DISSERTATION RESEARCH: Biotic interactions and the geographic range limit of Clarkia xantiana across a complex environmental gradient

为什么有些物种遍布地球的大部分地区（例如蒲公英），而有些物种只出现在一小块栖息地，这是一个长期存在的问题。同样，有些物种（例如，入侵物种）正在迅速扩大其活动范围，而许多物种却没有，这一事实仍然难以解释。弄清楚是什么使或阻止植物在某些地区生长，对管理入侵物种、在可变环境中保持作物的生产力以及保护受威胁的生物具有深远的影响。本项目使用加州的一种植物（Clarkia xantiana），该植物被限制在南加州的一小块区域，以探索限制物种分布的环境因素。研究通常只考虑气候因素，如温度和降水，作为这些分布的驱动因素。但是研究人员越来越多地认识到微生物在影响植物生长和分布方面所起的作用。本项目将描述黄天莲原生范围内外的土壤微生物群落特征，并使用一种新颖的野外实验来测试微生物和降雨如何相互作用以限制黄天莲的范围。研究人员还将在当地一所中学进行一系列的教育实地考察，向学生讲授假设检验、科学实验和南加州的自然历史。本项目利用新一代测序技术和野外操作实验，探讨了土壤微生物群落、降水和植物性状之间的相互作用，以及这些因素如何影响克氏Clarkia xantiana的地理分布。在南内华达山脉的山脚下。多变量统计分析将用于研究跨地理空间的群落转移模式，重点关注黄天麻分布边界内外的微生物分类区系分化点。一项原位土壤微生物移植试验，配合降雨操纵处理，将量化这些因素对范围外适应度的主要和交互影响。PVC生长芯安装在范围边缘外的地面上，通过接种范围内的微生物群落，用于控制单个黄天娜植物周围的当地土壤微生物环境。这与分块设计中的降雨操纵处理相匹配，其中一半的地块将获得50%的降雨量。利用方差分析分析了场地、降雨处理、接种量和所有双向交互作用对终生适应度和物候各组成部分的影响。

It is a longstanding question why some species are found across vast portions of the earth (e.g., dandelions), and some species only occur in small patches of habitat. Similarly, the fact that some species are expanding their ranges rapidly (e.g., invasive species) while many are not remains difficult to explain. Figuring out what enables, or prevents, plants from growing in certain areas has far reaching consequences for management of invasive species, continued productivity of crops in variable environments, and protection of threatened organisms. This project uses a Californian plant species, (Clarkia xantiana), restricted to a small area of Southern California to explore the environmental factors limiting species distributions. Studies often only consider climatic factors, such as temperature and precipitation, as drivers of these distributions. But researchers are increasingly realizing the role microorganisms play in affecting plant growth and distribution. This project will characterize soil microbial communities within and outside C. xantiana's native range, and use a novel field experiment to test how microbes and rainfall may interact to limit C. xantiana's range. The researchers will also conduct a series of educational field trips with a local middle school to teach students about hypothesis testing, scientific experiments, and the natural history of Southern California. This project uses next generation sequencing and a manipulative field experiment to explore interactions between soil microbial communities, precipitation, and plant traits, and how these factors influence the geographic distribution of Clarkia xantiana ssp. xantiana in the foothills of the Southern Sierra Nevada. Multivariate statistical analyses will be used to examine patterns of community shifts across geographic space, focusing on those microbial taxa differentiating sites within and outside C. xantiana's distributional limit. An in situ soil microbial transplant experiment, paired with a rainfall manipulation treatment, will quantify the main and interactive effects of these factors on fitness outside the range. PVC growth cores installed in the ground at sites outside the range edge will be used to manipulate local soil microbial environments surrounding individual xantiana plants via inoculation with microbial communities from inside the range. This is paired with a rainfall manipulation treatment in a split-plot design, where half of the plots will receive 50% rainfall addition. The effects of site, rainfall treatment, inoculum, and all two-way interactions on components of lifetime fitness and phenology will be analyzed using ANOVA.