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

为什么一些物种在地球的大片地区被发现(例如蒲公英)，而一些物种只出现在小片的栖息地，这是一个长期存在的问题。同样，一些物种正在迅速扩大它们的活动范围(例如，入侵物种)，而许多物种却没有，这一事实仍然很难解释。弄清楚是什么允许或阻止植物在某些地区生长，对入侵物种的管理、作物在可变环境中的持续生产力以及保护受威胁的生物具有深远的影响。该项目使用了一种加州植物物种(Clarkia Xantiana)，它局限于南加州的一小片地区，以探索限制物种分布的环境因素。研究往往只考虑气候因素，如温度和降水，作为这些分布的驱动因素。但研究人员越来越认识到微生物在影响植物生长和分布方面所起的作用。该项目将描述黄曲霉原生范围内外的土壤微生物群落特征，并使用一种新颖的田间实验来测试微生物和降雨如何相互作用来限制黄曲霉的范围。研究人员还将与当地一所中学进行一系列教育实地考察，向学生传授假说检验、科学实验和南加州自然历史。该项目使用下一代测序和操纵性田间实验来探索土壤微生物群落、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杆菌的地理分布。Xantiana位于内华达山脉南部的山脚下。多变量统计分析将被用来检查地理空间中群落转移的模式，重点是那些在C.xantiana分布界限内外区分地点的微生物分类群。现场土壤微生物移植实验，结合降雨处理，将量化这些因素对范围外适应性的主要和交互影响。安装在林场边缘外的地下的聚氯乙烯生长核心将被用来通过接种林区内的微生物群落来操纵个别Xantiana植物周围的当地土壤微生物环境。这与分割地块设计中的降雨操纵处理相结合，其中一半的地块将获得50%的降雨量增加。地点、降雨处理、接种量和所有双向交互作用对寿命健康和物候的影响将使用方差分析进行分析。

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.