Evolutionary and Ecological Aspects of Plant Selenium Hyperaccumulation

硒的过度积累是一种有趣的现象，某些植物甚至在低硒土壤中积累了异常浓度的这种有毒元素（高达干重的0.6%）。该项目的目标是深入了解植物硒超积累可能进化的原因，以及这一特性对其他物种在超积累栖息地的影响。总体假设为：(1)硒显著影响超积累植物与草食动物之间的相互作用。由于硒介导的威慑和毒性，硒保护植物免受一般无脊椎动物和脊椎动物的食草动物的侵害（基于初步结果）。另一方面，特殊的耐硒食草动物可能已经进化，进而积累硒，影响更高的营养水平。(2)硒对于高富集植物与非富集植物竞争的能力至关重要，因为高富集植物只存在于富硒土壤中。这些假设将以两种高蓄积植物黄芪（asagalus bisulcatus）和石柱（Stanleya pinnata）为研究对象，通过野外操作实验、野外调查和实验室研究相结合的方法，与当地相关的非蓄积植物进行比较。具体目的是确定：(1)硒是否在野外保护超积累植物免受无脊椎动物和脊椎动物的侵害；(2)不同硒形态保护植物免受无脊椎食草动物侵害的相对有效性；(3)硒超积累对草食和硒的可塑性响应；(4)无脊椎草食动物硒的耐受性和硒积累，以及草食动物硒积累对下一营养级的影响；(5)超积累型植物对相邻非积累型植物生长的影响及其在含硒或无硒土壤中的竞争相互作用。金属超积累生态学这一新兴研究领域有望揭示令人兴奋的生物现象。这项研究将揭示植物硒超积累的进化和生态学，这是一个仍然知之甚少的迷人生理过程。这项研究将把我们对超积累的知识从分子扩展到生态系统：从硒相关基因表达对草食的反应和不同硒化合物对草食的影响，到研究超积累者-草食动物-捕食者的相互作用。硒在植物体内的积累也具有重要的经济效益和应用价值。过度积累的“野草”造成了牲畜的重大损失，也可能影响到濒危野生动物。硒是一种环境污染物，植物修复为硒问题提供了一种有吸引力的治理策略。另一方面，硒是一种必需的营养素和强大的抗癌物质，富含硒的饮食已被证明可以改善人类和动物的健康。更好地了解控制植物硒积累的因素可能有助于发育硒积累改变或耐受的植物。这些植物可用于硒修复或作为强化食品。了解植物硒积累如何影响无脊椎动物的生长和生存，以及确定硒专业食用者，可用于控制无脊椎动物害虫和硒积累“lolo杂草”的种群。该项目将培养研究生和本科生以及高中生。

SummarySelenium hyperaccumulation is the intriguing phenomenon that certain plant species accumulate extraordinary concentrations of this toxic element (up to 0.6% of dry weight), even from low-Se soils. The goal of this project is to obtain insight into why plant Se hyperaccumulation may have evolved, and the consequences of this trait for other species in hyperaccumulator habitats. The overall hypotheses are: (1) Se significantly affects interactions between hyperaccumulator plants and herbivores. Se protects plants from general invertebrate and vertebrate herbivory due to Se-mediated deterrence and toxicity (based on preliminary results). On the other hand, specialist Se-tolerant herbivores may have evolved that in turn accumulate Se, affecting higher trophic levels. (2) Selenium is essential for the capacity of hyperaccumulator plants to compete with nonaccumulator species, since hyperaccumulators are only found on Se-rich soils. These hypotheses will be tested using the two hyperaccumulator species, Astragalus bisulcatus and Stanleya pinnata, in comparison with related local nonaccumulator species, using a combination of manipulative field experiments, field surveys, and laboratory studies. The specific objectives are to determine: (1) whether Se protects hyperaccumulator plants from invertebrate and vertebrate herbivory in the field; (2) the relative effectiveness of different Se forms in protecting plants from invertebrate herbivory; (3) the plasticity of Se hyperaccumulation in response to herbivory and Se; (4) Se tolerance and accumulation in invertebrate herbivores and how herbivore Se accumulation affects the next trophic level; (5) how hyperaccumulator plants affect growth of neighboring nonaccumulator plant species, and their competitive interactions in soil with or without Se. The emerging research area of metal hyperaccumulation ecology promises to reveal exciting biological phenomena. This study will shed light on the evolution and ecology of Se hyperaccumulation in plants, a fascinating physiological process that is still poorly understood. This study will extend our knowledge of hyperaccumulation across the biological hierarchy from molecules to ecosystems: from Se-related gene expression in response to herbivory and the effectiveness of different selenocompounds on herbivory to the study of hyperaccumulator-herbivore-predator interactions. Se accumulation in plants also has substantial economic consequences and applications. Hyperaccumulating "locoweeds" cause significant losses in livestock and may also affect endangered wildlife. Selenium is an environmental pollutant, and phytoremediation offers an attractive cleanup strategy for the Se problem. On the other hand, Se is an essential nutrient and powerful anti-carcinogen, and Se-enriched diets have been shown to improve human and animal health. A better understanding of the factors controlling plant Se accumulation may help develop plants with altered Se accumulation or tolerance. Such plants may be useful for Se phytoremediation or as fortified foods. Knowledge of how plant Se accumulation affects growth and survival of invertebrates, and identification of Se-specialist feeders may be used to control both populations of invertebrate pests and of Se-accumulating "locoweeds". The project will train graduate and undergraduate students as well as high school students.