DISSERTATION RESEARCH: Evolution of hyperaccumulation in wild Helianthus: a phylogenetically explicit assessment of evolutionary history and adaptive hypotheses

超过500种开花植物是金属超积累植物，这意味着它们有能力将极高浓度的正常有毒金属吸收到它们的地上部组织中。这种天然能力可用于有用的技术应用，包括植物修复(利用植物清理受污染地区的环境)以及生物强化(用铁等关键营养物质丰富作物)。这项研究的主要目标是了解金属超积累能力的发展如何依赖于金属耐受性，以及超积累能力如何使野生植物受益。超积累给植物带来的好处包括减少食草性和疾病，提高抗旱性，减少竞争。这项研究将使用向日葵属(向日葵属)来测试这些提出的好处，向日葵属是北美各地栖息地发现的一组不同物种。向日葵是农业和园艺上重要的作物品种向日葵，它本身就是已知的至少五种不同重金属的超积累者。除了提高我们对植物生态学的理解外，这项研究还将为向日葵的改良育种和技术应用提供直接的超积累生理方面的见解。通过一个由10个不同处理水平组成的土壤镍梯度的温室操作研究，将利用35种野生向日葵物种评估金属耐性和金属超积累的进化交互作用，其中耐性和超积累的进化被解析为独立的和不同的特征。温室实验将检验过度积累的假定成本和收益，这些实验将量化与健康相关的成本，同时评估五个领先的适应性假说。从系统发育的角度来研究金属超聚集演化可以极大地提高对金属超聚集的生态和进化背景的理解。更广泛地说，这项研究将促进新出现的进化毒理学领域的进一步发展，并将实施新的系统发育比较方法来评估环境响应特征，从而允许改进一系列工具，以解决现有和新出现的环境问题。

Over 500 species of flowering plants are metal hyperaccumulators, meaning they possess the ability to take up extremely high concentrations of normally toxic metals into their shoot tissues. This natural ability may be harnessed for useful technological applications, including phytoremediation (the use of plants for environmental cleanup of polluted areas) as well as biofortification (the enrichment of crops with key nutrients like iron). The broad objective of the proposed research is to understand how the development of metal hyperaccumulation ability depends on metal tolerance, and how hyperaccumulation ability may benefit wild plants. Proposed benefits of hyperaccumulation to plants have included reduced herbivory and disease, improved drought tolerance, and reduced competition. This research will test these proposed benefits using the genus Helianthus (the sunflowers), a group of diverse species found in habitats across North America. Sunflowers are known to many for the agriculturally and horticulturally important crop species Helianthus annuus, which is itself a known hyperaccumulator of at least five different heavy metals. In addition to improving our understanding of plant ecology, this research will provide direct insights into hyperaccumulator physiology for the improved breeding and use of sunflower in technological applications.The evolutionary interactions of metal tolerance and metal hyperaccumulation will be assessed using 35 wild Helianthus species, through a manipulative greenhouse study generating a soil nickel gradient consisting of ten separate treatment levels, in which the evolution of tolerance and hyperaccumulation are parsed apart as separate and distinct traits. The putative costs and benefits of hyperaccumulation will be examined in greenhouse experiments which will quantify fitness-related costs while simultaneously evaluating five leading adaptive hypotheses. A phylogenetically explicit approach to the study of metal hyperaccumulation evolution can dramatically improve the understanding of the ecological and evolutionary context of metal hyperaccumulation. More broadly, this research will promote further development of the newly emerging field of evolutionary toxicology and will implement novel phylogenetic comparative methods for assessing environmentally responsive traits, allowing for an improved range of tools to address existing and emerging environmental concerns.