Dissertation Research: Late Quaternary History of Balsam Poplar in North America

覆盖今天的俄罗斯东北部和阿拉斯加大部分地区的广大地区在最后一次冰川盛期期间仍然没有结冰。这种冰河时代的避难所，被称为Beringia，对于北方的乔木和灌木来说，其作用在很大程度上是未知的。关于北方木本植物类群的流行假说倾向于在遥远的北方灭绝，随后在大陆冰盖南部的避难所重新定居。这一长期存在的观点最近受到了挑战，因为从阿拉斯加发现的化石树花粉可以追溯到第四纪晚期，这表明苦瓜杨或杨树是Beringia内冰川事件的候选者。本研究旨在利用分子系统地理学和植物区系地理学的互补领域的证据来评估这一替代假说。这项研究的意义延伸到理解柏林考古学、Beringia对北极和北方植物物种和种群多样性的影响以及过去气候变化的影响。此外，本研究还将记录苦瓜杨遗传多样性的地理分布，为今后开发具有重要经济价值的杨树杂交种提供关键的资源知识库。杨树预计将在农林业、二氧化碳生物分离计划以及生物燃料和生物柴油生产中发挥关键作用。最终，这项研究将有助于开发基线假设，以了解过去人口统计事件对杨树基因组变异的影响。

A vast area covering much of present-day north-eastern Russia and Alaska remained ice-free through the last glacial maximum. The role of this ice age refugium, referred to as Beringia, for boreal trees and shrubs is largely unknown. The prevailing hypothesis for boreal woody plant taxa favors extinction in the far north, with subsequent recolonization from a refugium south of continental ice sheets. This long-standing view was challenged recently by discovery of fossil tree pollen from Alaska dating to the late-Quaternary which indicated balsam poplar, or Populus balsamifera, is a candidate for survival of glaciation events within Beringia. This research aims to assess this alternative hypothesis by drawing upon evidence from the complementary fields of molecular phylogeography and floristic plant geography.The implications of this research extend to understanding Beringian archeology, the impact of Beringia on species and population diversity of arctic and boreal plants, and the influences of past climate change. Moreover, this study will document the geographic distribution of genetic diversity within balsam poplar providing a key resource knowledge-base for future development of economically important poplar hybrids. Poplar is predicted to play a key role in agroforesty, CO2 biosequestration programs and biofuel and biodiesel production. Ultimately, this research will aid in development of baseline hypotheses for understanding the influences of past demographic events on genomic variation in poplar.