechanisms of PSF I predicted to be central to plant succession and metal movement on a mountainside contaminated and devegetated by two nearby zinc smelters. I asked whether soil amendments and seed mixes applied early in restoration affected plant community composition nine years later, how soil metals affect mycorrhizal fungal colonization of plant roots and how both of these factors affect plant metal uptake, and how encroachment into the restored grassland by the pioneer tree gray birch will affect soil chemistry, soil biota, and plant succession. My results indicate that soil amendments applied at the time seeds are planted can have meaningful and long lasting effects on plant communities. I also found evidence that mycorrhizal fungi are depauperate in my study site and have little to do with plant metal uptake, and that effects of the incoming gray birch trees on nearby plants and soils favor continued succession to forest. I conclude that efforts to restore contaminated areas should focus on remediating soil conditions and fostering desired plant communities, and that soil microbial communities can likely be left alone with little effect on restoration goals. I call for closer integration between restoration research and practice. Restoration treatments constitute experiments performed on ecosystems, and if we study them as such with detailed baseline data, thoughtful controls, and thorough monitoring, we stand to greatly improve our understanding of ecosystem function and the efficacy of future restorations