Do Symbioses Determine Plant Species Abundances? How Endophytic Fungi May Control Rarity, Dominance, and Invasiveness of Grasses

从根本上说，物种的丰富程度各不相同，从联邦濒危物种到杂草丛生的入侵者。人们提出了几个假说来解释这种模式，但没有一个能充分解释观察到的变化。在某种程度上，这种失败可能反映了这样一个事实，即微生物共生（微生物和植物之间广泛的、互利的联系）在很大程度上被忽视了。这一建议通过评估微生物共生在控制稀有性和侵入性方面的作用，开辟了一个新的方向。利用草和微生物内生菌（生活在植物叶片内的真菌）之间的实验可处理的共生关系，提出的实验和人口统计学模型测试共生体是否以及如何增加宿主丰度。在禾本科植物中，内生菌可以通过产生对昆虫和哺乳动物有毒的生物碱来提高寄主对草食的抗性，也可以增强寄主的耐旱性。对配对的稀有和常见禾草物种进行对比实验，将验证共生效益对普通禾草物种大于稀有寄主物种，并且在本地和非本地寄主物种之间存在差异的预测，从而提供迄今为止最全面的草内生共生生态学研究。对内生菌生态学的更清晰认识可以为珍稀植物保护和入侵植物控制提供新的策略（例如，通过增加或消除内生菌）。通过在印第安纳州和德克萨斯州建立的网络，信息将广泛地传达给州政府机构、保护区管理人员、种子公司和保护组织。这项工作还将通过培养研究生和本科生以及将当代研究带入课堂来整合教学和研究。

Species fundamentally vary in their abundance, spanning a range from federally endangered species to severely weedy invaders. Several hypotheses have been proposed to explain this pattern, but none sufficiently account for observed variation. In part, this failure might reflect the fact that microbial symbioses (widespread, mutually beneficial associations between microbes and plants) have been largely ignored. This proposal forges a new direction by evaluating the role of microbial symbioses in governing rarity and invasiveness. Taking advantage of the experimentally tractable symbioses between grasses and microbial endophytes (fungi that live within plant leaves), proposed experiments and demographic models test whether and how symbionts increase host abundance. In grasses, endophytes may improve host resistance to herbivory through the production of alkaloids toxic to insects and mammals and also may enhance host drought tolerance. Comparative experiments on paired rare and common grass species will test predictions that symbionts benefits are greater for common than rare host species and differ between native and non-native hosts, providing the most comprehensive study to date on the ecology of grass-endophyte symbioses. A clearer understanding of endophyte ecology can offer novel strategies for rare plant conservation and invasive plant control (e.g., via endophyte additions or eliminations). Through networks established in both Indiana and Texas, information will be broadly communicated to state agencies, preserve managers, seed companies, and conservation organizations. The work will additionally integrate teaching and research, by training graduate and undergraduate students as well as bringing contemporary research into the classroom.